CLAMPING CIRCUIT FOR COLOR DIFFERENCE LINE SEQUENTIAL SIGNAL

摘要

PURPOSE: To set a level difference needed for recording a color difference line sequential signal by producing a reference level signal whose level changes alternately for each horizontal scan period and then clamping the color difference line sequential signal after comparison with said reference level signal. CONSTITUTION:It is supposed that the output level VS of a switch 40 is lower than the level V1 of a reference level signal 51 when the switch 40 is turned on. Thus a differential V1-VS is amplified and integrated to be added with the input of positive phase DC amplifier 30. Then the feedback control is carried out to satisfy VS=V1. When switch 40 is turned off, the signal 51 is added continuously to the input of the amplifier 30 until the switch 40 is turned on again. When the switch 40 is turned on again, the feedback control is carried out to satisfy VS=V2. As a result, the color difference line sequential signal 31 outputted from the amplifier 30 is clamped at the level V1 with the signal R-Y and at the level V2 with the signal B-Y respectively.