Patent ID: 7953370

Claim:
A transceiver device for communicating with a tag comprising: a local oscillation circuit to generate a local oscillation signal; a transmission circuit to transmit a carrier frequency signal to a tag; a reception circuit to receive, from the tag, the carrier frequency signal modulated with information data at the tag; a duplexer connected to the transmission circuit and the reception circuit; and a control and signal processing circuit to control the local oscillation circuit to generate during an ordinary communication, the local oscillation signal as having a reference frequency which corresponds to one of a plurality of communication channels, for the tag, and to generate during sensing whether a carrier is present transmitted from another transceiver prior to the ordinary communication with the tag, the local oscillation signal as having a frequency, which is shifted by a prescribed frequency with respect to the reference frequency, wherein the reception circuit includes a demodulating circuit to demodulate the carrier frequency signal modulated with information data input through the duplexer, by using the local oscillation signal shifted by the prescribed frequency, and a capacitor circuit to cut off a direct current component from an output of the demodulating circuit.