Q:
I have a remote receptor in 27MHz band that stands over a 1.8 m vertical metal mast nailed on soil.
Is possible to use the mast like an antenna? Or to make a better reception of the signal?
I have made a receptor with Melexis TH7122 transceiver at 27.505 MHz
I will agree any help (circuits, examples, references, links, simulators ...)
Thanks for your help
Jordi
|
A:
I don't think you can use the mast when one end is in the ground. The receiver input must have a path for the input current to flow and if there is no ground connection or balanced input, there is no path for the current. If you connect an extra wire to the ground, it will just cancel out the signal which the mast is picking up.
|
Q:
I have the following questions concerning 13.56MHz RFID system:
1. What is the maximal output power (Is it covered by standard) for transmission between the reader and tag (Writing)?
2. What is the modulation used for transmission? Is it a Manchester code that modulates the 13.56Mhz carrier or something else in addition (ASK, FSK PSK etc)?
|
A:
The MLX90121 is designed to provide 250mWatt to a 50-ohms load. This is less than the maximum magnetic field of 7.5 A/m specified by the ISO standard. A power booster version with an external transistor can be implemented.
The MLX90121 is independant to the type of modulation used (Manchester, Biphase, NRZ). The external microcontroller will do the decoding.
The ISO standards ISO14443 and ISO15693 use a sub-carrier encoded in ASK, FSK or PSK. The data stream level can be encoded in Manchester (ISO15693 and ISO14443 A) or NRZ (ISO14443B). For more information, please refer to the related documentation of these standards.
|
Q:
We're making the 1W 12V power booster (cookbook, Application note, page 6 - 14).
We attached our self-made 50ohms antenne to the circuit and have 26 Volt peak to peak. When we hold a tag 30 cm above the antenne we can see it answer with a EM-probe (snuffelprobe in dutch). But, the RX doesn't encode the signal, so we get nothing on Dout. We think the problem lies within the attinuation T-network (3 resistors). We chose the resistors so 2 volt ptp appears on RX. The external diode detector network also doesn't work because it outputs 12 volt ptp which is to high for RX.
Are there other possible solutions to implement a working attinuation network, perhaps with a high impedance 1/1 opamp circuit.
|
Q:
Ok, I figured out that I should use the external detector, but still one single problem: The signal also has to be attenuated becaus the detector itself outputs something like 10 Vptp which is too high for our RX input. In a previous post you sugested to use several diodes in series to realize the attenuation, but my PSpice does not agree, I still see 10V on the ouput of the detector.
So now my questions:
- Can you give me some more details about possible solutions for attinuation the detector signal?
- Can you please give the internal network (or at least more details about the internal current source, ind, cap, res...) of the RX input, so I can simulate in PSpice before building the circuit.
|
A:
The role of the three resistors attenuator is to reduce the amplitude of the 13.56MHz carrier at the input of the MLX90121 to be correctly decoded. But, as a side effect, it also reduces the amplitude of the transponder's load modulation. Therefore, better results will be achieved with an external diode detector as implemented in the corresponding application note.
You should not get 10Vpp Vpp of useful signal (load modulation + rest of 13.56MHz) at the output of the external detector. The spikes of the command sent by the reader can be quite high but it is not important as it will not be decoded anymore.
I already made the test with 26Vpp of 13.56MHz carrier and I get 2.2-2.4Vpp of useful signal with correct decoding. Can you check the implementation of the external detector?
Do you correctly adjust R2 and C2 (22k, 100pF) which fix the time constant of the decoder?
Do you place the resistor R3 which insure a correct biasing of the MLX90121?
What is the register’s configuration used?
|
Q:
First of all, thanks a lot for repy !!! (I appreciate such a service).
Now, I have a few more questions. Recently I made 2 jpg's illustrating my problem to people. I send them to Melexis.
Concerning RFIDimage1.jpg: Is the answer A of B?
Concerning RFIDimage2.jpg: If I get your last reply well, this jpg is wrong. Anyway, it illustrates my main concern! Somehow you say that the external detector pulles the signal down (because the envelopped signal is to big, according to spice), only I don't know where in the circuit the pulling down happens? If I get it right R1 and C1 form a LF blocking filter. D1, R2 and D2 the envelope detector. C3 and R3 I don't know!
So my questions concerning RFIDimage2:
1: what i drew is wrong, right?
2: Than, what parts in your external detector are responsible for you getting 2.2-2.4 Vpp with 26 Vpp input?
3: What is the meaning of C3 and R3 and the 5Volt supply???
4: Could an extra notch filter (13.56) do a good job blokking the still present 13.56 rimpel in the envelopped signal?
5: Is it correct that the 100% (inventory command from reader) modulation is ignored by RX?
6: Could a comparator and smith trigger be usefull reconstructing the signal digitally using the hysteresiswindow of the smith?
If you could answer these (for you) simple questions, I'll have enough info about this to build the circuit and write about it in my thesisbook !
Thank you very much
Regards
Laurent Cattoir
|
A:
Dear,
As the command is sent using 100% of modulation depth, I think the response is compliant with the protocol ISO14443-A.
1: Yes, red arrow is not at the correct place.
2: 2.2-2.4Volts is the useful signal, corresponding to the residual 13.56MHz with the load modulation. The DC level at the Rx pin is set by the pull-up resistor R3 which is connected on the +5Volts power supply.
3: C3 cuts the high DC level due to the big amplitude of the 13.56MHz (about 10V) while R3 insures a correct biasing of the MLX90121 and therefore adjust the DC level at the Rx pin. Its value has been set to 27Kohm and must not be changed.
4: Not needed.
5: The command is ignored by the firmware which knows when it sends command to the transponder.After sending information, the firmware has to synchronize the MLX90121 on the transponder's response (asserting CK high at the beginning of the transponder's response). For more information, please refer to the application note "MLX90121: Communication with ISO standards" available on our WEB-site.
|
Q:
But our whole project is ISO15693 !!! (we just set the MLX registers to optain 100% mod depth)
Here's our reg:
0 -> 43h
1 -> 1h
2 -> 0h
3 -> 9h
4 -> BFh
5 -> EFh
6 -> FBh
7 -> FEh
8 -> 7Bh
9 -> DFh
10 -> 1Fh
11 -> 7Fh
12 -> 25h
Could you please answer ASAP for we haven't got much time left to finish this project.
|
A:
The register 0 of your register settings must be changed to 0x47 instead of 0x43 (bypass all bit must be set). Otherwise it is ok and correspond to the protocol ISO15693 Single sub-carrier.
Sorry It seems that I didn't understand you previous question. The amplitude of the load modulation will increase with the power transmitted by the reader. Unfortunately, the internal clamp of the transponder will act as a limitation. Therefore, I think the answer B is the most appropriate one.
|
Q:
Our hardware works fine and for the first time we understand the whole picture concerning 13.56 vs. long range.
Now just a software question:
- Wich one is best in obtaining the longest range: FSK or ASK?
|
A:
ISO15693 FSK should be used to get the maximal reading distance. Using two sub-carriers improves the robustness of the reading.
|
Q:
I'm developing a wireless application and I need longer range. I'm reading the application note http://www.melexis.com/Assets/TH7122_with_External_PA_and_LNA_5264.aspx and I'd like to know what is the consumption of the system at different value of the TXPOWER register.
|
A:
This depends on the value for the RPS resistor and the power setting. Section 6.3 of the TH7122 data sheet has a lot of information about this.
|
Q:
I am designing the loop antenna at 13.56Mhz for Rfid applications.I am searching for the connector, so wanted to now that which will be better option.
BNC or SMA, and what will be the noise level inserted by them at 13.56Mhz and what will be the losses due to this connectors
|
A:
The SMA connector is usually used for high frequency operation (GHz) and it not required for 13.56MHz (BCN connector is more than enough). At that time is only a question of size on the PCB.
For technical information, please contact the BNC or SMA manufacturers.
|
Q:
Could yuo tell me how to calculate the components in the antenna matching network?
I only need the components for the transmitter network.
I need to transmit at 187.5MHz.
|
A:
The evaluation boards use a simple PI network. There is quite a lot of free software around to design these. One called RF Sim99 is easy to use.
I usually tune out the 2.5pF of the output stage with a capacitor across LTX0 and then design the PI network assuming resistive loads. For this case, the load is 50 Ohms, but you can change it. The load presented to the IC is dependent on the supply voltage. The equation is in the TH7122 Cookbook on our website.
|
Q:
I want to use the design used on the EVB90109 to integrate it into our application. Could you provide me with a BoM/List of approved/tested parts for this board?
Perhaps a Gerber file? :)
I know, I am getting lazy, but we are under pressure with some other projects and I want to speed this up.
|
A:
You may find more information in the documentation EVB90109 available on our WEB-site. Otherwise, please note the EVB90109 is delivered with a DIL-10 connector which easily allow you to connect it to your application. To acquire an EVB90109, please contact the corresponding sales department of Melexis.
Best Regards
Denis
|
Q:
I am interested in design a class 1 receiver for ism band with th71112.
Is this possible?
I have problems in filtering the IF1 with a very narrow filter to reach the limits for receiver declared in EN 300 220.
|
A:
It's nearly impossible to achieved the class 1 receiver requirements with our receivers. Even if the limits for blocking could be reached with a high Q SAW filter in front of the receiver, the limits for adjacent channel selectivity is too tough for a wideband PLL with integrated ring oscillators as used in the TH71112.
Moreover, filtering the IF1 brings no further improvement.
|
Q:
I am having trouble locating the recommended CDSCB10M7GA136 discriminator. Any suggestions for a replacement. I tried a CDSCB10M7GA135 with no luck.
|
A:
OK, I think I fixed my problem. I replaced the resistor on the EVB7122 board across the discriminator with a 2-10pF variable cap. I also replaced the original discriminator with the CDSCB10M7GA135 for testing. I was able to get a demod signal by adjusting the variable cap.
|
Q:
I'm using a DVK90121 with the utcx.exe software. As I'm going to test some special tags that need a long series of command sequences, I thought to develop a custom PC software directly interfacing the Melexis board. Is it possible to get the specifications of the serial communication protocol used to control the DVK90121 kit ?
|
A:
More information can be found in the documentation, DVK90121 User manual. Otherwise, a firmware example is provided with the DVK90121 (UT121 firmware) which may help you to develop your application. Please let me know the version of the user interface software that you are using.
|
Q:
I'm using the software utcx.exe version 9.1 (2004). I checked the CD supplied with the development kit but I did not find any firmware example.
I had a look at the current DVK90121 User manual on your website and I saw it is now available a new user interface named UT121.
However I was not able to find the infos I'm looking for. What I miss is a raw documentation about the RS232 protocol. I mean, the format of the messages needed to interface directly the Universal development board via RS232 (without using the utcx or the UT121 application).
|
Q:
If I understand your question right, the answer is ASCII. To test this, just send the commands using a proper serial terminal like RealTerm (realterm.sourceforge.net). Use Baud 57600, Parity none, 8 data bits and 1 stop bit. It is importaint to end all commands with a carrage return. DVK90121 will answer with commands ending with '\r' or '\r\n'.
E.g. "WrReg 47010009BFEFFBFE7BDF1F7F3F\r" and "iso15 060100 crc slot 16\r".
|
Q:
I am using DEMO90121LR module for my project.
Unfortunately,I lost the CD that was supplied with DEMO90121LR module kit.
Can u provide me the data/software / help/other information contain in this CD?
|
A:
Please ask directly to our distribution partner from who you purchase the kit. They will take care of your request.
|
Q:
Did anybody ETSI (or FCC) certified the boards?
Any problems and suggestions?
Is anybody else interested in certification?
|
A:
we don't have an official ETSI certification for our EVB's. But they are equipped so that the regulatory requirements are fulfilled.
|
A:
Comment from customer: My TH72011 board already pass FCC certification.
|
Q:
I am implementing a new project on 2 way multichannel walkie talkie using FSK Modulation.I wanted to ask is the circuit diagram of FSK PUM mode transceiver module working? If so can u tell me any methods of testing the circuit.
|
A:
You will at least need a signal generator to test the receiver. The transmitter can be tested using another receiver, but a spectrum analyser is needed to check for spurious outputs.
|
Q:
I have the EVB71102 and want to use it for wide band FM (200KHz) with good linearity (+-5%), what are the changes that I have to do at the EVB?
|
A:
Make sure the discriminator phase shift capacitor between pins 15 and 16 is relatively large, i.e. 12pF and you may also use a small cap of about 2 to 4pF across the ceramic discriminator to lower the Q.
Alternatively you can use an LC discriminator tank. Then you have all the freedom to optimize the circuit in terms of lineraity by resistive loading of the tank.
|
Q:
I need to connect my EVB71102 pin26 to external reference frequency, according the Manuel I need to put C_RO=330pF.
What is the input impedance in this case?, cause I didn't find pin26 input impedance.
If I want to connect 50 ohm signal generator, what is the changes that I need to do?
|
A:
the C_RO is only a coupling cap. The real part of the RO input impedance is usually negative - it depends on the applied amplitude level. So there's no need for attention. The generator level should be adjusted to provide an amplitude of approx. 200mV.
|
Q:
In the EVB71120 data sheet in the fig. 6 the selection of 10,7 MHz IF is made by a connection of IFSEL to GND. Is it correct?
|
A:
For an intermediate frequency IF2 of 10.7MHz, the IFSEL has to be connected to Vcc (current setting of the EVB). For IF2 of 455kHz, the IFSEL has to be connected to GND.
You will find such information in the last version of EVB71120 available on our web-site.
|
Q:
We are developing a audio/voice device, FRS compatible. For prototyping, can we just configure the EVB7122 to work in 462Mhz(FRS)band? Or, Should we have to replace some components of EVB7122 board?
|
A:
You can use the TH7122 or TH71221 with an external narrow band IF as a dual conversion receiver. Modulation is done by directly modulating the VCO.
|
Q:
We purchased 3 EVB7122 evaluation boards. We have attempted to run them in the stand-alone user mode of operation. None of the boards run at the 915 MHz for which they were jumpered. We are running the boards at 5V. Any feedback would be appreciated.
|
A:
Are you using them for ASK or FSK? If you set the jumper for ASK, there is no carrier out if the data input is low. The receiver should work in any mode. Also make sure the jumpers are set for receive or transmit and not standby.
|
Q:
I found the problem. I incorrectly modified the boards for 915 MHz. Once corrected, the boards worked correctly. I have communication and a good FSK signal.
|
A:
Thanks for the feedback. I have also sometimes done this. The easiest way to check if they are operating is to measure the VCO tuning voltage on pin 23. If it is at gnd or Vcc, it is not locked and probably set to the wrong frequency.
|
Q:
We are designing a audio/voice device FRS compatible. For prototyping, Can we just set EVB7122 board to work in 462Mhz (FRS) band? Or, must we have to replace some components to put it to work on that band?
|
A:
The EVB7122 for 434MHz can be used for 462MHz. You only need to decrease the tank inductor L0 so that it can operate at the intended frequency. To tune the L0 inductor the voltage level at pin LF (loop filter) must be virtually centered around VCC/2 for both RX and TX mode ((VLF_RX + VLF_TX) / 2 ~ VCC/2). In any case the VLF should not exceed VCC-0.3 or below 0.3V for correct operation of the PLL (PFD/CP).
|
Q:
I have just modified two EBV71221 (FSK - 315 MHz) evaluation board to work at 27.505 MHz narrow band
The component values where from the document “EVB7122-special-27-FSK-NB-low side LO.pdf”,
I left de original CERDIP and IFFIL
and the XTAL that is set to 4.000 MHz to get ftx=27.505MHz and flo=38.205 MHz
To make the board working I have to change the value of LO from 3.3uH to 1.2uH and program the board at high side injection
The problem I have is that the board doesn’t receive if the power supply is below 3.7 V
And how to calculate the value of the components of the board for better performance at 27.505 MHz and a bandwith of 3KHz
(CERDISC, CERFIL, RLO,CPO,LIF1,CIF1,LO,LRX,LTX,….)
|
A:
Since you have changed to high side injection, the LO must must to higher in frequency, so the tuning voltage on pin 23 must go lower. If you could not tune it, the varactor diode may have too much capacitance. You use a smaller capacitor in series with it or a smaller the tuning inductance.
|
Q:
I have change the value of C01 (in series with varactor) from 1nF to 47 pF and now the board is receiving data @ 2.4Vdc.
|
Q:
we are currently trying to find a suitable RF transmitter for a RF remote control system. We made good expierence with the Melexis 72031 evaluation board with 50 Ohm connector. But our final design should include a printed loop antenna. The problem is that we have no capability to design one. So we are restricted to copying existing designs.
The description site
http://www.melexis.com/prodmain.asp?search=evb72031&Submit=Site+Search&family=EVB72031
claims 85 dBm output power for this board with loop antenna. Has this actually beeing measured or is this the theoretical output power of the chip? Is this the ideal loop antenna for the TH72031 or could the output power be increaesed by a bigger loop?
|
A:
please note the features listed in there: http://www.melexis.com/prodmain.asp?search=evb72031&Submit=Site+Search&family=EVB72031
are just copied from the TH72031 data sheet. It says: "Adjustable output power range from -12 dBm to +8.5 dBm". This is quite difference to 85dBm (which would be a power of 316W!). The 8.5dBm (or 7.1mW) is the conductive power into a 50Ohm load. The effective radiated power (ERP) is about 15dB less, so approx. -30 to -6dBm.
The EVB description must of course be corrected to reflect the ERP values.
|
A:
Can anybody tell me what is the gain in dBi at 868MHz for the loop antenna used on the EVB72032 evaluation board?
|
A:
PCB loop antennas usually have no gain, they rather experience loss. You would have to make the loop very large to achieve gain. And real size is usually not available on most PCBs.
The small loop on the EVB72032 features about -8 to -6dB gain at 868MHz. This means you can consider an ERP of about 2 to 4dBm at max. O/P setting.
|
A:
Thanks. I'm pleasantly surprised that the gain of this size loop is as high as -6dB.
Do you have any idea what radiation bandwidth could be expected around 868MHz?
|
Q:
Well, the 3dB bandwidth of this loop antenna loaded with the TH72032 output should be in the range of 30MHz, maybe a little less. This is just an estimation. But you could measure the bandwidth by sweeping the PLL reference signal. Usually a reference crystal is used (e.g. 27.1344MHz to yield an RF of 868.3MHz). But you can AC-connect the RO input to a generator to sweep the reference and so you can sweep the RF.
|
Q:
Is it possible to have a description of this antenna cause I'd like to build mine ?
|
A:
The loop dimensions are already given in the EVB description: http://www.melexis.com/prodfiles/evb72032_rev006.pdf . Nevertheless there are some postings and links regarding this issue: "TH72012: need more power" & "TH72002".
|
Q:
Is there a revision of the datasheet for the EVB90121 in which the connection table for JP2 (Table 2) and the schematic (Figure 1) agree? Which is correct?
|
A:
There is indeed a mistake in the documentation of the EVB90121. The table 2 (description of JP2) is incorrect.
We will make the corrections and a new version will be available quickly.
Many thanks for your remark.
|
Q:
While TH7122 is working in FM modulation and user mod,how to set the control words?i set to FSK modulation,but i can not check out any siginal from pin of out_dem,check pin of out_dta,the analog signal has been changed to digital signal.i use headphone connect with pin of out_dta,i hear audio signal,but full of noise.i think that this way is not correct.How to make SW1 closed and SW2 opened in TH7122?Please show me the right way of FM modulation.Thanks a lot!
|
A:
pls. have also a closer look to our Cookbook which describes the FM transmission. It can be found at:
http://www.melexis.com/Asset.aspx?nID=3961&sCmd=download
The OUT_DTA pin is not intended as an analogue output which is necessary for the FM stuff since it is used as a 1-bit A/D converter - the data slicer. As described in the cookbook the OUT_DEM pin should be used instead. It should be clear that also the signal at pin OUT_DEM should be buffered/amplified in order to drive the headphone.
|
Q:
i check the drive current of OUT_DEM,it is very small,about 3uA,it is very hard to deal with,i want to know yours way.
|
A:
The OUT_DEM is only intended for capacitive loading. If you want to drive a headphone from that you should pre-amplify and filter the signal as described in the cookbook. There should not be a resistive loading of pin OUT_DEM.
|
Q:
i have problem about FM modulation and demodulation.I am also confusing that how evalution board used for FM application.Is any
evalution board is available for FM application using TH7122.
|
A:
Please review the RF Cookbook for suggestions and approaches to FM mod and demod.
|
Q:
I wish to acieve as good a SNR as possible in an RF link. One way is I slow my baud rate down and limit the bandwidth of the receiver demodulator. What effect does changing the frequency deviation have? Currently I am using about +/-25kHz. Do I get any benefit from reducing this and using a narrower band IF filter? Any suggestions?
|
A:
A narrower IF filter will give some improvement. Since your data rate is low, you could go to a narrow band FM system, but this either requires a more expensive crystal IF filter or a dual conversion down to 455 or 450kHz so narrow band ceramic filters can be used. For instance, you could use 5kHz peak deviation and filters designed for 25kHz channel spacing. I have used 10.7MHz crystal filters with the TH71102 receivers and gotten -114dBm sensitivity. If you want a schematic, let me know.
|
Q:
we are designing 868 MHz ASK RECEIVER section for a reader. we choose melexis TH71112 receiver chip to design.
can you please help me to brief about using this TH71112 as a RECEIVER 868 MHz.
|
A:
I have not tried to use the receivers for this application. The problem is that the transmitted read signal is very strong and much higher than the maximum reciever input, so the receiver will be overloaded. You will need to experiment with your configuraion to see if it will work.
|
Q:
i am using this chip to detect/ receive 868 MHz ASK modulated signal max at +10 dbm. can i get the reception of signal ?
and will i able to get demodulated data at output?
|
A:
The typical demoboard will saturate at about -40dBm. If the LNA is set to low gain, this increases to about -15dBm. You might be able to get it to work by adding about 20dB attenuation on the input.
|
Q:
thanks for information. i am trying to use this receiver TH71112 in RFid reader at 868 MHz. i need to receive ASK demodulated output.
can you brief me more about "ENRX" pin which enables the rx. MEANS how to enable receiver, is there any precautions in RFID reader point of design i should take in to account?
|
A:
The ENRX pin just turns the receiver on or off. When it is off, the current is essentially zero. Remember that it takes about 1mS to start up after the ENRX pin goes high. This is caused by the start up time of the crystal oscillator. Also, the data slicer capacitor must charge up to the average signal voltage, so its value is a compromise between charging time and the longest data pulse.
Since you are the first to use the TH71112 for an RFID reader, it will be interesting to learn of your results.
|
Q:
can i make "ENRX" high for a longer time? i am trying to send ASK modulated encoded data through one transmitter and want to receive using this TH71112.
what is the "ask output" signal format? analog or digital . will it in the form of I or Q demodulated data?
|
A:
You can leave the ENRX pin high. It is used only to save power when the receiver is not needed.
The RSSI output is only the detected magnitude of the carrier, and this goes to a comparator to give the data out.
|
Q:
is this TH71112 supports I and Q modulation.
i.e. dose this chip outputs demodulated data in the form of I or Q ?[ in phase or quadrature].
if not,then can you please explain me how to use this output from TH71112 as i or Q signal.
|
A:
The TH71112 does not generate I and Q outputs. The RSSI is like an envelope detector and is proportional to the square root of Isquared + Qsquared. The IF output is available on pin 15 and goes to one input of the phase detector, named MIX3 one the block diagram. If you have a reference signal, you can apply it to pin 16 and get I or Q from pin 23 depending on the phase of the reference signal. You can add a second phase detector to get the other output.
|
Q:
i test TH71112 by transmitting some data. its receiving but not perfect as per transmitted one.
i want to know what is format of output analog or digital? if ASK modulation is used.
in earlier mail to generate i and q what ref signal i need to feed.
i want to transmit 866 MHz carrier modulated dat and same should be received.
what modification i need to do for TH71112 board?
|
Q:
i used this chip and tested the output.
i am unable to receive what ever i am transmitting. what is the output format of this ASK output ? is it analog?
can you please let me know how should i digitize this output if it is analog. i.e. dose it need external ADc?
|
A:
The RSSI output works like a diode detector. It will detect ASK signals if the receiver input singal is less than the maximum allowed. First look at the RSSI signal with an oscilloscope to see it you can detect the modulation.
|
Q:
i am transmitting preamble pattern for which a am getting square wave pattern at ask out signal. do i need to digitize this? is it analog wave form ? as i need to get digital data [ preamble ] that i am transmitting.
|
A:
The ASK output is a 0V or Vcc logic signal which you should be able to connect to your data decoder. The analog signal is available at the RSSI output.
|
Q:
i checked this chip and found following results:
1. sensitivity mentioned is -112dBm, but practically it shows -14dBm only. at 866 MHz.
2. data rate supported is mentioned as 260 kbps. so it should support minimum pulse width of 4 microsec. but practically its getting saturated at 50 microseconds only.
3. i am not able to get decoded pulse output of 6 microsecond which i required as i am transmitting the same.
4. is it due to chip limitation or circuit problem. my freq is 866 MHz. and i have design board as per eval board document supplied by melexis.
|
A:
The sensitivity is -112dBm in normal operation. At -14dBm it will be saturated. You probably have another carrier present when you are trying to measure the sensitivity.
The internal resistance of the RSSI output is about 36k. In order to get up to 260kbps, you must remove all capacitance on the RSSI pin.
|
Q:
is it possible for me to get a ready TH71112 receiver board from melexis tuned as per my application requirement?
my require freq is 866MHz at which i am transmitting with power of +5 dBm to +10 dBm.
minimum pulsewidth i should be get is 6.12 microsec.
it may be possible that any of my assembled component not functioning properly. so i need this help from melexis.
also can you please provide me circuit for decoder to obtained digital output.
regards -vijay
|
A:
I tested one of my boards with a pulse width is 6uS with C16 removed and the standard ASK circuit but with 100k for R4, and the LNA set for low gain. It will detect ASK signals from 0dBm to -50dBm.
|
Q:
thnks for information.
i tried with my board but its not giving proper results.
