Modeling And Simulation Of The Accelerometer Closed-Loop Control System

The capacitive micro-accelerometer is one of the most widely used MEMS sensors at present, because it has the advantages of high measurement precision, stable output and low temperature drift.Wherein, ??micro-accelerometers, which realize the digital closed-loopoutput using the ??modulation technology, not only have the characteristics of high bandwidth, good linearity and wide dynamic range, can also provide a high precision digital output, which can bedirectly interfaced with the digital signal processor. It has important applications in many harsh environments, such as inertial navigation/guidance, space micro-gravity, oil exploration and earthquake detection.In order to reduce the influence of quantization noise on the performance of?? micro-accelerometer systems, high-order??micro-electro-mechanical-system has gradually been in a hot research.In addition to the inherent stability problem of high-order ??systems, high-order?? micro-electro-mechanical-system also has the problem that the first stage integral output of the mechanical sensitive structure is not available.Therefore, the design of the interface circuit'sparameters has been a difficult problem in this field.In addition, the selection of the system's topology is also related to the tolerance capability of the system's electrical parameters, such as the sensing element mechanical parameter variations, the loop gain variation and the nonlinear feedback force.In this paper, firstly, a discrete-time model of the mechanical sensing element under the action of time-sharing feedback is built up.Through the simulation analysis, it is concluded that the time length of time-sharing feedback determines the effective amplitude of electrostatic force feedback, affecting the system's full range, and the central location of time-sharing feedback determines the total loop delay of the system, influencing the system stability. Based on Lee's criterion, that is max QNTF(27)1.5, the interface circuitelectrical parameters' design method of the high-order?? micro accelerometer system is elegantly optimized. Therefore, the lack of the freedom degree of the MEMS??system can be solved skillfully, greatly simplifying the system design process. What's more, based on the Matlab/Simulink, the system-level model of the fifth-order?? micro-accelerometer is established, and the parameter design is completed. According to dynamic simulation in an ideal case, the quantization noise floor of the fifth-order?? micro-accelerometer can be suppressed below-170 d B within the bandwidth of 250 Hz, at OSR=256, and the overload factor of the system is 0.6. The system SQNRfluctuates in the range of ± 3d B when the mechanical sensing element parameters vary from 80% to 120%. System-level comparative simulation analysis is carried out between the fifth-order Feed-Forward structure and the fifth-order Multiple-Feedback structure. Under the condition of the same sensing element and input signals, output signals of the two structures are with similar quantization noise floor. However, the Feed-Forward structure is insensitive to the loop gain, with the residual proof mass motion muchsmaller,the linearity of nonlinear electrostatic feedback better, and immunity to the mechanical parameter variations due to fabrication tolerances. As a conclusion, the Feed-Forward structureis more suitable for high-order??micro-electro-mechanical-system.