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DS160PT801: Upstream PCIe optical transceiver does not include common mode Rx detect on its input pins

Mike Ives
Prodigy 20 points
Part Number: DS160PT801


When connecting to an optical PCIe transceiver that does not have the common mode Rx detect circuit on its receiver (input) pins, will setting the RX_DET_BYP pin to L3 disable the attempt of the Tx pins to detect the far side Rx inputs on both the upstream and downstream ports? The optical transceiver is in the upstream direction. I would like to clarify that the retimer will attempt to train the link when the common mode Rx detection circuit is NOT on the far end as long as RX_DET_BYP pin is set to L3. Please let me know if that is the correct way to handle connecting to another device that does not include the common mode Rx detect circuit on its input pins. Thanks.

  • +1
    TI__Mastermind 27925 points

    Hi Mike,

    The Rx detection circuit is present on the Tx pins of the retimer, and it sends pulses out of the TX lines to detect a 50ohm termination at the far-end Rx.  There is no special circuit needed at the Rx input pins of a PCIe device.

    Bypassing the detection circuit of the retimer will bypass the 50ohm termination requirement and begin transmission regardless of the termination value; however, I would think the termination on the inputs of the optical transceiver should still be properly terminated with 50ohms to avoid signal integrity issues such as reflections.

    Regards,

    Nicholaus