Switched-capacitor self-oscillating capacitance transducers with duty-cycle or digital output

A current trend in the design of integrated transducers is the increasing demand for transducers which are able to communicate directly with microprocessors, i.e. the development of transducers with a microprocessor compatible output. The only analog output signals which are suited for such transducers are pulse-width (PWM) and frequency modulated (FM) signals. Such signals can easily be digitized by counting periods. Moreover, the signals can easily be transmitted over long distances. The authors consider exclusively switched-capacitor (SC) capacitance transducers with pulse-width (duty-cycle) modulated square-wave output voltages. A pulse-width modulation (PWM) signal can be regarded as an intermediate step between analog and digital signals. Such an analog signal can be delivered to a microprocessor without any extra interfacing. Although the authors discuss the realization of SC capacitance transducers, the proposed structures can easily be adopted for the realization of resistance and inductance transducers