Designing BangBang PLLs for Clock and Data Recovery in Serial Data Transmission Systems

Clock recovery using phase-locked loops (PLL) with binary (bang-bang) or ternary-quantized phase detectors has become increasingly common starting with the advent of fully monolithic clock and data recovery (CDR) Circuits in the late 1980's. Bang-bang CDR circuits have the unique advantages of inherent sampling phase alignment, adaptability to multi-phase sampling structures, and operation at the highest speed at which 8 process can make a working flip-flop. This paper gives insight into the behavior of the nonlinear bangbang PLL loop dynamics, giving approximate equations for loop jitter, recovered clock spectrum, and jitter tracking performance as a function of various design parameters. A novel analysis shows that the bang-bang loop output jitter grows as the square-root of the input jitter as contrasted with the linear dependence of the linear PLL.