| 摘要 |
PURPOSE:To generate a vertical synchronizing signal accurately from a video input signal by combining the output resulting from the comparison between the integral output of a composite video synchronizing signal and a prescribed threshold level and a signal which is obtained by allowing the synchronizing signal to pass two stages of one shot multivibrators and an FF. CONSTITUTION:The composite synchronizing waveform of the video signal inputted from a terminal 10 is inputted to an integrator 12 and a one shot multivibrator 18. The integrator 12 generates an output, which exceeds a threshold level determined by a threshold generating circuit 14, in response to a falling DC average level each time when a vertical synchronizing pulse 30 is generated. If vertical synchronizing information is completely uniform, the output signal of an output line 16 has the same time relation as each TV field. In case of the input from a VTR, a synchronization suppressing part 40 whose period and time are not accurate is included, and the first rise point 42 of an N-shaped waveform 38 is detected by the multivibrator 18 to trigger a one shot multivibrator 20, and the second rise point 44 is detected by the multivibrator 20 and is inputted to the data input of an FF 22. The output of the FF 22 and the output of the circuit 24 are inputted to a one shot multivibrator 24, and the N-shaped waveform is detected in accurate time relations from the multivibrator 24 and is outputted to an output line 26.
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