[SI-LIST] PCIe differential and common impedances

  • From: Boris Bakshan <bbakshan@xxxxxxxxx>
  • To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 7 Oct 2016 23:24:14 +0300

Hi experts!
I have a few queries regarding PCIe Gen3/4 channel impedance.
1. If the recommended differential PCB trace impedance is 85ohms, what
should be the common impedance of the traces? if it's 25ohms then tightly
coupled differential pair is mandatory.
2. In that case, which termination values would be considered as optimal at
the receiver/transmitter to account for minimum common and differential
reflections? (assuming we have a single resistor to power/ground per single
trace)

Thank you,
Boris.


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