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AFE7950: Noise presence in loopback with demo codes.

Abhishek Parikh
Prodigy 205 points
Part Number: AFE7950

Dear TI team, 

We're following simple loopback design step as per tutorials but we're getting very high amount of noise which is not expected from device.

Please find configuration and response here

We have attached the DAC and ADC configuration with both boards with keeping S1_OnboardClk_RX_250M_TX_FB_500M 

We've used Amphenol 135101-R2-18.00 18GHz 50Ohms RF cables.

We've kept AFE79xx_2x2TX_44210 for Tx and AFE79xx_2x2RX_24410 for Rx for channel 1 loop back and we're not getting good response on loopback.

Any help would be appreciated.

Regards,

Abhishek

  • 0
    TI__Genius 17891 points

    Hi Abhishek,

    This issue is that the ADC is being overdriven. If you look at the Fundamental power it will be above 0dBFS. To fix this you can reduce the amplitude of the input signal one of two ways. I recommend using the first method. 

    1. Decrease the amplitude of the tone being sent to the DAC. To do this you can update the scaling factor in the 'AFE TX' tab of HSDC Pro.

    2. Update the DSA setting of either the Rx or Tx channels. To do this you can use the following functions:

    • AFE.DSA.setTxDsa(ChNo,Dsa)
    • AFE.DSA.setRxDsa(ChNo,Dsa)

    Regards,

    David Chaparro

  • 0 in reply to David Chaparro
    Prodigy 205 points

    Dear David,

    Thanks for your reply.. But this didn't worked..

    We've introduced 20dB attenuation but still the signal seems to be the same

    AFE.DSA.setRxDsa(0,20)

    Please check the below image, We have made capture 10 times to confirm with ADCDACSYNC also multiple times.

    Please can you check and help us to figure out the issue?

    Regards,

    Abhishek

  • +1 in reply to Abhishek Parikh
    TI__Genius 17891 points

    Hi Abhishek,

    In order to make sure the DAC is also not being overdriven can you try reducing the scaling factor of the tone created in the AFE TX page?

    Regards,

    David Chaparro

  • 0 in reply to David Chaparro
    Prodigy 205 points

    Dear David,

    By mistake I clicked on This resolved my issue and there's no way back..

    Currently transmit DAC has scaling factor of 0.8 in previous result I have shared. 

    As per your comment We have reduced to 0.7 scaling factor at Tx and with Rx in attenuation of AFE.DSA.setRxDsa(0,20)

    Results were the same

    Thanks for your continuous help

    Regards,

    Abhishek

  • +1 in reply to Abhishek Parikh
    TI__Genius 17891 points

    Hi Abhishek,

    In the pictures above you show that the INI file is for LMFS 14810, which does not match the S1 configuration.


    Can you update the INI file to the 24410 LMFS as shown in our User's Guide?

    Regards,

    David Chaparro

  • 0 in reply to David Chaparro
    Prodigy 205 points

    Dear David,

    Yes it worked well with 24410, Please find in below screenshots.

    Can you guide us like why it's not working on 14810 or what changes can make it work with 14810 config?

    Regards,

    Abhishek

  • 0 in reply to Abhishek Parikh
    TI__Expert 5045 points

    Hi Abhishek,

    When using 14810 are you programming the AFE7950 in a 14810 mode like the "S6_OnboardClk_RX_TX_125M_10Gbps_2Lanes.py" script in the Latte GUI and are you using the "AFE79xx_2x2TX_14810" and "AFE79xx_2x2RX_14810" ini files in HSDCpro?

    When you change the LMFS in either the FPGA or the AFE you must change the other one to match.

    Best,

    Camilo