| 摘要 |
A digital AGC circuit is provided which includes an A/D converter, an AGC gate pulse generator and a TOP voltage controller. The A/D converter converts a video signal clamped to a reference level into digital data having a voltage between a predetermined reference voltage and a TOP voltage. The AGC gate pulse generator generates an AGC gate pulse for detecting a pedestal level region of the video signal, according to vertical and horizontal synchronous signals. The TOP voltage controller controls the TOP voltage of the A/D converter on the basis of a sample value extracted from the output of the A/D converter and a sync tip value of a standard signal, while the AGC gate pulse generated by the AGC gate pulse generator is enabled. All circuits but the low pass filter are digital circuits, so a special analog AGC IC is not needed. AGC is performed by controlling the TOP voltage of the A/D converter, thereby accomplishing an accurate AGC.
|
