The Sensitivity to Common/Differential/Pseudodifferential Mode Noise: ENRZ Versus NRZ

Abstract

Ensemble nonreturn-to-zero (ENRZ) signaling exhibits remarkable performance advantages in long-reach high-speed serial links due to its well-balanced Nyquist frequency, amplitude, and interwire coupling properties. This work investigates the noise performance of ENRZ compared to conventional nonreturn-to-zero (NRZ) signaling under six representative noise modes: three fundamental noise modes for both signaling—common mode (CM), differential mode (DM), and pseudodifferential mode (PDM), and three derivative four-wire noise modes specific to ENRZ. Performance is evaluated under three scenarios of increasing complexity: lossless channels with deterministicDC/AC level shifts, lossless channels with random AC noise, and lossy channels with random AC noise. Analysis reveals that effective signal swings remain constant regardless of noise type for both modulations; however, ENRZ experiences larger level shifts under DM/PDM noise in scenario 1, which can be eliminated through AC coupling. In scenarios 2 and 3, where random noise exists in both, 224 Gbps per-chord ENRZ outperforms 112 Gbps per-pair NRZ while ENRZ exhibits less degradation and comparable degradation as channel mode conversion increases. In addition to presenting the CM/DM/PDM noise analyses on ENRZ for the first time, we also highlight the incorrectness of the prevalent misconception that DM noise directly affects the differential output. Furthermore, the optimal position of the AC coupling capacitors in a channel is proposed from the CM noise removal perspective. This article concludes with practical design guidelines for maximizing ENRZ’s resilience against multiple noise scenarios