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Original question:

AFE7920: real-time DC_offset calibration

AFE7920: SPUR

JONGROH YOON
Prodigy 50 points
Part Number: AFE7920

Dear Sir.

spur is measured at 760.32MHz on DAC port and ADC port.(Serdes line rate of DAC/ADC  is 12.16512G and JESD204C is used)

12.16512G is a multiple of 760.32M.

I think that the spur can be related to Seredes line rate.

what do you think about it?

The following content is present in the data sheet.

" Each SerDes transmitter driver has an internal termination resistor of 100 Ω, and its maximum peak-to-peak differential output voltage is 1 Vpp and programmable down to 500 mVpp"

 

Please, let me know how to change the differntial output voltage.

I want to check whether  "differential output level" is related to SPUR" and Spur can be improved.

Thank you

Jongroh

  • +1
    TI__Guru 67904 points

    Hi Jongroh,

    To change the STX output swing, you may adjust the cursor value through C API: SetSerdesTxCursor()

    It is possible that through STX output swing and Serdes PCB line reflection that the harmonics or subharmonics of JESD204 data be "folded back" and aliased into 760.32MHz. Please use the STX output swing and check for the impact on the spur.

    You may also use TXDSA and RXDSA adjustment functions to see if it is related to external coupling. If it is a true external coupling, the spur should drop 1dB per 1dB of DSA change

  • 0 in reply to Kang Hsia
    Expert 1730 points

    Hello,

         We are also using this board but do not have access to the C-api. Please guide.

  • 0 in reply to SM
    TI__Guru 67904 points

    SM,

    You can request additional AFE79xx software through our secure server access.

    www.ti.com/.../AFE7920

  • 0 in reply to Kang Hsia
    Prodigy 50 points

    Hi Kang,

    I have confirmed that the spur drop 1dB per dB of TXDSA and RXDSA each as you recommended.

    I have test with serdestxcursor API as you guided.

    But, It doesn't improve SPUR.

    Anyway. I marked "resolve my issue" .

    and I will test further

    Thank you.

    Jongroh