Patent ID: 8260155

Claim:
A carrier detection circuit for performing carrier detection, comprising: a first comparing circuit; a second comparing circuit; and a logic circuit, wherein: said carrier detection circuit is for use in an infrared signal processing circuit including a photo-acceptance element for converting an infrared signal received into an electric signal, an amplifying circuit for amplifying the electric signal, a bandpass filter for extracting a carrier frequency component from the electric signal having been amplified, and an integrating circuit for integrating a carrier detected in the carrier frequency component; said first comparing circuit compares (i) an output signal of the bandpass filter with (ii) a first threshold voltage which is a noise detection level; said second comparing circuit compares (i) the output signal of the bandpass filter with (ii) a second threshold voltage which is a first carrier detection level, and whose level is higher than that the first threshold voltage; and said logic circuit outputs as the carrier an output signal of said second comparing circuit, and controls the gain of the amplifying circuit based on the output signal of said first comparing circuit so that the output signal of said first comparing circuit is not output.