Simulation of a micromachined digital accelerometer in SIMULINK and PSPICE

The development of a mathematical model of a closed loop micromachined silicon accelerometer is a very important consideration in the design of such a transducer. The sensing element being used for this work consists of a seismic or proof mass which is suspended between two sensing electrodes forming two capacitors in series. The acceleration force acting on the sensing element will cause the proof mass to deflect from its rest position resulting in a differential change in capacitance proportional to the acceleration. A model is derived for a silicon micromachined accelerometer and as well as the control strategy to provide a closed loop operation with a direct digital output signal. The model has been implemented both in MATLAB with SIMULINK and the MicroSim Design Centre: (PSPICE for Windows). The simulation process models the dynamic performance of the sensing element itself, the control electronics and the effects introduced by the method of reset employing electrostatic forces. This joint approach of employing a high level simulator in the s domain and a much lower level electronic component simulator proved a useful design approach.