Research On Multi-rate Digital Signal Processing Architecture For MEMS Gyriscope

With the continuous development of micro-mechanical technology,micro-electromechanical system(MEMS)gyroscope is widely used in consumer electronics,industry,aerospace,military and other fields due to its small size,light weight,low power consumption and batch production,and so on.Therefore,the requirements of performance for MEMS gyroscope have become increasingly higher.The two main reasons that restrict the performance of MEMS gyroscope are device structure and processing circuit.Under the current process level,the performance of MEMS gyroscope can be improved instantly from the point of processing circuit.Especially,the development of digital signal processing technology makes circuit optimization more convenient.For the purpose of high performance and low power consumption,a multi-rate digital signal processing control architecture is proposed and implemented in this research based on the study of high-precision digital signal demodulation algorithm in MEMS gyroscope control system.This architecture not only reduces the power consumption of digital module,but also improves the signal-to-noise ratio(SNR)of the output signal and the long-term stability of MEMS gyroscope system.The specific research and contributions are given as follows:1)Research on quadratic orthogonal demodulation for MEMS gyroscope.The demodulation performance of three quadratic orthogonal demodulation algorithms,multiplication demodulation(MD),least mean square demodulation(LMSD)and fourier algorithms demodulation(FAD),are analyzed and compared from three aspects:principle,MATLAB numerical simulation and experiment.That shows under the same demodulation bandwidth,FAD has the best performance.The performance of MEMS gyroscope is tested at room temperature and under atmospheric pressure.The results show that LMSD and FAD are better than MD in suppressing noise,and the angle random walk(ARW)of the system is improved by nearly 1.5 times.In particular,the bias stability(BS)of the system using FAD is improved by 1.98 times and 1.5 times than that of MD and LMSD,respectively.2)Design of Digital Signal Frequency Reduction Processing.The clock of the digital control system of MEMS gyroscope is reduced by 256 times before quadratic orthogonal demodulation,and the signal to be demodulated with high SNR is obtained.Firstly,an improved non-nyquist sampling method is proposed to realize the carrier demodulation of amplitude modulation signal.This method uses all the information of sampling points.In this design,the SNR can be improved by 15dB compared with the direct under sampling.Secondly,in order to eliminate the effect of spectrum aliasing caused by non-nyquist sampling,the contrast of three kinds of digital decimation anti-aliasing low-pass filters are analyzed,and a three-stage cascaded FIR half-band filter is designed to ensure the high SNR of the signal which is to be demodulated.3)Research on multi-rate digital control architecture of MEMS gyroscope.The architecture is based on the dual-loop control schemes of automatic gain control(AGC)and phase-locked loop(PLL)of our research group.Firstly,the processing frequency of all levels of signals is reduced to the appropriate clock frequency by using multi-rate digital signal processing,which significantly reduces the power consumption of digital modules.Secondly,the driving resonant frequency of MEMS gyroscope is used as the reference of the system clock,and then the carrier demodulation module is replaced by the non-nyquist sampling method,which greatly reduces the consumption of hardware resources.Finally,the driving resonance frequency of MEMS gyroscope is used as the sampling reference of the system,so each period of the MEMS gyroscope driving signal has the integer sample points.That not only reduces the impact of picket fence effect on the system,but also makes the quadratic orthogonal demodulation of drive mode and sense mode implemented by FAD,which has better performance than MD and better stability than LMSD.According to the performance test standard of domestic MEMS gyroscope,the experiments of the MEMS gyroscope are carried out at room temperature and under atmospheric pressure.The results show that the ARW is 4.07°/hr/VHz,and the BS is 0.71°/hr.Compared with the multiplication demodulation digital control system with the fixed sampling rate,the ARW is improved by 1.4 times and the BS is improved by 2.1 times.At the same time,the power consumption of the FPGA is reduced by 57.6%and the power consumption of the digital board is reduced by 40.5%.In conclusion,the multi-rate digital control architecture effectively improves the gyroscope performance and reduces the power consumption of the system.