| 摘要 |
A tire pressure detection side receiving circuit includes an antenna resonance circuit having an antenna, a capacitor and a coil, a capacitance changing circuit for changing a capacitance of the capacitor, 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 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 and changing the capacitor capacitance so that the measured resonance frequency is approximated to a reference frequency.
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