| 摘要 |
A video signal channel in a television receiver includes a keyed filter, followed by a keyed automatic brightness control circuit for establishing a desired black or blanking level for the video signal. The brightness control circuit operates during blanking intervals of the video signal to sense the blanking level of the video signal for deriving a control signal which is utilized to maintain a desired blanking level. The filter comprises a high-pass filter circuit which is decoupled for filtering purposes during image intervals, but is coupled to the video channel during the blanking intervals for suppressing high frequency signals including noise, when present, in the video channel during the blanking intervals. The sensed blanking level and the control voltage are therefore unaffected by noise components which would otherwise impair the control signal and thereby the operation of the brightness control circuit. |
