| 摘要 |
PURPOSE:To reproduce stably a black level applied to a CRT, by detecting and holding the black peak-to-peak value level of an input signal in the blanking time at the video signal input time and by reproducing this level in DC. CONSTITUTION:For a video signal input, a transistor Tr1 which operates as an emitter follower and a Tr6 which is provided in the output terminal through diodes 4 and 5 and performs the switching operation so that the Tr1 is clamped at a set potential only in the blanking time are provided. Tr3 where the output signal of the Tr1 is inputted to detect a black peak-to-peak value level out of the video signal of the effective picture part is provided, and the output potential is held by a resistance 7 and a capacitor 8. Tr11 for holding the set potential which clamps the output terminal of the Tr1 at the set potential through diodes 4 and 5 is provided, and the output potential in the blanking time is substituted by a potential corresponding to the black peak-to-peak value. |
