Oscillator-based signal conditioning for resistive sensors

A signal conditioning circuit for resistive sensors is presented. It is based on a relaxation oscillator in which both the frequency and the duty-cycle of the output signal simultaneously carry information from a pair of different sensors. The output frequency is linearly related to the resistive unbalance of a Wheatstone bridge, while the duty-cycle is independently controlled by a second sensor. For this purpose, a thermoresistor may be used for thermal compensation of the primary sensor. The design, analysis and experimental characterization of the circuit and its application to a thick-film pressure sensor are reported.