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Indication of a PN for RF Reading

Daniel Luis Martins
Prodigy 230 points
Other Parts Discussed in Thread: LMV221, LMH2121

Dear Sirs,

I work with the development of electronic circuits for the automotive area - and the RF part is not our specialty.

And we need to develop an electronic circuit to detect the presence of Jammers in the GSM and GPS signals in vehicles.

I think of developing a frequency detector, in the 900MHZ, 1500MHZ and 1900MHZ range, and with a DC output proportional to the amplitude of the RF signal in these ranges.

Within the TI line, would you have any PN that could meet our demand?

Kindly,

  • 0
    TI__Genius 17981 points

    Daniel,

     

    We have a couple of power detector families that could be possibly be useful for you.

    There is the LMV22x Family, more specifically the LMV221, which are log detectors and are used for GSM applications. The bandwidth of the LMV221 is from 50MHz to 3.5GHz and has a linear response between the RF input signal and DC output signal. Its power detection ranges is from -45 dBm to -5 dBm.

    There is also the LMH21xx family of RMS detectors that have a linear response between RF input and the DC output. The LMH2121 specifically has a bandwidth from 100MHz to 3GHz and has a power detection range of -28 dBm to +12 dBm.

     

    Although they are similar they have a couple differences. Such as the RMS detectors are independent from the waveform of the RF input because they are more about the average power of the RF input and are good for applications that contain signals with high peak to average power variations. The log detectors depend more on the waveform of the input and the output in volts changes linearly with the RF power in dBm.

     

    Both device families could possibly be used, but choosing one will depend on the specifics of their application such as the power range they will be detecting and how you want your signal detected.

     

    Hope this helps.

    Regards,

     

    David C

  • 0 in reply to David Chaparro
    Prodigy 230 points

    Hello David, how are you?

    Thank you for your return.

    I basically understood what you said.

    And based on this, maybe for this application, the RMS detector can give me a better perception of this signal. Thus, the LMH2121 family is perhaps the best option.

    Talking about this component, the LMH2121 - how do I determine the measurement frequency range I need, from 900MHz to 1900MHz?

    And for this, I need the inclusion of an antenna, correct? In this same frequency range. And this antenna, would I connect it directly to the RFin pin (pin B1)?

    Kindly,

  • 0 in reply to Daniel Luis Martins
    TI__Genius 17981 points

    Hi Daniel,

    There a couple of possible ways to determine the measurement frequency range you need. One way is to have three different bandpass filters, centered around the frequencies that you are interested in, and have some kind of switching mechanism to send the signal to each of them. Another possibility is to use a Triplexer, which takes a signal and splits it into three signals that go through different bandpass filters, however you may have to have this specially made.

    As your second question, you will need an antenna to receive the signal, best if it is designed for your frequency range. There will most likely need to be a filter and power amplifier after the antenna and before the power detector. Usually the power detector is used together with a directional coupler. The directional coupler has the signal pass through it and it takes a small part of that signal and sends it to the power detector. This allows the power level to be measured and the RF signal is still be sent to a receiver circuit.

    Hope this helps.

    Regards,

    David C