AUTOMATIC GAIN CONTROL FOR VIDEO AMPLIFIER

摘要

/77432 AUTOMATIC GAIN CONTROL FOR VIDEO AMPLIFIER An automatic gain control circuit for controlling the gain of a video amplifier of the type adapted to amplify a composite video signal comprised of a video data component and a synchronization component. The circuit comprises first means coupled to the output of the video amplifier for sampling the voltage level of the amplified composite video signal during a first portion (e.g. backporch) of the synchronization component. Second means is coupled to the output of the video amplifier for sampling the voltage level of the amplified composite video signal during a second portion (e.g. tip) of the synchronization component. Third means is coupled to the first and second means for comparing the actual potential difference between the sampled first and second portions with a predetermined reference potential and for generating a gain control signal representative of such comparison. Fourth means is provided for coupling the gain control signal to a control input of the video amplifier in order to control the gain thereof to maintain the actual potential difference between the first and second portions proportional to the level of the predetermined reference potential.