Loop circuitry with low-pass noise filter

Abstract

Phase comparators for use in loop circuits (i.e., DLL circuits and PLL circuits) are provided. The phase comparators include a phase detector for comparing a reference clock signal and a feedback signal derived from the loop circuit generated internal clock signal. The phase comparators also include a low-pass noise filter for filtering out erroneously detected phase differences between the reference clock signal and the feedback signal by requiring a certain net number of leading or lagging detections before the compensation circuitry of the loop circuit (i.e., the controlled delay line in a DLL circuit or the controlled oscillator in a PLL circuit) is adjusted. The number of net measurements required before these adjustments take place depends on a programmable bandwidth signal provided to the phase comparator.