Patent ID: 7320247
Filing Date: 2008-01-22
Classification: B60C

Abstract:
1. A tire pressure detection side receiving circuit provided in a tire pressure detector mounted on a wheel for detecting tire pressure and transmitting a result of detection to a body of a vehicle by radio, the receiving circuit receiving a radio signal from the vehicle body, the receiving circuit comprising: an antenna resonance circuit having an antenna, a capacitor and a coil with two terminals; a capacitance changing circuit for changing a capacitance of the capacitor of the antenna resonance circuit; an oscillation circuit capable of imparting a test wave to the antenna resonance circuit; a resonance level detector capable of detecting a resonance level of the antenna resonance circuit; a memory storing data of preset reference frequency; a resonance frequency detector changing a frequency of the test wave to be imparted to the antenna resonance circuit while the capacitor of the antenna resonance circuit is maintained at a constant capacitance, thereby detecting, as a measured resonance frequency, a frequency in a case where an amplitude level of the test wave has reached a peak; and a tuning control controlling the capacitance changing circuit so that the measured resonance frequency is approximated to the reference frequency, thereby changing the capacitance of the capacitor of the antenna resonance circuit.