| 摘要 |
PURPOSE:To easily form a timing pulse so as to output stable picture signals containing no noise to a helical scan VTR, etc., by generating the timing pulse when an input signal level continuously exceeds a fixed level for more than a fixed period of time. CONSTITUTION:When a reproduced FM output is supplied from a VTR, an envelope comparator 12 outputs a pulse 10 only when the reproduced FM output exceeds a reference voltage. By this rise of the pulse 10 a triggerable monostable multivibrator 13 is triggered and a pulse of a prescribed width which is longer than one-vertical synchronous cycle is outputted and, when the pulse 10 is again impressed within the prescribed width, the output state of the multivibrator 13 is held and does not change. Therefore, the output state of the multivibrator 13 changes only when the reproduced FM signal continuously exceeds a reference voltage for more than one-vertical synchronizing signal. As a result, a timing pulse is formed easily and surely without making setting of various time constants, etc., and, even when a track containing an erased section exists in a helical scan VTR, etc., stable reproduced picture signals containing no noises, etc., can be outputted.
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