Patent ID: 7542748

Claim:
A signal processing circuit, comprising an attenuating unit that attenuates a demodulated signal acquired by detecting a received signal; a detecting unit that detects a first signal indicating intensity of the demodulated signal; an attenuation rate setting unit that sets an attenuation rate of the attenuating unit, depending on the first signal and a second signal indicating a change in an envelope curve acquired based on an intermediate frequency signal of the received signal, or depending on the first signal, the second signal, and a third signal indicating electric field intensity acquired based on the intermediate frequency signal; and a difference determining unit that determines whether a predetermined threshold is exceeded by a difference between the demodulated signal and a signal obtained by smoothing the demodulated signal, to detect noise, wherein the attenuation rate setting unit sets a first attenuation rate for the attenuating unit based on the detection of noise by the difference determining unit, and after a predetermined period has elapsed from the setting, sets a second attenuation rate smaller than the first attenuation rate for the attenuating unit.