Signal Processing Of Three-axis TMR Magnetic Sensor Based On Principe Of Digital Quadrature Phase-Locked Amplification

With the development of weak magnetic detection technology,it is of great significance to design a magnetic sensor system which can collect low-frequency weak magnetic signals with high precision and sensitivity in the X,Y and Z axes.Tunnel magnetoresistance(TMR)sensor is one of magnetoresistance sensors,whose resistance value changes with the external magnetic field.Compared with other magnetic sensors,TMR sensor has the advantages of high sensitivity,low power consumption and small size.Taking tunnel magnetoresistance as the front-end sensitive element of triaxial magnetic sensor is a good choice.The disadvantage of TMR sensor is that its output signal will be covered by a large amount of noise.Therefore,how to filter noise and retain effective weak signal has become the key of system design.As a traditional method of extracting weak signal,phase-locked technology usually part or the whole of the system is still simulator,which can not achieve the overall digitization of the same system,and can not completely avoid the influence of the inherent temperature drift of simulator and device aging on the system.The system is designed to realize the complete digitization of quadrature phase-locked amplification principle through digital signal processor(DSP),process the three-dimensional magnetic field signal output by tunnel magnetoresistance,and obtain the amplitude and phase information of low-frequency signal,which is conducive to better signal noise level and more stable system performance.Through Serial Communication,the data information can be uploaded to the host computer,so as to display and store the low frequency and weak magnetic signal data information in the X,Y and Z three-axis directions.The system hardware takes the DSP chip TMS320VC5509 A as the core,and realizes the system functions through ADS1256 and other chips,and completes the overall hardware design of the system.The system software is based on the DSP/BIOS embedded system,which realizes the three-axis data collection and real-time data processing by the multi-threaded structure,and completes the upper computer software design that displays and stores the data processing results in real time.This thesis completed the hardware and software design of the three-axis TMR magnetic sensor based on quadrature phase-locked amplification,and completed the debugging and functional verification of the system.After calculation,the sensitivity of the system is 125 m V/Oe,its highest magnetic field intensity resolution can reach 0.76296 n T,and the corresponding magnetic field intensity range is ±25000 n T.The system can meet the detection and acquisition requirements of high-precision weak magnetic signals.