Patent ID: 7439723

Claim:
A system for determining a resonant frequency of a wireless sensor, comprising: a receive section for receiving a calibration signal and a sensor signal; a calibration path including: a calibration IF section for determining a phase difference between an energizing signal and the calibration signal; and a first phase lock loop (PLL) for adjusting a phase of the energizing signal based on the phase difference between the energizing signal and the calibration signal; a measurement path including: a measurement IF section for determining a phase difference between the energizing signal and the sensor signal; and a second PLL for adjusting a frequency of the energizing signal based on the phase difference between the energizing signal and the sensor signal; and an energizing signal generator for generating the energizing signal and varying a frame width of the energizing signal, wherein the frequency of the energizing signal is determined to be the resonant frequency of the wireless sensor when the second PLL is locked.