Capacitive Micromachined Accelerometer Detection Circuit

As an important inertial device, micromachined accelerometers have broad applications in fields such as automotives, consumer electronics, and inertial guidance. The improvement of performance has been the important research direction in micromachined accelerometers since its appearance. The performance of detecting circuits is becoming more and more important in determining the performance of accelerometers.A single-carrier modulation-type detection circuit is designed for an area-changing-type capacitive micromachined accelerometer. Also the closed-loop detection circuit is studied. These will provide theoretical basis for the choosing and designing of detection circuits for micromachined accelerometers.The major work of this thesis contains:(1) A single-carrier modulation-type detection circuit is designed, which includes carrier generator, charge amplifier, demodulator, low-pass filter and amplifier. Key factors constraining the performance have been studied, leading to the conclusion: the resolution of this circuit is directly influenced by the stability of carrier and the matching of two charge amplifiers. The specifications of open-loop accelerometer are given, with factors influencing each performance analyzed.(2) Two feedback adding schemes are analyzed, including one-bias-two-feedback and two-bias-one-feedback. The frequency properties of PID feedback modules are analyzed, which will guide the practical feedback design. Based on the aforementioned two analyses, a feedback circuit is designed.(3) A performance test scheme is made with reference to some test guides on accelerometers. The performance of open-loop system is measured according to this scheme.The measurement shows a sensitivity of 45mV/g, nonlinearity of 1.17%, and zero-shift of 4.4mg. The resolution of detection circuit is deduced to 0.1 fF. The single-carrier modulation-type detection circuit designed broadens the measurement range at the price of reducing resolution.