Patent ID: 6169774
Filing Date: 2001-01-02
Classification: H03D,H03L

Abstract:
A phase comparator for comparing a phase of a subject signal with a phase of a reference signal for producing a result signal representative of a result therefrom, comprising: a first phase shifter for advancing the phase of the subject signal by a predetermined angle to produce a first signal, the predetermined angle being substantially equal to .pi./4; a second phase shifter for delaying the phase of the subject signal by the predetermined angle to produce a second signal; a first phase comparator circuit for comparing a phase of the first signal with the phase of the reference signal during a plurality of periods of the reference signal or the first signal to obtain a phase difference in each of the plurality of periods to produce a first phase difference signal representative of the phase difference obtained; a second phase comparator circuit for comparing a phase of the second signal with the phase of the reference signal during a plurality of periods of the reference signal or the second signal to obtain a phase difference in each of the plurality of periods to produce a second phase difference signal representative of the phase difference obtained; a decision circuit operative in response to the first and second phase difference signals for determining whether the phase of the subject signal changes in a first direction in which the phase difference increases or in a second direction in which the phase difference decreases; and a reversible counter operative in response to said decision circuit for incrementing or decrementing a count to produce the result signal corresponding to the count.