Study On Signal Readout Technique For MEMS Gyroscope Based On Optical Interference Phase Detection

As a new type of inertial sensor, MEMS gyroscope has been widely used in the civil and military fields. The output signal of most of MEMS gyroscope is detected by capacitive detection technique, piezoelectric detection technique, piezoresistive detection technique, tunnel effect detection technique and optical detection technique. Currently, most of MEMS gyroscopes'output signal is detected by capacitive detection technique, but it's difficult to improve the detection accuracy as the capacitance detection accuracy has been basically reached the theoretical limit. The high-accuracy MEMS gyroscope is rarely reported yet. While the optical detection methods, in particular the interferometry, is of high measurement accuracy. The high precision and low cost MEMS gyroscope will be manufactured if the optical detection method is combined with the MEMS gyroscope, and the market prospect of it is broad. This detection method is seldom studied at home and abroad, so study this has not only theoretical significance, but also practical value. Subsidized by higher school specialized research fund for the doctoral program which afford by ministry of education, and based on the inventive patent"precision MOEMS gyroscope based on dual optical interference", this paper has done some basis work of MEMS gyroscope based optical interferometer, and it focuses on the dual optical interference signal detection of weak vibration and signal processing.Firstly, detection methods and principles of MEMS gyroscope's output signal is introduced. Then the brief introduction of optic interference theory is given, the signal modulation method of several common fiber optical interferometer is described, and the homodyne and heterodyne demodulation method to demodulate the interference signal is also described. The system's principle is proposed, and the optical module is analysed. Selection of components is completed according to the requirement. The driver circuit of diode laser, the bias circuit of photoelectric detectors amplifier circuit, filter circuit and signal subdivision of interference signal is designed, and most of them is simulated by Multisim 10. Then welding components into circuit boards on the basis of schematics and debuging the welded circuit boards, the results show that the designed schematics meet the requirement of the system.The two interference signals should be processed after got them. The signal processing module consists of direction discrimination circuit, signal subdivision circuit, MCU and software in upper computer. The signal subdivision circuit is a cascade circuit of five subdivision specific integrated chip JS0204 and fourfold frequency specific integrated chip JS0210, it achieves 20 subdivisions of input signal in a period and can discriminate the direction, and the output signal pulses are sent to MCU to count the pulses. The results of count are transmitted to PC by serial port RS232, and then processed by software.The simulation experiments are conducted by the circuit edsigned in this paper. The results show that the resolution in theory of MEMS gyroscope which introduced optical interference detection method could reach to 0.01°/s after do 20 subdivisions to the output signal. The resolution of MEMS gyroscope would be higher if do subdivision more than 20 to the output signal.