| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal detection circuit capable of preventing the occurrence of erroneous detection even if a noise level fluctuates, detecting a receiving signal at as small level as possible, and being used even in a place where noise level and its fluctuation are large. SOLUTION: This signal detection circuit is provided with a variable gain amplifying means 1 amplifying an input signal, a noise attenuation means 3 attenuating noise component from an output of the variable gain amplifying means 2, a receiving signal detection means 4 detecting the presence or absence of a receiving signal by comparing an output level of the noise attenuation means 3 with a threshold for detecting the receiving signal, and a noise detection means 2 which detects a noise level of the input signal and controls gain of the variable gain amplifying means 1 so that a noise level in an output signal of the variable gain amplifying means 1 becomes constant in accordance with the noise level.
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