Composite video automatic gain control amplifier

An amplifier for composite input signals having a periodically occurring digital component at a given repetition rate and video signals with frequency components substantially different from said repetition rate, said amplifier having an input stage for receiving said input signals, an output stage, means coupled to said output stage for providing a control voltage that is dependent upon the amplitude of said digital component and is independent of the amplitude of said video signals, said input stage comprising an amplifier with a control voltage terminal and having a gain and frequency response that varies as a given function of a controlled voltage applied to said terminal, said input stage comprising an input terminal, an active filter, and a voltage variable impedance connected between said input terminal and said active filter.

An amplifier for composite input signals having a periodically occurring digital component at a given repetition rate and video signals with frequency components substantially different from said repetition rate, said amplifier having an input stage for receiving said input signals, an output stage, means coupled to said output stage for providing a control voltage that is dependent upon the amplitude of said digital component and is independent of the amplitude of said video signals, said input stage comprising an amplifier with a control voltage terminal and having a gain and frequency response that varies as a given function of a control voltage applied to said terminal, said control voltage providing means comprising gate control means, and a high dischage time constant circuit connected to the output of said gate control means, said gate control means comprising an operational amplifier, the output of said output stage being connected to the non-inverted input of said operational amplifier, and synchronization signal detector means coupled to said output stage for applying selected signals to the inverted input of said operational amplifier.

A transmission system for composite video signals having synchronization signal portions and video portions occurring at different times, said system comprising a coaxial cable, an amplifier connected to the output end of said cable and having an input stabe with a control voltage terminal, means coupled to the output of said amplifier for deriving a control voltage responsive only to the amplitude of said synchronization signal, and means applying said control voltage to said input stage, the transfer function of said input stage being responsive to said control voltage whereby the overall level of synchronization signals and video portion is independent of the length of said cable.

A transmission system for composite video signals having synchronization signal portions and video portions occurring at different times, such system comprising a coaxial cable, an amplifier connected to the output end of said cable and having an input stage with a control voltage terminal, means coupled to the output of said amplifier for deriving a control voltage responsive only to the amplitude of said synchronization signal, and means applying said control voltage to said input stage, the transfer function of said input stage being responsive to said control voltage whereby the overall level of sychronization signals and video portion is independent of the length of said cable, said input stage comprising a series resistance formed by the source-drain path of an FET amplifier, and an active filter, said FET comprising the input impedance of said active filter, and further comprising means applying said control voltage to the gate of said FET, said means producing said control voltage comprising gate control means, means applying the output of said system to said gate control means, and synchronization signal detecting means connected to control said gate control means, whereby the output of said gate control means corresponds substantially only to the level of synchronization signals at the output of said cable.