Patent ID: 7245117

Claim:
A method for determining a resonant frequency of a wireless sensor, comprising: adjusting a phase of an energizing signal using a first phase lock loop (PLL) by: generating the energizing signal with a first phase and a first frequency; receiving a calibration signal via a receiver during a first period; sampling the calibration signal; determining a first phase difference between the sampled calibration signal and a reference signal; and based on the first phase difference adjusting the phase of the energizing signal to reduce the first phase difference; adjusting a frequency of the energizing signal using a second PLL by: energizing the wireless sensor; receiving a sensor signal from the wireless sensor during a second period; processing the sensor signal with the reference signal; sampling the processed signal; determining a second phase difference between the sampled signal and the energizing signal; based on the second phase difference adjusting the frequency of the energizing signal to reduce the phase difference; and determining the frequency of the energizing signal when the second PLL is locked; and using the frequency of the energizing signal when the second PLL is locked to determine the resonant frequency of the sensor.