| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic gain control circuit capable of effectively utilizing the input range of an AD converter independently of an input video signal system and suppressing vibration caused by AGC control. SOLUTION: An error detection part 30 compares an output signal V from and A/D converter 14 with a set value L1, outputs a difference when L1<V and outputs 0 when V<=L1, a peak level discrimination part 32 detects the peak level of the output signal V in each line, compares the peak level with set values L1 to L3, judges which level range out of ranges 1 to 4 includes the peak level, and outputs a discrimination signal 1, 2, 3 or 4 and an integration input control part 34 outputs the output of the error detection part 30 in the case of the discrimination signals 1, 2, a fixed value K in the case of the discrimination signal 3 and 0 in the case of the discrimination signal 4, integrates the output value, converts the integrated value into an analog signal, and outputs the analog signal to a gain control amplifier 12. Gain is held when the V is in an optimum level range 2 (L2<V<=L1), the gain is attenuated when the V is in a high level range 1 (L1<V) and the gain is amplified in the case of a low level range 3 (L3<V<=L2).
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