Research On High Signal-Noise Ratio Of Capacitive Micromechanical Gyroscope

In this paper, a kind of micromechanical gyroscope with high signal-noise ratiobased on MEMS technology is researched systematically and the structure is designedfirstly. Based on analyzing on the different kinds of the signal processing methods, anovel signal demodulation method as well as its corresponding circuits is proposedand designed. With above-mentioned circuits, some key parameters relevant toperformance are measured. The paper main work is as follows.1. The states of the art of the micromechanical gyroscope is reviewed. Subsequentlythe technical difficulties are analyzed and the main research work is put forward.2. A kind of capacitance micromechanical gyroscope is designed with de-coupledstructure and differential demodulation, thus it can effectively reduce noise. And itsmanufacture process is described.3. Faced with the long-term drift phenomena of the vibratory quality factors, threekinds methods of Auto Gain Control (AGC) close-loop driving, including DC AGCmethod, DC-AM AGC method and AC AGC method, is put forward, analyzed andcontrasted each other by means of simulation.4. After analyzing the phenomena of the phase shift during the signal demodulationand of long-term drift aroused by parasitical capacitance, a kind of differencedemodulation method with high signal-noise ratio is proposed and derived, and it cancut off the interference aroused by parasitical capacitance.5. On the basis of the differential demodulation method mentioned above, the relevantcircuits are designed and simulated, including improved pre-C/V convert circuit,High-Pass Filter(HPF) circuit, amplitude-limited circuit, AGC circuit, Angulardemodulation circuit, etc. Among these circuits, the improved pre-C/V convert circuitnot only reduces noise but also lessens resistance in amplifier, so it becomes easier tointegrate those circuits with ASIC. It is effective to reduce the interference aroused byparasitical capacitance by using the angular demodulation circuit.6. By means of above-mentioned circuits, some key parameters involved inperformance are measured, including the vibratory quality factor, resolution,bandwidth, the AGC static work point, sensitivity and linearity. It is the first time thatthe electrostatic driving-indirect displacement detection method is proposed, throughanalyzing and experimenting, the vibratory quality factor is obtained indirectly. Thepaper also gives the experimental method of the AGC's best static work point and theoptimization method of the bandwidth and sensitivity.