| With the rapid development of integrated circuits and the rise of the Internet of Things,miniature sensors are widely used in various fields.Among them,the magnetic sensor can convert a weak magnetic signal into an electrical signal,thereby indirectly detecting the physical quantity information related to the magnetic field.The triaxial magnetometer is a vector-type magneto-sensitive sensor that can measure the magnetic induction intensity in the three directions of the x-axis,y-axis and z-axis,and is widely used in the fields of industry,agriculture,marine,medical treatment,aerospace and so on.The research of triaxial magnetometer interface circuit is of great significance.Compared to other types of magnetic sensors,tunneling magnetoresistive(Tunnel Magnetoresistance,TMR)sensors have both high sensitivity and wide dynamic range.However,because the output of the TMR magnetometer header is a low-frequency weak electrical signal,a low-noise analog front-end detection circuit needs to be designed.The analog front-end detection circuit in this paper is mainly composed of low-noise instrumentation amplifier and Sigma-Delta modulator.By analyzing the topological structure of common instrumentation amplifiers and combining the characteristics of low-noise,high input impedance,and high CMRR of a analog front-end detection circuit using a triaxial TMR magnetometer,this paper uses a current feedback instrumentation amplifier(Current-Feedback Instrumentation Amplifier,CFIA)structure;The chopper stabilization technique is used to reduce the low-frequency noise and offset of the instrumentation amplifier,and a ripple repression loop is used to reduce the high-frequency ripple at the output of the op amp caused by chopping.Since the use of the loop causes the transfer function of the amplifier to introduce a notch at the chopping frequency,in this paper,using the multipath topology masks this notch while broades the frequency band.When the power supply voltage is 5V and the chopper frequency is 80 KHz,CFIA's post-simulation results: equivalent input noise is 16.39 n V/sqrt(Hz),the corner frequency of 1/f noise is 36.97 m Hz,closed-loop gain is 40 d B,GBW is 10.82MHz(Load capacitance 30 p F),PM is 74.82 deg,and the total current is about 1.5m A.In order to realize the digital output while guaranteeing the overall low noise and high signal-to-noise ratio performance of the analog detection circuit,a third-order full-feedforward one-bit-quantizes Sigma-Delta Modulator is used in this paper.The first stage integrator's op amp is chopped to eliminate the effect of low frequency 1/f noise.When the power supply voltage is 5V and the sampling frequency is 1MHz,the post-emulation result of the modulator: the signal bandwidth is 1KHz,the input signal frequency is 100 Hz,and the amplitude is-8d BFs(1V),the 1Hz dynamic range is more than 130 d B,and the SNR distortion ratio The SNDR is 110 d B,the corresponding effective bit number ENOB is 18 bits,and the total current is about 3.5m A.Finally,drawing and post-simulating the whole analog front-end detection circuit layout: the input signal frequency is 100 Hz,the amplitude is 10 m V,after 100 times amplified by CFIA,the final modulator output PSD's signal to noise distortion ratio is 106 d B. |
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