Capacitive sensor interface circuits for MEMS transducers with application to high-temperature data acquisition

The theory and design of a capacitance-to-voltage converter integrated circuit (IC) is presented. The design uses correlated double sampling in combination with delta modulation to achieve the adjustable signal bandwidth and sense resolution required to characterize and operate micromachined sensors and resonators. The IC exploits a fully differential, switched-capacitor topology. This work emphasizes interface circuits for capacitive sensors at room temperature, but includes a preliminary design for high-temperature.; Tests on the IC were made to characterize its dc and ac performance. The chip exhibits very low noise, equivalent to a 170-aF of input capacitance, with a 20-pF shunt capacitance and a sample rate of 6 kSPS. The IC has a 0.1-mV output offset, a sensitivity of 1.1 mV, ±1.7 − V linear region, and a dynamic range of 69 dB. A statistical noise model has been developed that accurately explains the results and clarifies the resolution/bandwidth/power trade-off. Ac tests demonstrate accurate capacitance-to-voltage conversion for time-varying input capacitance. A MEMS resonator was characterized using the IC. The measurement was made at various pressures. Quality factor and resonant frequency were obtained from the tests. The test shows the potential applications for making smart sensors using the chip.; In addition to the capacitance-to-voltage converter IC, a high-temperature sigma-delta modulator IC was designed for SOI technology. Both circuits use fully differential and switched-capacitor technology. A band-gap reference bias circuit, chopper stabilization and integral dither are used to obtain high performance at temperature near 300°C.