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ADRV9002: Phase offset of RX1 and RX2

Category: Software
Product Number: ADRV9002
Software Version: 2021_R2

hello.

I had another similar question but did not receive an answer, so I will inquire here.

I have input the same signal to RX1 and RX2 as follows..

I expected the phase offset between RX1 and RX2 to be 0 degrees.

However, the waveforms acquired by the IIO oscilloscope showed that the phase of RX1 and RX2 were offset by 180 degrees.
I turned the power off and on several times, but the phase offset was always 180 degrees.

Will this phase offset always be 180 degrees?
Also, is it possible to set the phase offset of RX1 and RX2 to 0 degrees?

Best regards
hsato

Thread Notes

  • I then repeated the experiment several times.
    And sometimes the phase offset was other than 180 degrees.

    Is the phase offset of CH1 and CH2 different every time I set the local frequency?

    Best regards
    hsato

  • Will this phase offset always be 180 degrees?
    Also, is it possible to set the phase offset of RX1 and RX2 to 0 degrees?

    In theory no... There's no 180 offset AFAIK. Can you paste the other windows from the osc plugin to checl the settings you have?

    There's also some debug patterns you can play with to make sure things work at the SSI interface level. Look at "Example of configuring SSI test modes" in the wiki...

    - Nuno Sá

  • Thanks for the reply.

    The settings for the IIO oscilloscope are as follows.
    The transmit DDS is set to 0.0999 MHz. The received waveform measured a phase offset of 180 degrees.

    And another setting was made for transmit DDS at 0.0110MHz. In this case, a phase offset of 180 degrees was also measured.


    I thought it might not be a sampling mismatch, but rather that there is always a 180 degree phase offset between RX1 and RX2.

  • The transmit DDS is set to 0.0999 MHz. The received waveform measured a phase offset of 180 degrees.

    Maybe I missed something but why are you setting the DDS? If I understood correctly, you're directly injecting a signal in the receivers right? Hence, I would just change both TX1 and TX2 to primed to not interfere at all with the reception.

    - Nuno Sá

  • I have the mode as FDD.
    I then set the local to the same frequency and loop back the transmit signal to the receive to check.
    (The image at the beginning of this Q&A.)

    I have also input the signal from a signal generator and the result was the same.
    Could the problem be that I am checking in FDD mode?

  • Hmm, I just realized you have different DDS frequency between your TXs. Like that, I think phase offset is expected. I did a quick test and things look good:

    And here are my settings:

    Should also mention that I'm using the master development branch... If at the same frequencies, you still see the same behavior, please try the 2022_R2 branch.

    - Nuno Sá

  • Thank you for your careful confirmation.
    I also checked with the same connection and settings.
    (The transmit waveform is branched so that it can be measured with an external oscilloscope.)

    The phase offset measured by the IIO oscilloscope was 0 degrees.

    What is interesting is that the waveform measured by the external oscilloscope has a phase offset of 180 degrees.


    Does TX2 have a phase offset of 180 degrees relative to TX1?
    Also, does RX2 have a phase offset of 180 degrees relative to RX1, so the final phase offset is 0 degrees?

  • What is interesting is that the waveform measured by the external oscilloscope has a phase offset of 180 degrees.

    Hmm, not really sure why that number...

    Does TX2 have a phase offset of 180 degrees relative to TX1?
    Also, does RX2 have a phase offset of 180 degrees relative to RX1, so the final phase offset is 0 degrees?

    Don't think so... It's expected for some offset between TXs and even RXs. It might depend on a lot of different things but I don't think there's any fixed phase offset between the ports.

    - Nuno Sá

  • I measured the phase offset between ports at several local frequencies.
    In most of them I measured a phase offset of 180 degrees, but I understand that this is not a fixed phase offset that changes with the settings.

    Thank you very much for your kind response.