| 摘要 |
PURPOSE:To obtain a circuit blocking generation of an aperiodic trigger signal by detecting the range of a trigger level corresponding to the amplitude of an input signal and setting the trigger level at the outside of the trigger level range when the range is narrower than a prescribed range. CONSTITUTION:A comparator 1 generates a high level trigger signal when an input signal S1 crosses a trigger level V3 given from a trigger level generating circuit 2. Since the comparator 1 has a hysteresis, when the input signal S1 crosses the upper limit level of the hysteresis, that is, the trigger level V3 from the lower side toward the upper side, a high level trigger signal is generated and when the input signal crosses a lower limit level V2 of the hysteresis from the upper side toward and lower side, the trigger signal restores to a low level. A trigger detection circuit 3 connected to the output terminal of the comparator 1 keeps generating, e.g., the high level output so long as the trigger signal S2 is generated within a prescribed period, and gives a low level output when no trigger signal S2 is generated within a prescribed time.
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