Can i get evaluation board for TH71112, with customised modification for 866MHz, and with changes for 6 us. from MELEXIS?
so that i can go ahead with my project.
|
Q:
i tried to make changes as you said in reply.
i am unable to get digital output also.
can i buy this board from melexis?with customise changes which you made?
|
A:
Please contact a sales representative to inquire about custom EVB's. Melexis normal does this as part of applications development for larger opportunities. A sales representative can assis in this process.
|
Q:
about th72011 ,i want to ask how to change the center frequency fc,and how to select the value of cx1 and cx2 according to crystal parameters,
|
A:
the center frequency is a virtual frequency between the two FSK frequencies. To change the center frequency the crystal's has to change according to RF/32. The two frequencies in FSK are achieved by deviation of the effective load capacitance seen by the crystal. To adjust the two frequencies CX1 and CX2 is needed. In case of the higher frequency only CX1 is connected, for the lower frequency CX1 and CX2 operates in parallel, connected in series to the crystal. Pls. find the formulae in the data sheet. For calculation of the deviation you need the tuning sensitivity of the crystal measured in ppm/pF and the intended deviation at RF also measured in ppm. Knowing this it is easy to estimate the two equivalent load capacitances (CL1, CL2) which the crystal must see to achieve the two frequencies. Then the value of CX1 can be estimated by using CL1, CRO (see data sheet). CX2 is then a calculation using CL2, CX1 and CRO.
Since the board will add some capacitance an exact tuning of the pulling caps must be done by measurement.
|
Q:
TH7122 3-Wire mode
I have a requirement to pass transmissions that can originate from either end. What is the correct selection for waiting, IDLE or RECEIVE?
Can the FSSI/LD be used on the Receive end (via code) to enable the Receiver - assuming was IDLE?
How much time is available from LD to the first NRZ data bit?
What is the correct way to detect and control a Line Turnaround ie: from Receive to Transmit or Transmit to Receive?
|
A:
normally in such applications a MCU (microcontroller unit) is used. The most convenient way is that both parties are fixed to a packet frame & timing or negotiate for the next transmission. The LD pin indicates the steady state of the PLL synthesizer. In TX mode this signal turn on the PA internally. In RX mode the first packet can be expected after LD goes high plus an additional time constant which is defined by the data slicer setup, i.e. the data slicer capacitor. This cap is set according to the data rate which is used in the system. Pls. refer to pg. 14 in the data sheet. For good results a preamble in the transmitted signal should be used before the pay load of the packet.
If no packet oriented approach is used both parties has to listen most of the time for a valid transmission, i.e. they operate in RX mode. If one of the end has to tell something, the related party should go to TX. But that could sometime be collided if both parties transmit at the same time. To avoid that an acknowledge transmission from the receiver back to the original transmitter should be considered to inform the transmitter that the message was sent successfully.
As can be seen a packet oriented approach has some benefits, e.g. the parties can go to sleep (stand-by or idle mode) at times where no transmissions are scheduled to save energy.
|
Q:
Thank you for the detailed description.
|
Q:
we are using the MLX90121 chip for the rf section in our reader and we have also implemented the amplifier ckt using IRFD110, but as mention in the document of that amplifier it just gives the output power of 1 WATT, but we required the output power of 4 WATT, so please can you suggest us any changes for increasing the output power.
|
A:
In the past we made some experiments to built a 5Watt reader based on the +5V power booster version (three complementary pairs of Pmos-Nmos). But, we didn't get any stable design that can be easily used and implemented.
|
Q:
As we know that to make a 5 watt amplifier from only 5 vilt power supply is near to impossible but we have tried it with 12 volt supply an then aslo we could only the out put of 2 watt. this work was done from the schematic given in your documents, so now the problem is for the return path. In return path (two schematics in your one of the documents )are not working for the power of 1 or 2 watt again we are also tring to make a amplifier of 5 watt so please suggest us any of the reliable return path for both low and high power reader system
|
A:
The time constant of the external detector can be a bit reduced by changing the resistor R2 from 22k to 12k.
At that time, we never implemented a power booster higher than 1.6Watt as describes in the power booster application note and we don’t have a complete solution to provide to you. But, the main problem with higher power is the saturation of the diode detector due to the high carrier amplitude and the relatively small amplitude of the back modulated signal. Therefore, a simple solution should be to add several diodes in series before D1, to reduce the carrier amplitude and to avoid the saturation of the diode detector.
Moreover, using several diodes will not reduce the back modulated signal and the ration data/carrier will increase.
|
A:
you should try to use an external detector. there are some app. notes from st micro. by the way we have just done a design with the MLX90121 it works fine
|
Q:
I have searched with the st. micro. but was not able find any optimize solution, actually we wnted to run a antenna of 1M by 1M giving the range of the of one metre. we have designed a reader with MLX90121 but its output power is not sufficient to run such antenna so then we have designed the amplifier which is capable to giving power to some extend, but the main problen is with the return path. so can i get any of the link supporting such problems or any optimize solution for the return path.
|
Q:
hi, try AN1954 from st.com http://www.st.com/stonline/stappl/productcatalog/app?path=/pages/stcom/PcStComDocumentTableView.showTechlitTreeDocs&level0=76&level1=1280&level2=406&level3=0&doctype=15&doctypecode=anp&enttype=4&tname=TL_APPLI_NOTE_PROD_TREE_X_DOC&latest=N
|
Q:
First of all thanks for the concern you have given to us. I have gone through the document given at the link (mentioned above) but the main problem is the range as given in the document it will only work for 10 cm range, small antenna and ISO14443 protocol. we are designing the reader for ISO15693 protocol and we required a range of 1 meter. we have got success in achieving the range of 25 cm but now we are not able to increase the range. so please sir if there is any optimize solution for this problem than reply to us
|
A:
As your requests are increasingly complex it is our suggestion that you contact a Melexis sales representative. That person will coordinate application engineering support for you particular challenge.
|
Q:
We are using the EVB7122-special-37-45-fsk-wb app note with a single frequency of 45.0Mhz.
CF2 100nF PLL loop filter
CF1 1uF PLL loop filter
RF 1.5k PLL loop filter
The time from transmitter start to LD high is 18 ms. Is that correct for those values in the loop filter? Can the PLL lock time be speed up? If so How much?
On the receive side, we are finding that the first 5 bit times (9600 bps right now) are garbage.
C3 10nf data slicer cap
C4 omitted demodulator filter
How can we reduce that start up delay?
For that design, what is the range of NRZ data rates?
|
A:
In this case where the loop frequency is quite low, the lock time depends on the loop filter values and the charge pump current. When the loop is being modulated to generate FSK, this is set by the lowest modulating frequency.
Also, the data slicer capacitor value depends on the longest data pulse. If Manchester or similar encoding is used, all the pulses are the same, a smaller data slicer capacitor can usually be used.
|
Q:
Im working with a PCB loop antenna which has an impedance of about 0.1+j50 at 433.92 MHz. I need to match this to the MELEXIS TH72015 transmitter device.
The datasheet does not give a definite impedance to match to, instead an apps note 'PA Output Matching' mentions an equation for an optimum load resistance. The equation is as follows:
Ropt = ((Vcc - Vsat)^2)/2*Pout
In my particular case, operating at 3V, and transmitting at -12dBm the optimum load resistance computes to 16200. Even using Q degrading to broaden the antennas bandwidth im finding it impossible to match anywhere close to this value (using real component values).
Im wondering is there another way to match my antenna to the device? Or is there some mistake in the method i have used?
|
A:
The Ropt is important only when you want to get the maximum power without saturating the PA. Since you can adjust the power level with the TH72015, it is sufficient to tune the antenna with CM1, CM2, LM2 and reduce the output power of the TH72015 by adjusting RPS. LM1 is there mainly to prevent radiation at harmonics and does not need to be changed.
|
Q:
Just to clarify... you suggest that I match the antenna to the Ropt for the higest power (+10dBm giving Ropt = 162 Ohm)??? This sounds a bit more reasonable value to match to
My main concern is that I do not have a definite impedance to match my antenna to, can you clarift the output impedance of the PA
|
A:
If your loop is about the same size as the EVB, I think you should use the same value for CM1 and LM1 as in the EVB schematic and adjust CM2,LM2 to tune your loop. If your loop is much smaller, then increase CM1 before tuning it with CM2,LM2.
The PA output is an open collector with about 2.5pF capacitance, so the output impedance is very high. The loop presents a load resistance which is determined by the voltage swing and output current. In your case, the current will be so small that the load resistance of the loop is not important.
|
Q:
Thanks for the info... however I'm still confused.
My loop is considerably smaller that the EVB (outer diameter = 12mm)
Am i to understand that the tuning is a 'black art' with no theoretical reasoning? Should I simply used multiturn capacitors, and examine the signal on a spectrum analyser? Then measure the input impedance to calculate the values of capacitances?
|
A:
The loop is simply a high Q inductor, and the problem is that the exact inductance and Q is not known. There are several equations available for round and rectangular loops which give a close value for the inductance, but in the end you must adjust the tuning. The same is true for the real part, so you will end up adjusting the components by trial and error.
One way to tune the loop is to use a signal generator to supply the reference signal to the IC (through a coupling capacitor) and adjust the frequency while observing the RF output with a reciever.
If the peak in the output is below the desired frequency, then increase the tuning capacitance and conversly.
|
Q:
Ok thanks for the help. We are now finding that we need 2 capacitors at the input to the antenna to match to 256Ohm (P = 8dBm)
Can u clarify the purpose of the Lm2 and Cm2 on the other end of the antenna? I think its for the application of bias (through Lm2) and providing an RF ground through Cm2? Is this right?? Is it ok to leave Lm2 at the dame value as for the EVB? And ensure Cm2 is 2 or 3 times bigger than Cm1?
|
A:
The combination of LM2 and CM2 is used to fine-tune the antenna. Usually, if only CM2 is used together with a large value for LM2, CM2 is quite small and one step in the value for CM2 up or down may tune the antenna to above or below resonance. In this case the larger value for CM2 can be used and LM2 can be adjusted to give the correct tuning.
|
Q:
Does Melexis have some product similar to NXP's MF3ICD21 (Mifare DESFire 2K)
|
A:
Melexis does not provide smart card IC's. Therefore, we do not have similar product to the IC you mentionned.
|
Q:
I have seen this IC used in a battery assisted RFID LF tag. I also know online sellers like HKinventory or Accord technologies are selling it.
PROBLEM is I am having ultra hard time locating its datasheet anywhere on the web.
|
A:
unfortunately, we can not help you. We do not have any product named MLX45101 on our catalog.
If HKinventory or Accord Technologies are selling this IC, may I suggest that you ask them directly for its data sheet and technical support.
|
Q:
Looking for the recommended land pattern (footprint). Datasheet has the package description but not the recommended footprint.
|
A:
The recommended footprint is the one used for a standard QFN5x5 package.
|
Q:
I understood from data sheet that with RZ coding like Manchester the average detection works better but if I try it on EVB71120 the DTAO signal is continuosly low. Only if I use peak detection I can see received data on DTAO.
Can someone explain it to me? Thank you
|
A:
Make sure you have a capacitor on pin 19 and pin 15 is grounded.
|
Q:
Request you to send us the Material Composition Declaration for MLX71121.
|
A:
Please contact your nearest Melexis Sales Representative to obtain this documentation.
|
Q:
I'm interested in finding out more about this device.
What is the general cost structure and can I buy samples at reasonable costs.
I can't go anywhere unless I've tried and tested them.
|
A:
You can request samples from the closest sales representaive or from the European sales office.
|
Q:
My interest is in fast startup time. I noted in the thread 'modes of operation(MLX71122)' that the significant factors are crystal startup and data slicer capacitor charging time... but I would like to know if there is a startup speed advantage by loading IFFPRES with a value obtained from an earlier IF filter calibration (therefore presetting IFFTUNE on startup)? Can you please give an indication of the settling time for the auto IF frequency tuning and the typical tuning range from the nominal 2MHz IF frequency.
|
A:
You have several possibilities. If you operated the IC by switching between standby and receive and do not remove the power from the IC, the last IFFPRES remains.
The crystal startup time is quite short because the dividers start operating before the reference oscillator reaches its full amplitude.
You can avoid the data slicer charging time by using the peak detectors.
Also, it is not necessary to make the data slicer capacitor so large that its voltage does not change during the data pulses. It needs to be only large enough so the longest data pulse is not shortened with weak signals. The same is true for the peak detector capacitors. Another trick is to add a silicon diode from pin 27 to pin 32 with the cathode on pin 32. This will charge up the data slicer capacitor when the receiver is turned on and will shorten the time required for the data to charge it.
The 2MHz IF can be adjusted over a wide range, but if it is to close to the limits of tuning, there will be no reserve for autotuning when the temperature changes.
|
Q:
I'm starting new design which includes mlx71122 device for double stage down-conversion, but I would be nice to get analogue audio out of it instead of clocked data (currently we are using fsk modem to generate audio tones out of data, and then modulate it onto carrier as FM signal – so we would like to get audio tones on receive end to feed same fsk modem). Is there a way to achieve it ?
|
A:
Yes. Just use the DFO output on pin 27. It is a very linear demodulator.
|
Q:
Question 2:
We are currently running FM signals with 5kHz bandwidth ... and IC seems to "not like it". At larger values like 100k, signal passes through almost intact, but with 5k signal is VERY distorted, regardless of power input ( even at -10dB straight from modulator ). Is there a way to improve it?
Ps. if any extra details are needed: 433Mhz, 5kHz bandwidth, audio tones of 1200Hz and 1800Hz are only signals that are passing on ...
|
A:
I checked one of my boards. At 5kHz deviation, my maximum S/N from the DFO output pin 27 is about 24dB. You may see noise instead of distortion because the FM detector is very linear, but the noise level is somewhat high. Check your power supply because the MLX71122 is sensitive to power supply noise, and with such a small deviation, any noise could be larger than the signal. Also, it helps to select Halt in the Frequency Control tab after the IF filter has tuned itself, and the high CPCUR in the PLL Control gives slightly better S/N.
|
Q:
I have a signal consisting of a 1kHz carrier ASK modulated with a 100bit/s datastream.
Is it possible to use the MLX71122 with a low frequency signal like this? If not, would it be practical to mix the signal up to 300MHz or
so and then use the MLX71122 for recovery of the data and a clock locked to the carrier?
|
A:
I think the best way to detect this low frqeuency signal is with a PLL like the LM565 or XR2211.
|
Q:
Where do I find information about how to control this chip from a microcontroller, and how to read the data from it? Should I just read data from it when the clock is high?
|
A:
At this time, the DVK90109 doesn't allow to download firmware examples. We have to update this feature as soon as possible.
|
Q:
I don't have a DVK90109, I only have the MLX90109 because I have other kits to use as devkits (AT90USBKEY and AVR STK500), but some kind of information on how to actually use the MLX90109 would be nice to have.
|
A:
The MLX90109 is a 125kHz transceiver very simple to use. You will find lots of information in the datasheet of this product available on our WEB-site.
It requires a DC voltage on the MODU pin to set the field ON (Two resistors). After that, the demodulated information, according to the pins SPEED and MODE, is available on the pin DATA and CLOCK. These two pins must be pulled-up by externally.
To modulate information (100%), you only have to change the voltage on MODU according to the schematic on page 11 of the datasheet. For fast data rates, an external diode and transistor may be added in parallel to the antenna to reduce the fall time.
What I suggest you get the EVB90109 which is a very compact module including a parallel antenna. It will help you to start working with the MLX90109.
|
Q:
please let me know if you have any solutions which customer can go for manufacturing directly.
|
A:
It is unclear what your question is? Do you mean a system level solution ready for a manufacturer to use in his production line to track goods? or do you mean a component that is available and ready for design into a system and production to sell that system? Melexis is a component manufacturer. We typically sell our IC components to customers who integrate board level or module level solutions. Melexis does not supply board or module level solutions only Integrated Circuits.
|
Q:
In the MLX90109's datasheet there is mentioned the reading distance up to 15 cm (with the specified antenna etc). What is the "reading distace up to" if power supply is 3 volts?
|
A:
it strongly depend on the antenna design but with 3V power supply, the maximum reading range should be in the range of 7 cm.
|
Q:
If MLX90109 tag reader chip will work always at the same speed and mode, can i connect pins 3 and 5 DIRECTLY to VCC or GND planes, without pull-up or pull-down resistors?
|
A:
If in your application the type of communication is fixed, the SPEED and MODE pins of the MLX90109 (respectively pins 3 and 5) can be directly connected to VCC or GND.
|
A:
I baught the EVB90109 and DVK90109.But the distance of communication is very short when I test by using your tag and tool and I must alter the position between the tag and the EVB90109 and put the tag on the EVB9019.
|
A:
The MLX90109 was originally designed for automotive immobilizer applications. Therefore the reading distance was targeted at a couple a centimeters. I suppose this is what you experienced with the DVK, right ?
It is possible to increase the reading distance by using a larger antenna. What kind of reading distance are you looking for ?
|
Q:
We need the distance is 5-7Cm.Does the antenna adapt to the application?Why do we need alter the position the tag opposite the antenna for communication.Can you provide the tag specification that provided by you to us?
|
A:
I seems that you were provided with ISO-card tags. In that case it is made with MLX90108, a read-only IC which is compatible with EM4102.
|
Q:
Now Why must I make the tag cling to the antenna to communicate.
another question:Can you customize the 100mm diameter antenna sample according the MLX90109?And pls provide the 100mm diameter antenna parameter for us.
|
A:
If you want customized coils, you will need to talk directly with a coil manufacturer. For historical reasons, MLX did offer one specifc coil (MLX90125) but it is not our intention to continue this route. If you wish I can provide the name of our MLX90125 supplier which is located in Spain but I am pretty sure you can find local supplier in China.
|
Q:
Can you tell me if the chip is the MLX90124 in the tag that you provide in your tools?If it is not,pls provide the tag datasheet to us.
|
Q:
he MLX90124 is only an IC. If you want to source an assembled tag, you need to refer to a tag manufacturer, like Sokymat (www.sokymat.com).
Sokymat manufacturer the tags we provide together with the DVK90109.
The MLX90109 can support the following standards : Unique ID, Hitag 1, 2 and S.
|
Q:
I am interested in making my own RFID reader system using the MLX90109 RFID tranceiver. The datasheet for this chip doesn't describe the instructions and instruction format necessary to interface the MLX90109 with my own microprocessor. I will buy the chip once I get this information.
|
A:
You can find examples of instructions in the datahseet of our Development Kit, called DVK90109.
|
Q:
I am using MLX90109 and I want to increase the read distance up to 7cm. I am getting 2.5cm at the moment. any help will be greatly appreciated.
|
A:
At this time the only solution to increase the operating distance with the MLX90109 is to change the transceiver's antennas. Please find below some points to improve this operating distance.
Increasing the area (size) of the transceiver’s antenna.
Reducing the inductance value of the antenna will increase the current Iant which will therefore, increase the magnetic field produced.
A high quality factor (Q) will improve the energy transmit to the TAG. Care should be taken that a too high quality factor reduces the side bands of the back modulation of the TAG. For more information, please refer to the application note “Antenna design guide” which was written for 13.56MHz systems but is also valid for 125kHz.
Care should be taken to keep the global impedance of the transceiver’s antenna higher or equal to 1kOhms to insure a good start of the MLX90109 (auto start-up impedance).
|
Q:
Do melexis already do an antenna designed for the 7cm range or is it down to the user to design their own for this. if so is there a spec and part no
|
A:
Melexis only makes ICs. We do make eval boards and dev kits to help get started. But in the end it is the user who must design for his own application. you can find some hints and help on antennae design on our web site www.melexis.com
|
Q:
I have build a transponder reader using the MLX90109 and a PIC16F628.
The reader seems to perfectly work with the transponders model TITAN and EM4150 (1 KBit Read/Write Contactless Identification Device).
Our supplier has delivered to model EM4450 (new design of EM4150) from the datasheet perfectly identical to the EM4150,
but do not come absolutely read from the MLX90109.
Which can be the problem?
|
A:
First please check if the transponder replies by measuring with a scope the load modulation on the COIL pin.
Then place the transponder at a distance of 2-3 centimeters to avoid strong coupling which may disturb the communication.
To finish, please have a look to the configuration of the chip (SPEED, MODU and MODE pins) and be sure that the Clock and Data signals are externally pulled-up.
|
Q:
I plan to use in my design RFID 125kHZ reader 90109. For comunaction with 90109 I will share DATA and CLOCK lines with other periferials.
So my question is when the 90109 is in power down mode (pin4-MODU= Vdd 3.3v) what is the state of pins DATA and CLOCK (hi or low)? Is there occur any collision when I send any data with shared lines?
|
A:
The two pins CLOCK and DATA are open drain outputs. Therefore, these pins must be pulled-up externally with two resistors of 100kohm (please refer to the FAQ section of the datasheet).
When the MLX90109 is in power down mode these two pins are pulled-up to the power supply.
Please note that DATA and CLOCK are output pins only. Modules connected to these pins will only receive decoded information from the MLX90109. Therefore, no collision are possible.
|
Q:
We have implemented the amplifier circuit given in your application note “A Power Booster for the MLX90121” (Page no 1 of 9).We have implemented the whole circuit with the RF chip and microcontroller which gets the supply from the USB. With the source of IRFD110 connected to the mod pin (pin 3 of RF chip),we performed different testing, but the required output is not achieved and faced the loading problem.
Case 1: We have taken 12 volt supply from the regulated dc power supply and 5 volt internally from the board means from USB itself. Since the ground of both the different supply is same, We faced the loading problem, which means we were not able to give the supply voltage upto 12 volt, but could only reach upto 7 volt…hence the output voltages are not to the mark.
Case 2: We have taken 12 volt supply from the regulated dc power supply and 5 volt externally from the 7805. but as soon as we connect the 5 volt supply point of the amplifier to the 7805, the voltages at that pin are reduced to 2 volt dc with some ac voltage…hence the output voltages are very less.
|
A:
To avoid this problem, a solution should be to use the +12Volts power supply which, is already needed for the power booster, to generate the +5Volts required by the MLX90121. Then both supplies will have the same reference.
If the circuit really needs to be supplied from the USB, a solution should be to use another power booster which required only one supply voltage (+5Volts). For this, please refer to our application note "A +5Volts power booster for the MLX90121" available on our WEB site.
|
Q:
I am trying to configure 125KHz RFID system using Melexis chipset MLX90603 but no data is on web site??
|
Q:
Would you be so kind as to provide MLX90603 (System in a Package combining MEMS and low power signal conditioning and 125kHz RFID interface)datasheet.
I can not find any info about MLX90603 in your web site.
I have found some introduction about this chip in an article but can not find any in details.
|
Q:
Hello
Could you please provide me a link or send me the datasheet for the product MLX90603. I've been looking for it in this site without any luck. Thank you for your time.
|
A:
Details on this part, MLX90603, can be obtained by contacting your nearest Mlexis Sales representative. www.melexis.com/contact.aspx
|
Q:
We are doing TPMS project. I wonder if the SIP MLX90603 can be realized by several on sale melexis chips.
|
A:
the RF transmitter and receivers are on sale. Especially the TH720xx family is very succesful due to its high power efficiency and stability down to 2.0V.
For Pressure sensing and low power management no standard products are available that can directly be applied for TPMS.
|
Q:
I tried to implement multiband switching circuit with th7122 but it doesn't works I don't know values of CF2, CF1, RF, RPS for this application . I want to work between 200 and 450 MHz
|
A:
First design the 220MHz VCO with an external Varactor diode. Then add a PIN Diode switched inductor in parallel with LO to tune it to the 450MHz band.
Normally an RPS of 22k will give about 10dBm output in this band. CF1, CF2, RF must be designed for the desired loop frequency and damping.
Tuning the receiver and PA sections is a little more difficult because of the wide frequency range. You can use PIN diodes or an RF switch IC to switch filters. The inductor in series with the LNA input can be 68nH as a compromise between the two frequencies.
|
Q:
I only have to transmit, I have implemented a wide frequency filter, but I don't understand your reply.You have described multiband circuit of cookbook that I've implemented. RPS=22k, but CF1,CF2 and RF must be different for each frequency? So I can't work between that frequencies with CF1,CF2 & RF fixed? or what values i have to put for that components?
|
A:
If you use 1uF for CF1, 100nF for CF2 and 3.3k for RF, it should be ok.
LO should be 56nH and then switch 22nH in parallel for 220MHz. The varactor diode is SMV1249 with 8pF in series.
You may need to adjust these values to get the frequency range you want.
|
Q:
Can you tell me if melexis has readymade kit for multichannel walkie talkie..with or without microprocessor..
|
A:
We don't have a complete radio kit. We have an evaluation board which can be set for your frequency and modulation. It can be controlled with a PC using its parallel port and a cable supplied.
|
Q:
can u tell any means fr testing of the circuit?? how can we kno whether all the data frm the words has been programmed into the IC TH7122......
|
A:
You can not read the data. The easy way is to check the current form the power supply. If the current is around 8.5mA in receive and 15-30mA in transmit, it is probably working.
Also, check the tuning voltage at pin 23. It must be between .5V and Vcc-.5V.
|
Q:
Does the 90121 support multiple tags in the field (collision support)?
|
A:
Anti-colllision has to do with the protocol. It should be implemented inside the microcontroller which controls the MLX90121 transceiver.
|
Q:
I want to know few things
1. Is it true Melexis TH7122 only accept NRZ signal for IN_DTA?
2.In technical data section (section 6 ) ,
a) What is the meaning of input voltage Vin min
- 0.3V and Max Vcc + 0.3.
b) What is the Min Input low voltage and Max input high voltage.
I confused because NRZ signal must have +V and -V.
3. Can I connect RS232 output signal (+6v , -6V) direct to TH7122 evolution board. (IN_DTA)
|
A:
I really recommend to have a closer look at the TH7122 data sheet and the brand new TH7122/TH71221 Cookbook. There you will find the answers of most questions and much more info.
