Patent ID: 7378880
Filing Date: 2008-05-27
Classification: H03L

Abstract:
1. A frequency comparator comparing frequencies of a first clock signal and a reference clock signal, comprising: a phase-frequency detector receiving the first clock signal and the reference clock signal, outputting an up clock signal and a down clock signal, wherein a pulse-width difference between the up clock signal and the down clock signal corresponds to a phase difference between the first clock signal and the reference clock signal; a comparison module comparing the frequencies of the first clock signal and the reference clock signal based on total pulse-width difference between the up clock signal and the down clock signal in a predetermined period; wherein the phase-frequency detector further outputs an inverted up clock signal and an inverted down clock signal, wherein the inverted up clock signal and the inverted down clock signal are respectively inverted signals of the up clock signal and the down clock signal; and wherein the comparison module comprises: