Sony Corporation

Sony Electronics Inc

Chun Yee

Duc Hongle Ngo

Mehrdad Nayebi

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.

Burst gate pulse generator

A circuit for removing every other equalizing pulse from a signal representing the sync pulses of a composite video signal, generates an output signal representative of every horizontal synchronization pulse and every other vertical synchronization pulse within the composite video signal. A sync separator circuit separates the synchronization pulses from the composite video signal. An output of the sync separator circuit includes all of the horizontal synchronization pulses and vertical synchronization pulses. The vertical synchronization pulses include equalizing pulses and serration pulses which have a frequency which is twice the frequency of the horizontal synchronization pulses. A capacitor is used to store charge. A current source charges the capacitor. A transistor controlled by the output signal provides a discharge path for the capacitor. A comparator monitors the voltage level stored across the capacitor and enables an output generation circuit when the level of charge stored across the capacitor is above a predetermined threshold level. The value of the capacitor and the value of the current source cause the time required to raise the voltage level across the capacitor to a level above the predetermined threshold level to be less than the time between horizontal synchronization pulses and greater than the time between vertical synchronization pulses. The output generation circuit generates the output signal as a pulse signal representative of the synchronization pulse. The output generation circuit is only enabled when the voltage level across the capacitor is greater than the predetermined threshold level. Therefore, the pulse signal is generated for every horizontal synchronization pulse and for every other vertical synchronization pulse.

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Chun Yee