| 摘要 |
A burst gate pulse generator generates a burst gate signal representative of a time period during which a burst signal is present within an input composite video signal. Each period of the input composite video signal includes a horizontal synchronization pulse, a burst signal and a video information signal. The burst gate pulse generator detects the end of the horizontal synchronization signal and begins the burst pulse at the end of the horizontal synchronization signal. A timing circuit including a charge storage device and a charge delivery device controls the duration of the burst pulse. When the burst pulse is activated the charge delivery device begins building a charge across the charge storage device until a threshold value is reached. Once the charge stored across the charge storage device equals the threshold value the burst pulse is deactivated. During the time when the burst pulse is active, the burst signal will be present on the input composite video signal. In order to have a fixed value for a sync tip of the horizontal synchronization pulse and to be able to apply certain thresholds within the burst gate pulse generator, the sync tip of the input composite video signal is clamped to a level equal to 2.5 volts. Preferably, the burst pulse has a duration equal to 3.5 nanoseconds.
|
