Circuit for preventing false detection of video sync pulses in a video signal which also contains copy guard signals

摘要

A circuit for preventing the false detection of vertical sync pulses included in a video signal which also includes copy guard signals inserted in predetermined intervals thereof, including signal generating circuitry which is responsive to vertical sync pulses separated from the video signal for generating a corrected vertical sync signal, and inhibit circuitry for rendering the signal generating circuitry non-responsive to the separated vertical sync pulses during the predetermined intervals of the video signal, thereby preventing any falsely detected vertical sync pulses due to misinterpretation of the copy guard signals from being included in the corrected vertical sync signal. The inhibit circuitry preferably functions to count a predetermined number of horizontal sync pulses also included in the video signal before allowing any change in the output of the signal generating circuitry. The predetermined number is selected to ensure that the time required to count the predetermined number of horizontal sync pulses is greater than the predetermined intervals of the video signal corresponding to the repetition rate of the copy guard signals.