+6/-6V would probably destroy the chip. It must be a positive voltage max. at 5.5V and min. at 0V. Again, please spend a few minutes to consult the data sheets etc!
|
Q:
Is it posible to build a pcb loop antenna for TH7122 at 27 MHz?
The pcb dimension are about 3cm x 4 cm.
Are any problem for the connector of the PCB?
Have anybody a soft tool to design the loop antenna?
|
A:
pls. have a look on our 13.56MHz RFID systems and antennas design guide:
http://www.melexis.com/prodfiles/0003929_AN90121_7.pdf
|
Q:
Thank you but what I need is the calculation for the PCB loop (loop width, loop height, number of turns, target capacitance and loop inductance for 27.505 MHz)
|
A:
The available space on your board is too small for an efficient antenna at this relatively low frequency. Pls. have a look at http://www.aa5tb.com/loop.html. Here you will find some formulas. You could also consider a whip antenna which is electrically enlarged by an inductor (as used for RC controlled toys etc.).
|
A:
Many applications at 27MHz use a ferrite antenna. You can make one with a coil which uses a ferrite core or wind one on a ferrite core.
|
Q:
For the last few days I was in trouble with the antenna booster AN from Melexis as can be found at [link] http://www.melexis.com/Asset.aspx?nID=3881 [/link]
I made the exact schematic as layed out on page 1 of the above mentioned AN.
I've set the duty cycle as the AN describes using two multi turn variable resistors of 2k ohm.
I installed the N and P fet, and hooked up the power supply.
The mosfets got really hot.
So my conclusion was that the mosfets were into a conducting state at the same time (which results in a short, as every one knows) since my schematic is the exact same as the Melexis, there must be an error in the AN’s schematic.
I solved it by connecting resistor "R4" to +5 volts and "R2" to ground (which in my case were the leeds of the respective variable resistors.
Some other solution would be to put the NFET into the ground path (instead of in the +5V path as it is with the Melexis schematic) and the Pfet in the +5V path switching speed may get lower, to be frankly I didn’t test this yet, but it should work.
Is there any one else who is experiencing/ has faced the same trouble?
Or did I make a mistake without seeing it.
|
A:
Dear,
After carefully reviewed the situation, it seems that everything is ok in the schematic of the "1watt 5volts power booster" application note.
As you requested, the P-MOS Q2 is connected to VDD (source to VDD) and the N-MOS Q1 is connected to GND (source to GND).
Care should be taken to well adjust the duty cycle of the command signals of both transistor Q1 and Q2 to avoid overlapping and then high power consumption. Following values give good results: R1=R3= 1400 Ohms, R2=R4= 1500 Ohms. The instantaneous power dissipation of both transistors can be up to 1.2Watt but the average power consumption will be less than 500mWatt.
|
Q:
I want to design my own proximity reader but I am new to the design. I want to use MLX90109 but I did not understand the logic of how does it work ,especailly the use of the clock out pin. Also how does it read the ID from the proximity card? and how can take the data into the microcontroller?
|
A:
I think the best is for you to purshase our Development Kit, called DVK90109
|
Q:
I am in the process of building an UHF (915 MHZ) RFID reader. I was reading through the TH71111 receiver and read that it is "Well suited for NRZ, Manchester and similar codes". The tags we will be using will backscatter FM0 (Bi-Phase Space) coded signals. Will this receiver be able to decode this signal, or even just demodulate the signal to baseband and we can use a dsp chip or similar to decode the base band signal.
|
A:
the TH71111 uses an average slicing method for extracting the data from the demodulator output. This is well suited for DC-free codes. Since the FM0 code inverses its baseband phase at every symbol boundary it should be no problem.
The TH71111 RF receiver can be configured to receive ASK information up to 260kbit/s. This is enough to decode the FM0 signal from the UHF TAG at 80kbit/s (because of bi-phase encoding).
Nevertheless, an external treatment must be done to remove the bi-phase encoding.
Another RF transmitter is required to generate the field to power the UHF transponder. As a receiver the TH71111 cannot be used to generate such a field.
Please reduce a bit the RSSI output low pass capacitor C16 (200pF instead of 1.5nF) to work with high data rate.
|
A:
|
Q:
TH71071 vs TH72011
I am doing FSK transmission at 433MHz.
Which transmitter gives longer range: the TH7101 (monopole antenna) or TH72011 (loop antenna) ??
|
A:
You will be limited by the regulations. The monopole antenna is the most efficient and so would give the longest range. The TH72011 can be used with a loop antenna or monopole antenna.
|
Q:
I am designing an FSK receiver using the TH71101 at 433MHz, with data rates up to 40Kbps. I am having problems setting the threshold of the comparator, such that the output swings to Vcc. I have incorporated the AFC using a 10.7MHz discriminator and varactor, feeding the data output from the TH71101 back into the junction of the varactor and capacitor. The tuning of the parallel capacitance with the discriminator lowers the Q, but in so doing, reduces the threshold of the comparator. Pull ups do not improve the output, typically to 1.3v. Any practical suggestions would be welcome.
|
Q:
Application appeared to be trying to drive a resistive load - the output always swings up to Vcc but the drive current is very low. Usually these receivers drive a CMOS gate, so, in this case, it was not a problem. Also, the wide band detector should work without needing an AFC - please refer to the FSK circuit in the latest revision datasheet for the TH71101 which can be found on the Melexis website here > http://www.melexis.com/prodfiles/th71101_rev009.pdf
|
Q:
We have a simple resistive sensor designed to sit in the mouth and wish to transmit values to the outside world through the cheek approximately 10" to a much larger receiver.
Obviously size is critical (like less than 100 sq mm electronics + bit more for flexible antenna). Which product would you recommend for interfacing to A/D and transmission of the resistance measurements?
|
A:
the smallest size FSK/ASK transmitters are in micro leadframe packages (MLP) measuring only 3mm x 3mm. They are:
TH72005 (290 to 350MHz),
TH72015 (380 to 450MHz),
TH72035 (850 to 930MHz).
We have seen much smaller than 100sqmm PCBs using these TXs together with a low profile SMD crystal, a small MCU etc.
|
Q:
Hello sir,
I am working on 13.56 Mhz RFID (MLX90121) project. I am little bit confuse on using symbol transmission method. T CK and Din lines are used to transmit the symbols, but I still not clear about the following:
1. Is that the width of the CK pulse be concerned?
2. Does the microcontroller need to provide the addresses of the symbols to be transmitted ?
3. Does the microcontroller send any neccessary signal through Din line during the transmission time(request)?
4. To transmit sym0, does the microcontroller need to send any pulse clock?
5. According to the MLX90121 data sheet(Mar/04), page 13 of 25, the three start bits are used to transmit sym0 to sym6. I really confuse because sym1, sym2 and sym4 all have one CK pulse what make the hardware encode the right symbol to transmit? is that the address involved to encode this symbols?
|
Q:
Melexis is selling a development kit called DVK90121 which comes with the basic ISO commands.
I would recommend that you use this kit to help with the development of your application.
Here are the answers to your questions:
1. The maximum frequency of the CK pin is 1MHz (page 4),
2. Yes. The address should serialy given on the DIN pin using the rising edge of CK (page13),
3. See 2.
4. Sym0 can be encoded with only 1 bit on DIN, requiring only one CK pulse if you use only 2 symbols; or with 2 bit on DIN, requiring 2 CK pulses if you use up to 4 symbols; or with 3 bit on DIN, requiring 3 CK pulses, if you use up to 8 symbols (page13).
5. The initial 3 pulses on CK are used to intiate the transmission. Then you use as many CK pulses you need to encode the address of the symbol you intend to send out.
|
Q:
I am recently using the 13.56 MHs RFID Transceiver, MLX90121 for my project. I went through the datasheet but did not see the internal SPI port. Is that ok if I interface with the SPI of the microcontroller? Please ive me an advice what how can interface with the AVR microcontroller !
|
A:
The MLX90121 doesn't feature a SPI port. The interface is proprietary in order to allow for real time data transfer.
In principle, this interface is clearly described in the datahseet.
It has a 3 wire interface than can be hooked at any of the I/O ports of an ATMEL.
|
A:
|
A:
|
Q:
We would like to develop RFID reader for 915 Mhz frequency.Is any chip available for this frequency ? Or maybe any analog frontend that can be used for this UHF frequency ?
|
A:
The problem with UHF RFID readers is the requirement for a very large dynamic range of the receiver because the transmitted signal is large and is present when the receiver is operating. This usually requires a passive mixer or an active one operating at a realtively high current. If you can find a way to reduce the signal level, you might be able to use the RSSI output of our TH71111 or TH71112 receivers.
|
A:
thank you for you inquiry. We are just about to develop a 860 to 960MHz reader. The plan is to have first engineering samples in Q4-09. Here are some general features of the IC:
Full-duplex transceiver
Highly linear RF input
Fully integrated PLL-based synthesizer
Quadrature direct down-conversion architecture
Digital channel filtering and base-band processing
Low shut-down current consumption
Wide operating temperature range
Highly sensitive Listen mode
ASK or PR-ASK modulated RF carrier for Reader-to-Tag communication
On-chip power amplifier
High over-all frequency accuracy
32-pin package 32L QFN7x7
You can check the TH71221 RF transceiver data sheet. It could be used as an analog front-end. Of course, this 27 - 930MHz transceiver wasn't optimized for use in UHF RFID.
|
Q:
I would like to know which RFID cards manufacturers could use with mlx90121 reader.
|
A:
You can use all the RFID cards which are compliant with the following standards:
ISO14443A
ISO14443B
ISO15693
Manufacturer doesn't matter.
Please see the MLX90121 datasheet for more details about the conformity with RFID standards.
|
Q:
for a senior project, thinking to make something like this, RFID PC security
, can someone please suggest the Melexic's RFID tag and receiver? And can someone gives me some insights and suggestions ?.
we are required to use our own 68hc12 Microcontroller to interface the RF signals ..
the project goal would be .. somehow, program our own TAG(transponder if it's what it is) ..and send RFID data to the MLX90109 transceiver .. then MLX90109 would send the RFID data to the 68hc12 microcontroller, and then to the PC .. in which we will make our program to determine the data and verify the user identity for access rights ..
do all these sound logical and doable to you?
will all those pieces(transceiver and transponder) i mentioned do the job in this case?
had been trying to read more information ..
thinking to use MLX90109 125khz rfid transceiver ..
in which i can still found on Melexis webstore ... and about the transponder ? .. can someone gives me a suggestion ?
i couldn't find any of these three transponders from the webstore .. MLX90108, MLX90110, MLX90111 ..
Will any of these 3 work well with MLX90109 for the project i plan to do? ..
|
A:
I will try to answer to all yours questions:
Melexis has two RFID transceiver ICs available: the MLX90109 (125kHz) and the MLX90121 (13.56MHz). The selection between the two depends on your system requirements (reading distance, size of the antennae, ...)
Both of them can be driven by the 68HC12.
Please note also that Melexis doesn't offer standard transponder ICs any longer. This is why you couldn't find on our WEB site obsolete references such as MLX90108, MLX90110 and MLX90111.
Our DVK boards are built according to the system you described TAG <-> Reader (beased on either 90109 or 90121) <-> PC. So, it shouldn't be any problem to develop the application you described. Please note that the reading distance of the MLX90109 will not exceed a couple of centimers, unless you use very large antennae.
|
Q:
We have the MLX90121 Evaluation and Demonstration board. As I tested the Demo board, when I connect your coil to output, there is no power transmission and I should set the port and send command by computer to make transmission on. We want to use this reader just as a power transmitter. My concern is that whether it is required to use a microcontroller to power up the reader chip or we can just connect the supply of reader and use it as power transmitter. In the other way, does the reader need any data for starting power transmission or can we use the reader without microcontroller for power transmission.
|
A:
After power-On, all registers of the device are set to default values. According to the datasheet page 20, the two bits of Power states are set to "00" meaning that the device is in Idle mode (oscillator on but field off). As a consequence, you will need an external microcontroller to configure these two bits with the value "01" (field ON).
|
Q:
I was wondering if you could email the quality roadmap for RoHS compliance? Or if you have a list of currently available product in lead-free, that would also be a big help.
|
A:
Hello,
You can find our ROHS statement via:
http://www.melexis.com/quality_leadfree.asp
We don't have a list with leadfree products.
But I you have a specific question, please just ask and we will try to answer you asap.
Thank you!
Best regards
Evi
|
Q:
The part I am interested in is TH71102ENE, is this one RoHS compliant?
|
A:
Yes, the TH71102ENE is ROHS-compliant.
|
Q:
Has anyone got an RSSI output plot of some sort for the TH71101 rather than just the two points shown in the data sheet?
|
A:
If you send me an email, I can send you a plot taken from a typical receiver. Remember that the absolute level is not well defined, but the slope is very consistent.
|
Q:
i use the th72011,we find a abnormity signal with spectrum analyser.
i have three pictures, but i don't know how to post them.i will send them to you if somebody can help me. thank you!
PS:
1st picture: circuit diagram
2nd picture: copy screen of spectrum analyser
3rd pciture: Frequency Sweep of the crystal(13.56MHz 20ppm)
|
A:
I have not seen the pictures but can guess what the problem is. The load impedance presented to the output stage is too high, so it is saturating and causing instability. You should change your matching network (make the C across the PA output larger) so that the load impedance is lower.
|
A:
I have now seen the pictures. It looks like the crystal has a strong spurious resonance close to the main resonance. This is probably causing the high spur level. There is an application note
called Crystal Selection Guide which deals with this.
|
Q:
Is there a spice model for the TH7122? in particular I am interested in modelling the PLL.
Thanks
|
A:
It would be almost impossible to provide a spice model for a device as complex as the TH7122. If you need any help with a specific PLL application, we may already have the circuit designed.
|
Q:
My new application is based on the 3rd generation fsk transmitter th72031 specified to work at max 125 degree celcius. what are the design considerations to be counted when the device as well as reference crystal are affected by temperature simultaneously?
|
A:
From the chip point of view nothing special has to be considered other then using this chip at 85 degree C or at room temperature.
Regarding the crystal issues please contact your crystal supplier directly.
At these high frequencies, the crystal drift becomes the most important parameter. The IC itself will meet all the data sheet specifications, but for FSK applications, you may need a receiver with a wide band detector or AFC. Most of the crystals are AT cut with an S shaped temperature coefficient.
|
Q:
I'm looking the datasheet of this product, which I guess is obsolete and might be produced by Thesys. Could you help me?
|
A:
This is an ASIC which has been developed for a specific customer and we are not allowed to disclose any details without their permission.
|
Q:
We are having issues with Canada's reinterpretation of occupied bandwidth (OC) with this chip now 'failing' the 0.25% occupied bandwidth requirement at 433.92MHz (99% of TX power must fall within 1.08MHz or so). The people we are talking to are bent on getting rid of the whole mask/general limit go-no go gage and are simply summing the power from the transmitter to come up with the OC.
Modulation is AM-OOK and the spectrum distribution matches the curve found on your rev 8 datasheet, however the test stipulation is that you have to use the actual modulated pattern, not simply CW, causing a loss in the S/N and losing more margin on the OC calculation. Do you have any PLL filter or XTAL oscillator optimizations/changes to rectify this issue, or is the noise inherent in the divider/PFD architecture (right now the latter is my bet, in which case do you have a better chip available)?
While this doesn't affect our current product mix, new designs will have to deal with it.
|
A:
Because of recent changes in the measurement method, we are having some difficulty understanding the Canadian regulation RSS-210, sections 5.9.1 and 6.1.1. I will continue to study them.
|
Q:
Hi, I need to set TH7107 center frequency to 369.5MHz and frequency deviation to +-35kHz. The evaluation board datasheet has component values for 315MHz and 433.92MHz only. Could you provide the setting for 369.5MHz+-35kHz?
|
A:
the component values should be in between the values for the 315 and 434 MHz versions, but we don't have a tuned EVB for 369.5MHz. This is because we don't have quartz crystals for each non-standard frequency available. You should replace the existing crystal on the EVB (or your board) by a 11.54688MHz crystal. The rest is only fine tuning of the matching/antenna network and the pulling caps.
|
Q:
Can anyone plz tell me what is the range for TH71071?
|
Q:
It doesn't make much sense to specify the range of a transmitter IC alone. First, the chip has to be used on a board/module together with an antenna (incl. matching network). This defines the ERP (effective radiated power). Second, there is a receiver needed at the other side. This device has a certain input sensitivity. The lower this value (e.g. in dBm or uV) the better (from a range point of view).
I can tell you other customers usually use this IC in applications were they transmit data over a range of up to 200m outdoor. This is with good antennas in the TX and RX. If the antennas are bad (which is the case in most of applications), then you can typically still count with 10 to 20m.
|
A:
i think i will use TH71071 for transmitter, and for reciever TH71101.
Actually i was doing a third year project, where i have to make more than two fire detector talk to a remote terminal wirelessly. Thats why i need the recievers to understand that the control terminal wants to talk to one perticular detector! not the other!
is it possible with TH71101? And if it is posssible can u give some idea how to do it? because i do not have much ideas about these transmitter & recievers!
|
A:
You should use an encoder in the transmitter and a decoder in the receiver. So you can assign a code to each detector. The receiver should then check the data to decide from which detector they come.
Companies like Microchip or Holtek are offering a range of encoders and decoders for that purpose. Please have a look at their web sites.
|
Q:
The frequency range of TH7108 is 850MHz-920MHz.
Can I use it in 800MHz? Thank you.
|
A:
The 850 to 920MHz freq. range is to guarantee operation over full temp. and supply range.
It should work at 800MHz at 3V and 25degC. But you should test it yourself as we are not testing this during production test (because it's out of spec).
Note that the TH7108 is not recommended for new designs. I assume your application is low volume? In this case you may order some samples at your local distributor.
Regards
Karl
|
Q:
I'm building an FM transmitter/receiver for audio use using the above
mentioned chip. However I haven't been able to locate a suitable crystal
(27.1344 MHz required for 868.3MHz operation) anywhere. I did
get
some crystal oscillators (XO) from Taitien, but I'm wondering if I can
use
these at all. TH7108 uses both RO1 and RO2 for the xtal and
modulated freq. inputs.An XO in the RO1 input should work OK, but the varactor diode in the analog input & RO2 presents a problem. How should it be connected?
|
A:
first please note the TH7108 will be phased out in 2007. I don't know what your volume demand is. Please tell me. But I guess your volumes are low and so you may just place one or a few big orders very soon to cover your lifetime demand.
You can purchase 27.1344MHz xtals from many vendors, e.g. ECS (via Digi-Key) in the US, Hongkong Xtals in Asia, Euroquartz or Telcona in Europe.
An external XO is not needed and would be too expensive.
The FM circuit emplyoing a varactor diode is shown in the latest data sheet on page 9.
|
A:
Hello Lasse,
some websites of the Xtal manufacturers mentioned by Andreas:
http://www.digikey.com
http://www.chinafronter.com/ (Hongkong Xtals)
http://www.euroquartz.co.uk/
http://www.telcona.com/
http://www.ndk.com/
best regards,
Tanguy
|
Q:
Hello guys, and thanks for the replies.
Yes, my volume is low (just a proto for now). I already have those XO's so I might as well use them if it's possible. I have the datasheets and I also got some schematics on how to connect the XO's to the RO inputs of TH7108 and TH71112. But no idea about the varactor/RO2 input...
|
A:
if you input a signal from an external source (in your case the XO), the source itself should carry the modulation. You cannot pull the XO like we do with an XTAL + varactor.
An alternative way of applying modulation is thru the loop filter. Means you input your audio signal via an RC low-pass filter to pin LF2. This is so-called direct VCO modulation. The problem here is that the audio signal bandwidth should be larger than the PLL BW. But the TH7108 PLL BW cannot be much smaller than say 200 to 500kHz. Nevertheless you can try this.
|
Q:
I am doing a project using the TH71081 IC with ASK modulation. For ease of implementation, I used the test circuit from the data sheet as a basic circuit design (with a frequency of 915MHz instead of 868.3MHz). The problem I'm running into is that the output power is far too low (-38dbm on spectrum analyzer @ 915MHz) compared to what I expect. I've set R1=0 and left R2 open so that power output should be max. I'm also wondering if there is a way to model (on SPICE) the impedance matching network on the output (comprised of L1,L2,L3,C1,C2,C3) so that I can set the right values for these components.
Any other help would be appreciated.
|
A:
Make sure the voltage on pin 4 is 2V or greater. If it is low, the output will be low. Otherwise, you can use the values on the data sheet. 915 is close enough to 868 that you can use the same values. The output is open collectors so Spice values are not much help
|
Q:
It seems that in my door transmitter chip TH71081 doesn't work anymore. Can you suggest any replacement and what I will have to change in
my transmitter.
|
A:
We can suggest following replacements:
TH72031 Transmitter - 868/915MHz, FSK (SOIC8)
TH72032 Transmitter - 868/915MHz, ASK (SOIC8)
TH72035 Transmitter - 868/915MHz, FSK/ASK (10L QFN 3x3 Dual)
For an overview of the main parameters you can download our quick section guide:
http://www.melexis.com/Asset.aspx?nID=3752
For pricing, sampling and purchasing I would like to point you to our local partner in Slovenia:
IC Elektronika d.o.o.
Vodovodna cesta 100
Ljubljana.
1000 Slovenia
Phone +386 1 5680111
Fax +386 1 5689107
E-mail prodaja@ic-elect.si
Web www.ic-elect.si
|
Q:
The circuit is a varactor tuned narrow band FSK application as in the datasheet. The center freq. is 445.3625Mhz (Confirmed with a RF generator-Signal strength at max (RSSI=2.15V) when in center. A 5kHz modulation deviation with a 1kHz as modulation is used the check the output. The modulation signal (1kHz) only appear on the output if the center freq. is lowered by about 110kHz. The RSSI is then 1.8V and the 10.7Mhz IF is stable in both cases although much smaller at the lower freq. If tried to change the R3 and CP component values to change the modulation back to the 445.3625Mhz center freq. but with no success. Any advice how to go further? The Sch and PCB layouts are available in PDF.
|
A:
I suspect the problem is the ceramic discriminator tuning. You can do it without a varactor by increasing C12 to 12pF and adjusting CP for correct tuning of the discriminator. I have a circuit for 447.65MHz which I can send you.
|
Q:
An RF signal generator has been connected to the antenna with a carrier of 433.92MHz and modulation of 10KHz. With a known input at IN_LNA, the signal at OUT_LNA has been adjusted for peak signal by adjusting the values of the tuned LC circuit. This gives a gain of 10 including a front SAW filter. According to the app. note, the internal LNA has a gain of 25dB. How can this been achieved and is this a suitable procedure for maximising the gain of the system. What effects does this have on the sensitivity, or does this affect the image rejection. Please advise on achieving the optimum performance.
|
A:
The LNA is just a cascode bipolar amplifier with very low feedback capacitance. The gain is set by the load impedance and the LNA current. I have never seen any instability in the application circuits, so I am not sure how high you can make it. It will be limited by the largest inductance you can tune with the approximately 2pF output capacitance of the LNA stage plus and capacitance coupling to the mixer. You will not get much improvement by making the gain much higher because the overall receiver noise figure is determined by the standard cascade noise figure equation. The current receiver overall NF is about 8dB. The single conversion receivers have virtually no image rejecton without a SAW filter on the input. If you use the TH71102 dual conversion receiver, it has about 5dB image rejection and slightly better sensitivity. The inage rejection can be increased to about 30dB by adding a double tuned circuit between the LNA and mixer
|
Q:
I am designing an FSK receiver using the TH71101 at 433MHz,but we can't find where to buy this thing part No. CREDIS, SMDtype value :CDSCB10M7GA135"
Can you tell me please
|
A:
The device in question is a ceramic discriminator.. The part number listed is a Murata part number (www.murata.com).. Toko also makes a discriminator that has been used in our evaluation boards..
P/N CDF107F-A0-013. This device is a through hole device (www.tokoam.com)..
|
Q:
I need a TH71102 circuit schematic for 415MHz and some propsal for FM.
can someone please send them to me?
in addition:
I want to use TH71102 as FM receiver
|
Q:
you can find all info to setup the TH71102 for 415MHz in the data sheet. Page 5 shows details on frequency planning. It's esentially just another crystal - compared to the standard 433.92MHz circuit for example. Some LC matching components can also be modified slightly.
The FM circuit is shown on page 14.
|
Q:
I'm looking at using the TH71102 as the receiver for a packet radio setup in the ~440 MHz vacinity. I would use it as an FM receiver and decode the two low frequency audio tones somewhere else. Does the TH71102 have enough selectivity for essentially very narrow bandwidth FSK, i.e. 1200 Hz frequency separation.
|
A:
you could use 455kHz as the second IF for very narrow band apps. There are 3kHz BW filters. This should work for an FSK deviation of 1200Hz. I guess you mean pk-pk?
But in this case, as with all narrow band stuff, the xtal should be trimmed and the ceramic discriminator's loading capacitor as well (if you use a discri).
|
A:
Yes, pk-pk frequency deviation. The carrier would be modulated with 1200 and 2400 Hz signals.
Do you mean there are 3kHz BW filters on the chip itself, or that I could place one externally to the chip?
Is there a version of the eval board with which I can test this manner operation? Or at best could I modify a particular version?
|
A:
there are no on-chip IF filters at the TH711xx receiver family. This should be an external ceramic filter. E.g. CFULA455KH1A-B0 from Murata. This one has a 6dv BW of +/-3kHz. Please have a look at Murata's web site for more info.
All the standard EVB711xx are using crystal to yield 10.7MHz IF filters. But you could inject an external reference signal from an RF gen. to check the performance with a 455kHz filter.
|
Q:
I was wondering if you could recommend a design guide besides the application note AN71102-Low RF to help me design using the TH71102 at 27MHz.
