Analysis of false lock in Mueller-Muller clock and data recovery system

Abstract

As serializer/deserializer (SerDes) architectures evolve to support multi-Gbps data rates, Four-level Pulse Amplitude Modulation (PAM4) has emerged as the dominant signaling scheme owing to its superior spectral efficiency. However, the conventional Mueller-Muller Clock and Data Recovery (MMCDR) architecture exhibits critical false lock artifacts when processing PAM4 signals, leading to significant degradation in Jitter Tolerance (JTOL) and Bit Error Rate (BER). Through theoretical analysis, we demonstrate that the root cause lies in the misalignment between the sampled signal and decision values during phase detection. To address this limitation, we introduce a novel Phase Detector (PD) architecture. A comprehensive CDR behavioral model integrating the proposed PD is developed in Simulink. Simulation results demonstrate that the improved PD avoids false lock compared to conventional MMPD implementations. Furthermore, the proposed PD achieves superior jitter tolerance performance. These advancements provide a hardware-efficient and readily implementable solution for high-speed PAM4 SerDes systems operating in lossy channels.