ISI Tolerant Signaling: A Comparative Study of PAM4 and ENRZ

A thorough analysis has been carried out to study and compare the sensitivity of two signaling methods (PAM4 and ENRZ) to inter-symbol interference (ISI). While both signaling methods are considered to be major candidates for implementing 56+ Gbps serial communications, our analysis based on the new concept of ISI-Ratio shows that ENRZ signaling exhibits much less sensitivity to ISI. As a conclusion, ENRZ signaling provides a much wider eye width operating over a high loss channel. The superior performance of ENRZ signaling makes it a very good candidate for next generation 56+ Gbps short, medium, and long reach standards. The analysis introduced in this paper can be used to assess the sensitivity of any type of signaling scheme to ISI.