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DS160PR410: will de-emphasis influence link training?

Ann_Lien
Genius 15420 points

Part Number: DS160PR410

Hello expert,

My customer want to know if linear re-driver like DS160PR410's de-emphasis influence link training? As we know, link training is to communicate sink/source capability and de-emphasis will distort original waveform, will it make link training fail? Thanks a lot!!

Best regards,

Ann Lien

  • 0
    TI__Guru* 93570 points

    Hi Ann,

    As you noted, DS160PR410 is a linear redriver. Meaning signal on input would be replicated on output with high speed signal distortion restored due to the ISI or Inter symbol Interference. PCIe layer 3 and higher send link training along with de-emphasis. DS160PR410 linearity allows de-emphasis to pass through. This allows link training negotiation between root complex/CPU and end point. DS160PR410 does not insert de-emphasis but it passes this between root complex and end point.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Genius 15420 points

    Hello Nasser,

    Thanks for reply! I want to double check with one point. So linear redriver's de-emphasis will not distort link training signal, just bypass de-emphasis? I'm not sure about "DS160PR410 linearity allows de-emphasis to pass through" meaning. Thanks a lot!!

    Best regards,

    Ann Lien

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser,

    Thanks for replying. I still have some question about re-driver below.

    1. Does the normal linear re-driver, including DS160PR410, have pre-emphasis or de-emphasis setting internal? If yes, when will it work, after linking training?

    2. The DS160PR410 part has DC gain setting. Does it influence the link training and why?

    Thank you very much,

    Howard

  • 0 in reply to Howard Tu
    TI__Guru* 93570 points

    Hi Howard and Ann,

    1). The answer to your question is no. Internally does not have de-emphasis. Imagine DS160PR410 device as an analog buffer and thus is is seamless or passes through the pre-emphasis generated by CPU and end point.

    2). In some cases, DC Gain may influence link training. In majority of cases we do not need to enable DC gain. In cases where there is high pre-channel loss or high loss on the input of the DS160PR410 the DC gain can help the link training. DC Gain essentially increases low frequency content of the signal bandwidth while the CTLE increases the high frequency content.

    Regards,, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser,

    The information you replied is clear, thank you very much :)

    Best,

    Howard