Research On Low Noise Technology In CMOS And Signal System For FM Gyroscope

After nearly thirty years of development,MEMS gyroscopes have achieved tremendous success in terms of structure and measurement and control circuits.For traditional MEMS gyroscopes,increasing the quality factor helps to improve the scale factor and resolution of gyroscope,but reduces the maximum range and effective bandwidth;The PCB circuit built with discrete components has large parasitic capacitance and external interference at the electromechanical interface of the gyroscope,which results in relatively large power consumption and area,making it difficult to achieve miniaturization and unable to reflect the advantages of low power consumption,low cost,and small volume of MEMS gyroscopes.Focusing on the development demands of high-precision MEMS gyroscopes,this article delves into the issues on system model accuracy,low noise driving circuit,high-precision frequency extraction circuit and CMOS circuit design of FM gyroscopes.The specific content and stage achievements are as follows:Firstly,based on the background of FM gyroscope,and a Quad Mass Gyroscope（QMG）designed by the MEMS research team of Nanjing University of Science and Technology,the research on low noise control circuits for Lissajous Frequency Modulation（LFM）gyroscope is conducted;Based on the requirements of high-precision gyroscopes for the noise of circuit systems（closed-loop driving circuit and frequency digital conversion circuit）,a mathematical limit based method is proposed to solve the phase noise of FM gyroscopes,and an overall phase noise model including structure and control circuits is established;On the basis of this model,the rationality of the low noise signal system of FM gyroscope was demonstrated,and the proportion of gyroscope structure and circuit error sources in the bias stability of FM gyroscope was revealed.The overall noise level and zero-bias performance of the FM gyroscope were accurately predicted,which can guide the optimization design of structure and circuit.Secondly,based on the analysis of the requirements for the performance of the self-excited closed-loop driving circuit in the FM gyroscope low noise system,research on the low noise technology of the gyroscope electromechanical interface circuit and Automatic Gain Control（AGC）circuit was carried out.A cascaded band pass front-end amplifier circuit has been designed.The first stage uses an pseudo resistance network with ultra-high resistance to reduce the equivalent input current noise of the device.The second differential stage provides stable and configurable bandwidth and gain through proportional capacitance technology,the band pass gain is greater than 140 dB,and the equivalent input current noise is less than 10 fA/ Hz^1/2,the phase error is about 1°;For the Analog multiplier in AGC circuit,a variable gain amplifier with low noise and wide input swing is designed to reduce the effect of multiplicative noise on the phase noise of the closed-loop system and the output voltage noise is 3μV/Hz^1/2;For the influence of low-frequency flicker noise in the circuit,a continuous chopper is designed.The low-frequency flicker noise in the closed-loop drive circuit is reduced by using the chopper stabilization technology,and the design goals of low noise and low power consumption is achieved.Then,based on the performance requirements of frequency digital conversion circuits for FM gyroscope low noise systems,research on high-order digital analog mixing Sigma-Delta frequency digital converters was carried out.The digital phase-locked loop circuit with dead zone three state phase frequency detector is designed,which realizes the fast locking of the gyro output frequency（<800us）;A phase sensitive demodulation interface circuit with Analog multiplier is designed to eliminate the amplification noise introduced by the digital comparator and achieve high phase locking accuracy;A Sigma-Delta frequency digital converter with phase-locked loop and reset counter was designed.The first order reset counter was embedded in the phase-locked loop system,resulting in a third-order noise shaping characteristic of quantization noise,suppressing quantization noise at low frequencies,and the frequency resolution is 10μHz/Hz^1/2（@50Hz）.Finally,the ASIC chip and gyroscope structure was joint debugging.The equivalent input current noise of the front-end amplifier in the self-excited closed-loop drive circuit is 9.2fA/ Hz^1/2,and the equivalent output frequency noise resolution is 80μHz/ Hz^1/2（@100Hz）.The frequency noise resolution of high-order Sigma-Delta frequency digital conversion circuit is 10μHz/Hz^1/2（@50Hz）.After repeated acquisition test,the bias instability of FM gyro prototype is less than 1.4°/h,and the angle random walk is less than 0.07°/h^1/2.The scale factor nonlinearity in room temperature is less than 30 ppm,the detection bandwidth is 50 Hz,and the dynamic range is more than ±1000 °/s.Therefore,this article achieves the design goals.