I am trying to understand the sizing of components at 27MHz the app note indicates it is designed for 40.68MHz
My design must be able to recieve at 300 yards using FSK
|
A:
thanks for considering the TH71102 for your 27MHz application. OK, the xtal freq. can be calculated by REF = (RF+IF)/2 = (27+10.7)/2 = 18.85MHz. Other passive components that should be tuned from 40MHz to 27MHz are L2, C4, L3, C6, C7, C8, L4 and L5. You can use the well-known equation for a parallel resonant circuit for the single tank combinations of L2/C4 and L3/C6. This is f0 = 1/(2pi*sqrt(L*C)). The same eq. applies for the combination of L4/C8/L5 but you use just 1/2 of the C-value as there are two Ls in the circuit. C7 defines the coupling between the two LC tanks. I would try something between 27 and 33pF. You may use the same 100nH inductors and just tune the capacitors a bit up to resonate at 27MHz. That's it.
|
Q:
i have some problems:
1,how to connect the pin27(ENRX) and pin 21(RSSI)
2,from the datasheet and EVB we can see that the CERRES(made by muRata) has 2 pins,one is connected to pin16 and the other is connected to GND, but from the test circuit of the CERRES,i find that the CERRES should connect to the VCC.
|
Q:
1) Please have a look at the data sheet. ENRX is to enable/disable the receiver IC by applying either a logic LOW (0V) or a logic HIGH (Vcc). Go to page sec. 1.4 for details. RSSI is the RSSI output. Go to page sec. 3.4 for details.
2) Again, please read the latest DS and EVB description. CERDIS is always placed between IN_DEM (pin 16) and GND.
|
Q:
I'm currently working on receiver for japanesse standard. I chose a frequency to have 10mW (429.2MHz) power. Unfortunatly the receiver does not meet the ACP power 40dB limit (i'm near 35dB).
Can somebody confirm me if there is an issue to reach or surpass the 40dB or if as i think the max value i obtain is inherent of the TH71102.
Sorry for my mistake. It's on the transmiter TH72011 that the ACP for 12.5kHz BW doesn't complies the -40dB level needed for ARIB STD67. The receiver TH71102 work fine at the chosen fréquency.
|
A:
This is a very difficult standard to meet. We have had some success by adding a 100 Ohm resistor in series with pin 3, the FSK switch. If this does not work, it might be better to modulate the crystal with a varactor diode. The modulating signal can also be filtered with a simple RC low pass so the transitions are slower.
|
Q:
I try the RC filter (Bridge T filter too) on the command with no sufficient improvement. I have the same conclusion as you that the varicap is prehaps the best way to get some good result.
For the moment, because i need a prototype rapidly, i change the frequency to 426MHz that allows less power but need only 25Khz band pass, so it esealy meet the 40dB ACP.
|
Q:
My evaluation board evb71102 , TH71102 was
faulty , after change the IC ,measure the XTAL RO pin26 ,no oscillation , check ENRX pin is high ,total supply current is 8mA @5V,use ASK
circuit , OUT_OA have some noise pulse , the RO pin26
is 4.8V @ supply 5V
,check Xtal OK ,PIN27 5v ,PIN25 0v
it ssem like RO voltage have problem ?please advise
|
A:
first I would like to know why you think the original IC soldered on the EVB was damaged. Normally our EVB's are intensively checked and tuned before they will be delivered to our customers. Now you have problems with the new soldered IC. Please note that measuring the pin RIO with a probe (which applies additional capacitance to the RO input) will decrease the negative input impedance of the oscillator which is necessary for a stable and reliable oscillation. So the measurement can cause the stop of the oscillations. Pls. try to observe the oscillation at pin ROI with a low-capacitance probe (max. 2pF).
I assume the original population of the board is still there, except the IC - otherwise pls. indicate what was changed.
|
Q:
I check the Xtal 23.5Mhz cannot probe using oscilloscope probe , or multimeter probe , it will cause the oscillator to stop , need to check it with sort-wave radio , or spectrum analyzer .
I think the oscillator design is very low power ,
anybody think this is correct behavior ?
|
A:
Measure the DC voltage on pin 29. This is the control voltage for the VCO. If it is between 1V and 2V, the Xtal oscillator is running and the receive is working. Make sure you are checking the receiver at the correct frequency, 433.92MHz. Check the RSSI signal with the signal generator.
|
Q:
I'm working in an FSK application with 650 kHz BW, 1 Mbps. What is the factor that limits the FSK maximum data rate to 180 kbps? Can this rate be increased with some external circuitry like buffering for the quadrature demodulator? Or do I need a separate demodulator?
|
Q:
Maybe there is a typo in the part number you listed? (TH71112 is Melexis 868/915MHz receiver, not TH7112). The TH71112 max data rate is limited to 180kbps, the output stage impedance with capacitance to ground limits the response. Also, please verify 650kHz BW / 1Mbps data rate / your intended FSK frequency deviation, this is not practical for an FM detector = discriminator based FSK demodulator. The FSK deviation will also be low for matched filter (mark / space) type FSK detectors.
|
Q:
Although the TH711xx family specs indicate 315Mhz and above, will they work reliably at 216Mhz?
I need bare bones FM audio, RX only, at 216-217Mhz. Is the TH71221 my only option?
|
A:
the lowest input frequency is 260MHz if the double conversion receiver (TH71102) is used. This is because the range of the internal VCO. The TH7122x contains an VCO having an external tank circuit which can easily achieve an input frequency of 216MHz.
|
Q:
To use the TH7122x in RX only mode in the range of 216-217Mhz for FM audio voice, which components associated with transmit mode could I leave out of the circuit to reduce costs without causing undue problems?
|
A:
Pin OUT_PA can be connected to VCC and pin PS_PA to ground w/o any additional components. Also pin FSK_SW can be left open because CX2 is not necessary in RX mode. The antenna matching would be much easier - pls. have a look in the data sheet for the LNA input impedances.
|
Q:
Thanks for prompt reply and info.
|
Q:
I have bought a few TH7122. I need them to transmit at 187.5MHz. Is there a way to calculate all the external components for this freqency?
I can see i need to add an external varactor diode, but what size components do i need??
|
A:
The internal capacitance with a 3V supply it approximately 3.37 to 4.34pf. With a 5V supply, the minimum is approximately 3.06pF. Theoretically, you could just use a coil to tune with this capacitance, but the impedance would be very high and this results in high oscillator phase noise. The external varactor allows you to use a smaller coil and achieve a wider tuning range and low phase noise. I can send you a spreadsheet for calculating values if you provide me with an email address.
|
Q:
I would like use this chip (TH7122) at frequency 500MHz~600MHz.
, but I don,t know the external LC tank value, or
to alter any value.
Lo=?(VCO tank inductor)
LTXO=?(TX impedance matching inductor)
|
A:
You can calculate (f2/f1)^2 and divide L0 and LTX0 by this value. It is easier to change the capacitor on the LNA tank bu this ratio. f2 is the new higher frequency and f1 is the frequency of the evaluation board.
|
Q:
can Th7122 return Rx mode automatically after transmit mode
to wait new data ?
or do we change the state between RX and TX mode ?
|
A:
please have a look at the data sheet, you have always switch between TX and RX and vice versa
|
Q:
Hi, I have some questions about TH7122:
1 I think a signal "LD=1" should be detected after power up to show that the transceiver chip TH7122 is in a normal state, then I can not detect such a signal even though I have tuned the external inductor and capacitor, what may be the problem please?
2 How can I know the control words are successfully programmed into TH7122?
|
A:
LD=1 when the loop is locked. Check the tuning voltage at LF, pin 23. If it is not between about .3V and Vcc-.3V, the VCO tuning is not correct. If the voltage is low, the inductor is too large or conversly. I find the easiest way to know if the programming has been successful is to monitor the power supply current. If it is around 8.5mA in receive or 15-30mA in transmit, it is usually ok.
|
Q:
Need info on if this IC can be used for 2-Way RKE
|
A:
The TH7122 is a RF transceiver front-end (Reception and transmission modes) that can be used for all ISM bands between 27 to 930MHz. After, it depends on your application and the ISM band it may use. You may find more information on our WEB-site www.melexis.com.
|
Q:
Sorry to bother but just ran into another question.
I just realized that my driver has a hole.
If the Mode is set to IDLE will the Receiver detect the carrier and cause the LD?
If no LD during IDLE, how can I know that the Receiver requires attention?
Thanks & Happy New Year!
|
A:
You have two choices for Idle Mode. One is the reference oscillator running, and the other is the PLL and reference oscillator running. The LD signal is available only when the PLL is running.
If the reference oscillator is running, the current is less than 1mA, but the start-up to receive or transmit is very fast. If the whole PLL is running, the current is around 3.5mA.
Remember that if the Idle Mode is set for the PLL running, the PLL remains at the frequency it was set to when Idle Mode is enabled.
The receiver is not operating in idle mode.
|
Q:
TH7122 used with external 3W interface from Atmel AVR series.
I am somewhat math-challenged so need some help.
Can someone tell me how to set the registers for TX freq 31.0mhz and RX at 49.0Mhz assuming 8.00mhz crystal?
Also, I will be leaving the RX freq listening for traffic, so guess need to know how to set the Ref Osc.
|
A:
The easiest way is to run the TH7122 software and set it to the desired settings. The Register Settings tab gives the hex settings for the registers.
Your settings depend on whether the receive LO is above or below the input frequency and if you want to tune to different channels.
If these are the only two frequencies, the settings are for 100kHz channel steps: RR=RT=80
Having the receive LO on the low side puts the image frequency at 49.0-21.4 = 27.6
Receive LO on low side:(VCO=49.0-10.7=38.3)
A Word = 0x9F450
B Word = 0x5EE850
C Word = 0xA4017F
D Word = 0xE80136
Transmit:
A Word = 0x9F850
|
Q:
I purchased the eval board and connected to the pll port, and have set the registers as suggested.
When I run the program, I am assuming that the Load Data writes to the port.
How can I tell if something is going buzz whir? The RO output pin does not have a signal when I set RX or TX mode. If it does, the scope fails to see it. In this test, I have connected only +5V, Grd and the pll port cable. No data connections were made to the eval card.
Is there a signal that can be sampled that indicates functionality? I got the same results when connected to my micro, which doesn't mean anything in itself.
I have even tried connecting the eval board to a different computer with same results: nothing seems to work.
And now for the best news: I had contracted with an Analog/RF engineer to do the RF TH7122 implementation, and now he has dropped out. So we have two digital guys groping in the dark without a clue as to how to proceed. We have assembled the first unit and the digital stuff runs, but not sure what to do next.
Thanks in advance.
|
A:
Moved the Eval board from the 2 XP systems and onto a W98SE. Now the program works!
We can see the RO active while in TX or RX modes, but the freq seems way high. Set for TX=31.0Mhz and see > 400Mhz. Could be artifact of the scope?
Now that we can see a change (such as the RO) investigation needs to follow on the micro/3W to see whats going on.
|
A:
I should have noticed that you were using a 5V supply. The parallel port on some computers does not go up to 80% of 5V as required by the TH7122, so it will not load the data. You can add 10k pull up resistors on the TH7122 board or reduce the supply to 4.5V and then turn it back up to 5V after the data is loaded.
The RO should be a pretty clean sinusoidal signal. Ampitude is about 100mVp-p. It is running in all modes except standby.
|
A:
Thx for reply to Pll port program. At this point it's just as easy to use the W98se system. I'll look closer when time permits.
But even now, the RO is fine at 7.1mhz but when I load with the Melexis EVB7122-SPECIAL-37-45-FSK-WB settings, it seems that in TX node the RF frequency is >400Mhz. I expect to see an offet to the frequencies due to the fact that these settings are for 8.0Mhz and 3.6V, while with the Eval board we are at 7.1mhz and 5.0V.
We have not been able to affect this TX frequency no matter what we do. Tried different eval board, same results. No matter what programmed, RF freq at coax at <400mhz.
Dos anyone have an answer why the Tx freq will not change?
|
Q:
I would like use this chip (TH7122) at frequency 500MHz~600MHz.
, but I don,t know the external LC tank value, or
to alter any value.
Lo=?(VCO tank inductor)
LTXO=?(TX impedance matching inductor)
|
A:
You can calculate (f2/f1)^2 and divide L0 and LTX0 by this value. It is easier to change the capacitor on the LNA tank bu this ratio. f2 is the new higher frequency and f1 is the frequency of the evaluation board.
|
Q:
I saw in the Application Note "TH7122 and TH71221 High Speed Data Communication" that the transceiver could be used at a data rate of 115kb/s, and not only the 40kb/s indicated in the datasheet.
Could this data rate be obtained in ASK modulation ? because explanations are only given for a FSK use.
|
A:
this high speed VCO modulation can only be done for FSK or FM (just as the app note explains). At ASK, the max. data rate is limited by VCO load pulling effects. The on/off switching of the PA leads to a "frequency kick-off" of the VCO. If you really want to transmit high speed ASK data, you would have to use an external PA with high isolation and an external modulator following this PA.
|
Q:
can Th7122 return Rx mode automatically after transmit mode
to wait new data ?
or do we change the state between RX and TX mode ?
|
A:
please have a look at the data sheet, you have always switch between TX and RX and vice versa
|
Q:
I have bought a few TH7122. I need them to transmit at 187.5MHz. Is there a way to calculate all the external components for this freqency?
I can see i need to add an external varactor diode, but what size components do i need??
|
A:
The internal capacitance with a 3V supply it approximately 3.37 to 4.34pf. With a 5V supply, the minimum is approximately 3.06pF. Theoretically, you could just use a coil to tune with this capacitance, but the impedance would be very high and this results in high oscillator phase noise. The external varactor allows you to use a smaller coil and achieve a wider tuning range and low phase noise. A spreadsheet for calculating values. Please contact your local sales representative to coordinate the request to an applications engineer.
|
Q:
I need to transmit at 600MHz in programmable user mode-FSK application circuit, because no 600MHz at TH7122 datasheet FSK test circuit component list.
1. Is there a way to calculate all the external components for this freqency? ( example:impedance matching inductor,tank inductor,matching network etc.)
2.I am use TH7122, no use EVB7122
|
A:
Stuff like this will be well explained in the TH7122 cookbook that will be released in the first week of May. It will be available on the Melexis web site.
The internal varactor diode between pins 20 and 21 tunes from 3.3 to 4.3pF (at 3V) or 3.0 to 4.3p (at 5V). This should give you a handle to calculate the tank inductor. I would try to start with values of 18nH or 22nH.
|
Q:
I need to transmit an analog signal(PWM from a uP)(490Hz) on 187,5MHz with a th7122.
I have a schematic of: EVB7122B-218-219-NB-FSK.UTSCH - EVB7122.
I was told to just increase C13 and C9. Would C13=18pF instead of 15 pF, and C9=10pF instead of 6 pF do? Or do i need to go higher?
Now i have read the cookbook. It says that i need an extra varator and a sallen key filter at RO and DEM_out to make an FM-transmitter?
Could you help me with the right design please?
|
A:
the cookbook circuit in para. 3.7 shows how to generate an FM via crystal pulling. This circuit can process data containing DC (like NRZ code). The direct VCO modulation circuit in para. 3.4 is according to the schematic you are referring to. It works fine if the modulating signal is DC free (like Manchester code). This circuit should be fine for PWM.
|
A:
You are correct that selectivity is a funtion of the IF filter.I originally used a SAW filter between the LNA and the TH7122 input in order to reduce a blocking signal.
I found that this somtimes causes instability in the TX mode.It seems to me that this is caused by the PLL becoming unstable at cetain frequncies due to the VCO interacting with the SAW.
I was also interested to learn how important the use of a SAW is in actual operation.Here in Israel we founnd that despite good sensitivity ( better than -105 dBm) in the lab we could only get a rsnge of some 20 m outside until we added a SAW filter.Then the range was over 200m with a +10dBm TX.
I am interested to know if the use of a SAW is recomended in other countries and if it is also recomended for a 433.92 MHz sytstem?
Also I am intriged to know if the 10.7 Band pass filter you suggest , in your cookbook,might be a good replacement for the SAW as it offers an extra 30 dB
|
Q:
|
A:
|
Q:
I am using 7122 in a 868 MHz OOK tranceiver.
I use a SAW filter in the receive mode to improve my RX selectivity but this causes oscillation in rcecive
|
A:
A SAW filter can't improve selectivity because this is done with the IF filter. But it improves image rejection and blocking performance. A SAW filter is best placed between LNA output and mixer input. Capacitive loading at the LNA input (e.g. caused by a SAW filter) can lead to instabilities - please also refer to para. 7 of the cookbook for details.
yes, sometimes a real world environment changes the performance quite a lot. I think Israel is a country with lots of wireless services (obviously too many). It's maybe similar to the UK in Europe.
If your application is expected to be faced with harsh or maybe unpredictable disturbing signals then a SAW filter is always recommended. It must protect the RF section from jammers, so it should be placed either in front or after the LNA. The first approach is problematic at the TH7122 at frequencies higher than say typically 434MHz - for the known reasons.
A better IF filter can "only" improve selectivity and sensitivity but is not necessarily a help to improve blocking and jamming immunity. So you are on the right track using a SAW filter, but it would be better to have it after the LNA.
|
Q:
I saw in the Application Note "TH7122 and TH71221 High Speed Data Communication" that the transceiver could be used at a data rate of 115kb/s, and not only the 40kb/s indicated in the datasheet.
Could this data rate be obtained in ASK modulation ? because explanations are only given for a FSK use.
|
A:
this high speed VCO modulation can only be done for FSK or FM (just as the app note explains). At ASK, the max. data rate is limited by VCO load pulling effects. The on/off switching of the PA leads to a "frequency kick-off" of the VCO. If you really want to transmit high speed ASK data, you would have to use an external PA with high isolation and an external modulator following this PA.
|
Q:
we are using your chip TH7122 on our board, and now we have TX freq deviation defect recently.i am analysing on that.
my question is: Do you got any test regulation/method to test the TH122? or other suggestion helpful to do the analysis.
FSK via direct VCO mod;
operation freq 433.9MHz
no channel spacing
Modulation: FSK; +/- 50 kHz (peak-to-peak)
28kbps data rate
|
A:
The occupied bandwidth depends on many factors:
- operating frequency
- channel spacing (if there is any)
- modulation type
- data rate
- FSK via crystal pulling or direct VCO mod.
Different wireless standards call for different bandwidths and test methods.
your FSK operating conditions sound reasonable. I am wondering what the "TX freq deviation defect" might be. Can you explain this a bit in more detail? Feel free to send your circuit schematic with components values and a spectrum plot to my privat messenger.
I assume it's for an application in Europe, according to EN300220?
|
Q:
I am using 7122 in a 868 MHz OOK tranceiver.
I use a SAW filter in the receive mode to improve my RX selectivity but this causes oscillation in rcecive
|
A:
A SAW filter can't improve selectivity because this is done with the IF filter. But it improves image rejection and blocking performance. A SAW filter is best placed between LNA output and mixer input. Capacitive loading at the LNA input (e.g. caused by a SAW filter) can lead to instabilities - please also refer to para. 7 of the cookbook for details.
|
Q:
I designed a board based on the external vco as shown in the document EVB7122-special-37-45-FSK and cannot seem to get any reaction from the th7122 after programming with the external host.
So far we have confirmed that the SCLK, SDATA and SDEN are all correct, including the bit order MSB->LSB, SDATA stable prior to rising SCLK edge and the SDEN pulse after sending the 24 bit frame.
The only test that I can come up with is to set Receive mode and check for the RO signal. In all cases my target has no RO activity.
With this external VCO control, is the RO test still a valid measure of functionality?
|
A:
The RO level is about 100mVp-p, and if it is not running, nothing will work. I find that monitoring the power supply current is a good indication. In receive, it will be about 8.5mA and in transmit around 20-30mA depending on the value of RPS. If the supply current is zero, and it was loaded for anything except standby mode, then the registers did not get loaded properly.
If you are using a PC to load it, and the power supply is 5V, the output voltages from the parallel port are sometimes not high enough. In this case, reducing the supply to 4.5V usually solves this problem.
|
Q:
Thx for the info. Was important to know that RO always active in Rx/Tx. Found a artwork error SDEN & SCLK swapped at 7122. Fixed this error and now can program to the high speed fsk at the target freq of TX 31.0.
Found that the cap <CF1> was stuffed 100nf instead 1uf so loop filter looks ugly in TX mode. But since we are sw guys, no parts available tonite.
Will know more tomorrow.
|
Q:
TH7122 3-Wire mode I have a requirement to pass transmissions that can originate from either end. What is the correct selection for waiting, IDLE or RECEIVE? Can the FSSI/LD be used on the Receive end (via code) to enable the Receiver - assuming was IDLE? How much time is available from LD to the first NRZ data bit? What is the correct way to detect and control a Line Turnaround ie: from Receive to Transmit or Transmit to Receive?
Anyone with similar issues? Thanks
|
A:
The LD output can be used if the TH7122 is programmed with the SPI bus. The wait time is determined by the time for the PLL to switch between the transmit and receive frequency and the time required for the data slicer capacitor to charge. After LD is high, the wait time is only the data slicer capacitor charging time, and this depends on the data rate which determines the slicing capacitor value. If the peak detector is used, the time is shorter.
|
Q:
I have a question about the maximum RF input level @ LNA input:
The datasheet specifies +10dBm, but is this applicable only during TX? (when the input is shunted to ground via 33ohm)
Or is it OK for the input to experience +10dBm - even during RX, with the LNA in high gain mode? (ie. the part will not be damaged) – regardless of functionality at this level.
The back ground is that my application has the device receiving in the near field for short periods with peak levels up to +20dBm. Our testing shows that this is OK functionally (I’m guessing there’s enough time with the input < -20dBm for FSK) but I want to protect the device from permanent damage in this situation.
Are there any recommended methods for clamping the input swing?
|
A:
I don't know what it takes to damage the LNA. You could put Shottky diodes on the input to limit the amplitude.
|
Q:
I'm trying to set up the PLL for direct VCO modulation at 40MHz. I have a BB149A external varactor and have so far got it tuned and running over the desired frequency range. The only problem I have is that if I switch the TH7122 to IDLE mode, the PLL does not recover. If I turn the power on and off and then set to transmit mode it works fine.
pps: I just noticed that if I go from IDLE to mode to STANDBY mode and then to TRANSMIT it works fine, but I cannot go direct from IDLE to TRANSMIT.
Any idea what might be causing this?
Could it be the LF? Also, now that I have it running should I measure the voltage on the LF pin, change the N divider and work out the gain of the VCO. Is the gain from this, the gain I should use to calculate my LF values. This is what I have done so far.\
ps. Oh yeah, I forgot to mention. When I switch to IDLE mode the LF voltage becomes 0V. When I switch back to TRANSMIT the voltage sits at 3V (VCC).
|
A:
You mentioned that the LF is at VCC level after switching from IDLE to TX.
Then can you see the a carrier above 40MHz?
Maybe the PLL cannot lock correctly because of a parasitic oscillation which might be caused by your external tank configuration.
Is there any dependence on the VCOCUR setting?
If there's a parasitic oscillation it could be useful to decrease the Q of the tank as can be seen in the TH7122 Cookbook on pg. 5.
Note that the VCO frequency in IDLE mode (IDLESEL=1) is set by RR, NR or RT, NT depending on the last active mode before entering the idle mode. E.g. if you switch from TX to IDLE the VCO in IDLE runs at the TX settings (RT,NT).
|
Q:
I use TH7122 as FSK receiver with 62.5 kps data rate. The problem is the lowest receiving signal is about -66dbm, and it is a lot higher than the number on data sheet. Can anyone tell me the possible problem is or where should I start checking setup?
|
A:
-66dBm is really bad. Is your schematic like the one I sent? Look at the OUT_DEM and see if it looks ok. It is an analog detector and will show the transmitted waveform. The average level should be around 1-2V. Make sure the AFC is turned on.
|
Q:
What is the maximum achievable Adjacent channel selectivity in a narrowband application at 173MHz ? Although using single conversion with a low 455KHz IF (with 2 cascaded filters) would reduce coupling between pin 32 and pin 1, presumably the ACS is still limited by VCO phase noise. Is a 60dB ACS spec achievable ? What is the expected phase noise at +12.5/25KHz ?
|
A:
60dB ACS is too tough for the TH7122 as it has not been designed/optimized for narrow band. You can count on 40dB.
The phase noise at that low offset freqency should be about 60 to 70dBc/Hz, depending on the actual Q of the external VCO inductor and varactor diode.
|
Q:
What should i do with the OUT_MIX pin?(Transmit 490Hz(PWM) on 187.5 MHz)
|
A:
the receiver part is shut off in transmit mode, except for the PLL synthesizer. If you only use the TH7122 as a TX, then you can simply leave these RX pins open: IN_LNA, GAIN_LNA, OUT_LNA, IN_MIX, IN_IFA, RSSI, IN_DEM, OUT_DEM, INT2_PDO, INT1, OUT_DTA.
|
Q:
Do I need to use the ceramic discriminator(connected to pin3)if i´m only using the th7122 as a transmitter? If no, what should i do with the pin?
I dont need the recieve pin(26) as well. Should i ground it, or?
|
A:
Sorry, forgot this pin. As it is also an RX pin: leave it open.
Karl
|
Q:
I'm interested in example circuits for analog fm use of the TH7122. I have drawn a circuit according to the datasheet and the cookbook but would like to compare because I don't know if I got everything right. I.e. how can I set the deviation?
Regards
Martin
|
A:
There are a lot of circuits for almost any frequency. I usually use a receiver to check the deviation. Just calibrate it with a signal generator. Any receiver with an analog detector will work.
|
Q:
I buy th7122 and evb7122
I have a question about "FSK Application Circuit"
In TH7122 rev003 datasheet and EVB7122 re002 datasheet,th pin32(OUT_MIX) of IC is connect throught CERFIL to Vcc.
