| 摘要 |
PURPOSE:To separate a vertical synchronizing signal and a frame synchronizing signal which are invariably in constant phase relation with respect to a composite synchronizing signal by providing a reference oscillator and a synchronizing signal detecting circuit and utilizing the difference in duty ratio of pulses consisting of a horizontal synchronizing signal and the vertical synchronizing signal by using the output of a reference oscillator. CONSTITUTION:The reference oscillator 1 is set with the composite synchronizing signal 1a inputted from a terminal 1A, so a signal 2a is outputted which has a specific phase and also has a frequency twice as high as the frequency of the horizontal synchronizing signal. The time required from the leading edge of the composite synchronizing signal 1a to the trailing edge of the signal 2a is shorter than one period of the reference oscillator 1, so it is <=0.5 H. The level of the composite synchronizing signal 1a is held by a D type flip-flop DFF 23 at the rise of a signal obtained by inverting the signal 2a to obtain the vertical synchronizing signal 1c which is at an H level for 3H. The phase of the output signal of the reference oscillator 1 is determined digitally. Further, its frequency is an integral multiple of the frequency of the horizontal synchronizing signal, so its phase is fixed with respect to the frame synchronizing signal and never varies.
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