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quadrature modulator TRF3705 sideband suppression

Giuseppe Gottardo
Prodigy 150 points

In our TSW30SH84EVM the last stage is a quadrature modulator TRF3705. Theoretically it has carrier feed-through and Sideband Suppression. The first one seems to be good, the second one not at all. Changing values in TSW GUI ("Digital" page) there is the possibility to make offset Adjustment, that I left disabled, and QMC corrections. I tried to use a lot of values of QMC PhaseAB but the biggest sideband suppression I obtain is 2 dB. Is it normal or can I reach more suppression?

At the moment we see in the spectrum analyzer 2 peaks at LO-fbb and LO+fbb and a noise floor of -70dBm. It seems good. Could be any other possible errors in our baseband design (generation of signal in the FPGA) those give us this problem of the sideband suppression at frequency LO-fbb?

Thanks a lot in advance.

Best regards

Giuseppe

  • 0
    TI__Mastermind 18065 points

    Yes, this appears to be a HW error.  Sideband suppresssion should be around 40 dBc and can be improved with QMC correction.  If the suppression is nearly non-existence then likely one of the BB channels is open-circuit.  Checkthe BB signal path and check the DC levels on all four of the BB lines.  DC should be nearly the same on all paths.

    --RJH