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Invalid AC Coupling values on PCIe

Aenerine

The board uses the default AC-coupling capacitor values on the PCIe edge connector.
This probably comes from the GTH transceiver user guide and doesnt take into account requirements comming from the PCIe standard.
As such, the board might have difficulties working at PCIe Gen 3.0 / 4.0.

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  • The specification for the PCIe does define a larger coupling cap (up from 100nF to approximately 200nF) so it is more than likely an oversight on the value utilized. The AUBoard-15P physical interfaces has been validated to operate up-to 16-Gbps w/ PRBS-31 LFSR patterns. I will send the team a note to update the BOM to support an upgrade to the coupling capacitors. It looks like 220nF is a suitable replacement for those AC coupling CAPs.

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  • The specification for the PCIe does define a larger coupling cap (up from 100nF to approximately 200nF) so it is more than likely an oversight on the value utilized. The AUBoard-15P physical interfaces has been validated to operate up-to 16-Gbps w/ PRBS-31 LFSR patterns. I will send the team a note to update the BOM to support an upgrade to the coupling capacitors. It looks like 220nF is a suitable replacement for those AC coupling CAPs.

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