The Design Of Magnetic Sensor Readout Circuit Based On Delta-sigma Modulation

With the rapid development of IOT and high-tech manufacturing industry, the magnetic sensor plays a more and more important role in many aspects including electronic compass, disk read, in the non brush motor, automobile, intelligent transportation, power equipment, environmental monitoring. As an important part of the connection between magnetic sensor and computer, the design of the magnetic sensor readout circuit becomes more and more meaningful.The output voltage of the magnetic sensor is generally the analog signal of the mV magnitude, which can not be directly identified by the computer, and it is easily to be overwhelmed by the disturbance and noise of the subsequent circuit. The function of the readout circuit is to amplify analog signals. And then converted to digital signals. So the readout circuit consists of two main modules: a preamplifier and an analog to digital converter.In this paper a 12 bit, 3 kSPS magnetic sensor readout circuit was proposed under CSMC 0.5 um process.In view of the chopper amplifier’s good effects in offset cancellation, this paper uses chopper amplifier as the preamplifier. And taking into account the very low output frequency of the magnetic sensor, Delta-Sigma ADC is the best choice for the readout circuit analog to digital converter.This paper introduces the basic principle of readout circuit, including Delta-Sigma modulation and dynamic imbalance elimination.Then we analyzes the various non ideal factors and effects of readout circuit.Then ideal and non ideal system level of the readout circuit are modelled and simulated by using Simulink. At the end of this paper, the circuit level design of the readout circuit is presented in detail.After analyzing the working principle of each block, the Hspice is used to simulate and the simulation results are given.In the case of the input frequency of 1.3125 KHz sine wave, the effective number of the readout circuit is 12.38 bits, SNDR is 76.3 dB, SFDR is 83.4 d B, the overall circuit power consumption is 8 mW.