Carrier regenerating circuit for a synchronous detector

Abstract

A synchronous detector for detecting an information signal modulated onto a carrier, such as a video IF signal, is disclosed in which there are provided a circuit for supplying the modulated information signal in the form of a vestigial sideband signal, a filter circuit coupled to the supplying circuit which includes a tuning circuit tuned to the frequency of the carrier on which the information signal is modulated, an emitter follower circuit connected to the output of the filter circuit, a limiter circuit connected to the filter circuit, for producing a switching carrier, and a multiplier having first and second input terminals coupled to the output of the limiter circuit and to the supplying circuit, for multiplying the modulated information signal and the switching carrier to obtain said information signal. In one embodiment, the limiter circuit includes a differential amplifier having first and second transistors, base electrodes of which are connected to the emitter follower circuit, and third and fourth common base transistors, emitter electrodes of which are respectively connected to collector electrodes of the first and second transistors and collector electrodes of which provide output terminals for supplying the switching carrier.