Phase comparator for determining in which direction the phase of a signal changes on the basis of a rotary vector

摘要

A phase comparator compares the phase of a subject signal with that of a reference signal to produce a result therefrom. The subject signal is shifted in phase by pi/4 and -pi/4, separately. The two phase-shifted signals are respectively compared in phase with a reference signal. Resultant, two phase difference signals are applied to a decision circuit, which is operative on the basis of a rotary vector defined by the phase difference signals. The decision circuit determines the phase difference alpha and whether the phase of the subject signal changes in one direction in which the phase differenece increases or in the opposite direction in which the difference decreases. A reversible counter is responsive to the decision circuit to increment or decrement its count accordingly. That allows the phase difference to be measured over many periods of the subject signals without requiring a frequency divider dividing the subject and reference signals.