PCIe line impedance

[dominicmusgrove]

Hi

I am using PCIe to communicate between an IMX6 and IGLOO2 FPGA, both mounted on the same PCB.

The IMX6 hardware development manual says to route PICe at 85 ohms differential impedance, yet the SABRE_SD evaluation board, IMX6 REX and other designs I have seen all route PCIe lines at 100 ohm differential.

The IGLOO2 can terminate to 80, 100 or 120 ohm differential, should I use 85 or 100 ohm impedance lines?

Can anyone explain why the hardware development guide says 85 ohms yet everyone else seems to use 100 ohm lines?

Regards,

Dominic

[igorpadykov]

Hi Dominic

differential impedance is 85ohm in PCIe gen2 according to

PCIe specification in PCI-SIG.

Also one can references to it, like IDT AN808 or others.

Best regards

igor

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