Crosstalk Analysis for PCIe 6.0 (PAM4) Under Different Transmitter Conditions

Previous studies have shown PAM4 signaling is ~3x more sensitive to noise interference comparing to NRZ mode. Furthermore, because of the backward compatibility requirement, PCIe needs to support both PAM4 and NRZ signaling mode. As a result, the crosstalk scenario can be much more complicated than a sole signal modulation mode. In this paper, we present a thorough analysis for the crosstalk impact on PCIe 6.0 link (PAM4) with backward compatibility of previous generations, such as PCIe 5.0 (NRZ). Several key factors, including voltage swing, equalization, modulation type, number of aggressors and port partition or bifurcations, have been studied to show their impact on the crosstalk behavior and the related effect on the full link performance. This methodology will serve as a guideline to thoroughly study the crosstalk impact for platforms with PCIe 6.0 links. It is demonstrated that, after including all the considered variables about the crosstalk, the total degradation could add up to ~22% for EH and ~19% for EW.