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TRF7970A: ISO15693 sidebands

Christoph50
Prodigy 220 points

Part Number: TRF7970A

Hi,

Which Subcarrier Sideband does the TRF7970A use for demodulation?

If i want to use the ISO15693 standard the frequency for the sideband is +/-424 kHz -> so i will get 2 additional spectral lines at 13,56MHz +/- 424kHz.

-> Which of the two sidebands is used for demodulation?

-> if the TRF7970 use for example the upper sideband (13,56MHz+424kHz) -> does it make sense to tune the antenna circuit to this frequency?

thanks a lot

chris

  • 0
    TI__Guru* 91336 points

    the reader IC will transmit on the carrier frequency and will receive on the sideband(s), (where single or double subcarrier reception instruction is transmitted to the tag via the bit 1 of the request flags and configured in the TRF79xxA devices via the ISO Control Register (0x01)

    Common practice is to tune the antenna to fc of 13.56MHz and set the Q of the tank circuit (@ 50Ohms) to ~16, which accommodates both sub-carriers. 

    The image below shows the concept. 

  • 0 in reply to Josh Wyatt
    Prodigy 220 points
    hi josh,

    thanks for the fast answer.

    but i have one more question :-) -> for demodulating the TRF7970 uses only one side of the spectrum? -> e.g. the upper bands -> f0+484kHz and f0+423kHz? (if i use double subcarrier) -> is this correct?

    or does it use the lower band? oder both?

    thanks
    chris
  • 0 in reply to Christoph50
    TI__Guru* 91336 points

    as i tried to state - the TRF7970A is configurable for using one or both sidebands and it must tell the tag how to respond (by using the bits in the tag request flags byte) - see table 3 in the ISO15693 standard.

    if set for SSB, the sideband (which is fs1) is 424kHz,  if two subcarriers are used, fs1 is same, fs2 is 484kHz (see ISO15693-2)

  • 0 in reply to Josh Wyatt
    Prodigy 220 points

    hi,

    i think i understood the mechanism with the single and double sidebands..... but i don't understand which frequency bands (upper sidebands or lower sidebands) are actually used for demodulation.

    For example: i use SSB with 424kHz. ->  Does the TRF7970 use 13,56MHz+424kHz=13,984MHz OR 13,56MHz-424kHz=13,136MHz for demodulating? (...or from another point of view -> in The TRF7970 needs a band-pass filter to filter out the sideband  -> is the band-pass filter then adjusted to 13,984MHz OR 13,136MHz ?)

    thanks again.

    chris

  • 0 in reply to Christoph50
    TI__Guru* 91336 points
    the TRF79xx output impedance matching circuit also includes the filters for the subcarriers - it was created for you to copy and use freely.