Research On Interface Circuit For High Precision Silicon Micromachined Gyroscope

Gyroscopes are important measurement devices for angular velocity,mainly in aerospace,defense and industry field.Micro electro mechanical system(MEMS)silicon gyroscope has the advantages of high integration,high precision and mass production,and is applied more and more widely.The integration of the silicon gyroscope interface circuit can realize self adjustment debugging,performance matching of MEMS devices with circuitry design,and high reliability,which is crucial to gyroscope performance improvement.Ingeration of interface circuits for gyroscopes has been already realized abroad.However,study of gyroscope interface circuit in China has been carried out late,and there is a significant gap between China and foreign countries.This has already become the bottleneck for research of silicon gyroscopes.ASIC chips of silicon gyroscope interface consist of driving circuit,sensing detection circuit,and specialized circuit for depressing nonidealities in gyroscope structures.Besides,overall gyroscope performances are mainly decided by phase noise in driving loop,detection noise,signal coupling,parasitic Coriolis force,quadrature errors,temperature peculiarities.In order to solve these relevant issues,low-distortion closed-loop autoexcitation driving,low-noise sensing detection,coupling interference suppression,and temperature compensation are researched in this paper.In addition,forward design and independent researched ASIC chip are employed,and verified by measurement methods.Autoexcitation driving system in gyroscopes is based on the principle of auto gain controlling to guarantee stability of driving force amplitude,characteristic of nonlinear system.Due to randomness of charge injection produced by systematic thermal noise and 1/f noise,phase noise caused by it cannot be omitted in high-precision gyroscope design.Usual linear analysis of noise is unsatisfactory.A nonlinear time-varying model specialized for capacitive silicon micro-gyroscopes is proposed for phase noise analysis in this paper,instead of existing linear time invariant model.Analytical mathematical models of influence of noise in low-frequency and high-order harmonics in driving loop on driving phase noise are obtained.Methods of quantizing phase noise are presented.Circuit topology architecture and means of circuitry coefficient optimization for optimized performances of driving loop are proposed.Sinusoidal driving circuits based on nonlinear auto gain controlling are advantageous in low phase noise and quick start.Circuit noise is the most important factor to gyroscope output stability.By means of analysis of noise source in detection circuit,systematic noise sources consist mainly of thermal noise of charge amplifier at the forepart of detection circuit,phase noise of demodulation reference signal,and 1/f noise of low-pass filter.A more complete mathematical model of noise source specialized for several noise sources is established.By means of structural optimization and coefficient adjustment of charge amplifier,low noise in detection circuit is achieved.And low systematic phase noise is realized by sinusoidal driving.Further optimization of systematic noise is achieved by sinusoidal high frequency carrier signal based on closed-loop amplitude controlling for silicon gyroscopes with low quality factors.Coupling of syntony signals with the same frequency is solved,while decreasing noise efficiently.Influences of parasitic Coriolis force,quadrature coupling,electrical coupling,signal phase shift,and coefficient mismatch on output stability are analyzed.Stable analytical mathematical models are established.And comprehensive optimization methods of improving output stability are presented.Temperature adaptation of silicon gyroscopes is an important condition for practicality.Specialized for silicon micromechanical gyroscopes' zero temperature drift,this paper researched the temperature properties of sensing structure and circuit,established temperature model of scale factor and zero output.Original methods of temperature compensation in-chip based on AC driving amplitude fitting and digital circuits controlling fuse array are proposed for gyroscopes with low quality factors.Constant transconductance operational amplifier with low temperature drift can decrease signal phase shift within full temperature range.Voltage reference with low temperature drift can eliminate influences of circuit on zero output.Finally,circuits with low temperature drift and methods of temperature compensation are simulated.According to relevant integration techniques and mathematical models,an interface ASIC with the function of closed-loop autoexcitation driving and open-loop weak signal detection.This chip for silicon interface ASIC is designed and fabricated by 0.35?m four-metal double-polycrystal BCD process,occupying an area of 4.5mm×4.0mm.Experimental results show a capacitor resolution of 1.8 ×10-9 in forestage of detection circuit,a maximum phase drift of 0.1° within full temperature range.The whole gyroscope realized low-distortion quick autoexcitation driving,angular velocity detection,short-term zero stability of 1.12o/hr,zero temperature drift of 29.48 o/hr within full temperature range.Theoretical analysis,model establishment,and integrated circuit design are verified by experimental results.Advantages of integrated circuits are shown.The whole circuit reached the criteria for high-precision gyroscope interface circuits.