Output-Jitter Performance of Second-Order Digital Bang-Bang Phase-Locked Loops With Nonaccumulative Reference Clock Jitter

Abstract

Bang-bang phase-locked loops (BBPLLs) are inherently nonlinear systems due to the binary phase detector (BPD). While they are typically used for clock and data recovery, the ongoing trend toward digital loop implementations has resulted in several digital BBPLLs (DBBPLLs) suitable for frequency synthesis. This brief investigates the effect of nonaccumulative reference clock jitter (due to white phase noise) in second-order DBBPLLs, comparing the output jitter with that of first-order DBBPLLs. For small clock jitter, the nonlinear loop behavior is modeled as a 2-D Markov chain, and the output jitter is smaller than but close to that of a first-order loop. For large clock jitter, the BPD nonlinearity is linearized, and the output jitter is larger than that of a first-order loop; it is proportional to the clock jitter and inversely proportional to the square root of the stability factor-the ratio of the proportional-path gain to the integral-path gain of the digital loop filter.