DS80PCI810: PCIe x4 downgraded to x2 issue

Hi CK,

The eye looks slightly overequalized.  Have you tried to reduce the EQ to Level 1?

Regards,

Lee

Hi CK,

Do the eye diagrams look better or worse with EQ settings of level 1 and level 3.  Can you post the waveforms?

Thanks and Regards,

Lee

Dear Lee,

So far, we bypass RX redriver and only use TX redriver, the issue will not be duplicated.

So we think the root cause is on the RX side.

But if we reduce the EQ of RX redriver to level 1, it still occurs this issue.

Do you have any idea??

Hi CK,

Do you have two redrivers in series?

Regards,

Lee

No, we don't have two redrivers in series.

But there is a switch (HD3SS3415) in series.

TX: redriver --> switch

RX: switch --> redriver

Do you have AC coupling capacitors between the switch and the redriver?

No, there is no ac cap between the switch and the redriver. But I think it's fine.

The block diagram and ac cap shown as below:

From HD3SS3415 datasheet, this switch requires a bias voltage, so the capacitors must only be placed on one side of the switch.

In this situation, the switch is biased by the redriver.

I think this architecture is the same as the figure11 in HD3SS3415 datasheet (page14).

Dear Lee,

Would you please tell me where the datasheet mentions the input common mode of DS80PCI810 is 2.5V, and the output common mode is about 1.1V.

I cannot find it in the DS80PCI810 datasheet. I need to explain for customer.

Thanks for your help!!