Study Of Micromachined Capacitive Accelerometer Detection System

Accelerometer is a kind of important inertial sensor that can be used in inertial navigation, consumer electronics, motor electronics and geologic exploration. Silicon micro-accelerometer can measure the acceleration of the movement, and there are many kinds of Micro-accelerometer based on piezoelectric, tunnel, piezoresistive, capacitive effect.Capacitive MEMS micro-accelerometer is widely used because of its high resolution, large dynamic range and low temperature drift. Capacitive MEMS accelerometer consists of acceleration sensor and capacitance detection circuit. The performance of capacitance detection circuit has a direct impact on the performance of accelerometer system. The improvement of capacitance detection circuit performance is important in determining the performance of accelerometers.A single carrier modulation capacitance detection circuit is designed for an area changing type capacitive MEMS accelerometer. The principle of this circuit is analysed, and temperature characteristics of this circuit is analysed and measured, at last miniaturization and engineering of triaxial MEMS accelerometer was finished.The major work of this thesis contains:(1) A single carrier modulation capacitance detection circuit consisting of DDS module, BFP module, charge amplifier module, instrument amplifier module, active phaser module, synchronously demodulation module and LPF module was designed, while operation principle and constraining factor of every module was anlysed, and parameter of every module was figured out according to theory.(2) According to single carrier modulation detection circuit, the parameter of every module and the influence of PCB board parasitic effect was figured out. The impact of temperature on accelerometer system was also analysed minutely. Duing to temperature drift of previous accelerometer system, a new triaxial MEMS accelerometer system was design which has lower power consumption and better heat emanation design. (3) A performance test scheme was made with reference to test guides on accelerometers. The measurement shows that capacitive MEMS accelerometer has asensitivity of 115.43mV/g, zero-draft of 2.246*10^-4g. Start-Up time of 1500s,threshold value of 0.12mg , resolution of 0.1 mg, linearity of 99.999% and bandwidthof 140Hz.