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DS80PCI402 - usage for non PCIe datarates

Kawai
Guru 19775 points
Other Parts Discussed in Thread: DS80PCI402

Hi Team,

Our customer is considering to use DS80PCI402 for non PCIe datarates, such as 5.94Gbps and 6.75Gbps. This part is registered part at their company. I understand this part is optimized for PCIe datarate, however, it could be used as a general repeater.

Here are some questions to use in such situation.

[Question]
When using at 5.94Gbps and 6.75Gbps, how should you set the RATE pin ?
Could you use in GEN2 mode for these datarates ?
Could we keep OPEN or should we set to Gen3 mode with DEM ?

[Question]
How does the effect of DEM differ by setting RATE pin to each of  the 4 logic levels ?
What is the relation between the RATE pin setting and the DEM ?

[Question]
What does the "inner amplitude" in the table 3 of datasheet page 14 ?
Does this mean the attenuated voltage for lower frequency component ?

Best Regards,
Kawai

  • 0
    TI__Mastermind 29635 points

    Hi Kawai-san,

    You may use the DS80PCI402 for other data-rates, so long as the customer takes responsibility for compliance testing to ensure that the DS80PCI402 can accommodate for signaling requirements for their proprietary interface protocol. The DS80PCI402 is only spec'd at production for operation in PCIe applications.

    Please see answers to your question below:

    A1: Setting the RATE pin determines whether the driver will output signals in limiting or non-limiting mode. I advise that since you are not using the device for a PCIe application, you should manually set the device in limiting or non-limiting depending on what you require. If you tie RATE via 1kOhm to GND (PCIe Gen 1, 2), the device will operate in limiting mode. If you tie RATE via 1kOhm to VIH (PCie Gen 3), the device will operate in linear (non-limiting) mode with de-emphasis. Leaving the RATE pin open may cause the DS80PCI402 to pick an output operating mode that is different than what is desired. I recommend setting RATE either to Logic State 0 or Logic State 1 to ensure the desired operation mode. Overall, unless you have specific needs to pass sensitive Tx FIR coefficient negotiation as in PCIe Gen-3, it may be better to operate in "Gen 1, 2" mode by tying the RATE pin via 1kOhm to GND.

    A2: The difference in output DEM depends on whether the output is in limiting or non-limiting mode. In limiting mode (RATE tied via 1kOhm to GND), the output driver will output de-emphasis that corresponds to the programmed level, ignoring any de-emphasis that may have been applied prior to the repeater. In non-limiting mode (RATE tied via 1kOhm to VIH), output de-emphasis is added to the amount of de-emphasis present in the signal prior to the repeater. Therefore, for example, if you program -3.5 dB de-emphasis on the DS80PCI402 while in non-limiting mode, the output de-emphasis from the DS80PCI402 could be more than -3.5 dB if any additional de-emphasis was provided before the DS80PCI402 input.

    A3: Yes. Inner amplitude refers to the attenuated voltage for the lower frequency components after the de-emphasis post-cursor.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19775 points

    Hi Michael-san,

    Thanks for the detail information.

    I will recommend our customer to set RATE pin to the PCI Gen1/2 mode (Limiting Mode).

    Best Regards,
    Kawai