Robust Timing Error Detection for Multilevel Baud-Rate CDR

Baud rate timing recovery, for which the Mueller-Muller approach is the most prominent, has become the mainstay of high speed serial links because of the simplicity of its implementation. The foundations of Mueller-Muller - Type A timing function and its propensity to lock to erroneous sampling points when applied to high order pulse amplitude modulation is studied. Using the timing error detector characteristics, the probability of the Mueller-Muller - Type A phase detector (PD) to settle to undesirable lock points is investigated. The impact of prevailing approaches to mitigate the effect of this behavior on the performance of clock and data recovery (CDR) systems is quantified, and a new low-overhead PD approach without any of their drawbacks is proposed. Simulink simulations of the CDR phase acquisition, jitter tolerance and timing margins are used to demonstrate the effectiveness of the proposed PD in achieving superior CDR performance while avoiding any of the convergence issues.