Importance

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Abstract

A synchronous detector suitable for use in a color television receiver detects both a video signal and an audio IF signal, but in a fashion in which these two signals do not interfere with one another. In the detector, a tuner provides an IF signal in which the video signal and audio or sound IF signals are modulated on a carrier; a signal generator, such as a phase-locked loop, provides both a detecting signal synchronized with the carrier of the IF signal, and a comparing signal having the same frequency as the carrier of the IF signal but phase-shifted .pi./2 therefrom; a synchronous detecting circuit for synchronously detecting the IF signal by the detecting signal to produce the video signal; and a phase comparator for phase comparing the IF signal with the comparing signal to provide the sound IF signal. In one arrangement, the phase comparator provides a filtered version of the sound IF signal as an AFT control signal to control the fine tuning of the tuner. In another embodiment, two phase comparators are included so that the sound IF signal and the AFT control signal are provided separately.

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First Claim