What is the common mode voltage for the PCIe receive inputs?

[cbobek]

Hi,

We have measured eye diagrams for our i.MX8 design and they meet specification.  We also measured common mode voltage for the PCIe receiver inputs (PCIE1_RXN and PCIE2_RXN) and they are 0V on the BGA pads.  I normally expect to see a DC bias voltage above 0V on this type of interface.

What is the common mode voltage or DC bias voltage for PCIE1_RXN and PCIE2_RXN?

Thank you,

Chris

[igorpadykov]

Hi Chris

i.MX8 PCIe interface is compatible with PCIe specification, which defines

PCIe Rx AC common mode voltage VRX-CM-AC-P < 150mV,

description can be found for example on p.87

https://www.keysight.com/upload/cmc_upload/All/PCI_Express_Compliance_Testing.pdf 

Best regards
igor
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