Carrier recovery circuit for a facsimile system

摘要

A receiver for a facsimile system in which a local carrier is either derived from a modulated signal or is generated when the carrier component of that signal is not detectable which employs a first variable frequency oscillator and a second variable frequency oscillator responsive to the first variable frequency oscillator for reducing the frequency variation of the local carrier in response to the first variable frequency oscillator. In the preferred embodiment, the second variable frequency oscillator which is frequency controlled while the first variable frequency oscillator is voltage controlled. The frequency controlled variable frequency oscillator preferably includes a stable clock driving one counter and a second counter being driven by the output frequency of the first oscillator. The respective counter states are compared in a comparator and the local generated carrier frequency is the frequency at the counts of the first counter equal the count of the second counter as determined by the comparator.