But in TH7122 rev004(new release) the pin32(OUT_MIX) is connect throught CERFIL to ground.This is a lot different
Please give me a answer
|
A:
Since reference node of the external IF filter is connected to AC ground there is no difference between VCC and VEE. The external IF filter must not have a DC path between the input/output to the reference node.
|
Q:
When are the EVB7122 boards going to be available and is there an approximate price for the eval board ? Also are there going to be any more in depth app notes on using the 7122 in analog voice applications in the near future ?
Mike
|
A:
EVB7122s are available for a long time. The price for a standard EVB7122 is USD198 per unit (incl. PC cable).
The TH7122x Cookbook (avail. on our web site) also deals with analog modulation (sec. 3.7) and demodulation (sec. 5.7). It shows you how to use the TH7122x for analog FM, the rest of the circuit, like a microphone amp or an audio PA, is up to you.
|
Q:
I want to apply your EVB7122-433-FSK in 200 meters.pls help me to provide a helical antenna parameter,I need the antenna is 3.5Cm length.For example,the length,diameter,Screw-pitch.
|
A:
pls. find at:
www.inf.fu-berlin.de/inst/ag-tech/scatterweb_net/ews/downloads/433_helicals_antenna.pdf and
www.inf.fu-berlin.de/inst/ag-tech/scatterweb_net/downloads/868MHz_helix.pdf
some examples of small helical antennas. Note that there are no simple numerical expressions for a small helical antenna (circumference << wavelength). For resonant helical antennas (circumference ~ wavelength) some design curves can be found at: http://www.poynting.co.za/tech_training/snec_designcurves.shtml.
Unfortunately we cannot give more support on this issue.
|
Q:
I am working on a battery operated emergency runway light which needs to be activated by an airband (118-136 MHz) radio. Traditionally, runway lights are turned on by simply keying the mic on the radio.
Can the TH7122 be configured as a receiver with a simple carrier sense output, tunable to a particular channel within the airband while consuming as little power as possible? If so, can you provide a spreadsheet with component values and, possibly, a schematic?
Also, how can I obtain an evaluation board for the TH7122?
|
A:
We can provide you with schematics if you contact your local sales representative. The receive power consumption is only about 9mA, so you could probably leave the receiver on. You will need a micro to program the TH7122, but it could be quite simple since you do not need to do any complex data decoding.
|
Q:
I'm interested to develop a trx module with the TH7122; my need is to have a unique module which can transmit ASK or FSK modulated signals. My question is: can I use the TH7122 with a unique BOM to transmit ASK or FSK data stream only switching the ASK/FSK line or there could be some problems?
In detail I'm referring to possible problems which could arise concerning Loop Filter Bandwidth and with the capacitors which charge the oscillator and define the FSK
|
A:
You are correct in thinking that the loop filter bandwidth is important. What frequency will you be operating at and what channel spacing do you require? This has been done with the TH7122.
|
Q:
I operate at 868.30MHz and the product will be a wide band trx. I'll use a 10.7MHz IF filter with 280kHz bandwidth...I'll use it as a single channel because it will operate as a stand alone module with the default registers settings...
|
A:
This is a problem for ASK operation. At higher frequencies, it is necessary to use the highese possible PLL reference frequency, so you will need to use it in programmable mode. The best way is to use a 1MHz or higher PLL reference and calculate the crystal necessary to get exactly 868.3MHz. Also, reduce Kvco as much as possible by using 3.9nH for the VCO coil and add a capacitor in parallel with it. The PLL Filter values are RF=12K, CF1=330pF, CF2=39pF. For the receiver, it is not critical, so a value of R and N can be found to work for the receiver.
|
Q:
I've tried anyway to implement an ASK transmission with the default settings of TH7122 in stand alone mode; I made use of a quartz near to the adviced 7.1505MHz so I got a tx frequency quite close to 868MHz. Fine trimming of the resistor of the loop filter allowed me to obtain a quite good unmodulated carrier but when I put a square wave on the data-input pin, the spectrum was very distorted also at very low bitrates with a lot of spurious due to transient of the PA on-off.
Subsequently I tried a different solution: I set the FS0, FS1 lines to 434MHz band and made use of a quartz with approx. doubled frequency with respect to the former.
The final result is again to obtain a frequency very near to 868MHz but with a visible improvement on spectral purity of the modulated carrier. Since my need would be to transmit at low datarates I would like to know if in your opinion this could be a feasible solution...
|
A:
This is a good idea. I tried it but did not get enough improvement. One problem with the stand-alone mode at 434MHz is that the PLL reference frequency is quite low because the R setting is 32. You really need to use it in programmable mode to get good ASK.
|
Q:
We want to use the TH7122 as an FSK tranceiver at 142.050 Mhz and +/- 3kHz FSK deviation, in a radio-tag. What components do we need to use/change in order to get this to work?
|
A:
The final circuit depends on your requirements. The TH7122 circuit alone will give about -107dBm sensitivity and a maximum of about 40dB selectivity. If you need better sensitivity and selectivity, it can be used with a narrow band IF IC in a dual conversion circuit. There are available circuits for both, contact our applications engineers through your local sales representative.
|
Q:
I want to use TH7122 in a FSK communication system at 27 MHz, so I need some help about the varactor diode and all components around there, because in the datasheet the table with this information appears empty.
|
A:
With a 10.7MHz IF, and low side injection, the tuning ratio for the VCO from transmit to receive is about 1.66.
This requires a varactor with a large tuning range. I have used the Infineon BBY65 diode for this application.
It has more than enough tuning range. The VCO coil will be 2.2uH, with 10nF in series with the diode. Don't forget to add a resistor in series with pin 20 or in series with the tuning diode to prevent parasitic oscillations. If you want to use high side injection, the coil is 1.2uH with 330pF in series with the diode.
|
Q:
I would like use this chip (7122) at 30 MHz range FSK transceiver. I can't find any isruction in a datasheet of the external VCO critical element. (Like Varactor diode type and values of capacitros and inductors.) How can I calculate this values? Please semd me some tips or sample circuit if yuo can.
|
A:
Well, you should calculate the VCO tank circuit to operate at 30MHz +/- your IF (in this case probably 455kHz). The varactor can be a BBY65, the inductor a 1200nH one and the capacitor a 330pF. For a schematic contact our applications engineers through your local sales contact.
|
Q:
I'm considering TH7122 in my design - working at 40.68MHz. Currently I'm not sure if I use FSK or ASK. I've seen there are documents describing exact values for 27MHz (and of course default 433 etc) range. It will be my first "hands on" this chip and I'd like to make some easy to run desing.
|
A:
the first estimation on the VCO tank population can be made using the formulas in paragraph 3.3 on pg. 5 of the TH7122x Cookbook. For the rest the values for 27MHz are a good starting point. Note that all values listed in the documents are related to our EVB. In any case you have to tune the external circuit according your board for the best performance.
|
Q:
I tried to purchase a FSK 27MHz EVB board about a couple of years ago. I was told by a Melexis employee that none were available. Is there currrently a 27 MHz FSK EVB board available for sale?
|
A:
We have a custom design for the 27MHz band for FSK, ASK with high or low side LO for the receiver. There is also a design for 37MHz. If you want to purchase a demo board, we can make one up, or you can have the schematic free.
|
Q:
I'd love to have schematic for 37MHz.
Right now I'm drawing something like this:
- design with additional varactor diode BBY65
- modulation via direct VCO injection
Please correct me if I'm wrong - chip alone is rated for quite large voltage range - but as far as I understand - voltage changes during work (I'm not talking about voltage drops etc. - let's say it's powered from alkaline battery - and voltage changes during work - from almost 5 - down to 3V) will detune whole circuit???
I'm considering using some LDO for powering modulation circuit (to obtain same modulating voltage level). Or maybe it's ridiculous since proportional vcc drop will cause modulation change in some way?
|
A:
If the output stage is not saturated at maximum power and the tuning voltage is not too low when using a 5V supply, nothing will change at 3V. for more detailed assistance and schematics please contact an applications engineer through your local sales representative.
|
Q:
can I accomplish audio and data wireless transmission with one chip th7122? That is both the TH7122's FM and FSK(or ASK) funtion is used. Then another FM and FSK(or ASK) receiver receives the former's signal.I am looking for one cheap IC can realize both data and audio transmission, does melexis have other chips that can realize this funtion?
|
A:
This combination is possible. Please have a look at the cookbook:
http://www.melexis.com/relinfo_detail.asp_Q_id_E_374
|
Q:
I bought recently a demo eval board for the TH7122 and I intend to use it in my application based on a microhip microcontroller.
Do you have any applications note with source code examples
that demonstrates the use of the chip ?
|
A:
sorry, but be don't have code examples available for using in a microcontroller by now. Also that would be different from micro to micro. Usually we use a little program for sending the SCI data via the printer port. I spoke to an SW guy and he told me that it will not help you further because it's completely different. But if I remember in my time at the university, such a program in C which sends a bit-stream over a single port should not that difficult. Pls. see also to the timing diagram of the SCI interface denoted in the data sheet for further help. The available programming software on our web page offers also an register view which help you to translate the settings into an binary or hex word.
|
A:
I need to redesign the TH7122 for 418 Mhz at 0 dBm. I am trying to understand your example EVB7122 for 433.92Mhz. LTX0 is j41 and CTX4 (6.8pF + 3 pF) is -j38. You calculate RL as 260. Where does RL come in? Is this what the PI network is looking at? Are you matching 50 ohms on the antenna to 260 ohms of the PA? I am running 3.6V at 0 dBm which gives me 4.2K. Is this what I should match to?
|
A:
The PA load is about 260 Ohms and the PI network matches it to 50 Ohms. Attached is a schematic for you.47E_EVB7122B-418-FSK.pdf
|
Q:
Thanks for the schematic. It helps with the other values. Getting back to the load, I am using 3.6 volts and for FCC reasons can only run 0 dBm. Would you recommend I redesign the PI network to match 4.2K or leave your 260 Ohm match and adjust for the inefficiency with the RPS value?
|
A:
I would re-design the matching network. You can also set the chip to maximum power and adjust the power by changing RPS to a smaller value. The receiver will be a little more sensitive when you change the matching network because its input impedance is high. Attached is a note on transmitter output matching. You may already know all about this.
Transmitter_Output_Matching.PDF
|
Q:
I´m sendeing the 4 words(A, B, C and D)via spi from a uC(Atmega128). But i can only send 8 bits at a time.
Should i just send the first 8 bit, then the next 8 and then the last 8. And then the SDEN bit?
something like this(pseudo):
SPDR=1/3 A-word
wait for flag
SPDR=2/3 A-word
wait for flag
SPDR=3/3 A-word
wait for flag
SDEN=1
delay=100nS
SDEN=0
Or does the second 8 bit(2/3)just replace the first 8 bit(1/3)in the 24 bit shift register?
|
A:
Of course the 24 bit can be divided into 3 parts. After shifting the last bit, the rising edge of SDEN will program the A,B,C or D latch.
|
Q:
I am having a problem when debugging the transceiver. My design is completed acording to EVB7122-special-27-FSK-WB-low side LO. A 8MHz oscillator is applied at pin 10(RO), then pin pin19(lock detector output) must output a high-voltage after PLL locks. I cannot detect such a high voltage. why? Please help????
Another question, how will I know the control words are successfully programmed into the transceiver?
|
A:
If the lock detect is not high, the VCO is not locked. The best is to check the tuning voltage on pin 23, the LF output. It must be between 0.5V and Vcc-0.5V. If it is at Vcc, then increase the value of the inductor and conversly. You must also have the 22 Ohm resistor in series with the inductor or the VCO will oscillate around 800MHz.
|
Q:
I'm designing a transceiver using the TH7122 at 40MHz. I was wondering what would be the best IF to choose. Are there any example circuits for 40HMz and the values of external components?
|
A:
We would need to know what are your channel steps, type of modulation and data rate? Please contact an applications engineer through your local sales representative.
|
Q:
The Murata product is Specified and samples are difficult to obtain.
The Murata part is CDSCB10M7GA136-R0 10.700 ±30kHz 140 min. 120 min.
What are the important characteristics of the descriminator?
We would like to use a substitute
|
A:
You can use almost any discriminator by adding a tuning capacitor in parallel with it. Which one would you like to use?
|
A:
You may find more information about the ceramic discriminator CDSCB10M7GA136-RO on the melexis web-site:
http://www.melexis.com/Assets/Spec_CDSCB10M7GA136_TH7122x_3900.aspx
|
Q:
I'd like to use the TH7122 for AIS - that is approx. 160MHz GMSK. Is it possible?
Does this work without using ceramic filters (simple circuit)?
How about a circuit diagram for vhf NBFM?
What are the main benefits for using the TH7122 instead of the NT2906 devices from Num Tech?
|
A:
Since the VCO is modulated in narrow band applicaions, GMSK modulation only requires that you apply the correct analog modulating signal to the VCO. You will still need an IF filter unless you go to direct conversion, and ceramic filters are cheap and have good performance. I have several circuits for nbfm. I assume it is for 160MHz. If you want very good sensitivity, dual conversion is the way to go.
It will be difficult to do as well with a direct conversion receiver.
|
Q:
I would like to receive the mentioned NBFM circuits to have a first try.
|
A:
Please contact an applications engineer by reaching out to your local sales representative for assistance.
|
Q:
This is also my question.I also would like to develop a transceiver in 144 MHz.But, i find out nothing about external varactor diode infomation for the VCO tank that will extend the frequency range to 27M~930MHz.Can i get some infomation about that.
|
A:
The TH7122 output power is specified at 10mW. At lower frequencies, it is slightly higher and if you use a 5V supply it can be higher because the output voltage swing is higher. However, it probably won't be more than 30mW.
As for varactor diodes, pick one you can easily get. It's capacitance is just in parallel with the one in the TH7122. Digi-Key has some of the Infineon ones which I usually use.
|
Q:
My questions conern using the TH7122 in an amateur packet radio application. Specifically, I'm looking at creating a highly integrated amateur packet radio transceiver module for aerospace applications that will communicate over the standard amateur packet radio networks in the USA and around the world.
Ideally, I would like to operate the transceiver in the 2m band (144 MHz), but I had some questions regarding the chip. The datasheet gives an external varactor diode setup for the VCO tank that will extend the frequency range of the device. However, there are not any specific examples for component values.
Also, for amateur packet radio, two audio tones (1200 Hz and 2400 Hz) are modulated onto the carrier frequency. It seems the main operational mode for the TH7122 is FSK/ASK modulation. However, I would need to use it in FM modulation mode, which the datasheet says the TH7122 is capable of, but does not give any real examples. Is it operationally feasible to use the TH7122 in FM
|
A:
We have schematics for this as well as almost any frequency from 27 to 915MHz. If you want one, send email to jon@melexis.com
Also, loop at the TH7122 cookbook available on our website. By adding a narrow band IF to convert 10.7 or 21.4 MHz to 455kHz, you can make a good receiver/transceiver.
For more specific customized RF circuits please contact an applications engineer through your local sales representative.
|
Q:
Could ayone tell me whether it should be possible to use the TH7122(1) to impliment a high speed (115200) RF FSK modem which could be transparent to ansynchronous UART transmission? Carrier would be somewhere between 27 and 80MHz, transmission would be bursty or brief to exploit quasi peak power levels.
The application notes say direct VCO modulation is necessary for high data, but that encoding must be manchester, whereas I would like to be able to interface it directly to a UART....would this be possible?
|
A:
Modulation of the VCO as part of a PLL is a high pass function. The low frequency limit depends on the loop cutoff frequency, and this limits the number of 1's and 0's which can be transmitted in sequence. Usually a ratio of 4 or 5 to 1 is about the limit. One solution to this is to also modulate the reference through a complementary low pass filter, but at the low frequency you are operating, it is difficult to modulate the reference crystal with enough deviation. If Manchester or some similar encoding is used, it has no DC component, so this is not a problem. Remember also that the TH7122 does not recover any clock signal.
|
Q:
1. Is there any similar constraint (no dc component) in the FSK RX direction?
2. Is there any similar constraint (no dc component) in either ASK TX or RX directions and can the high speed also be acheived with ASK?
3. Is it possible to use ASK in one direction and FSK in the other?
|
A:
If you put a fixed voltage on pin 5 and adjust it to be equal to the voltage on pin 6 at the center frequency, the FSK detector will have response down to DC. However, this requires a low frequency tolerance on the transmitted and receive crystals and low drift of the FSK discriminator.
ASK can also be used to DC, but it requires the voltage on pin 5 to be fixed at a threshold.
You can use ASK in one directon and FSK in the other. However, the maximum data rate for ASK is limited to about 10kbps because ASK always causes some incidental frequency modulation of the VCO.
|
Q:
Did you mean ASK can only ever be used to 10kbps or is that applicable only when you have ASK in one direction and FSK in other?
Summarising the facts then:
- the TH7122 is claimed to support data rates up to 115200 but,
- direct VCO modulation is required for FSK data rates > 20kbps (which is most data rates) and,
- direct vco modulation requires that manchester/bi-phase code be used, or else avoid dc components in the data stream (hard with NRZ async comms).
Producing manchester coding with a microcontroller uart is easy but decoding manchester is very cpu intensive at the higher data rate. Are you able to suggest any accessory IC/method to recover the clock to facilitate the manchester decoding?
|
A:
ASK transmission is limited to about 10kbps. Reception rate can be much higher.
Your summary is correct.
I think you could add a simple PLL like an LM567 to recover the Manchester clock.
|
Q:
Can TH7122 operate at frequency below 27MHz? If not, which functional block inside the IC (for ex. LNA, PA, MIXER OR SYNTH.) prevents it from working at lower frequency?
|
A:
Due to the internal AC-coupling between the building blocks the characterized lowest frequency is 27MHz. The chip is functional also at lower frequencies, e.g. 20MHz - but the customer do this at his own risk because the IC is then driven outside the specification.
|
A:
The receiver works quite well at 13MHz. The transmitter output is quite distorted because of the effects mentioned above, so good output filtering is needed.
|
Q:
I was looking over the TH7122 datasheet (Rev. 004 - Sept. 05) at the FSK Circuits on page 30 and 31 and I noticed that the signal from the OUT_PA pin (pin 25 - output pin), can migrate up through the LC tank circuit (through LTX0 and CTX4) and connect to VCC, the supply voltage. Normally, in RF design the output signal is isolated from the power supply. Can you tell me why this connection needs to be made? Is it a necessary (required) connection which must be made?
|
A:
Yes, the DC path from OUT_PA to Vcc is required. Because OUT_PA is an open-collector bipolar transistor and it needs to get its bias thru the inductor LTX0. Please have a look at page 8 of the DS. It shows the internal circuitry of the pin OUT_PA in more detail.
This is a very common approach in RF design. The inductor that ties an RF output (or input) to supply is usually called "RF choke". The choke has usually a large inductance. It stops RF signals but provides a DC path for the supply current. In this particular case, we modified it a bit by adding CTX4. This way we have formed a parallel tank circuit. That's even better than the choke as it provides some bandpass characteristics and helps to increase the RF power while it is suppressing the harmonics.
Look at pin 28 OUT_LNA for example. It's the same story.
|
Q:
I am using TH7122 as FSK transceiver.we have two board,one transmitter,one receiver.While senting BARKER code, the result on receiver port was wrong,the polarity is just invertted. Crystal pulling Modulation. DTAPOL is '0' as default.If set as '1',the polarity is correct.Why?To me,it is reasonable that the DTAPOL is setted as '0'.
|
A:
I assume your transmitter is ok. The inverse polarity might be caused for the following reasons:
1. If you use an LO high-side injection (which means that the VCO is running at RF+IF) then the signal band is inverted because of the mixing process.
2. When the demodulator tank is de-tuned so that the phase slope is inverted because it is tuned to a 'parasitic resonance' the demodulation is done inversely.
|
Q:
How do i go about implementing high side LO injection to invert the received data?
|
A:
All you need to do is to change the VCO tuning so it is on the high side and change the register settings to get the right frequency. If the IF is 10.7MHz, it will be 10.7MHz above the received frequency. It may require a smaller value for LO to reach the correct frequency.
|
Q:
So at 915Mhz operation with IF of 10.7Mhz I tune the VCO to 925.7Mhz (i.e. RR = 80, NR = 9257 with 8Mhz RO)?
|
Q:
Also, does this method work for ASK modulated signals?
And, you've also said:
"It may require a smaller value for LO to reach the correct frequency."
Does this mean that I would need to start at VCO = 925.7MHZ and decrement VCO slightly using trial and error until I see VCC at OUT_DTA pin with no CW input (ie. inverted data)??
|
A:
Since ASK does not use an FM detector, the phase is the same for high or low side injection.
Your settings for 925.7 are correct.
If the CW signal is at 915, then you may need to adjust the VCO to get VCC at OUT_DTA. 100kHz steps are probably too large for this. You chould reduce it to 50kHz. Normally, if the signal is FSK, it will be above or below 915.
|
Q:
I have already started my project with ASK so i guess i'll have to use an inverter to invert the received data.
|
A:
Would you like a schematic for the EVB7122-special-915-ASK? It is important to use a PLL comparison frequency of 500kHz or above. Please contact an application engineer through your local sales representative.
|
Q:
I’m developing an RF network for irrigation control at licensed freq. 27.505 MHz (FM), An order to upgrade and simplify the electronic circuits I am thinking the possibility of work with the IC TH7122 or TH71221.
Is it possible to work with TH7122 at 27.505 MHz? What is crystal value an the registers values of the TH7122? Is possible to amplify the output to 4 W ?
|
A:
the maximum output power delivered by the IC is 10-12dBm at 27MHz. We don't have a fixed solution for your requirements. If you want to boost up to 4W (36dBm) the output signal has to amplified by an external PA having at least 2 stages. Usually such a PA is driven by a separate power supply (e.g. 12V). The Sanyo 2SC2078 could be a candidate for the final stage. Pls. not that we release an application note by next week which deals with an external PA for output powers up to 100mW (20dBm) - pls. stay tuned.
The crystal can be calculated (as described in the data sheet) by the relation fxtal/R = fvco/N. Pls. bear in mind that you need to address 2 VCO frequencies from the same crystal:
1. in TX mode fVCO=27.505MHz
2 in RX mode fVCO=27.505MHz +/- IF: since the RF is at the low end of the specified range I would suggest to use high side injection of the Local Oscillator (LO) -> fVCO =27.505MHz + IF,
with a typ IF of 10.7MHz -> 38.205MHz
I suppose that you want to have FSK modulation. Could you pls. tell us more regarding the frequency deviation of your system and some other data (data rate, data format, regulatory requirements).
|
A:
I can send you a circuit diagram for a 27MHz application. For the PA section, you could just use a driver+PA circuit from a CB radio. You will need about 26dB of gain, and 2 stages should do it. I prefer to use low side injection because it gives good image rejection. I have circuits for both. If you want them send email to jon@melexis.com
For 27.505MHz, you will need a 5kHz PLL refence. Since the maximum value for the R counter is 1023, you will need to use a crystal of 6MHz or less. 4MHz crystals are very common.
|
Q:
I would like to use the TH7122 in my application, but I have a requirement that the receiver use a 455 kHz IF. The spec sheet says the IF low end is 450 kHz, but the cookbook says the discriminator won't work at 455 kHz. Is is possible or not?
|
A:
it's true 455kHz is difficult to make directly with the TH7122 because the FM discriminator capacitor is on-chip and measures only 1.5pF. So it's too small for 455kHz ti build up a 90deg phase shift. Therefore we are recommending an external IF circuit at 455kHz. We already have a circuit proposal and will put it to the cookbook at the web site.
|
Q:
Is it possible to get the IF Frequency out of the chip after the limiter that it can be used for a i.g. an following I/Q demodulator?
|
A:
You can get the IF signal from pin 3 (IN_DEM) but it is coupled from the IF amplifier with 1.5pF and the internal resistor to Vcc is 10k, so the amplitude is quite low.
|
A:
|
Q:
I'm designing a FSK transceiver to operate at 40MHz using the TH7122. At the moment I'm looking at the matching network. To start with I am looking at the examples given in the datasheet. Does anyone know what value for Vcc was used when calculating RL in order to design the matching network? I have simulated this network with Microwave Office and it seems to have an input impedance of about 100 ohms at 315MHz using the values that are given for that frequency of operation.
Also, how can I find the required value for Rps. The graph given in the datasheet only covers frequencies as low as 315MHz.
|
A:
For matching please refer to chapters 7 - 9 of the TH7122x cookbook.
The cookbook can be downloaded here for example:
http://www.melexis.com/relinfo_detail.asp_Q_id_E_374
|
Q:
I am worried that I may have damaged the TH7122 IC while soldering with a "hot air pencil", what is the maximum temperature before thermal damage and how can I test the IC for damage.
|
A:
The maximum soldering temperature is defined in the datasheet by the solder reflow profile (usually around 260C but with limited time at this temp). A 'hot air pencil" represents an uncontrolled time and temperature exposure potential so it is possible to damage a device although our applications engineers use similar methods frequently for prototype work without causing harm.
Fully testing the IC for damage would require sophisticated equipment and test software routines which are only practical in our production test facilities. However, if you turn on the receiver and the current drain is about 8.5mA, then it is probably working OK. Always check the charge pump voltage on pin 23. It should be between .5 and Vcc-.5V. This is the tuning voltage for the the varactor.
Meanwhile if this device is to be used in a critical or high reliability application it might be safest to replace the device with a new, known good unit before continuing. And for production purposes it is recommended to follow the solder reflow profile given on the datasheet to ensure long term preformance and reliability.
|
A:
Dear herman01,
the equation can be simplified to N=A+16B. Assume that A is 4-bit wide (0..15) and 16B represents a 4-bit shift of B. Now it can be easily seen that the A and B value can be expressed in one word: N=[a0 a1 a2 a3 b0 b1 .. b12] = [n0 .. n16]. This arrangement is very handy because the overall feedback divider value N is automatically divided into A and B so that there's no need to know the A and B values separately.
