Patent ID: 7711345

Claim:
A receiving circuit that receives a plurality of digital signals output from a wireless smart key system and a tire pressure monitoring system, comprising: an antenna that receives the plurality of signals generated by modulating carrier waves having a substantially same frequency according to digital signals having different bitrates output from the wireless smart key and tire pressure systems; a front-end portion that tunes and outputs the signals received by the antenna; an analog-to-digital converting portion that converts the signals output from the front-end portion to digital signals; a signal processing portion that processes and demodulates the digital signals; a transmitting portion that transmits a request signal to a portable device: and a variable digital filter portion in which a passband is switched in accordance with a bitrate of a digital signal output from the wireless smart key system for a predetermined time after the transmitting portion transmits the request signal to the portable device, and which extracts the digital signal output from the wireless smart key system from the demodulated signals output from the signal processing portion.