Design And Analysis Of Low Noise Analog Circuit Of Magnetoelectric Sensor

Magnetic sensor as a new type of magnetic field sensor with low noise,low cost,easiness to produce features,is very suitable for high-precision magnetic field measurement.In order to improve the measurement accuracy of the magnetoelectric sensor,it is very important to design a low noise analog circuit.In this paper,a low noise driving circuit based on the principle of phase lock amplification was designed according to magnetoelectric sensor's resonant characteristics and the modulation characteristics of the bias magnetic field.The driving circuit was divided into signal channel,coherent device and reference channel,in which the signal channel use a low noise JFET as a pre-input device,coherent device use a low noise analog switch,excitation clock and phase shift of the reference channel was implemented by a CPLD.The advantage of using CPLD is that you can use programming to meet different clocks and phase shifting requirements of different sensors,while having very low phase noise.Based on the designed low noise driving circuit,this paper carried out noise analysis and MATLAB simulation of the various modules in the circuit,especially the charge amplifier,analog switch and low pass filter.In this paper,the noise test of each module of the analog driving circuit was carried out respectively.The JFET charge amplifiers were tested with input capacitance of 220 nF and 2.2uF,and the test results were basically in accordance with the results.Compared with the basic charge amplifier,it is found that the noise characteristic of JFET charge amplifier is better than that of basic charge amplifier,and the noise figure is 0.049 dB under the sensor input of this paper.The noise test results for the low-pass filter are in good agreement with the simulation results,and the noise level in the passband is about 150 nV / rtHz.If the driving circuit input is a 6.8nF capacitor,test results show the driving circuit noise level in the passband is about 200 nV / rtHz.Finally,the test results show that the system noise level is 1.78 nT / rtHz.