Apparatus and method for producing symmetric capture range in two-quadrant phase detector PLLs using nonsymmetric pulse waves

摘要

A symmetric capture range is produced in a two-quadrant phase detector phase locked loop that utilizes nonsymmetric pulse waves. The phase detector is enabled only during VCO pulses. A latch stores the relative relationship between the leading edge of the input pulse and the center of the VCO pulse in the previous cycle. If the phase angle theta form the VCO pulse center to the leading edge of the input pulse is 0 deg< theta <180 deg, then the phase detector incrementally decreases the VCO frequency at the next VCO pulse. If the phase angle theta is 180 deg< theta <360 deg, then the phase detector incrementally increases the VCO frequency at the next VCO pulse.