| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal detection circuit prevented from being influenced by noise variation in a detection output of an objective signal even when a threshold for detecting a received signal is lowered. SOLUTION: A noise attenuation means 1 attenuates a frequency component other than the frequency of an objective signal of an input wave and a received signal detection means 2 outputs a signal detection output when the signal waveform voltage of the input signal reaches an optionally set detection threshold. On the other hand, a noise detection means 4 outputs a noise detection output when a receiving noise level other than the input signal reaches the optionally set detection threshold. Since a detection output switching means switches the detection output so as not to output it on the basis of the noise detection output, the signal detection output is not outputted from a detection output terminal 19.
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