TH7122 Frequently asked Questions

TH72001 modulation

Question
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 ?

TH7122 for amateur packet radio

Answer
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.

Question
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
Answer
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.

TH7122 Receive Problem

Question
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.

TH7122, Maximum input signal.

Question
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?

TH7122 vs. TH71221

Question
Whatt's the main differences between TH7122 and TH71221? The databooks of the parts look very similar!

Answer
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)

TH7122 Adajcent Chan Selectivity

Answer
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.

UART & TH7122

Question
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

Answer
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.

TH7122 matching network

Question
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.

Answer
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

NRZ Voltage

Question
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)

Answer
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!

th7122 again!

Answer
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.

Question
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?

Antenna matching network

Answer
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.

TH7122 at 27 MHz

Question
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.

TH7122 size

Answer
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?

Answer
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?

audio and data transmition in one th7122

Question
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?

TH7122 IF Frequency

Question
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?

Answer
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.

TH7122 Calculations

Answer
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?

TH7122 Standby mode

Question
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?

TH7122EVB Antenna

Question
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.

TH7122 start-up time from idle mode

Question
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?

FM with all TH71xxx /TH72xxx

Answer
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.

Question
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?

Answer
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?

TH7122 theory of operation

Answer
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."

Answer
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

Question
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

Question
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.

Question
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?

TH7122 operation frequency

Answer
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

TH71221 FM transmitter

Question
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?

TH7122: FSK-SW to switch external devices

Question
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?

TH7122 VHF narrowband, 2-point modulation

Question
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 ?

Answer
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.

Question
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 ?

TH7122 OUT-PA bias voltage

Question
We would like to run the TH7122 at 3V, but bias the PA with 6V at the OUT-PA pin. Can this be done?

Answer
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.

Programming the TH7122 using the PC

Answer
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.

TH7122 and EVB7122

Question
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

TH7122 and EVB7122 ?

Answer
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.

TH711xx family

Question
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?

Answer
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.

Question
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?

TH71221 problem!

Question
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.

Answer
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

power pmplifier for Th7122

Question
Please recommend the power pmplifier for Th7122 or some information

th7122 SCI and comp. interfacing

Question
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?

Question
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.

Answer
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.

TH7122 or TH71221 at 151MHz

Question
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.

TH7122 FSK signal polarity

Question
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'.

TH7122 @ 40MHz with direct VCO modulation

Question
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).

Answer
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).

th7122 FSK Circuit

Question
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?

TH7122 at 40.68MHz

Question
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.

Answer
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.

TH7122 RoHS complience

Question
Is TH7122ENE RoHS compliant?

TH7122@5V connected to 3.3V DSP

Question
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.

TH7122 for AIS useable?

Question
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?

FM of TH7122

Question
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!

Question
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.

How to use TH7122 at 27.505 MHz 4Watts

Question
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 ?

TH72011

Answer
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.

Question
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?

PCB antenna @ 27MHz

Question
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?

Programming the TH7122 with a microprocessor

Question
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.

Help with TH71221

Question
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?

Question
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??

Answer
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.

Answer
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?

Question
[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.

Question
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???)

Answer
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.

TH7122 third harmonic on 315 MHz

Question
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.

TH7122 for HF RF modem, h-speed

Question
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?

Answer
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.

Question
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?

TH7122 at 142 Mhz FSK

Question
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?

Answer
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.

TH7122 analog fm

Question
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

TH7122_Trasmitter circuit_915MHz

Question
Can you send me a TH7122_915MHz transmitter schematic & board component values for FSK_915MHz.

TH7122 Max. Soldering Temp.

Question
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.

Multichannel Walkie Talkie Kit

Question
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......

multi-Band switching

Question
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

TH7122 with OTP registers

Question
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?

Answer
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.

TH7122 C code

Question
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 ?

TH7122 Design

Question
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?

TH7122 frequency range

Question
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?

Th7122 start-up time

Answer
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)

Audio transmission

Question
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?

TH7122@27 MHz

Question
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?

1.8 m mast used as antenna@27MHz

Question
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

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