| 摘要 |
Apparatus is disclosed in a video signal processing system for automatically monitoring and controlling the blanking (black) current level of an image reproducing kinescope having cathode and grid intensity control electrodes. When cathode blanking current is monitored, a reference voltage is applied to the cathode over the entire monitoring interval, and an auxiliary voltage is applied to the grid electrode during a portion of the monitoring interval. A version of the grid voltage appears as an induced cathode output voltage proportional to the level of cathode blanking current conduction. A voltage responsive sensing network coupled to the cathode provides an output voltage proportional to the difference in cathode current conducted over the monitoring interval. This voltage is processed by a sampling network to produce a control voltage for modifying the cathode bias in a direction to produce the desired cathode blanking current level at or in the vicinity of kinescope cut-off. The sampling network includes two similar time sequential sample and hold circuits. The first circuit samples the induced cathode output voltage, and the second circuit subsequently samples the cathode reference voltage. The sampled voltages are differentially processed to remove unwanted common mode interference signals from the control voltage. |
