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Improve TRF370417 Performance

Brian May
Prodigy 30 points
Other Parts Discussed in Thread: TRF370317, TRF370417

Currently using the TRF370317 as a quadrature modulator with an advertised operating RF output from 400 to 4000 MHz.  A customer requested RF output at 200 MHz.  The TRF370417 has an advertised RF output from 50 to 6000 MHz, however, sideband supression is degraded down to 70 MHz according to the datasheet.  IC swap from '317 to '417 shows that '317 has better amplitude imbalance and phase error at 200 MHz.  That was a surprise!  What steps are required to tune the circuit for use with a '417?  What are the equivelent circuit models for '417 LO/IF/RF pins?

thanks,

B.May

  • 0
    TI__Intellectual 1650 points

    Hello Brian,

    I always point folks to this app note when side band suppresion issue as the issue maybe related to LO harmonics. This app note also discusses the LO poly phase network of the TRF3703 and the TRF3704.
    http://www.ti.com/lit/an/slwa059/slwa059.pdf

    What level of SSB are you targetting? Are you able to adjust the phase of the baseband I/Q inputs?
    In the datasheet figure 18 shows the unadjusted SSB is below -40dBc between 500M and 5G. At frequencies less than 500MHz (and greater than 5G) the LO poly phase network 0 and 90 degree phase offset has more phase error than it does between 500M and 5G. At <500M LO this LO phase error then creates a unadjusted SSB spur >-40dBc on the output. What we recommend at LO frequencies less than 500MHz is to adjust the phase between your I and Q baseband signals. The phase adjustment at these frequencies (<500M) will be the dominate knob you can turn. In general since the SSB issue at low LO frequencies is related to the LO poly phase network, the I/Q phase adjustment should trend in the same direction for all parts. So depending on the level you are targetting a constant I Q phase adjustment maybe realizable at given temp or LO frequency.

    Depending how low you need to adjust the SSB level, you may also need to adjust the gain levels between the I and Q signals. However, at the LO frequency you are using the gain adjustment should be a secondary knob.  Also once the gain adjustment knob is tuned around your LO frequency it should hold fairly well over temp and LO frequency.

    let me know if this answered questions.

    Thanks
    Chris