BR Rumburak
|
A:
Dear Ivo,
Sorry for the delayed response. The N-dividers are located in C and D word. As I can see from your programming pattern, the divider settings in transmit mode are:
RT=96
NT=5202 (or if you like AT=2 and BT=325 ==> ==2+16*325)
gives a PFD working freq. of 8MHz / 96 = 83.834kHz
and a RF of 8MHz * 5202 / 96 = 433.500 MHz
If your IF is 10.7MHz the LO must be at 422.8MHz or 444.2MHz. Note that if you have high-side injection of the local oscillator (444.2MHz) the base band is reversed (inverted data signal). Your pattern in receive mode is not properly set because:
RR=80
NR=2114 (2+16*132)
so that fLO= 8MHz * 2114 / 80 = 211.4 MHz
it is possible that there is some functionality in receive mode because of the down conversion by the 2nd harmonic of the LO (2*211.4MHz) but the sensitivity is probably too low. In order to have a stable PLL setup the R counters should not differ that much, so that th
|
A:
Dear herman01,
it is maybe a simple programming error of your software. In order to find the bug please submit:
- your xtal (reference) frequency
- your intended RF
- programmed N & R divider word
Could you also precise your last question?
BR Rumburak
|
Q:
I have problem with register N. Is really divided to part A-counter = N00 to N03 and B-counter = N04 to N17, because when I use Your equation
N=17A + 16 (B-A)
The IC is functional only when number for B-counter is directly written into register from N00.
|
Q:
Again, when I use Your equation about N-counter, the PLL is not functional. When I write directly b-counter to N register, the PLL is functional and lock detected is indicated. In this case A-counter is not used and b-counter started on 0 position.
Must set some bit in any registers for this funcionality?
Next question is - is carrier frequency detect on the same level on data FSK output??
|
Q:
Dear Rumburak,
- my xtal reference frequency is 8 MHz
- my intended RF is approximately 434 MHz
- my register A with N is 09 F8 50 for transmit
09 F4 50 for receiving
my register B is 5D E8 60
my register C is AC 08 42
my register D is E8 14 52
Thank You for Your answer how compute A and B counter.
BR Ivo Herman
|
Q:
I would like to ask whether the operation frequency for this chip is able to transmit and receive at the range of 100Mhz-500Mhz?
is it possible to vary the frequency using the software without changing the external circuit that provided inside the cook book?
|
A:
The tuning ratio (fmax/fmin) of the VCO is approx. 1.135 at VCC=3V and 1.19 at VCC=5V. Using an additional hyper-abrupt varactor diode this ration can be increased up to 2. In your case the required ratio is 5. It's therefore impossible to operate in that huge frequency range without any change of the external tank circuitry. A Multi Band Switching circuit is explained in the TH7122 and TH71221 Cookbook http://www.melexis.com/relinfofiles/AN7122x-Cookbook_rev-003.pdf
|
Q:
Thanks for the kindly reply. I have doubt on the user mode on this chip as well... since we can program or select the 4 bands which is 315MHz,433.92MHz 868.3MHz and 915MHz by connect to pins such as FS0/SDEN, FS1/LD and etc... why are we need to change the electronic component suit for different frequency band as stated in data sheet?
to add on for my missed part for the previous post, I would like to ask how should I modify the external circuit if I wanted to have FSK and AFK modulation to run on the same chip besides set Hi/Low on the ASK/FSK pin .
|
A:
Since the VCO operates on the same frequency as the intended RF, the VCO range has to cover the frequency band of interest plus the separation of the IF in RX mode. For RX low side injection (default) it would be fmin_vco + IF .. fmax_vco. For example with a tuning ratio of 1.1 and an IF of 10.7MHz, the frequency range of the TRX at a center of 915MHz band is 877 .. 953MHz. This can be achieved with a proper tuned tank circuit. If you intend to operate at another frequency band, the tank circuit has to be changed. This can be done by means of an band switching circuit mentioned in the cookbook.
For ASK operation the comparison frequency (fxtal/R) should be as high as possible (e.g. 1MHz) in order to allow a faster correction of disturbances caused by load pulling effects in the ASK-modulated PA. So the bandwidth of the loop filter is usually higher than for FSK. The higher comparison frequency means also that the channel spacing is higher since comparison frequency == c
I made a mistake...
If you only want to address a fixed frequency within a certain band you should make fxtal/R ~ 1MHz and the bandwidth of the loop filter 100...200kHz.
|
Q:
I wish to make a 151-152mHz system using either a TH7122 or a TH71221. I want to be able to switch the frequencies within this band when necessary. I also want to vary the power levels. It seems this can be done when in the 300-930MHz band but I cannot see if this is possible in the extended frequency bands. Can someone please advise.
|
A:
frequency operations below 300MHz requires an external varactor. Please find related informations in our Cookbook which is available at: http://www.melexis.com/relinfofiles/AN7122x-Cookbook_rev004.pdf
Best regards
Rumburak
|
Q:
We would like to run the TH7122 at 3V, but bias the PA with 6V at the OUT-PA pin. Can this be done?
|
A:
The maximum supply level should not exceed 5.5V. The OUT_PA pin can be supplied by 5.5V and the rest of the IC by 3V because the ESD protection devices at the open-collector output will clamp at higher levels than 2.5V (VCC_PA -VCC). But why do you introduce different supply levels? The TH7122 could also operate at 5.5V or 5V completely.
|
Q:
The reason we want to use different voltages is because we are using a board powered by a 6V battery. Other components on the board require a 3V supply, so we were going to use a passive voltage regulator, which is cheap, but inefficient. Power consumption is a major concern, so we thought that if we could run the PA off the 6V supply (since it draws a lot of current) then the inefficieny of the voltage regulator would not be a major concern. The other option is to use a switch-mode voltage regulator which is more efficient, but more expensive and introduces switching noise. Do you have any suggestions?
|
A:
the best way would be to have a battery of e.g. 4.8V (2x 2.4V). If this is not possible I would suggest to use a LDO regulator to provide a supply level of 5V. Also it's better to have the whole IC at this level, because the VCO tuning range is better because of more headroom for the VCO control voltage (VLF). I've also doubt concerning switching regulators, but it could be tested using an efficient de-coupling.
|
Q:
I'm having some problems trying to get the PLL to lock at 40MHz. I'm using two BB149 varactor diodes, 680nH inductor and a 220pF series cap. I've checked the voltages at LF and its about 1V, is this too low? I'm a bit worried I might have cooked the varactors when making the PCB. Is there any way to see if the PLL can lock at another frequency and test my VCO tank ?
Regards,
Alan.
|
A:
At low frequencies, the VCO sometimes will oscillate around 800MHz because the gain is higher at high frequencies. The resonance is determined by the trace with the varactor, and the VCO inductor is just in parallel with this. The resistor prevents the spurious resonance. A resistor in series with the varactor circuit will prevent this. Also, the varactors designed for TV applications have a lot of capacitance variation at low voltages, so I switched to a low voltage varactor for the demo boards.
|
Q:
Hi
I've been developing successfully with the TH7122 for a number of months now but have just come upon a problem that I can't solve.
Basically I can't seem to setup the device to use certain feedback divider numbers (NT). Specifically the ranges:
N=85 to N=95 (using RT = 31)
N=187 to N=191 (using RT = 62 or RT = 55)
Use of any of these numbers results in the PLL generating the frequency at the bottom of the above range. Ie. NT=91 generates the same frequency as for NT=84 (Though N=83 and N=96 both generate the correct frequency)
I have this problem using my own circuit, as well as the “EVB7122 Special” board + the LPT setup software, and just can’t seem to find a solution. I was wondering if anyone else had this problem at all? Or if someone can suggest what I might be doing wrong?
|
A:
The PLL topology is a pulse-swallow. Therefore the A counter must be smaller than the B-counter. Otherwise the right hand part in formula in pg. 11 in the data sheet (N=17A + 16(B-A)) becomes negative - and this is not allowed. In other words the B counter must finish the cycle after the A counter (they count on the same clock signal). Therefore, some counter settings are not allowed, and you have found some of them. If you can keep N>255, there is no problem, so the best solution is to make R larger so you can use a larger value for N. If you need a high PLL reference frequency, a higher frequency crystal will make it easier.
|
Q:
Thanks for your help. That makes a lot more sense now.
|
Q:
I'm trying to use your TH7122 transceiver in a narrow band (25kHz) AFSK/FSK mode around 435MHz. I experience serious problems while setting up the ic in TX mode. First I would like to have a clear carrier without any spurs, but unfortunately I cannot get rid of the comparison frequency spurs (reference osc./RT) around the carrier. If I use the loop filter suggested in your application note for narrow band transceivers, I don't have spurs, but the carrier has really heavy phase noise and therefore it sounds terrible and of course it's spectra is very bad too.
Can you help me please with your advice to solve this problem? The best compromise solution, I could find out so far is a simple series RC loop filter with 4.7uF and 220kOhm. In this case the carrier is good, but I still have the comparison frequency spurs -30dBc lower. And at start up they seem to be the same level as the carrier, but 30-60 seconds after they decay to the mentioned level.
If I connect a higher value(around 1uF) capacitor between the loop filter output and Vcc (or GND) the carrier gets distorted very much.
|
A:
I have used the following filter values: CF1=1.0uF, RF=3.3k, CF2=100nF with good results. Your value for RF seems to be much to high.
High spur levels can have several causes: 1. Not enough loop filtering (RF too large or CF1 too small) 2. The tuning voltage is too close to Vcc or Gnd so the phase detector is saturating. 3. Leakage on the PCB usually from solder flux. This can usually be fixed by rinsing the board with hot water and then drying it with air.
If you have distortion problems, remember that the loop cutoff frequency must be less than the modulation frequency. When the loop is modulated, it is best to design the loop to be heavily damped with a damping factor of 5 to 10.
|
Q:
Unfortunately I still cannot reproduce the results, you achieved and published in the application note for narrow band usage. With the component values, you suggested, I don't have any spurs, but the carrier has very significant phase noise and it is totally distorted (it is just noise when I listen to it), although the tuning voltage is around 2.7V (operating from 3.3V), so the PD probably does not saturate. I tried both with the internal and external varicap too, and with external the results were slightly better.
I suspect some layout issue, although it is very similar to the one in your application note about the TH7122 with external PA and LNA.
To me it seems that the comparison frequency disturbance gets to the VCO by bypassing the loop filter somehow (if I mount the VCO's inductor perpendicular to the LF line, the spurs get lower by 30dB, but still there... this somehow proves my hypothesis), so I really have no idea how to get rid of them. Another interesting issue is that the spur levels are very sensitive to outer disturbances: when a disturbance occurs, they get much higher, although later decay to their original level. Any idea about this? I am afraid that the modulation of the loop will cause them to increase to unaffordable level.
Cleaning the board didn't help either.
Seems that either I have the spurs at significant level or I have heavy phase noise on the carrier.
I achieved kind of satisfying results with RF=43k, CF1=1.5u, CF2=1n, but the spurs become really high when any outer disturbance occurs.
|
A:
I think 2.7V is a little too close to 3V, but it should still work. You can add a small C in parallel with the LO coil or increase the value of the C in series with the external diode. Also, 43k for RF is very large. It should be 4.3k or less.
If you are using an antenna, it is possible that there is feedback from the antenna to the VCO.
The last possibility is that there is a bad solder connection somewhere. I have had this happen. Usually, one end of a capacitor looks like it is soldered, but it is open. I recently had one board become unstable because one of the output matching capacitors had this problem.
|
Q:
Please recommend the power pmplifier for Th7122
or some information
|
A:
I guess there are a lot of RF amplifiers available - probably the RF2114 is one of them but it depends on your application. We don't have a fixed solution containing an external amplifier.
|
Q:
I am having some problems with the receiver side of the circuit as per my previous post. I have built an identical replica of the original circuit and the OUT_DTA pin is staying high with no input. After testing i have noticed that the RSSI pin (p7) is siting at 1.25VDC with no input compared with the working circuit at 0.53VDC. I have the peak detector active and the resistors the right way around. The transceiver is sort of working only for very high data rates.
Just to add. Changing the threshold resistors is not working either and it seems the problem is to do with the RSSI being held higher somehow. I've tested external components and could not find any problem. Can the problem be internal??
|
A:
This is a little hard to diagnose. First try setting the LNA gain to "low" with the software and see if the RSSI voltage decreases. If it does, you probably have a parasitic oscillation at about 1.8GHz due to the external components. This can often be fixed by connecting the tuning capacitor at the LNA output to ground instead of Vcc.
|
Q:
I will test what you have just mentioned and see if this is the problem. If you can think of other possible causes please let me know.
Also, i am using the same crystal off the micro to run the transceiver via a cap divider. Could the problem be due to wrong loading of the crystal or EMC?
PS. The transciever transmits very well and at a reasonably accurate frequency.
PPS. I've just tryed to vary LNA gain and it doesn't have any affect on the RSSI voltage. Any other idea's?
|
A:
One possibility is a harmonic of the crystal oscillator which is at the receive frequency or at the image frequency of the receiver. If your IF is 10.7MHz, the image is 21.4MHz below the desired frequency if the LO is below the desired or conversly.
|
Q:
Initial tests revealed that the problem was due to a harmonic of the crystal. To verify that this was the problem we removed the crystal from the board and supplied both the micro and the transceiver an 8meg signal from signal generators. The problem was still there.
We then compared what could be different from the working board and this one. We had added an inverter to the OUT_DATA Pin on this circuit (for our data transmission method) and connected the pin directly to the inverter. We then connected an inverter to the OUT_DATA pin of the working board and now it doesn't work properly either.
It seems that connecting the inverter damages the internal OA2 data slicer. We removed the inverter and the signal at this OUT_DATA pin jumped from GND to VCC with no input. When we apply a RF signal until the data rate of this signal reaches 10 Khz or more the glitches are still present.
We are now going to try to see if we can filter out these gliches as they appear to be a higher freqency than our data rate. If this doesent work we'll prob need to order another IC.
|
A:
pls. check the following:
- put one channel of a scope to OUT_DEM, and another channel to INT1
- pls. use the same offset and V/div settings for both channels
- apply a modulated RF signal to the board and vary the input power
--> for correct demodulation of the signal the demodulated 'raw' signal (OUT_DEM) should always cross the detection level (INT1)
--> if the detection threshold is outside the range of the demodulated raw signal the divider ratio of the resistor string between PDO-INT1-GND has to be changed
--> alternatively you can use the 'average data slicer' when your coding scheme has a nearly constant DC compound (advantage of this is that the detector threshold is always an average of the raw data signal)
P.S. as long as the inverter operates at the same supply level and the IC is handled carefully regarding ESD no damage of the OA's will occur
|
Q:
I've tried what you've just mensioned and i don't beleive that is the problem. Further testing has revealed the following:
The circuit is not transmitting very well as previously mentioned...
-> When i apply a logic 1 to IN_DTA pin, the output is at a peak of -10dBm (we've set this low TX_PoWER setting) but the signal on the spec. analyser is not a sharp pulse as expected. The span of the signal is wide ~ 2-3 MHz and not very clean (i.e. there is a series of peaks and troughs on each side of the centre freq)
-> When i apply a logic 0 to IN_DTA pin, there is still an output of about -48dBm. There should be no signal since the modulation scheme is ASK.
Can this signal be some sort of RF leak which is causing the problem for both the tx and rx modes. And what can cause it..
Can i have your email to send you our schematic and testing results and waveforms. Maybe they can help explain the picture of whats going on..
|
A:
The peaks on either side of the main carrier are the "reference spurs". They can be caused by saturation of the phase detector or pcb leakage across CF1 or CF2 in the loop filter. Measure the voltage on pin 23 when the loop is locked. If it is within less than about 1V of Vcc or ground, it is too close to the limits, and you should adjust the tuning components.
There is always some VCO leakage when in receive or when the ASK input is "0". It depends on the pcb layout and the IC itself. -48dB is more than enough for ASK. -38dB is equivalent to 98% modulation.
|
Q:
I noticed that you have software on the website to program the EVB. I looked at the EVB datasheet and I can see that the SDTA,SDEN and SCLK pins are connected to a header, but it doesn't specify how these pins are connected to the parallel port.
|
A:
please check out the Help button or tab in the TH7122 software. You will find the right connections for the LPT port. Pls. note that we will upload the next revision of the software within the next days. But these informations are also available in the current program version.
|
Q:
I am able to program the TH7122 with microprocessor. However, I have found that when I do so, the receiver sensitivity is reduced by about 4-5dB. I have checked all of my settings and they are identical to those used from the parallel port programmer.
I also thought that it may have been caused by noise from the microprocessor so I tried programming the MCU to run a simple LED flashing program and then programmed the TH7122 with the parallel port. The receiver sensitivity was good. I have checked VCC, the control lines etc for noise and they seem OK.
I was wondering if there is a specific order that I should program the registers of the TH7122. If I adjust VCOCUR (make it low for receiving) do I need to go to standby mode before going to receive?
I have tried all sorts of combinations and have had little success. If you could tell me the order that your parallel port program does the programming of the registers that would help.
|
Q:
Can anyone help me here?
I'd just like to know the order that the parallel port programmer programs the registers. For example, does it go A, B, C, D or reverse? Does it go straight into receive mode or does it program all registers in standby first and then switch to receive/transmit?
If I want to receive mode and drop the VCOCUR to 00, do I need to go to standby first and drop the current and then go to receive or can I just go straight to receive?
|
A:
there's no special requirement on the order of programming the register. I think the program does the A, B, C and D order, but it should be of secondary influence. The SW program does simply straight-forward send the information to the IC, regardless of the operation mode of the IC. E.g if you want to change the VCOCUR in RX mode you have to program the A (because change of OPMODE to RX) and the C word (because of changing VCOCUR). After the positive transition of SDEN the changes will be valid immediately. So you can play with the order (e.g. A first then C or vice versa). One thing should be noted: after supply power-up the IC operates in stand-alone mode until the first positive or negative transition at SDEN. That means the very first data packet (which is either target for A, B, C or D) will be lost because the the first transition at SDEN is sent at the end of the first data packet. To overcome this, the very first packet could be sent twice.
|
Q:
Thanks for your reply. Yesterday I got a digital storage CRO out and had a look at the data coming out of the parallel port. I discovered that it programs in the A,B,C,D order and has a SDEN pulse at the very start to switch to programmable user mode.
My microprocessor program was not doing this and causing me some strange problems that are all fixed now that I pulse the SDEN line before programming.
I also discovered that in my program I was forgetting to clear the SDTA line at the end of a transmission of a register word and sometimes it would remain high. I am hoping (will be testing today) that this was causing noise and was therefore the cause of the drop in sensitivity I am seeing.
|
Q:
We're using the TH7122 as an VHF narrowband ASK receiver. Frequency range is roughly 150-175MHz. The IF is 21.4MHz with a 15KHz BW. We can achieve typically -124dBm sensitivity.
However, the receiver is showing significant desense (~3-8dB) in certain portions of the band. For example, the middle of the operating frequency range, say, 155-165MHz, is much more affected than the band edges, though it shows up at an upper bandedge frequency as well.The phenomenom is also much more apparent at cold temperatures (< 10deg C).
Here's a clue: If the RF test generator is moved off frequency by, typically, 3-4KHz (though sometimes only a few hundred cycles will make a difference), the desense phenomenom essentially disappears.
We believe that the problem may be in the TH7122 mixer or LNA. Our theory is that the IF amplifier output is mixing with the LO in either the LNA or mixer input and producing a product at the RF frequency which can cancel the desired signal.
|
A:
sounds like a real high sensitivity application. Can you tell me what your channel spacing, loop bandwidth and settings for the VCO current and charge pump current are? Did you already try to play with the VCO and charge pump current settings to find the optimum?
This is the first application using a 21.4MHz IF I have heard of, and you are getting very good results. I suspect the problem might be too high an impedance for the LO tuned circuit. Sometimes the LO will have parasitic oscillations because its gain is higher at high frequencies. You might try different VCO currents and maybe a varactor with more capacitance.
|
Q:
Further testing indicates that the problem can be mitigated by changing the bypassing at the VCCIF supply pin. Choosing a capacitance value that is series-resonant at the LO frequency appears to at least greatly reduce the effect described. We suspect that this supply pin (pin2) is shared internally by several circuit blocks operating at disparate frequencies which makes proper bypassing problematic. We are in the process of modifying and testing and number of additional units to confirm a satisfactory fix.
|
A:
Do you have 100 Ohms in series with the LNA Vcc supply?
The IF signal can get back into the mixer via this route.
|
Q:
Yes, we do have the series 100 ohms feeding the LNA.
|
A:
I was working on a transceiver for 83MHz and noticed this
problem. It looks like IF instability but is not. I am not sure what it is but suspect that it is the VCO signal getting into the IF. Is your VCO on the low side? This does not show up in receivers operating at high frequencies. I would like to know what you discover.
|
Q:
Yes, we use low-side LO injection.
We continue to believe that the problem is caused by the sharing of the VCCIF pin with too many internal stages. It's appears that the IF amp output signal is mixing (summing) with the LO at either the mixer or LNA input. The result is a partial cancellation of the desired RF signal. Careful bypassing of VCCIF pin is needed to minimize the problem.
|
Q:
Is TH7122ENE RoHS compliant?
|
A:
Yes it is.
|
Q:
I examined, using an oscilloscope, the outputs of SDEN, SCLCK,and SDTA signals, utilizing the th7122-V3018 program supplied by Melexis.
If a 32 bit control word, such as C000F35C (hexadecimal value),were sent to the 24 bit shift register, the least significant bit is first in (rightmost bit of C000F35C is the first in), which register would be loaded (A,B,C,or D), what binary value would be sitting in the address decoder, and what 22 bit value would be contained in the register (twenty two - zeroes or ones in reply would be easiest to understand)? I wish to make a positive identification of which bits are utilized and which bits would be ignored.
I would like to know if the transition from zero to one from the SDEN bit then causes either registers A,B,C, or D to latch to the programmed input state?
|
A:
Please load the new software version (4.08) for our web page. Therein you will find an 'register view' card which lists all the internal registers bitwise. Also you can see the hex values of all 24 bits (including the two address bits). You can change each bit by clicking on the binary value.
According to the data sheet pg. 19 the most significant bit has to be first in. During the described cycle (fig.13) a whole word (A,B,C or D) will be programmed. For instance if you want to change only one bit in either A,B,C or D word you have to program the whole word which contains the bit.
Also it should be noted that the software can only be used for programming the IC. For the TX data signal you should use an extra source (e.g. square wave generator).
|
Q:
The reason why I had posed the question to you was because the "wording" in the data sheet is not clear. A definite reply to my question will leave no doubts as to how the th7122 inputs data.
If I send 32 bits in some bits will be ignored if I have a 24 bit register. The 32 bits which I am sending in, data stream from the parallel port line to the SDTA line of the th7122, has an equivalent hex value of C000F35C (C=1100, F=1111, etc.) The rightmost C (=1100) is going in first, then the 5 and then the 3 and so on till the last leftmost bit goes in. My question is how will the th7122 input the data? Which register will be loaded, what data will be be contained in the register. If you sent a reply with 22 bits of data (and the name of the register loaded) in zeroes and ones (22 zeroes or ones) and labelled what the least significant bit(s) of your answer and most significant bit(s) of your answer will represent in the workings of the TH7122, there will no room for interpretation.
I re-read the question and I want to make some modifications so you will understand my question:
If I send 32 bits in, some bits will be ignored and some bits will be entered into the register since I have a 24 bit register. The 32 bits which I am sending in, serial data stream from the parallel port line to the SDTA line of the th7122, has an equivalent hex value of C000F35C (C=1100, F=1111, etc.). The rightmost C (=1100) is going in first, (the zeroes of the C=1100 go in first) then the 5H and then the 3H (H=hexadecimal value) and so on till the last leftmost bit goes in.
|
A:
Just for imagination: The TH7122x contains a 24-bit shift register which shifts at the rising edge of SCLK. A rising edge at SDEN load one of the register words. The register word which will be loaded is defined by the first two bit's (23 & 22) out of 24 you have shifted in. With a rising edge of SDEN only the last 24 bit's which you have shifted in previously will be loaded. In your case: You have sent 32 bit's, so the first 8 bits doesn't have any effect (5C is ignored). The good thing here is that you can share the SDTA and SCLK line with some other devices - you only have to separate the SDEN.
|
A:
i am thinking about using TH7122 for an application, but i must know the size of the chip.i couldnt find it in the datasheet.what is the size?
|
A:
Why do you need to know the chip size? If you want the device with a smaller form factor, you can us the TH71221. It contains the same chip inside but the package is an MLPQ (QFN) with only 5mm x 5mm.
Can you tell us a bit more about your application? What's the projected volume?
|
Q:
5mm x 5mm is enough for us. but we look for minimum power consumption because we want to use the chip for an implantable device for our biomedical project.do u have another chip for less power consumption? our application is for short range communication.
|
A:
Do you really need a transceiver for your implantable device? Those kind of applications are usually one way. So you may use a transmitter in the implant and a receiver outside the body. In this case you could use one of our TH720x5 series transmitters (packaged in 3mmx3mm MLPD). The current consumption is between 3.5 and 12mA, depending on the RF power setting. The receiver could be one of the TH711xx series.
Please have a look at the Melexis web site to download data sheets, EVB docs etc.
|
Q:
We just finished putting a board together using the TH7122 at 359MHz. We are using your parallel port code loader to set the registers, while we do the evaluation.
On transmit it puts out about 9.8dBm draws about 23mA at 3.3V.
When we go to Standby mode it draws about 46mA at 3.3V?
On RX it draws 54mA at 3.3V. On Idle it draws 46mA at 3.3V. What are we doing wrong here? This is the current measured for the TH7122 only!
