| 摘要 |
PURPOSE:To perform accurate AGC operation, by detecting the amplitude of a vertical synchronizing signal after eliminating high frequency region from a video signal through a low pass filter and making gain control so that the amplitude value becomes a constant value. CONSTITUTION:A video signal applied to an input terminal (a) is outputted to a terminal (b) via a gain variable amplifier 11, and a part of an output of the amplifier 11 is applied to a low pass filter 12 and the amplitude information of a vertical synchronizing signal only is outputted. This output is applied to a sample hold circuit via a clamp circuit 13 to detect the amplitude of the vertical synchronizing signal, and the output is applied to a gain variable amplifier 11 as a gain control signal via a low pass filter 15 and an amplifier 16. |
