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Original question:

DS100BR111: register config for 10G operation?

DS100BR111: Transmit De-emphasis capability

Jerry Chen
Expert 5110 points
Part Number: DS100BR111

Hi team,

I saw that this part has  +36dB Receive Equalization and -12dB Transmit De-emphasis. Does -12dB De-emphasis have the equal effect with +12dB Equalization to the same channel? We tested the 10Gbps data BER of one lossy channel with +12dB Receive Equalization and -12dB Transmit De-emphasis respectively. We found the Transmit De-emphasis had much worse BER. 

Thanks.

  • 0
    TI__Mastermind 19235 points

    Was the lossy channel at the input or the output of the redriver? If lossy channel was at input but the output channel insertion loss is low then applying Tx de-emphasis may actually degrade performance. 

    Thanks,

    Rodrigo Natal

  • 0 in reply to Rodrigo Natal
    TI__Expert 5110 points

    Hi Rodrigo,

    Below is the system. There is no BER at ingress with EQ applied on DS100BR111. The Egress BER is much worse, and the eye diagram measured at optical module is bad with just 0.20UI. We tried to adjust the DEM of DS100BR111, but no help, even the jitter measured in eye digram go worse. So I have the question about if +12dB Receive Equalization and -12dB Transmit De-emphasis have the same impact on the channel.

    Could you give advice to configure DS100BR111 for egress? I'm thinking about setting EQ=0dB and increasing DEM gradually to see if improved.

    Thanks.

  • 0 in reply to Jerry Chen
    TI__Mastermind 19235 points

    Related to: Could you give advice to configure DS100BR111 for egress? I'm thinking about setting EQ=0dB and increasing DEM gradually to see if improved.

    • That would be my suggestion. Based on your block diagram it's likely that the PCB channel between FPGA and redriver is very short. If that's the case then applying redriver Rx EQ will result in over-equalization.

    regards,

    Rodrigo Natal

  • 0 in reply to Rodrigo Natal
    TI__Expert 5110 points

    Hi Rodrigo,

    I found DS100BR111 is really close to FPGA, so that the minimum 2.5dB EQ might be over-equalization. Is there any internal register that can make EQ smaller？

  • 0 in reply to Jerry Chen
    TI__Mastermind 19235 points

    Unfortunately, it does not look like this redriver part number has EQ bypass option. If you initially set EQ = 0 and Tx de-emphasis = 0 but then apply de-emphasis in single step increments does the observed output eye opening improve?

    -Rodrigo