TRF372017: I channel not working

Expert 1500 points
Part Number: TRF372017


     We were side tracked into some other work and hence could not follow up for this issue. 

Since the last discussion we tried the following:

1) Fed the DAC's I channel out to the Q port of the IQ modulator and there was an output (while Q from the DAC was disconnected). 

2) Fed the DAC's Q channel out to the I port of the IQ modulator and there was output (while I from the DAC was disconnected). 

Status: When the I from the DAC is connected to the I of the modulator, there is not output!

Please advise and thanks for your continued help,

  • Hi,

    Let's go back to the original thread to keep all the tracking/history correctly.

    You may reply back to this forum listed above.

    The simple answer to this that we need to check any soldering and rework. Please see if it possible to connect a SMA wire directly to the I input of the modulator to see if there is an output to the TRF372017.


  • I tried replying to the original thread but it is locked. 

    We have replaced the modulator IC and the issue remains. 

  • This is an excerpt from the last post on this topic.

    As I recall, you previously executed an experiment where you turned off the signal at DAC for the I channel and found that there was no change in the modulator output.  Similarly, if you turn off the signal at the DAC for the Q channel the entire modulator output goes away.  This indeed points to a bad I channel.

    I cannot think of a register setting issue that would disengage the one channel in the TRF3720.  So let's confirm a couple of things first.  Have the DAC output a low frequency signal, say 30 MHz.  Then with a probe, you should be able to walk down the I/Q traces up to the coupling cap, past it, and to the pin of the device.  In this experiment do you truly see a quadrature 30 MHz tone all the way to the modulator pins for each channel?

    Also, check the Vcm before and after the coupling cap.  Before the cap, you should see the common mode voltage that the DAC wants to operate at.  After the cap you should see 1.7V on all four BB inputs.

    So when we last communicated you were able to determine that there is no I signal.  Recently, you swapped the modulator IC and saw no change.

    I think there is a problem with the DAC channel that is supplying the I side.  I will tell you a story...I had a very similar issue recently.  I had a DAC + modulator working fine and then all of a sudden the sideband and carrier feedthrough went bad.  Similar to your situation, I found the I channel Vcm was way off and further found there was no signal on the I channel.  I poked around and found my problem was intermittent and was impacted by the flex of the board.  I suspected a bad DAC or a bad solder joint on that channel pin.  Ultimately I replaced the DAC and that fixed the problem.

    Please try to change the DAC part next to see if that fixes the problem.