| 摘要 |
PURPOSE:To easily isorate a vertical synchronizing signal from the pulse state of a composite synchronizing signal by counting clock pulses and driving a circuit digitally generating fixed time with the aid of the pulse fo the composite synchronizing signal. CONSTITUTION:A 'high' part included in the composite synchronizing signal is of 4.6-4.8 musec except for a vertical synchronizing signal part. Accordingly counters 6 and 7 and a flip flop 1 generate a digital one shot, and expand the 'high' part in the composite synchronizing signal to about 6.4 musec. When the signal samples the composite synchronizing signal again, the vertical synchronizing signal VD is extracted. Only the signal VD cannot identify a field. However, by exploiting that seven pulse strings with 1/2 H widths exist after the vertical synchronizing signal in the 1st field, the seventh string is identified to identify the top of a frame.
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