The Sigma-delta Micro-accelerometer System,

The accelerometer is one of the most important inertial measurement units used in inertial navigation and guidance of a series of military systems. The capacitive micro-accelerometer has been commonly used due to their high accuracy, low drift, low power dissipation, low noise, low temperature coefficient and high sensitivity characteristics.Compared with bulk micromachining,the surface micromachining has the advantages of low manufacturing cost and easy integration with CMOS circuits.Compared with operating in open-loop mode, the accelerometer operating in close-loop mode can improve its linearity, dynamic range, and bandwidth, meanwhile, decrease the requirement in fabrication. The sigma-delta modulation is a technique normally used in high-resolution A/D conversion in low frequency domain. The sigma-delta micro-accelerometer is a micro-electro-mechanical system, which operates in close-loop mode by applying the technique of sigma-delta modulation to surface micromachining capacitive micro-accelerometer. It is particularly attractive for that it provides digital output, can be easily implemented in high density CMOS technologies, and enables integration with digital signal processing circuitry.The principle of micro-accelerometer has been introduced in this paper, and advantages of close-loop mode have been presented. Combining the technique of sigma-delta modulation, a model of one kind of capacitive micro-accelerometer operating in close-loop mode-sigma-delta micro-accelerometer has been designed.A simulation model of sigma-delta micro-accelerometer is created in MATLAB SIMULINK. The spectrum analysis has been done on outputs of the simulation model. A digital signal processing block has been designed for outputs of the simulation model, via a software program written in MATLAB. The PWM output is demodulated and the input acceleration is recovered by using the digital signal processing block. Simulations have been done through adjusting parameters such as input signal amplitude, feedback gain, amplifier gain, comparator gain and the position of the phase compensator. Analyses have been done on the waveforms recovered using the sinusoidal minimum error method.An equivalent electrical system for mechanical structure of the sigma-delta micro-accelerometer has been created. Synthetically, the advantage and disadvantage of the model has been compared when when compensator location varies in the model. A PSPICE simulation model of the total system has been created, in which the...