Research On Key Technologies Of Closed-Loop Structure AMR Magnetic Field Sensor

As one of the basic resources of the earth,the geomagnetic field is closely related to human production and life.It has important applications in geological surveys,mineral surveys,and military explorations.In view of the huge application value of the geomagnetic field,choosing or designing a magnetic field sensor to use this resource has become an important means.In recent years,AMR magnetic field sensors have stood out from existing magnetic field sensors due to their high sensitivity,good linearity,low power consumption,and easy miniaturization.However,most existing AMR magnetic field sensors use an open-loop structure when they are in use,so their performances such as noise and sensitivity need to be further improved.In this regard,in order to improve the magnetic field measurement performance of the AMR magnetic field sensor,the paper studies the sensor noise performance optimization technology,zero drift suppression technology and cross-axis effect suppression technology.The main research contents are as follows:Firstly,In order to optimize the noise performance of the sensor and ensure the high sensitivity output of the sensor,a proportional integration circuit and a closed loop feedback circuit are designed.Through theoretical analysis and experiments,the gain of the preamplifier is 10,the integral circuit parameter is 100uF,and the feedback resistance value is 100?.Secondly,In order to suppress the sensor signal drift,a set/reset circuit is designed.In order to synchronize the sensor output signal with the set/reset signal and obtain a DC output signal at the same time,a switch synchronous detection circuit is designed.In order to further improve the performance of the sensor,the circuit was improved.A coupling capacitor was added to the circuit to eliminate the DC offset of the signal by means of AC coupling.Thirdly,In order to suppress the cross-axis effect and avoid the complexity of the existing software compensation methods,a hardware compensation method is proposed.A three-dimensional Helmholtz coil is designed to replace the bias current band of the sensor.The advantage of the unidirectional magnetic field generated by the Helmholtz coil solves the problem of cross-axis interference.Based on the research of the above key technologies,a prototype of a closed-loop structure AMR magnetic field sensor was designed and its performance was tested.Experimental results show that in terms of noise performance,while the sensor sensitivity reaches 50?V/nT,its signal-to-noise ratio is improved by 15.55dB,and the noise power spectral density is about 40pT/(?)?1Hz;in terms of zero drift,the linear deviation of the sensor obtained by the test is only 0.088%,and at an output of plus or minus 2.5V,Its zero offset is only 28mV,the signal fluctuation range is only 2nT,it can be seen that its drift is well suppressed;from the cross-axis effect suppression,it can be seen from the simulation results that the magnetic field direction of the feedback coil of the sensor is arc,and The direction of the magnetic field inside the Helmholtz coil is a straight line.It can be seen that this structure can effectively suppress cross-axis interference.