| 摘要 |
Composite sync is separated from a video signal and integrated in order to produce a vertical control pulse. This pulse is then applied to the input of a one-shot multivibrator which provides an output essentially equal in duration to the time from the end of vertical sync to the start of the active picture, blanking the entire vertical interval with the exception of the vertical sync pulses. Optionally, a second one-shot multivibrator may be triggered at the horizontal sync rate and used to inhibit blanking during the times corresponding to equalizing, horizontal sync and color burst in order to preserve these legitimate parts of the signal. The first one-shot multivibrator may be replaced by a counter which counts at the horizontal rate and is reset by the vertical pulse. An increase in accuracy allows blanking of the period just before the vertical sync. Also, video presence may be sensed with a simple low-pass filter and CMOS gate and used to apply power to the main processing circuitry thus extending battery life. Blanking may be achieved by the use of a FET which simply shorts the video to signal ground during periods when blanking is desired.
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