| 摘要 |
PURPOSE:To suppress the variation of the black level by correcting a dark current component based on the dark current component extracted from a video signal. CONSTITUTION:The video output current delivered from an image pickup tube 1 of photoconduction type undergoes current-voltage amplification by a preamplifier circuit 2 and is applied to a dark current correcting circuit 3. A dark current detecting circuit 4 extracts a DC component from the output signal of the circuit 3 and sampling and holding it in a video effective period, i.e., a signal of a video part excepting a blanking period. This sampled/held component is compared with the reference voltage. Then the difference between them is delivered as a dark current correcting signal. The circuit 3 corrects the level of the video output signal in response to the dark current correcting signal. The corrected video output signal is applied to a TV monitor 6 via a process amplifier circuit 5. |
