Miniature Sensing System With FBAR-Based Oscillators and Frequency Shift Detector

This paper describes a highly sensitive sensing system for remote sensing applications. Typically, a resonant sensor based on film bulk acoustic resonator (FBAR) requires a frequency counter, impedance analyzer, or network analyzer to measure the shift of the resonant frequency. This paper presents a hand-held, low-cost but highly sensitive sensing system built with an FBAR-based oscillator and a phase-locked-loop for ppm-level detection of frequency shift as well as signal processing. The achieved voltage-frequency sensitivity is 1.035 V/kHz with the minimum detectable frequency shift of 4.81 ppm (5.21 kHz) and the dynamic range of 134 ppm (145 kHz). Also, the output of the sensing system is purposely designed to be a DC voltage that is linearly related to the frequency shift. To our knowledge, it is the first FBAR-based sensing system that converts the frequency shift to DC voltage.