Compensating circuit for use with filters - is used in phase shift keyed demodulators and uses phase sensitive detector to control VCO coupled to mixing circuit

摘要

A filter circuit for use in a phase shift keyed demodulator and operating with a small band width is coupled to a compensating circuit to provide automatic control of the frequency. The filter circuit consists of two filters (12, 14) coupled in parallel over input and output switching circuits (10, 16). The switching circuits are operated with a square wave input signal of a constant mark/space ratio of 1:1. The input is multiplied (20) and is mixed with the output of a voltage controlled oscillator (VCO). The VCO generates an output proportional to the output of a phase sensitive detector (PSD) operating on the input to the filter and the output after passing through a limiting stage (28).