Wireless sensor reader

Abstract

A wireless sensor reader is provided to interface with a wireless sensor. The wireless sensor reader transmits a narrowband, fixed frequency excitation pulse to cause the wireless sensor to generate a ring signal. The ring signal corresponds to the value of the physical parameter being sensed. The wireless sensor reader receives and amplifies the ring signal and sends the signal to a phase-locked loop. A voltage controlled oscillator in the phase-locked loop locks onto the ring signal frequency and generates a count signal at a frequency related to the ring signal frequency. The voltage-controlled oscillator is placed into a hold mode where the control voltage is maintained constant to allow the count signal frequency to be determined. The low power, simple circuitry required to generate the excitation pulse allows the reader to be a small, battery operated unit. Alternative method of frequency determination are also disclosed.