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AFE7900EVM: Issue with FMCW Transmission and reception in loopback mode

Aditya Amrit
Prodigy 20 points
Part Number: AFE7900EVM

Tool/software:

I tried FMCW Transmission (100MHz bandwidth around 5.4GHz) and it's reception using AFE7900EVM and TSW14J56EVM. Transmitted spectrum was obtained correctly and was verified using spectrum analyzer but when I tried looping back it to RX port of AFE7900EVM, in continuous capture mode, I am observing an additional DC component, which is unwanted.

Can you please help me with resolve this issue?

  • 0
    TI__Expert 5035 points

    Hi Aditya,

    Could you please share your configuration scripts, waveform file and .ini file for us to test as well?

    If you would not like to post these on the forum, let us know and we can move the discussion to email.

    Best,

    Camilo

  • 0 in reply to Camilo Garcia Trujillo
    Prodigy 20 points

    Hi Camilo

    The configuration scripts, waveform file and ini files are attached here. 

    Files.zip

  • 0 in reply to Aditya Amrit
    TI__Expert 5035 points

    Hi Aditya,

    We have tried your test and we believe the issue is coming from the test setup in HSDCpro.

    Could you try doing the following:

     

    1. Go to Test Options > Notch frequency bins
    2. Set the filter parameters (Notching) to 0 like in the picture below

     

    What we believe is happening is that because HSDCpro believes your NSD is at -60dBFS, it is notching some points at DC to -60dBFS making it look like there is a tone there.

    Please let us know if that did not resolved your issue.

    Best,

    Camilo

  • 0 in reply to Camilo Garcia Trujillo
    Prodigy 20 points

    Hi Camilio

    Thank you for the response. I tried notching in the test options menu.  Now the issue of DC component appearing in the RX spectrum is resolved. 

    I still have an issue while I am transmitting and receiving in loopback mode. My requirement is to mix TX and RX FMCW samples (4096 samples) for extracting the intermediate signal for range calculation in FMCW Radar. But on mixing the TX samples (which are loaded into the AFE TX) and RX samples (ADC captured), I am not getting the exact intermediate frequency. Ideally it should give a Frequency difference close to 0 Hz when I mix TX and RX in loopback mode. But I am getting IF close to 40MHz.

    I just wanted to clarify that my way of mixing TX and RX samples using AFE7900EVM with TSW14J56EVM in loopback mode for extracting IF signal of frequency difference corresponding to time delay is correct. 

  • 0 in reply to Aditya Amrit
    TI__Expert 5035 points

    Hi Aditya,

    Let us check internally and get back to you.

    Best,

    Camilo

  • 0 in reply to Camilo Garcia Trujillo
    Prodigy 20 points

    Hi Camilo,

    I tried sending 100 MHz sweep from TXA to RXA using loopback cable and now I get an IF signal of frequency close to 2MHz upon mixing TX and RX data samples. Even though no delay is introduced, it gives an offset IF frequency in place of near zero IF. Is there any internal delay happening while DAC send and ADC capture?

    Hope that you can help me with this once you test the loopback condition at your end. 

  • 0 in reply to Aditya Amrit
    TI__Expert 5035 points

    Hi Aditya,

    Closing this post as this was discussed over email.

    The reason for the beat frequency changing is that the J57 is not sending ad capturing the data at the same time. This is not a limitation of the AFE79xx.

    Best,

    Camilo