| 摘要 |
PROBLEM TO BE SOLVED: To avoid causing the false detection if a satisfactory attenuation effect is not obtained, even using means for attenuating unwanted frequency components when noises having short duration times such as spike noises are received or superposed in an ultrasonic wave detector. SOLUTION: The signal detector circuit comprises a means 22 for forming an envelope waveform of an input signal, a receiving-detecting means 23 for comparing it with an arbitrarily set detection value to output a signal in the form of a square wave having a long duration time and a noise in the form of a square wave having a short duration time, a charging-discharging means 24 for outputting a long-duration time signal in the form of a wave having a high peak value and a short-duration time noise in the form of a wave having a low peak value, and a received signal detecting means 25 for comparing them inputted thereto with an arbitrary detection value to thereby output a signal only.
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