Study On Detecting Technology Of Capacitive MEMS Accelerometer

The geophone based on MEMS accelerometer has excelled the traditional geophone on bandwidth, dynamic range and off-axis sensitivity. The performance of the MEMS accelerometer should be improved in satisfied with the high resolution, high-fidelity, high precision what seismic prospecting needs. For the capacitive accelerometer, the order of magnitude of aF～fF should be detected, so the interface circuit should be high performance also. The detecting technology about the MEMS capacitive accelerometer is studied in this dissertation.Firstly, based on the sensor's dynamic equation and differential capacitor, the equivalent electrical model is founded. So it is possible to simulate the senor with the interface circuit together. By the simulation of the model, step response, frequency response, sensitivity and linearity are analyzed and its optimized parameters are obtained.Then, two types of force feedback are approved the same in the effect of electrostatic force. By the simulation of the model, it is proved that only one type of opposite DC voltage configuration has the possibility to configure the force balance. It is also be analyzed that the effect of non-parallel capacitive plates reduce the reliable operation range of the accelerometer. And the reliable operation range of the accelerometer in light damping is smaller than which in quasi-static situation.Lastly, according to the modulation and demodulation scheme, two types of the interface circuit are designed. The latter one is improved on carrier wave, preamplifier, demodulation and layout. The interface circuit is simulated with the sensor's equivalent electrical model together in PSpice for step response and sine response. From the test, it shows that the accelerometer has the good linearity and frequency response, the resolution has reached 0.1 mg (54aF), which is improved ten times compared with the one designed first. The performance of the MEMS accelerometer is close to the traditional geophone and makes good progress in contrast with the former accelerometer.