SAW based passive sensor with passive signal conditioning using MEMS A/D converter

Abstract

A monolithically packaged surface acoustic wave (SAW) radio transponder and pressure sensor are developed for the application to a tire pressure monitoring system (TPMS). The device contains the wireless transponder, which converts analog signal into digital one without any auxiliary electronic circuits and transmits the converted data wirelessly. No power sources are needed for wireless transponder and pressure sensor. The touch-mode pressure sensor converts externally applied pressure into capacitance, and the SAW radio transponder radiates sensor values with pulse train to the interrogation (measurement) unit. The realization of the mechanical A/D conversion is possible since the SAW radio transponder is connected to the touch-mode capacitive pressure sensor. The SAW radio transponder and touch-mode sensor are fabricated using a surface micromachining and a bulk micromachining technologies, respectively. The performance of the integrated, passive and wireless pressure sensor meets the design specifications such as linearity, sensitivity and noise figure. Finally, experimental results for the radio transponder and the sensor without power source are presented.