Method of and apparatus for removing equalizing pulses without using external pins

摘要

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.