Synchronous detector particularly adapted for a video IF signal

A synchronous detector adapted to detect an information signal modulated onto a carrier, such as a video IF signal, comprising:

• means for supplying said modulated information signal in the form of a vestigial sideband signal having a broad bandwidth sideband on a first side of said carrier and a vestigial sideband on a second side of said carrier;
• filter means coupled to said means for supplying, said filter means including a tuned circuit having a center frequency substantially equal to the frequency of the carrier on which said information signal is modulated and having a passband which passes said vestigial sideband and which also passes only a portion of said broad bandwidth sideband having a band of frequencies substantially equal to the band of frequencies of said vestigial sideband for limiting the spectrum of the signal passed thereby to a double sideband signal having a bandwidth substantially equal to twice said vestigial sideband;
• a differential amplifier having first and second inputs for differentially receiving the double sideband signal passed by said filter means, said differential amplifier being effective to limit said double sideband signal and to thereby derive a switching carrier therefrom, the frequency of said switching carrier being equal to the frequency of the carrier on which said information signal is modulated;
• emitter-follower means connected between said filter means and said limiter means for coupling said double sideband signal from said filter means to said limiter means;
• and
• multiplier means having first and second input terminals coupled to said limiter means and to said means for supplying, respectively, for multiplying said modulated information signal with said switching carrier to obtain said information signal.