Research And Design Of A High Resolution And High Linearity MEMS Accelerometer

Micro-mechanical accelerometers are key components and widely used in consumer electronics, automotive safety, military defense and some other applications. Due to the advantages of the high linearity, large dynamic range and simple structure, the capacitive closed-loop accelerometer has attractived considerable attention. Based on the five plates MEMS capacitive accelerometer sensor, the design and implementation of the continuous closed-loop accelerometer readout circuit is presented in this thesis. The main specifications for the proposed accelerometer is as listed:the input range of±30g, bandwidth of1KHz, less than0.1%linearity;, and minimum resolution of1mg.The design of readout circuit adopts the procedure of "from top to down" in this thesis. Firstly, the working principles of the MEMS capacitive accelerometer sensor is analysed and modeled. The influence of electrostatic force to the sensor model is added, whitch provides necessary help to the subsequent design of closed-loop read-out circuit. Secondly, through the simulation and analysis to the model with the given design specs, the design of the closed loop accelerometer readout circuit is determinded. Then the basic structure of the closed loop accelerometer readout circuit is presented. Through the analysis of the working pinciples, the complete solution of the closed-loop acceleration detect system is with the constant improvement of the strcture design; And then by building the behavior model of the whole readout circuit, the corresponding simulation and functional verifycation is completed. Finally, the whole circuit design and the physical design of the proposed readout circuit are implemented. The post simulation has been completed.Through the analysis of the accelerometer sensor, the main bottleneck restricting of the linearity of the detection system is accelerometer sensor self-limited. The design of closed-loop detecting structure is designed to improve the linearity; With the analysis of the stability problem of closed-loop feedback accelerometer detection system, the PD controller is designed to compensate the stability; Through the analysis of the noise contribution to the whole system, the adjustion of the gain of all stages is determined, and a new method is designed to reduce the noise of the first stage in the readout circuit, so as to improve the dynamic range of the whole system,after the post simulation results with accelerometer readout circuit part show that the detection of acceleration range of≈30g, and the output of the corresponding output voltage range of0.37V to2.93V; After noise simulation of the system, the equivalent input noise is0.2mg/sqrt (Hz), and the equivalent input SNR is more than106dB; Minimum resolution of1mg, and the output resolution of43.6μV/mg,;The input dynamic range of96dB, meet the design requirements.This paper focuses on the design of the continuous closed-loop accelerometer readout circuit, from the initial selection of system structure to the final circuit implementation, and each step has carried on the detailed analysis, which provide the certain reference significance for the other closed-loop accelerometer readout circuit design.