| 摘要 |
PURPOSE:To decide whether a frequency is higher than a prescribed reference frequency or not with high responsiveness, even if a frequency of a signal to be decided is varied remarkably, by providing a retriggerable monostable multivibrator for outputting the second pulse signal whose pulse width is wider than a pulse width of the first pulse signal. CONSTITUTION:For instance, in case when a frequency of an output signal S1 being a signal to be decided is lower than a reference frequency, a period TTP of a trigger pulse TP becomes longer than a pulse width W1 of the first pulse signal P1, therefore, it becomes an 'L' level before the next rise timing of the trigger pulse TP of the first pulse signal P1, and a controlling circuit 23 responds to the first pulse signal P1, and only in case when its level is an 'L' level, a repeated pulse signal PS is supplied to an input terminal AIN of the second retriggerable monostable multivibrator 25. As a result, the second retriggerable monostable multivibrator 25 is triggered at each rise timing of an input signal SIN, and operated so that a level of its Q output terminal becomes 'H', during W2 from the triggered time point.
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