Research And Design Of High Accuracy Capacitive Digital Micromachined Accelerometer System

The micromachined accelerometer includes the micromachined acceleration sensor and the peripheral detection circuit. the micromachined acceleration sensor is the core part of the micromachined accelerometer, playing a key role of the micromachined accelerometer's function. The micromachined acceleration sensor is used to measure linear accelerationinertial sensors, like the inertial parameters of inertial force, angle, vibration and shock. The micromachined accelerometer has a very wide range of applications in inertial guidance, automotive, consumption, electronics, geology and so on.The micromachined accelerometer of capative detection type is paid close attention because of high sensitivity and good linearity and good Stability. It includes capacitive micro-mechanical sensor chip and the capacitance detection circuit, the final output of the accelerometer of the system energy. Depends on the performance of capacitive detection circuit. In this paper, by changing the area of capacitive micromachined acceleration sensor, design the detective curcuit of single-carrier moduation type with high accuracy and large range. In order to better understand the working process,this article also briefly analyzes the parameters,which affect the sensitivity, resolution and other performance indexes. This paper is mainly according to improve the resolution, expand its range and improve its stability, which provides theoretical basis and experience inrational design and optimization of capative micromachined acceleration sensor. The work has some ralevant Significance to future practical use.The major work of this thesis contains:(1) According to the requirement of the accelerometer with high accuracy and large range, the detective curcuit is designed. By analyzing the noise performance the whole and every part of accelerometer system, propose the method that includes moving gain ahead, choosing lower noise chip and digital bandpass filter instead of analog bandpass filter to improve the resolution of the accelerometer system. By analyzing every part of accelerometer system limiting the range of the system, according the actual situation that the resolution can be suitably reduced when the input acceleration is large, design the plan that classify the range. This plan can guarantee that the accelerometer system have large range, also have very high accuracy when the input acceleration is small.(2) According to the characteristic that the system is effected by temperature easily, in order to improve stability and accuracy of the accelerometer system, propose two method—real-time temperature compensation method and high accuracy temperature control method. Moreover propose a new method to compensate the characteristic of the detective curcuit.(3) According to the above improvement plan, test the accelerometer system. We get that the system resolution is 0.70μg/νHz. Under the situation with well stable temperature, the standard deviation for 1.5 hours output data of the accelerometer reachs to 20μg. if choosing 10 minutes'datas the standard deviation of the accelerometer reachs to 14μg. Using the method of real-time temperature compensation to compensate the bias instability of the accelerometer system, when the temperature characteristic is good, the fluctuation of bias by temperature of the system is reduced from 30.5mg to 0.91mg in the temperature range of 25℃to 60℃. Moreover by testing iprove feasibility and necessity of the temperature control plan.