Optimization of Electrical Oscillators for an Efficient Operation of Resonant Piezoelectric Sensors

Abstract:
Many piezoelectric sensor concepts, such as quartz crystal microbalances or piezoelectric temperature sensors, exploit the frequency shift of their resonance frequency as an electric output signal. The resonance frequency of the sensor has to be converted into a frequency-proportional output signal by a subsequent oscillator circuit. Therefore, reliable sensor data processing requires a matching of the resonance frequency and the oscillator frequency at any ambient condition. This contribution focuses on the design of low-cost oscillators with a piezoelectric sensor as the frequency- determining component. Different oscillator topologies will be analyzed regarding their suitability for measurement data processing. In order to achieve a simple and efficient circuit layout, we developed a hybrid design concept based on analytical models and circuit simulations. Experimental results, based on a piezoelectric temperature sensor, prove the proposed design concepts. In the temperature range from -20 °C to 85 °C, an extremely small deviation of less than 0.2 % between the resonance frequency and the oscillator frequency was obtained.