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DS320PR1601: Gain issue

Jeff YANG
Mastermind 7795 points
Part Number: DS320PR1601

Tool/software:

Hi,

We have used Broadcom's eye diagram drawing software to draw the eye diagram of DS320PR1601 REDRIVER.

We have tried all the EQ combinations so far, and only a few can link gen5, but the performance is not good. If the eyes are not opened, the mask will hit.

The first attachment is the eye diagram of the redriver, and the second attachment is the eye diagram of using the 2meter QDD CABLE loop back without the redriver.

There should be no problem with the signal. I don’t know if the gain of the driver is not large enough. we refer to Broadcom’s spec here what is sent is 36DB. The maximum GAIN of DS320PR1601 seems to be only more than 20DB.

Jeff

  • 0
    TI__Mastermind 18850 points

    Hi Jeff,

    Can you give us more details about the hardware setup using the redriver? For example:

    • Was this test conducted on a TI evaluation module or is the redriver on a customer board?
    • What is the host system or baseboard?
    • What is the total insertion loss between the root complex and the Broadcom endpoint?
    • What are the "EQ combinations" that have been tested?
    Jeff YANG said:
    I don’t know if the gain of the driver is not large enough. we refer to Broadcom’s spec here what is sent is 36DB. The maximum GAIN of DS320PR1601 seems to be only more than 20DB.

    I'm not sure I understand what you mean here - if the Broadcom endpoint is following the PCIe Gen 5 specifications, then it allows for up to 36 dB of insertion loss in the PCIe link between the root complex and endpoint if there is no additional signal conditioning. So most likely Broadcom is saying that if the link has less than 36 dB insertion loss, then the signal quality should be good and there is no need for using a redriver. If the link has more than 36 dB of insertion loss, the signal quality is not guaranteed to be good and a redriver could help.

    The DS320PR1601 gain is EQ boost, which is is not insertion loss. In the typical use case, the EQ boost is supposed to compensate for additional insertion loss that is over the 36 dB specification. For example, if my PCIe link has 46 dB of insertion loss, that is higher than 36 dB by 10 dB, so the endpoint and root complex could have problems with signal quality. Then the redriver could help by applying ~10 dB of EQ boost to compensate for ~10 dB of insertion loss, so the endpoint and root complex see a more manageable amount of remaining insertion loss that their TX/RX can compensate for.

    If the test setup here does not have >36 dB insertion loss, the redriver is less likely to show benefits because the root complex and Broadcom device can already achieve a good link quality and eye diagram by themselves. So we would like to understand the situation better.

    Best,

    Evan Su