It appears that the TX current is ok. But Standby, RX and Idle are way off? Any idea what the issue is?
|
A:
indeed that sounds strange. The difference in current consumption between RX and Standby mode is approx. the target operating current in RX mode (8mA). Do you share some control signals with another IC (e.g. micro controller) which operates on a different supply level? Is there a slight, linear or exponential increase in current consumption when you change the supply level, e.g. from 3.3 to 5V?
|
Q:
Thanks for insight - But oops - my mistake, I had tied the LD output to VCC, because we we running it in stand- alone mode previously. By disconnecting this we cured the problem. Thanks again.
|
A:
this means also that your external VCO tank (L0) is not properly tuned, because in RX mode the PLL does not lock (LD is driven to 0V). Pls. be sure that the VCO control voltage (at pin LF) is well in between ~0.2V .. VCC-0.2V for VCO frequencies at TX 359MHz & RX 359MHz-IF (359MHz+IF for LO high side injection).
|
Q:
what's the time needed from standby to Idle state? What's the time from idle to rx mode? What's the current consumption between these states? What's does the IC do in idle state?
|
A:
what's the time needed from standby to Idle state?
SBY to IDLE:
- if IDLESEL=0 (B21) -> = start-up of the RO (typ. 1ms)
- if IDLESEL=1 -> few us (30-50us) more than above due to the whole PLL is active
What's the time from idle to rx mode?
IDLE to RX:
- depends on the data rate because the average data slicer time constant is adjusted to this frequency
What's the current consumption between these states?
Ref. to page 27 of TH7122 data sheet.
What's does the IC do in idle state?
IDEL states:
- if IDLESEL=0 (B21) -> only the RO is running
- if IDLESEL=1 -> the whole PLL is running (RO+CP/PFD+DIV+VCO), i.e. higher current consumption (typ 3.5mA if BAND (C17) =0; 6.3mA if BAND=1)
|
Q:
The start-up time stated in the TH7122 datasheet (Rev. 003) is for standby to transmit/receive mode.
However, there are 2 idle modes that the TH7122 can be in. Is the time to switch from these idle modes to transmit/receive the same as from standby mode? If not, can you kindly provide these information.
Also, what is the current consumption during the start-up time? Am I correct to assume it is the same as in transmit/receive mode?
|
Q:
The start-up from Idle mode is shorter because the quartz crystal is always running. For normal applications the start-up time of the crystal (800u .. 1ms) is dominant. When you choose IDLESEL = 1 the whole PLL is running and locked before entering RX or TX mode. Note that the VCO frequency in Idle mode is set by RT,NT if the mode before entering the idle mode was TX and vice versa. If IDLESEL = 0 only the quartz crystal oscillator (RO) is running and the whole PLL starts by entering RX or TX mode. So the time required for that is in the range of 200us if the standard settings are used. When the PLL bandwidth becomes narrower as well as the PFD comparison frequency becomes lower, the PLL start-up and switching time is higher. In RX mode also the time constant of the data slicer threshold generation (set by 200kohm * C3) adds some delay.
|
A:
After reviewing all the literature on the TH7122, I believe that some fundamental questions need to be answered about the chips operation in programmable user mode (PUM) transmission and reception mode.
For Transmission:
1) With respect to the timing signals and process of loading of the ABCD registers, specifically, after you send the first 24 bits to the A latch register, does the system automatically reset and seek to determine which next register requires to be loaded?
In opposition to the "automatic reset" theory of operation:
Page 26 of the data sheet states:
"The control words are 24 bit lengths; 2 address bits and 22 data bits. The first two bits (bit 23 and 22) are latch address bits. As additional leading bits are ignored, only the least significant 24 bits are serial clocked into the shift register."
|
A:
1) As explained in the data sheet the SCI contains a 24-bit shift register which is not the register latch (A,B,C or D). Each programming word has a length of 24-bits (2 address bits and 22 steering bits). After shifting the 24-bits, a rising edge of SDEN loads the 22 steering bits from the 24-bit shift register to A, B, C or D Latch with respect to the two address bits (Fig. 13 on pg. 19). There is no automatic reset or seeking function. The programming must be done for each register word separately. Note that after first power-up (not switch from standby to idle, rx or tx mode), the TH7122 runs in stand-alone user mode. After a first logic change on SDEN the device operates in programmable user mode. Therefore a pulse (or edge) on SDEN before the first programming is necessary. Otherwise the first register latch will not be programmed correctly. But again this is only necessary for the very first register programming.
2) Since the programming is done only by a rising
|
Q:
With respect to hardware interfacing the th7122 IC, melexis
corporation directs its customers to its downloads, where the three control pins of the IC are interfaced with a parallel port which emulates the SCI control bus.
For FSK reception:
1) With respect to interfacing the IN_DTA pin, what hardware do you believe would be ideal to interface the IN_DTA pin for an ideal data processing environment (assume that you are utilizing the parallel port environment as directed to by melexis corp.)?
What I mean by "ideal" hardware environment, is what hardware components would you purchase to ensure a "stable data processing" environment to a microprocessor?
(would you interface with buffers, comparators, A/D etc., The idea is to ensure that signal integrity is maintained and properly "captured" for data processing.
2) With respect to interfacing the OUT_DTA pin for maximum signa
|
Q:
1) All digital control signals of the TH7122 can be driven by any hardware which fulfills the specification of the TH7122. The hardware (algorithm) which evaluates the received signal from OUT_DTA must be able to extract the expected data from the stream.
2) The isolation between the RF output and the OUT_DTA is not that important because during receive the PA is normally off. Also the base band and the RF are fairly far off. If you intend to use an external RF amplifier (e.g. RF2117) a good isolation between the VCO tank of the TH7122 should be provided by the board. That includes separate VCC traces for the components with good de-coupling.
|
Q:
The frequency range of the RF2117 is typically between 400 and 500 MHz. Do you know of external, signal and power, RF amplifiers that have been tested with the th7122 at approximately the 27 to 150 Mhz range?
Also, with respect to the statement:
"If you intend to use an external RF amplifier a good isolation between the VCO tank of the th7122 should be provided by the board. That includes separate Vcc traces for the components with good de-coupling..."
What exactly do you mean by the phrase, "That includes separate Vcc traces for the components with good de-coupling". What specific operating conditions did you have in mind which required separate Vcc traces and can you elaborate upon the term "de-coupling". The term, "de-coupling" has more than one meaning depending upon the circumstance to which it is applied. Can you define the term with respect to the components and circuit conditions?
|
A:
I guess there are a lot of RF amplifiers available - probably the RF2114 is one of them. We don't have tested a solution containing an external amplifier.
The separate pcb traces means that every VCC (VCC_DIG, VCC_IF) of the IC as well as each building block which is supplied by VCC (Tank of the LNA, Tank of the VCO, Tank of the PA and possibly an external PA), should be routed as close as possible to the supply. If e.g. a long trace supplies the PA and in between the connection of the loop filter is located, it may happens that large current transients caused by the PA, produce a voltage drop over the trace which causes disturbances in the VCO control voltage (VLF). As a result the VCO contains more noise than normal.
De-coupling means that each VCC trace should contain a high Q capacitance (300pF .. 1nF) to ground as close as possible to the circuit. The ground (VEE) should be preferably a very conductive layer within the pcb (bottom side of a double laye
|
Q:
I have a project using TH7122.1 IC for a FSK transceiver operating at 315 MHz frequency range, It is found that there is a 945 MHz 3 Harmoic came out.
I strictly follow the data sheets information as well as the application layout for design.
Could anybody help to remove the unwanted frequency for me.
|
A:
Of course there will be a 3rd harmonic which has to be suppressed by the antenna matching/filter circuit. Normally with our EVB population a suppression of ~ -50dBc for the 3rd harmonic is achieved. It depends on the local regulations if this is suppression is sufficient. If not, probably the order of the antenna matching/filter has to be increased.
|
Q:
I am having a problem with the receiver side of the transceiver. The circuit is running off a 5v supply with ASK modulation and I am able to transmit an ASK modulated signal at 915Mhz with no worries but when I switch to receive mode I am getting about 3.7 VDC at Out_Dta (pin 8) without any input (no CW). I have the Peak Detector active and it seems that for a number of different setting there is no change on pin 8. I am using the following programming words:
TRANSMITTING
------------
A-WORD - 0x 35 E8 50
B-WORD - 0x 78 E8 08
C-WORD - 0X AE 23 53
D-WORD - 0X E8 03 93
RECEIVING
---------
A-WORD - 0x 31 24 50
B-WORD - 0x 78 E8 08
C-WORD - 0X A2 23 53
D-WORD - 0X E8 03 93
I have tested some DC voltages (with no input) at various pins and some values don't seem right:
Pin 4 - 760mV
Pin 5 - 100mV
Pin 7 - 580mV
Pin 8 - 3.7V
Pin 25 - 5V
Pin 26 - 0.8V
Pin 28 - 5V
Pin 30 - 5V
Pin 32 - 3.7V
Pin 1 - 5V
|
A:
Have you added two resistors to set the set the threshold voltage on pin 5 so it is below the peak voltage on pin 4? For the EVBs, I use 100nF on pin 4 for the peak hold capacitor, 100K from pin 4 to pin 5 and 680K from pin 5 to ground. This has worked well. You can change the threshold by changing the 680K.
|
Q:
The data sheet has the 100k and 680k the other way around to what you say...but the cookbook says to place the resistors the way you have just mentioned. I have built it according to the data sheet (and not what you've just stated) and as you can see in the previous post the voltage on pin 5 is below the voltage on pin 4.
|
Q:
I have resolved the problem. I switched the peak detector resistors around and everything seems fine now. You should probably fix the error in the data sheet.
|
A:
I am glad it was so easy to fix the problem. We will change the data sheet.
|
Q:
I m very very new in this field, i tried to read the datasheet for TH7122, but didnt understand anything.
I m trying to comunicate through a UART module of a PIC microcontroller to a moderately far wireless tarnsiver module!
My question is that can i use TH7122 with the UART( connecting UART to TH7122) to comunicate to the wireless ttransiver module? I mean does TH7122 takes in serial data? and give a serial data output after recieving the data from the far transiever module?
PLZ anyone give some dea!
THANX
|
A:
The TH7122 can receive/transmit serial data. It does not perform any manipulation of the data. The only restriction is the maximum data rate. For data rates up to 20kbps, you can use the "normal" FSK modulation approach by switching the crystal (as shown in the data sheet). For data rates in excess of 20kbps and up to about 115kbps, you should use direct VCO modulation. This is explained in more detail in the application note: "TH7122 and TH71221 High Speed Communication". The note is (like many other app notes) available on the Melexis web site.
please note, UART as a protocol is just a serial communications protocol. The hardware associated to it is the "Universal Asynchronous Receiver/Transmitter (UART) controller". Of course the controller is not part of the TH7122, it's the hardware in your PC, MCU or what ever you use for data processing.
|
Q:
We're optimizing the TH7122 transmitter design to use DC modulation. Do you have any recommended circuits for splitting the tx mod for 2-point modulation ?
I’ve designed a sallen-key lowpass/highpass combination to split the tx mod to the ref osc+varactor/VCO respectively but the resulting modulation doesn’t provide a flat enough freq response.
What is the ideal crossover freq ?
|
A:
When the channel spacing is 12.5kHz the max. data freq. should be 125..250Hz for xtal pulling. In that case the bandwidth of the PLL should be adjusted to 1.25kHz. This results in a minimum data freq. of 12.5kHz for direct VCO modulation. Your data freq. is DC..600/1200Hz. Therefore it is necessary to reduce the PLL bandwidth so that significant spectrum contents can be applied directly to the VCO. For determining the PLL bandwidth the average PSD of the modulation signal should be analyzed. It should be located in a minimum side-lobe of the spectrum (if exists). Then the 3dB LP/HP frequency should be 10 times lower/higher. You can try to decrease this factor stepwise (maybe also non-symmetrically). For the quartz crystal modulation I would suggest to use a varactor diode as depicted in the TH7122 Cookbook.
|
Q:
Unfortunately as we’re using the TH7122 as a narrowband 12.5KHz chan spacing txcr and my understanding is that we cannot transmit using indirect ref oscillator modulation at 1200/2400 Bd FSK because our PLL loop filter b/w is ~300Hz.
Our demo board is curently set for direct VCO modulation which filters out any tx mod signal below ~500Hz as expected from the inherent low-pass synth characteristic.
But modulating via the indirect mod path causes significant overshoot when the modulating frequency gets up to the PLL loop bandwidth. Can this be overcome by increasing the phase margin without significantly degrading spurious performance ?
From the datasheets, the recommended lowest modulation freq for direct VCO mod is 10x more the PLL loop bandwidth, wheras for indirect mod, the highest mod freq is 5x less than the loop b/w. How difficult is it to control the overall modulation frequency response when applying 2–port modulation ?
|
A:
the two-point modulation approach is quite sophisticated. We don't have a solution ready. Pls. check if it's sufficient to have a modulation frequency from DC to 10kHz. In that case the normal "crystal pulling" approach can be used.
|
Q:
Whatt's the main differences between TH7122 and TH71221? The databooks of the parts look very similar!
|
A:
it's the same chip inside, the only difference is the package
TH7122 - LQFP32 (for "normal" use)
TH71221 - MLPQ32 5x5 (for small form factor apps)
|
Q:
I’m working with TH7122 at 27MHz in Programmable User Mode, I need to update the transceiver in previous equipment but it is impossible to program then TH7122 with the microcontroller.
There is any way to program the TH7122 with the PC at my working frequency end then use TH7122 in Stand-alone User Mode without losing the registers value at each power failure.
Is possible to program de register permanently acceding to the EEPROM?
Is possible to request to Melexis a customised TH7122 with my working frequency selected in Stand-alone User Mode? How may units?
|
A:
the TH7122 contains no non-volatile memory. The usage at 27MHz isn't possible in stand alone user mode. Therefore the setup of the transceiver can only be done using the programmable user mode. This can be done by means of a micro controller or PC. A change of the stand alone mode settings is not possible because it is set by chip lithography. A change of this would generate a new IC related to your special requirements. If your expected volume is very high pls. contact your local sales representative to find out if we can find a special arrangement.
|
Q:
We would like to use the TH7122 with a power amplifier (2 Watt).
I saw that on the receiver, the maximum input power was -10dBm.
What could happen if the signal is stronger.
Is there a solution for use this component in a power application?
|
A:
You will probably burn out the LNA and several other parts if the input power is 2W (33dBm). I don't know how high you can go, but at this power level, you will need to use a PIN diode T/R switch. I could not find any IC switches which operate at 2W. Look at some 2 way radio
circuits to get some ideas. Usually there is a PIN diode in series with the TX output to isolate it from the receiver and another shunt diode at the receiver input.
|
Q:
I'm developing a product with the TH7122, and we've been using the ".1" revision for most of our development/testing - but are now moving into pre-production and the chips we have purchased are all the ".2" revision.
I am interested to know what differences there are between the two revisions so I can assess the impact of this change. Could you possibly provide a list of changes that might affect us? (I can provide you email address if you want to discuss)
Also there seem to be changes to do with the RSSI output in the new datasheet. Can you provide any details on these changes?
|
A:
For your application, there are two main differences. The fixed capacitance of the VCO is about 0.5pF more, so you may need to adjust your VCO tuning if the tuning voltage is too close to gnd.
The IF amplifier has been improved so there is less feedback from the output to the input, so the discriminator impedance does not affect the IF filter response. Additionally, the RSSI voltage is now consistent and it always starts around 0.7V. In the .1 version, there was a lot of variation in the start voltage.
You can also use the peak detector in FSK mode.
|
Q:
We are using the TH7122 by directly modulating the VCO. Therefore, the FSK-SW is not needed. We would like to turn on an external PA when the TH7122 is in transmit mode. By using the TH7122 to do the switching we can save pins on the MCU. I'm not sure of an easy way to do this in conjunction with the OPMODE, so my thoughts turned to the MODSEL register and FSK-SW.
Since FSK-SW and IN-DTA is not needed, I thought we may be able to use it via the MODSEL register. If we ground IN-DTA, then when MODSEL is set to 1, the FSK-SW switch is closed and the output grounded. If we set MODSEL to 0, then if IN-DTA is 0, the PA will turn off (via ASK), this is OK. What happens to the FSK-SW? Does it still stay open since MODSEL is 0 (ASK mode)?
Do you have any better suggestions on how I can accomplish my aim?
|
A:
In FSK mode the FSK_SW is controlled by IN_DTA. The polarity can be changed by DTAPOL (A20). In ASK transmit mode the switch is open as well as in general in RX mode. Therefore it's probably a good idea to use the switch for turn-on the ext. PA when the VCO is modulated directly.
Unfortunately there's no extra pin to control an external PA. So I guess it would be the best to proceed in the proposed way.
|
A:
That's exactly what I wanted to know. I'll use the FSK-SW to switch my external PA.
|
Q:
I have the schematic of TH7122@5V, I want it connected to 3.3V DSP. Can I simply change the supply voltage of TH7122 to 3.3V? Then I wonder if all the component values have to be changed.
|
A:
It should be ok unless the tuning voltage on pin 23 is less than 2V. The voltage across the internal varactor is Vcc-pin 23.
|
Q:
what does it mean? can I still use the varactor diode SMV1249?
Besides, is the supply voltage a digital or analog one?
|
A:
All the demo boards and schematics I send out are designed for 3V unless the customer requests 5V. If they work with 3V, they will work with 5V. With 5V, the VCO has a larger tuning range because the tuning voltage goes from .5 to 4.5V, so your circuit should work at 3.3V.
|
Q:
Can you send me a TH7122_915MHz transmitter schematic & board component values for FSK_915MHz.
|
A:
The EVB7122 data sheet on our website has schematics, pcb layout and component lists. The Gerber files for the board are also available.
|
Q:
I am using TH71221 in both high speed and extended frequency applications. According to the cookbook, it needs an external varactor and direct VCO modulation. And this design is quite the same with the Narrow Band application which is only suitable for low speed applications. Is this a problem I have to solve and how?
|
A:
the high speed application could also be used at frequencies where an external varactor is required. The difference to the narrow band application is the higher FSK deviation and the component values for injecting the data signal.
|
Q:
As part of bigger project i need to design FSK transciever (for short (only few bites at a time) sporadically send packets of data) at 86,79 MHz, and TH71221 is probably the best solution. But i'm little inexperienced in this area. Can be found (somewhere) some sort of ste-by-step guide for design this sort of circuit??
|
A:
I think you will find the help you need in our "Transceiver Cookbook" which contains details about the external components you need to make your application.
|
Q:
If i correctly understand this "Transceiver Cookbook", for my aplication is reference at 4.1 (FSK Crystal Modulation). But are needed some other components for work at lower than standart 300Mhz (Stand-alone mode)(i need trancieving frekvency 86,79MHz)? Must then enter Programable User Mode or 71221 only transmit signal generated by oscilator to output (antena)?
|
A:
A normal crystal can only be modulated up to ~ +/- 40ppm. That means at 87MHz the FSK deviation would be around +/- 3kHz. If this is sufficient for your system crystal modulation can be done. If not you probably have to move to direct VCO modulation as stated in 4.3. As you mentioned the operation below 300MHz requires some external components like an additional varactor which is also described in 4.3. Since the 'standard frequencies' are 315, 434, 868 and 915MHz you have to setup the dividers etc. according your operating frequency in programmable user mode.
|
Q:
Please advise when this device is available.
I have a requirement to replace a legacy system operating at 458.025MHz and 469.950MHz. The system uses FSK, 2400bps lower tone; 4800bps upper tone; FSK deviation is 3KHz. The IF bandwidth is some 18KHz wide. RX sensitivity is some -90 to -100dBm and the current system radiates 2Watts. (I intend amplifying the chip Po using a Mitsubishi PA.)
The complete system consists of a Controller scanning (polling) 100 downrange nodes and latency is paramount. I use the Controller TX continuously radiating to lock downrange RXs and each addressed downrange TX activates on command returning response to the Controller RX.(Duplex Controller; Simplex downrange transceivers) This gives reasonable latency of around 2 seconds to interrogate 60 nodes (at present.)
Would the above device provide a similar performance as described or would I be better off using one of your discrete TX / RX chips instead?
My problem lies in the unavailability.
|
A:
you may use the TH71221 (or TH7122) but it requires a 10.7MHz crystal IF filter if a 18kHz BW is needed. The smallest BW 10.7MHz ceramic filters have about 30kHz (e.g. Murata). So this could make the circuit a bit expensive. Make sure the PA is well isolated from the IC (small S12). Otherwise the 2W booster can load pull the VCO and kick off its frequency.
The receiver TH71102 could be used at 455kHz IF where you can use a cheaper narrow-band ceramic filter. But with this IC you would have to switch the reference xtals to achieve your two RFs. The same for the transmitter, of course.
|
Q:
Is there an anticipated release date for these devices?
I wish to purchase Qty: 1-9 for development. What cost in this volume?
|
A:
Both devices TH7122 and TH71221 are available.
You should contact the Melexis representive in Australia to ask for samples and for a volume quote. This is the company called Alliance. Contact is Dick Naylor at: d_naylor@bigpond.com
What volumes are you talking about?
|
Q:
[QUOTE=karl] Both devices TH7122 and TH71221 are available.
You should contact the Melexis representive in Australia to ask for samples and for a volume quote. This is the company called Alliance. Contact is Dick Naylor at: d_naylor@bigpond.com
What volumes are you talking about?
Regards
Karl
[/QUOTE]
Only the 1-9 at present. Will contact Oz Agent.
|
A:
[QUOTE=karl]
Your 'Agent' in Australia bounced?
The Agent appears to be:
dave.symonds@aztronics.com.au
AZTRONICS?
[/QUOTE]
|
A:
Please contact our other representative in Australia: Alliance (you will find the contact details on our website)
Email:
d_naylor@bigpond.com
|
Q:
QUOTE=karl] Both devices TH7122 and TH71221 are available.
You should contact the Melexis representive in Australia to ask for samples and for a volume quote. This is the company called Alliance. Contact is Dick Naylor at: d_naylor@bigpond.com
Regards
Karl
[/QUOTE]
Did this and this is the reply:
The cost to send just 1 sample by courier direct from Melexis is more than the total price I quoted you for 10pcs and I understand your total project number is just 10~ 25pcs which is generally not a large enough project volume for any semiconductor manufacturer to provide free of charge samples , please provide the following project details and I will consider sending a sample to you.
(NBB I have 6 samples of SAW 465MHz from JRC in-hand???)
|
A:
you may use the TH71221 (or TH7122) but it requires a 10.7MHz crystal IF filter if a 18kHz BW is needed. The smallest BW 10.7MHz ceramic filters have about 30kHz (e.g. Murata). So this could make the circuit a bit expensive. Make sure the PA is well isolated from the IC (small S12). Otherwise the 2W booster can load pull the VCO and kick off its frequency.
The receiver TH71102 could be used at 455kHz IF where you can use a cheaper narrow-band ceramic filter. But with this IC you would have to switch the reference xtals to achieve your two RFs. The same for the transmitter, of course.
Karl[/QUOTE]
Thanks for info, Karl. Intention would be to use 2 chips in the Controller (TX + RX) and switch TX/RX at nodes.
Just printed data to study.
|
Q:
I am designing a narrow-band FM transmitter with the TH71221 in the frequency range (150-174)MHz. I am using direct VCO modulation, and a rebuild evaluation board works fine. In order to make the PCB as small as possible, I intend to use a (3.2 x 2.5)mm TCXO for external reference frequency. Can I go a little higher than 16MHz stated in the datasheet, say 16.625MHz? During power on the microprocessor keep the TH71221 in ASK receive mode and a 10 MHz ASK signal from a remote control transmitter is coupled wireless to the IF input (pin1). The demodulated datastream from pin 8 is feed to the microprocessor for setting up the frequency and the power level and switching to TX-mode. To be able to reprogram the transmitter, we have to switch the TX off and on once more. It would have been very nice, if the IF- and ASK demodulator sections could have been kept alive during transmit-mode. Is this in any way possible?
|
A:
-The external reference frequency of 16.625 MHz shouldn't be a problem.
-During TX mode the RX chain is completely off - so there's no way.
|
Q:
We are using Th71221 as FSK transceiever.
Frequence138.350-138.850Mhz.
We designed Pcb according to the datasheet.But there are problems in debugging.First work in tx mode.When write data to register,input any datas,the output frequences around 250-290MHz,and can not detect the PFD,the 8MHz reference oscillator state is normal.Then we cancelled the varactor diode,work in Stand-alone use mode,the output is the same result.Please show me where the wrong happens by any possibility.
|
A:
as indicated in the data sheet, the VCO tank must be adjusted to the target frequency of operation. Since the VCO in your application runs around 250MHz the PLL will never lock at 138MHz because the PLL settings has to fit into the VCO tuning range. When you measure the voltage level at the LF pin you will find a permanent high level. That indicates that the PLL try to lower the frequency but without success because of the de-tuned VCO tank. You should increase the inductance of the tank to lower frequency. For further informations pls. have also a look in the TH7122 cookbook which can be found at: http://www.melexis.com/relinfofiles/AN7122x-Cookbook_rev004.pdf
|
Q:
Thanks for your help,the problem has done,i increased the inductance of the tank to 250nH,i got the frequency.
|
Q:
We are designning the remote meter reading system.I want to know how long the distance that measured by using your EVB is.And give me a parameter of antenna according your EVB(7122-FSK-433.92MHz) Please.We need it can work in 350 meter distance,how can we do?
Another question.You know,the MC33593 and MC33594 are the freescale company chips.We transmit the signal using the TH72011 and receive it using the MC33594, the signal can't be received,but it can be received transmiting the signal using the MC33593 and receving the signal using the MC33594.The signal intensity using TH72011 is higher than using the MC33593. Make the distance short,The signal can be received by the MC33594 when transmit it by using the TH72011.
|
A:
1) The EVB7122 contains a 50ohm SMA connector for RF in/output which can be used for a lambda/4 monopole antenna. This antenna is more efficient than a PCB loop antenna. A distance of 350m line-of-sight should be achievable, but it depends on several environmental conditions.
2) It should be ensured that the TX center frequency is equal to the RX center frequency. Of course also RX and TX should operate on the modulation scheme. Pls. also check the output power of the TH72011 in comparison to the MC33593. If the TH72011 antenna network is properly tuned there should be an improvement of approx. 3dB in comparison to the MC33593.
