| 摘要 |
PURPOSE:To reproduce a stable black level, by performing two times waveform modifications on a composite video signal, by using the black level detected in the picture signals as a reference level and inserting a false black level into the composite picture signal as the reference level when the black level does not exist. CONSTITUTION:A composite video signal supplied to an input terminal 1 is derived from the emitter of a transistor 1A after it is amplified by the transistor 1A and supplied to transistors 2 and 3. A blanking pulse and a synchronizing signal are supplied to terminals 5 and 6 and added to the base of the transistor 3 after they are combined with the composite video signal. A minimum level detecting circuit composed of the transistor 3, etc., detects the black level as the minimum level when the black level exists in the video signal and detects a false black level as the minimum level when the black level does not exist in the video signal, and supplies the black level or the false black level to the base of a transistor 13. |
