Signal phase comparator circuit - uses beats between natural and phase modulated input signals to determine frequency stability

摘要

The phase comparator periodically provides a phase difference signal indicating the relative phases of two input signals of the same nominal frequency. A local oscillator provides a third signal which is used to phase modulate the first input. A mixer provides a beat signal of the phase modulated signal and the second input. Two pulse generators provide outputs at separate given moments in the period of the beat signal, and a bistable logic circuit gives a square pulse output with pulses of length determined by the two pulse generator outputs - indicating the required phase difference.