| 摘要 |
PURPOSE:To make synchronizing signals fixed level and to correct maximum value of video signals within a specified range by providing an AGC circuit between a video detector and an A/D converter, and at the same time, providing a means that corrects a reference signal of above-mentioned AGC circuit. CONSTITUTION:A variable gain controlling circuit 13 is provided between a video detector circuit 12 and an A/D converter 15. An AGC loop consisting of the controlling circuit 13, a comparator 19, a cumulative adder circuit 22 and a D/A converter 23 operate to conform the synchronizing pulse level of digital video signals with the reference level RE. On the other hand, the peak level of digital video signals of the A/D converter 15 and the maximum allowable value is compared by a comparator 24. A circuit consisting of a continuous deciding circuit 25, a selector 26, a delay unit 27, a coefficient multiplier29, an adder etc. reduces output level RE of a reference level generator 20 when abovementioned peak lovel exceeds the maximum allowable value for a specified period, and thereby, corrects the maximum level of video signals within desired limits at all times.
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