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 it 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 transducer 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 /spl mu/s. Experimental results are also given to confirm the analysis.