It is also important that the data rate selection bits (DR0,DR1) of the MC33593 are set according to the TX data rate. I don't know if it's necessary to send a kind of sync word to the RX in order to start-up data decoding - this should be checked by your side.
|
Q:
You mean that the 350 meter distance can be achieved by using your EVB and antenna.But I only measure 150 meter distance.Because I don't have the antenna from you,I don't know if the antenna parameter is correct according your EVB.Pls describe your antenna parameter to me,for instance its length and radius etc.
|
A:
the antenna I mentioned is a simple whip antenna which has a length of 0.25*3e8/frequency /[meters]. The antenna impedance is quite close to 50ohm (theoretically 36ohms if an infinite conducting ground plane is used). You should ensure that an conductive ground plane/patch is below the antenna, otherwise the efficiency is not that good because the antenna impedance is rised by the lossy ground.
If that is not enough to achieve the distance an additional PA stage can be added and/or and additional LNA in front of the IC.
|
Q:
Where can I find some information of the exact impedance of the RF out and RF in of the TH71221 ic? I want to design the matching network exactly to a certain antenna.
Can you pls tell me where I can find information about the quarter wave antenna, focussing on the impedance of the antenna not using a perfect ground plane.
I forgot to tell you, but the tranceiver will work at 400MHz.
|
A:
The S-parameter of the LNA are given in the data sheet pg. 38..39. The input impedance slightly depends on the loading of the LNA output. For 400MHz the values are close to the 433MHz S-parameters given in the data sheet. You can use tools like RFsim99 to put these S-parameters in an 2 port model.
The output impedance of the PA itself is not important because of the open-collector output stage - the most important design issue is the impedance which loads the output node (OUT_PA). On pg. 15 of the data sheet you will find the necessary informations.
The optimum load impedance for the PA is close to the input impedance of the LNA which makes the combining network much easier.
The monopole antenna is derived from the dipole antenna assuming a perfect ground plane (mirror). When the ground is not ideal the impedance and the radiation pattern differs from the theoretical prediction, but the antenna still radiates. The important thing here is that the load impedanc
|
Q:
I'd like to use the TH7122x for wireless audio transmission.
Despite reading the cookbook, especially application note 4.2/6.7, I'm not sure how to implement my project...
I read something about "analog signal reception". Would that make it possible to feed one transceiver with an analog audio signal, and again get an analog audio signal out of the other transceiver?
|
A:
Since the FM detector is analog, the signal at OUT_DEM can be used for your receive signal. You can also use OA1 as a buffer amplifier by connecting pins 5 and 8 together and using pin 8 for the output.
You have 2 possibilities for modulation: One is shown in fig 4.2 and the other is by direct modulation of the VCO like in figs 4.3 and 4.4.
|
Q:
Is this series compatible with any ISO standards or not? For eg: Latest ISO 18000-6 ( EPC GEN 2)
|
A:
We have one customer using them in high volumes for this application and a demo board available.
|
Q:
Can you give me more details regarding the demo board like technical specification.. price...shipping charges... etc.
|
A:
These special boards are ordered from the U.S. The price is $206 plus shipping.
|
Q:
I need to have a technical datasheet, would request you to help me with that.
|
A:
Please send me an email to jon@melexis.com
|
Q:
I'm looking for a low-cost IC for a simply analog signal transmission (with FM) on the european ISM-band.
Is it possible to solve this problem with each of the transmitter chips of the 2end /3erd generation?
Which one can I take for this project (maybe TH71071 or TH72012)?
|
A:
Since the FSK modulation in our transmitter IC's is done by quartz crystal pulling, it is possible to pull the crystal by means of an audio signal by using a varactor diode. The audio signal should be pre-filtered in order to limit the occupied bandwidth. A circuit example can be found in the TH7122x Cookbook pg.6 http://www.melexis.com/relinfofiles/AN7122x-Cookbook_rev-003.pdf which is essential the same circuit that can be used for the TH7201x. I would suggest to use the 3rd generation of our transmitters (TH720XX) because there are much more power efficient. The TH7107x transmitters are not recommended for new designs.
|
Q:
I've bought some of your RF IC's -> TH72011
I have another little question to the topic below, can you tell me the function of the capacitor "CX1" in the circuit example for analog FM transmission found in the TH7122x Cookbook pg.6?
Is it possible to use this capacitor for fine tuning the transmission frequency of the IC (by replacing it with a variable capacitor for example)? Which values can be used?
And what about the varactor diode? Which one can I take (for audio transmission)? BB535 or perhaps another one?
|
A:
I've bought some of your RF IC's -> TH72011
I have another little question to the topic below, can you tell me the function of the capacitor "CX1" in the circuit example for analog FM transmission found in the TH7122x Cookbook pg.6?
Is it possible to use this capacitor for fine tuning the transmission frequency of the IC (by replacing it with a variable capacitor for example)? Which values can be used?
And what about the varactor diode? Which one can I take (for audio transmission)? BB535 or perhaps another one?
|
Q:
Thanks for your example.
But when I use a crystal (13,5600Mhz) with e.g. CL=20pF or CL=32pf and not one with CL=12pF (used in the datasheet) I have a problem:
-VCC = 3V, VD = BB639, CL_Quartz = 20pF
-C_BB639 (@1.5V)~ 40pF
-CX1 = 1 / (1/CL - 1/CRO - 1/C_BB639) with CRO~18pF
-> CX1 should be approx. -33pF!! to achieve a quartz crystal load capacitance of 20pF
Is it impossible to achieve the required frequency of 13,5600Mhz -> 433,92Mhz, in this case?
I don't need to get exactly 499,92Mhz but something between 433.065 - 434.775 MHz.
How can I solve this problem? Or shoud I just use a crystal with CL=12pf?
|
A:
according to the data sheet the load capacitance of the quartz crystal should be 10 .. 15pF. That's because the equivalent capacitance offered by the oscillator is ~18pF (pin ROI). Since the CX is a series connection between ground and crystal, the capacitance seen by the quartz crystal can never be greater than 18pF. When you apply a crystal with a specified CL of 20pF the frequency will be above the specified. If a varactor is used, the total capacitance seen by the crystal is the series connection of CRO, CX and CVD. Pls. have a look on the data sheet for further information regarding crystal pulling.
I would suggest to use a CL of 12pF.
|
Q:
Two questions regarding the interesting 72001 Tx
1) Is it possible to use analog FM on the 72001, for example using the same scheme for the th7122 - if so, what would be the maximum bandwidth attainable ?
2) Would it be possible to shift the lower operation bound to 250 MHz ?
|
A:
1) Analog FM can be done simply by using a varactor diode put in series to the crystal. The circuit is similar to the one shown in the TH7107 data sheet, page 11. The max. mod. BW is in the order of 20kHz, depending on the FM deviation you can achieve with the varactor.
2) The on-chip VCO's lower freq. limit is 290MHz. This is the spec from -40 to +125degC and 1.95 to 5.5V. It should work at lower freq. within a limited temp. and supply range. 250MHz is probably too low even at 3V and room temp. but it's worth to try.
|
Q:
I am using the TH72002 transmitter for TPMS application and I am quite new in designing the microstrip antenna. Is there any details document in explaining how to calculate the antenna impedances and also determine the matching impedance capacitance and inductance? The Application Notes provide here is not so clear.
|
A:
A very good article regarding the design of small loop antennas can be found at:
http://www.mwrf.com/Globals/PlanetEE/Content/18046.pdf
The tapped matching is also used in the EVB720xx. Herein LM1 and LM2 provide the supply of the open-collector output stage and a better suppression of the unwanted harmonics. Note that the Antenna has to be matched to approx. 300ohms at 315MHz. The transmitter output capacitance is approx. 3pF so that the matching network has to be slightly inductive.
|
Q:
How do the values of LM1 and LM2 shown in EVB720xx come about? Is there any calculations?
I couldn't find any document stated that the Antenna needs to be matched at 300ohms @ 315MHz. Need help on this.
|
A:
The TH720xx contains an open-collector output stage having a well controlled collector current. Because of the finite headroom of the collector level, the voltage swing of the output node is limited. Assuming these two constraints the optimum load can be calculated and yields in approx. 300ohms for the TH7200X and TH7201X. The TH7203X requires approx. 250ohms. You are correct the current version of the data sheet doesn’t contain this information. If the impedance becomes higher the swing at the open-collector will be increased and the PA operates more and more in the saturation region. This results in an increase of the unwanted harmonics and possibly instable operation of the PA.
The circuit should be carefully tuned in the lab in order to have the maximum efficiency & stability of the PA. The component values of the EVB description can be used first because the circuit isn’t that sensitive to different loop geometries. Now something regarding LM…:
LM2 is used to bias the
|
Q:
Pls give me a instruction about the TH72002.
We use the TH72002 in RKE.Because we don't use the mcu in the system,and we must concentrate the current consumption,how to control the ENTX.For example,I active the ENTX=1 always,how much is the current when we don't transmit signal.
|
A:
When the ENTX is high the ASK devices (TH720X2) operates in power step '0' if ASKDTA ='0'. The current consumption in power step '0' is typ. 2.3mA as already well described in the data sheet.
|
Q:
Can you give me a advice about TH72002 in the RKE application?In the system,no cpu.The input signal directly come from the keyword coding chip.How to control the ENTX?
In the system,I use the HCS300 as the code chip and input the pwm signal to Th72002.Pls give me some advice how to decrease power consumption.Because I don't have a good way to control the ENTX.
|
A:
I recommend a carefully reading of the data sheets. The power-up transmit timing of the HCS300 defines a 'TTD - transmit delay from button detect' which is min. 10ms. When you have a look on the TH72002 data sheet you can see a start-up time (ton) of typ. 1.2ms. So it's very easy to start the TX (ENTX) at same time as the button is pressed.
|
Q:
I know these parameters.I want you give some advice about how to control the TH72002,Which signal in HCS300 can be used to control the ENTX.I can't use the push button signal to control it ,because it is wobble.
|
A:
I'm not very familiar with the microchip stuff. You should contact their engineers.
Maybe the LED output can be re-used for that. Note that there is an app note regarding this matter at:
http://ww1.microchip.com/downloads/en/AppNotes/91042a.pdf
Herein a HCS362/365 is used to control the transmitter.
|
Q:
I tried the demo boards EVB72011 and EVB 71102 and everything works well. In order to avoid possible troubles, what is the XTAL brand and model?. I am using the boards at extreme temperature (>100°C).
|
A:
for the center frequency of 433.92MHz we use for the
1. EVB72011 the 13.56MHz crystal from ECS (www.ecsxtal.com), part no. ECS-135.600-CD-0374
2. EVB71102 the 23,5122MHz crystal from ECS (www.ecsxtal.com), part no. ECS-235.122-CD-0378
pls. not that these crystals are specified for temperature range -10..70C°. Of course the crystals should work also outside this specified range without any abrupt malfunction, but the frequency tolerance would be higher than normal (20ppm). Currently we evaluate some other crystals from Telcona (www.telcona.com). Please feel free to talk to them about your requirements.
|
Q:
I started some design with TH72011 and found it pretty - easy to be done and with very clean spectrum. But since I'd like to use it in different applications ( mainly alarm systems), I'll need to know the output impedance to mutch the device in the right way. I don't see in the data sheet any information about. Is somewhere data for S22 parameters or/and Smith chart for the output impedance of TH72011?
Next will be TH72031, for it also :)
|
A:
The TH720xx series contains an open-collector output stage having a well controlled collector current. The loading of the open-collector output stage is done externally - apart from a little capacitance of 2-3pF introduced by the pad and the collector capacitance. Because of that it makes not a lot of sense to provide s-parameters for the unloaded open-collector output stage.
Because of the finite headroom of the collector level, the load impedance of the output node can be calculated as described in the data sheet of the TH7122. This yields in approx. 300ohms for the TH7200X and TH7201X. The TH7203X requires approx. 250ohms.
The matching network should provide this load to the IC including the intrinsic capacitance of the IC mentioned above.
|
Q:
So, seems, a should accept , that there is a Reqw of a 300 ohms( or 250 for '..03serias) in paralel with 2-3 pf.
I throw a look to TH7122 datasheet and find there the well known formula for the equivalent load. But for TH72011 at 10mW output I found (5-0.6)^2/2*0.010=1232 ohms.You wrote 250 - 300. Which is the thrue walue?
Do I make some mistake somewhere?
|
A:
the values mentioned above are optimized for a supply level of 3 .. 4V. When the supply voltage is higher the power delivered to the load can also be higher because of the higher headroom. Note that VCEsat is ~1.2V in case of our TH720XX transmitters. When a supply of 5V can be guaranteed (e.g. no drop over the battery life-time) the load can be ~700ohms.
|
Q:
After some pause I started again work woth TH72011 and I have not bad resulults. I use it as a stabilizated oscilator for a transmitter in 450-470 MHz band, with analog FM directly at the crystal by a varicap diode. A small ( 1-5pF) trimmer - capacitor from the output to GND adjusts the matching circuit well. The spectrum is pretty clean , but the phase noise is a little bit loudy.
Very important was to use exact cystals- 12 pf paralel resonant.
The output is about 6-7 mW at 50 ohnm, mesured with HP8920A RFcommunication test set.
|
A:
thanks for the report. The output power seems to be ok. You should measure a phase noise around -88dBc/Hz at 200kHz from the carrier. If not pls. check your supply / decoupling. The best straight-forward way to check this is to use a battery.
|
A:
Thank you for the advice, I'll try with battery. :)
I'd like to share with others my experiance with the output matching of TH72011. As wroten above, the equivalent resistance Req is about 700 ohms. The capacitance of 3 pf means Xc=122 ohm at 433 MHz. Transfering the impedances in serial mode will result Z=20.64-118.4 ohm. The inductor to Vcc( in fact-shunt) is 33 nH, to make a tank at 433 MHz with the output capacitance of TH72011 is nessesery to add 1-3 pf; a small SMD trimmer-capacitor 0.6-5 pf allows to match exactly the thank frequecy. Thus the output impedance becomes only active 720 ohms and a serial inductor between 33 and 56 nH( depending of the PCB layering) matches to 50 ohm active impedance. The tolerances are matched by the trimer pretty well. If the antenna is 1/4 lambda, the impedance should be matched to 37.5 ohm; then the output serial inductor should be increased to 68-75 nH .
|
A:
In my FSK application I use a TH72011 with a 13,5600MHz
crystal series CM6035 from comtec crystal. The data for
this crystal are according your specification for TH72011.
At factory test the all units worked well but after a few weeks some units returned from the custumer with the crystal not oscillating. Do you have an idea what happens ?
|
A:
under normal operating conditions the TH72011 should operate without any problems. If the shunt capacitance C0 of the quartz crystal is below 7pF (today, most of the xtal designs have less than 3pF) the crystal's ESR could also be higher. The oscillation margin is > 600ohms measured on our EVB. Nevertheless pls. reply if the phenomenon exists over the whole supply range (2..5.5V). In addition to that pls. also reply all the numbers marked on top & button of the IC.
|
A:
From the crystals datasheet C0 is <5pF and ESRmax is 60Ohm.
The phenomenon exist over the whole supply voltage range.
The marking of the IC :
on top : TH72011.2 - 0240:
on bottom : 3B319 9901
|
A:
der date code ist mir sehr alt. Alte design versions hatten Probleme mit dem Anschwingen bei supply voltages > 3V. Ab design version .26 this is fixed.
Bitte neue/aktuelle samples über disti oder rep beziehen.
|
A:
The IC is powered by a Lithium Cell, so the max. Voltage 3.2 Volt and they did function at delivery to the customer.
We have 580 parts on stock with the following marking
on top : TH72011.2 0441
on bottom : B3920 2A
Is this design version .26 ? We got them on in july 2005.
I replaced the IC with one from our stock and the crystal also does not oscillate.
|
A:
please find below a test in order to check for design version .26:
You have to lower the supply voltage below the LVD threshold.
Please go ahead in the following way:
-put the device in the highest power step (no RPS)
-measure supply current @ 2V (transmit spectrum is present!?)
-measure supply current @ 1.7V (no transmit spectrum / off state!?)
=> If the current jump about some mA
then it's the older design version,
otherwise .26 or newer.
|
Q:
I have a short antenna (about 12cm)which is far less than 1/4 wavelength . How to get the maxium power without changing layout but parameters only
|
A:
What frequency?
Which Melexis product?
|
A:
Sorry, now I realized it's the TH72011 you want to match. I guess the freq. is 433MHz? If your antenna is shorter than quarter wavelength (which would be about 18cm for 433MHz) then you can electronically increase the length of the antenna. Just add an inductor in series to the circuit diagram shown in the DS. You may play with values of 12 to 33nH.
|
A:
We use TH72012 for 434MHz ASK Transmitter. at first, we
bought hundreds chips marked:"TH72012.2 0306", the
performance were OK.
After, we bought another hundreds chips again,
marked:"TH72012.2 0347", this time, we found many chips
transmitting frequency are at 404MHz, but if i touch
the crystal by finger,frequency will change to 434MHz.
Can you help me to solve this peoblem?
|
A:
both pins ENTX and ASKDTA are protected by ESD diodes. This is shown on page 7 of the data sheet. The upper diodes are forward biased in case no supply voltage is applied but ENTX or ASKDTA is high. That creates a path to supply the IC (and is quote normal). But there is no good reason to supply the IC through these pins. Please us the regular VCC pin for supply but ENTX to enable/disable the IC and ASKDTA to apply the modulation.
|
Q:
Based on your suggestion, I have tested again, it is ok.
But I have another find: I don't reduce the voltage(+5V), but I cut off the voltage supply, only keep Enable and Data. at this situation, the chip also can work properly. can I let the chip work at this state permanently ?
|
A:
this could be a startup problem that occured at a few parts of a ceratin lot. It appears only at supply voltages larger than ~4V. Could you please try to reduce the supply voltage and check again?
In any case this issue has been solved with the latest design revision of all TH720xx transmitter chips.
|
Q:
I'm trying to use a TH72012 to improve trasmission power in an application where I send data with a bitrate of 3Kbit/s, with an on/off modulation on 433.92MHz. I'm using suggested circuit in datasheet, but I don't know how to match the antenna. I would like to try a stylus 170mm long (lambda/4) or, better, a closed loop 50mm long printed in a PCB. How can I modify the circuit to have more power?
NOTE: using as transmitter a RF transistor (BFR93A) with a SAW resonator and a 50mm long closed loop as antenna, now I can measure, with a spectrum analyzer placed to 10mt, about 10dB more than with the circuit using TH72012 and a stylus 170mm long. WHAT'S WRONG???
|
A:
The IC delivers up to 10dBm to a load impedance of typ. 300ohms. This real load impedance must be offered by the parallel circuit (which consist of antenna/matching network and the intrinsic elements of the IC) at the desired frequency. Since the IC is intrinsically capacitive (1-3pF) because of the capacitance of the open-collector output transistor, the matching network has to be slightly inductive. A simple 50ohm PI-match is illustrated in the EVB description. This network can be used to match a simple whip antenna (lambda/4 monopole) because the antenna impedance is close to 50ohm (theoretically 36ohm over ideal conductive ground).
Another way is to use a PCB loop antenna as described in the EVB description. But the efficiency of a PCB loop antenna is only 0.05..0.1 because of the fact that the radiation resistance of the loop is 20..10 times smaller than the metallic/dielectric loss of the loop.
If you want to maximize the effective radiated power the lambda/4 monopole is t
|
Q:
I started some design with TH72015 and found it pretty - very easy to use.
But now my crystal has some troubles.
How uses TCXO(only one output pin) to substitute for normal crystal?
|
A:
of course you can also use an external oscillator like a TXCO. If you go to the TH72015 DS, pages 3 and 4, you will find the schematic of the crystal oscillator. You just have to input the signal to pin 4 (ROI). Make sure the signal is AC-coupled and the level is between 100 and 500mVpp (try a bit until you get the optimum suppression of PLL sidebands).
But what is your problem with the xtal? It should work quite easily. Please have a look at the DS, page 8, where we provide the recommended xtal specs. Many xtal suppliers have those xtals needed for our RFICs on stock. Note that FSK modulation via xtal pulling requires an xtal!
|
Q:
Thank for your reply.
I checked your TH72015 DS, pages 3 and 4, in the schematic of the crystal oscillator - pin 4 is ROI, pin 3 is FSKSW.
When I uses TCXO to substitute for normal crystal, just input the signal to pin 4 (ROI).
How about the pin 3?
|
A:
as you can see from Fig.2, pin 3 (FSKSW) is the internal switch to FSK modulate the xtal. If you apply an external signal to pin 4 (ROI), then this pin has no meaning anymore. In this case the modulation must be on your TCXO signal already.
Again, what's your problem with the xtal? I understand you're from Switzerland, right? Feel free to contact Telcona: Hofstrasse 21, CH-8181 Höri/Zürich, Tel.+41 1860 2550, Fax+41 1860 2822, http://www.telcona.com. They have all the required xtals for our RFICs.
|
Q:
I try using TCXO(single output) apply an external signal to pin 4 (ROI),and pin 3 (FSKSW) is open. How can I make a FSK modulation?
|
A:
well, as I said, in this case the modulation must come from the TCXO. Some of them can be FM-modulated. Can you tell me the TCXO part number and manufacturer, and provide a link to the data sheet? I would like to have a look at it.
|
Q:
The link of data sheet :
http://www.kdk-group.co.jp/pdf/58%7E59_nto.pdf
Can you give me your mail address. I can send circuit to you.
|
A:
thank you for providing the TCXO data sheet. I would use the NTO-80xFL with frequency adjustment and voltage control. The voltage control input can provide up to +/-10ppm frequency tuning. So if your RF is for example 433MHz, the FSK deviation can be up to +/-4.3kHz.
|
Q:
My component part number is NTO-801BL.
NTO-801BL don't have voltage control function.
|
A:
NTO-801BL is bad.
|
Q:
I have an application where I'm upgrading an old sub-assembly module with a TH72031 design that needs to periodically power up and transmit data (868MHz, FSK, 1200baud).
The main constraint is that I only have 3 connection lines available between the main PCB and this module i.e. ground, data and V+.
Is there any reason why I can't tie the ENTX (pin4) permanently to V+, knowing that when I apply power to the IC, it will be ready in transmit mode?
By doing this, my measurements show that the startup time doen not appear to be adversely affected - it is still around 1 msec.
|
A:
You can do it this way, but your driving circuit for V+ must supply all the current for the transmitter.
|
Q:
We are using the TH72032 and even unmodulated we are getting very strong phase noise, actually at 2Mhz from carrier still we get -36 dBcarrier noise when carrier power is 6dBm. According to the spec this should be much lower. We are using a good layout practice with ground plane one side and also under the IC body. Can anyone help please?
|
A:
the resolution bandwidth of your analyzer should be 100kHz for this test. What did you use? If a larger RBW is jused the noise level is higher because more thermal noise comes in.
Is your circuit according to the standard schematic (as shown in the data sheet)? If not let me know your schematic and BOM.
|
Q:
The information given at:-
http://www.melexis.com/ProdMain.aspx?nID=131
Suggests that TH72035 can be modulated down to DC. Is this actually possible ?
The data sheet shows in internal loop filter but no values or bandwidths are shown. I wish to modulate the RF carrier by pulling the crystal reference at around 100 to 300Hz. Can this be done?
|
A:
Since the crystal is modulated, the loop follows it, and the response is down to DC.
|
Q:
I am using TH72035 Transmitter 868.35MHz with a 3.3v voltage regulator(TC55RP33)The circuit is fed from a 6V Battery.Please advice how to avoid oscillation when the battery drops to about 2v.(CE Standard Requires).
/The additional filtration does not help/
|
A:
the TH72025 should automatically shut down the PA if the battery voltage drops to 1.85V. Please refer to the data sheet, sec. 2.7 Low Voltage Detection. Have you seen any parasitic oscill. at 2V? If so, could you please describe it a bit more detailed?
Why do you expect a drop down to 2V if you use a 6V battery with a 3.3V regulator? In other words, what is the drop you would expect from your 6V battery?
|
A:
the TH72035 contains an open-collector output stage. Therefore the output stage needs to be loaded at the desired operating frequency. Assuming the collector load as a RLC parallel tank, the residual load will be only resistively at resonance. Since the collector current is well controlled by the IC, the voltage swing at the collector (output) node is directly related to the real part of the load impedance. To avoid instability, the collector potential must not drop below the base potential of the output transistor, so that the output stage operates fairly in linear mode. For the TH7203X the real part of the optimum load impedance is approx. 250ohms which gives a stable operation over the whole supply range (1.9 .. 5.5V). For the TH7200X & TH7201X this is approx. 300ohms. If the lowest provided supply level guaranteed by the application can be e.g. 3V (instead of 1.9V), the available voltage swing at the output node will be higher so that the load resistance can be increased which res
|
Q:
I use TH72035 in a remote control.
The oscillation appears during the discharging of the battery from 6V down to 0V (This test is according to the ETSI European Standard) The problem is the high internal resistance of the voltage regulator in the switching point’s area .The oscillation appears as a ripple(1-50KHz) on the VCC(voltage regulator's OUT) and this causes parasitic modulation on the carrier.
|
A:
OK, so your voltage regulator is the source of oscillation. Its strong VCC ripple modulates the VCO in the TH72035. So you should better remove the root cause of the problem. Wouldn't it be easier to use just a Z-diode for voltage regulation? I don't know how you turn on and off the transmitter. If it's just by battery on/off switching, then the extra current of the Z-diode should be no problem. Otherwise you can use a bipolar tansistor and a Z-diode (at the transistor's base) for regulation.
|
Q:
I'm having trouble finding a company that supplies the required 28.59375 Mhz crystal for 915 Mhz operation. Could you inform me of a company which supplies this crystal.
|
A:
There are many crystal suppliers. Some examples:
http://www.ndk.com/ (one of the biggest)
http://www.chinafronter.com/
http://www.euroquartz.co.uk/
http://www.telcona.com/
|