Design Of Sense Mode Circuit For Micromechanical Gyroscope Based On Sigma-delta Bandpass Modulator

As an important branch of MEMS(Micro Electro-Mechanical Systems)sensors,micromachined gyroscopes have continuously improved their performance with the development of integrated circuit technology and have played an important role in both military and civilian applications.As an important component of the micromachined gyro,the main research direction of the gyro interface circuit is the integration and digitization.Compared with analog interface circuits,integrated digital interface circuits can reduce the peripheral devices of the chip,reduce the influence of parasitic parameters,and improve system stability and accuracy.The Sigma-Delta ADC(Analog to Digital Converter)is widely used in low-speed and high-precision digital output gyro interface circuits.In this paper,a micromachined gyro detection modal circuit based on a bandpass Sigma-Delta modulator is designed.First of all,the paper analyzes the working principle of the interface circuit and determines the structure of the sense mode interface circuit.A bandpass Sigma-Delta modulator is used in the circuit to convert analog signals into digital signals,and a self-locking clock technique is used to provide a system clock that can be connected to gyros with different drive frequencies.The main circuit modules in the detection modal circuit include a bandpass Sigma-Delta modulator,a phase-locked loop circuit,a C/V conversion circuit,and a digital down sampling filter.In this paper,the non-ideal factors and noise sources in the modulator are quantitatively analyzed.The system-level model of fourth-order single-loop feedback Sigma-Delta band-pass modulator is designed and simulated using Matlab,and the theoretical analysis results are verified.The circuit design and simulation of the bandpass Sigma-Delta modulator,phase-locked loop,and C/V conversion circuit were completed in 0.35 um CMOS process,and the layout drawing and post-emulation verification were completed.The front-end design of the digital decimation filter was completed.In the simulation environment,the power supply voltage is 5V,the sampling frequency is 40 k Hz,the input sine signal frequency is 10 k Hz,and the amplitude is-9.5d BFs.The post-emulation result shows that the signal-to-noise ratio of the detection modal circuit before demodulation is 93.80 d B(bandwidth 100Hz).After demodulation,the signal-to-noise ratio is 96.45 d B(bandwidth 50 Hz),dynamic range is 101 d B,and 1 Hz dynamic range is 110 d B,which meets the requirements of the subject.