AUTOMATIC GAIN CONTROL CIRCUIT

摘要

An AGC control section (110) has a first operation mode for controlling the gain of a variable gain amplifier (103) so that the amplitude of a synchronization signal measured by a synchronization signal amplitude measurement circuit (108) is maintained constant and a second operation mode not increasing the gain even if the amplitude of the synchronization signal measured by a video signal processing circuit (109) is smaller than a predetermined first reference value and reducing the gain of the variable gain amplifier (103) only when the video signal amplitude has become greater than a predetermined second reference value. Here, when the synchronization signal amplitude is smaller than the predetermined first reference value and the video signal amplitude is greater than the predetermined second reference value while the AGC control section (110) is operating in the first operation mode, the mode is switched to the second operation mode. On the other hand, when the synchronization signal amplitude has become smaller than the predetermined first value while the AGC control section (110) is operating in the second operation mode, the mode is switched from the second operation mode to the first operation mode.