| 摘要 |
PROBLEM TO BE SOLVED: To quickly recover a clamping level or to quickly return it into a range when the DC level of an H sync is rapidly lowered than the clamping level or when that DC level exceeds an upper limit of the range of an A/D converter in the case of converting a video signal to a digital signal. SOLUTION: When an output signal is ordinarily lowered than a clamping code, a capacitor 11 on an input signal path is charged from a first buffer 3 based on the output of a first comparator 21, and when the output signal exceeds the clamping code, on the other hand, the capacitor 11 is quickly discharged. When the DC level of H sync is rapidly lowered in this case, a second buffer 4 is operated based on the output of a second comparator 5 and a current is additionally supplied to the capacitor 11. When the output signal of the A/D converter exceeds an upper limit level longer than one cycle of H sync, on the other hand, the capacitor 11 is discharged by operating a third buffer 3. |
