| Research Abstract |
The purpose of this study is to develop signal processing circuits for capacitance sensors using switched-capacitor circuits.
First, a novel switched-capacitor bridge is developed for high accuracy and high speed capacitance measurements. Its principle of operation is based on the two-step quantization of the capacitance under measurement. The first step of measurement is a coarse quantization, which corresponds to the main scale, performed by the charge-balancing M-bit analog-to-digital (A/D) converter. The second step is a fine quantization to interpolate the quantization error of the first step into K bits. This interpolation, which corresponds to the vernier scale, is performed by the single-slope A/D converter. The total resolution is M+K bits. A prototype bridge using discrete components has confirmed the principles of operation.
For high-accuracy signal processing of differential capacitance sensors, an interface circuit based on a switched-capacitor sample/hold circuit is develop
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ed. Driven by nonoverlapping two-phase clocks, the interface produces the output voltage which is proportional to the ratio of difference-to-sum of two capacitors of a differential sensors. Spice simulations show that 0.1% resolution is easily achievable with the simple configuration. Experimental results are given to confirm the simulations.
Furthermore, a time-domain method for measuring circuit parameters of RLC and active filter circuits is presented. The principle is based on the oscillatory response to a step excitation. A digital oscilloscope is used to observe the step response. Receiving data thus acquired via the RS-232 interface, a computer calculates required parameters. Accuracy estimates show that the measurement error is less than 2 percent when an oscilloscope with an 8-bit resolution is used. Experimental results are given to confirm the principles of measurement and accuracy estimates.
Fabrication process of the switched-capacitor circuits compatible with IC sensors is best suited for the built-in interface of intelligent capacitance sensors. Less
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