A high-accuracy, high-speed signal processing circuit of differential-capacitance transducers

For high-accuracy signal processing of differential-capacitance transducers, an interface circuitry is developed based on a relaxation oscillator. The interface consists of an integrator, a differentiator, and a comparator and uses two capacitors of the transducer, one for the integration and the other for the differentiation. This configuration allows the ratiometric operation in the amplitude domain and provides a square wave whose amplitude is proportional to the ratio of the capacitance difference between the two transducers capacitors to their sum. A circuit analysis shows that the interface can detect the capacitance change as small as 0.1% of the total capacitance in 10 μs. Experimental results are also given to confirm the analysis