Improved Acquisition in Phase-Locked Loops with Sawtooth Phase Detectors

Phase-locked loops are frequently used to estimate bit timing in baseband digital transmission systems. The investigation reported here examines the applicability of a frequency-sensitive phase detector to timing estimation of randomized data. A new edge-triggered sawtooth phase detector is described. The reduced magnitude of circuit-induced imperfections made possible by the new detector, in conjunction with the little-known frequency discrimination characteristic of the sawtooth detector, is shown to allow significant improvements to acquisition performance. A potential problem with this and other phase-locked loops, falselock, is studied experimentally, and techniques for avoiding it are discussed.