Research On Integrated Analog Interface Circuit Design Of Tri-Axis Microgyroscope

With the wide application of micromachined gyroscope in military,consumer electronics and other fields,multi-axis micromachined gyroscope has gradually become an important research direction.Through the structural design,the monolithic tri-axis micro gyroscope with single drive axis and three sense axes is realized.Meanwhile,the integrated design of the interface circuit can improve the integration and stability of the system and further reduce the circuit size.Combined with the characteristics of low frequency and narrow band of gyroscope signal and the band-pass ΣΔ modulator with low speed and high precision,the interface circuit based on bandpass ΣΔ ADC is designed in this paper.The design of each circuit module is completed.The feasibility of the interface scheme is also demonstrated.Firstly,the structural design of tri-axis micro gyroscope with unilateral unequal height comb is presented in this paper.Then,the closed-loop drive and sense circuits of tri-axis gyroscope are analyzed according to Simulink modeling.Therefore,the interface circuit scheme based on band-pass ΣΔ modulator is proposed.The basic principle of the ΣΔ modulator is introduced.In order to achieve a higher signal-to-noise ratio,the modulator structure of single loop fourth-order feedback and sixth-order feedforward is determined.The bandpass modulator model under non ideal factors is analyzed and established.The behavior level simulation shows that the signal-to-noise ratio of fourth-order feedback and sixth-order feedforward can reach88.3db and 105.9db respectively.The sixth-order feedforward structure has a larger input signal amplitude concurrently.Secondly,the analog interface circuit is designed based on SMIC 0.18 μM CMOS process for the tri-axis micro gyroscope,including the CV conversion circuit in the form of switched capacitor,band-pass in the form of 4th and 6th order ΣΔ The modulator circuit,bandgap reference and the charge pump circuit for boosting in the power module.the functional parameters of each module meet the set indicators.Through the joint simulation of the modules in the analog interface circuit,the signal-to-noise ratio of the final output bit stream is 80.4db.The number of effective bits is 13.06 bits.Finally,the verified interface circuit and the subsequent digital signal processing methods are introduced in this paper.Through the joint commissioning simulation of the whole interface circuit,the feasibility of the designed interface circuit scheme of tri-axis micro gyroscope is demonstrated.In addition,an experimental platform is built to test the performance of the triaxis micro gyroscope.The bias instability of pitch,roll and yaw mode is 1.1924 ° / h,1.2821 °/ h and 1.0507 ° / h.The noise density is 0.1011 ° / √ h,0.1635 ° / √ h and 0.0708 ° / √ h respectively.The test results indicate that the tri-axis micro gyroscope can complete the detection of the three-axis angular velocity with certain accuracy and performance.