| 摘要 |
PROBLEM TO BE SOLVED: To eliminate noise even in the case that the opening/closing of a gate can not follow the cycle of generated noise. SOLUTION: In the case that noise components exceeding an inputted signal level are detected, the gate of a gate circuit 20 is closed and signals outputted from a signal amplifier circuit 10 are not outputted to the outside. In the case that the opening/closing of the gate of the gate circuit 20 can not follow the cycle of the generated noise, the signals for which only a prescribed frequency band is passed through in a narrow-band filter 50 are outputted. Thus, the noise included in the signals is eliminated.
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