| 摘要 |
PROBLEM TO BE SOLVED: To provide a circuit which analog-processes an image signal for a digital conversion, wherein the black level of the image signal is stably fixed without exceeding a predetermined level. SOLUTION: When a signal of a black reference period is extracted during a horizontal blanking period of an output digital signal of an A/D converter 3, an addition average circuit 4 is controlled by a counter 5, thereby sequentially adding and averaging within the black reference period in the output digital signal of the A/D converter 3 for outputting. Also, a value obtained by D/A-converting a difference between the output value and a clamp level set value is compared with a reference value in a subtraction circuit 9 during the clamp pulse active period, the result is output to a control terminal 2a of a DC control circuit 2, and a DC voltage is controlled during the black reference period in a signal to input to the A/D converter 3 according to a magnitude of a terminal voltage of the control terminal 2a. Such a loop is constituted. COPYRIGHT: (C)2006,JPO&NCIPI
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