PCIe (2023, Age 18)

I was in need of a PCIe differential pair. The standard advice, especially for the slower revisions, is to ensure your differential pair is the correct impedance, be smart about how you route it, and move on with your life. But I wanted to make sure I got it right the first time, and if nothing else, to go on the adventure that entails.

I first used Sonnet EM to design a differential pair that matched correctly and seemed to have low insertion loss, and scaled this design to multiple lengths, 10”, 20”, and 30”. I then exported the four-port S-Parameters from the device to include cross-talk effects and imported them into the MATLAB Serial Link Designer. It’s quite a clever tool, it uses a known PBRS with both statistical and time-domain simulation of the differential pair using the S-parameters to calculate backward to the impulse response and thus the eye diagram by simulating the frequency effects on the input signal. That let me validate not only that my pair would work, but would work for quite a long run — although I don’t think it would ever get to be quite that long.