• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 12 subscribers
  • Views 1533 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TRF372017 4*Lo leakage

Leo Teng
Prodigy 60 points

Hi,

   we are evaluating the TRF372017 for inclusion into a new product of ours, and I am having some trouble with 4*Lo frequency leakage problem. 

   we are using eval board and using GUI download from TI web. Use on board 40MHz CLK source and on board 5V to 3.3V regulator.

   Now we set frequency=710MHz without any data input. Connect RF_out port to spectrum.

  Set by GUI. However we saw a small 4*Lo frequency on SA.(~2.8GHz).

  Toggle PWD_BB_VCM=PU, we saw a huge 4*Lo frequency.

  Please see attached file. Is there anything I forgot to do? The result is strange.

  Leo

  • 0
    TI__Mastermind 18095 points

    Leo:

    I do not think that you are exactly seeing the 4th harmonic.  To generate a 710 MHz LO signal, the internal VCO is tuned to 2840 MHz along with a divide by 4.  The 2840 MHz signal will bleed through to the output and I think that is the signal that you are seeing.

    You show that when the internal VCM is engaged that the 2840 MHz tone increases from -40 dBm to -18 dBm.  This may be expected as the modulator will then be operational.

    Overall, I think that your set-up is functional.  The proper test will be if the RF output performance is as expected.  Note, the LO signal should be naturally suppressed to about -35 to -40 dBm.

    --RJH

  • 0 in reply to RJ Hopper
    Prodigy 60 points
    Hopper,

    Yes, you are right. The 2840Mhz signal comes from VCO feedthrough. But I don't know you said Lo signal should be naturally suppressed to about -35 dBm to -40 dBm mean. This Lo signal means 2nd /3rd harmonic or 2840 MHz?

    Leo
  • 0 in reply to Leo Teng
    TI__Mastermind 18095 points
    Leo:

    In your configuration the LO frequency is 710 MHz (2840MHz/4). The 710 MHz LO will be naturally suppressed by the modulator at the RF output. The VCO fundamental at 2840 MHz will bleed through to the output and the LO*4 (also 2840MHz generated by the modulator) will be at the output. The combination of those signals is what you are seeing at the output.

    --RJH