DUAL MODE GEN-LOCK SYSTEM WHICH AUTOMATICALLY LOCKS TO COLOR BURST OR TO SYNC INFORMATION

摘要

A dual mode gen-lock system generates high frequency clocking pulses which are automatically synchronized to an external video signal. During the presence of color burst information in the external video signal, the clocking pulses are synchronized to the color burst. However in the absence of the color burst, the clocking pulses are synchronized to the horizontal sync pulses of the external video signal. This is accomplished by providing a phase locked loop which has an oscillator which free runs at the desired clock frequency, and which has a phase detector for comparing the phase difference between a selected portion of the PLL reference signal and a selected portion of either the color burst or horizontal sync pulses.