A Research On Bandpass Sigma-delta Based Closed-Loop Detection Method Of MEMS Gyroscopes

Silicon microgyroscope(SMG)is a kind of inertial sensors that uses Coriolis effect to detect the angular velocity of an object.It is widely used in attitude locating,navigation control and other fields.The closed-loop detection circuit based on band-pass Sigma-delta modulator(SDM)can make the gyro with digital output and effectively suppress the quantization noise in the bandwidth,and the closed-loop characteristics can effectively eliminate the error of detection output caused by the machining error,improve the bandwidth of the detection loop.It is a hot topic in the study of relevant research institutions at home and abroad.As its SDM loop is difficult to confirm,the loop parameters is difficult to obtain,and at abroad,the institutions who have relatively mature research make their technology confidential.So it is necessary to have a more in-depth research on bandpass sigma-delta based closed-loop detection method of MEMS gyroscopes,the main work of this article are expressed as follows:Firstly,the basic principle of Sigma-delta modulator is studied.The structure of SDM is preliminarily selected for gyro structure,cascade and multi-bit quantization are abandoned,single-loop and one-bit quantization is adopted to design the entire closed-loop detection circuit.Secondly,the SDM loop structure is analyzed theoretically based on the discrete-time form of gyroscope sensitive structure.It is concluded that the CRFF structure is the ideal form to establish the closed-loop detection circuit.According to the specific parameters of the gyro structure,the suitable loop parameters of the discrete-time SDM structure for the gyro are obtained by taking the band-pass,bandwidth,range and resolution as the constraints and using the discrete-time SDM design tool Dstoolbox.Finally,the conversion from discrete SDM to electromechanical integrated SDM is completed by the equivalent design principle.The design flow of a complete closed-loop detection loop of electromechanical integrated band-pass SDM is established.Then,according to the structure and parameters of the gyroscope,the whole loop of SDM closed-loop detection loop is decomposed and the parameters of the loop are adjusted.Simulink simulations are carried out to validate the feasibility of the scheme,providing the basis design for the subsequent hardware implementation.Finally,the design and experimental verification of the closed-loop detection circuit based on Sigma-delta are presented,including the design and fabrication of the hardware circuit,the writing of the Verilog code in FPGA and the debugging,observation and data acquisition of the experiment.The closed-loop architecture and parameters are verified in real hardware.Finally,by analyzing the power spectral density(PSD)of a quantized output,it can be seen that the designed SDM closed-loop detection circuit has a obvious noise shaping effect,and the quantization noise is suppressed in the signal bandwidth.The noise level within the bandwidth is about-70dBV/Hz1/2?-80dBV/Hz1/2.Unedr the full range input of 200°/s,the signal to noise ratio of the quantized output is about 70dB,the effective bits is about 11.33.