| The GMR magnetic field sensor converts the magnetic field signal to an analog signal,the output signal amplitude is small.In the transmission process,it is susceptible to signal distortion caused by noise,temperature,humidity,electromagnetic interference,etc.Instrumentation amplifiers can effectively suppress common-mode interference signals and have low noise.It can detect the output signal of the GMR magnetic field sensor and become part of its signal processing circuit.In this paper,by analyzing the basic structure and working principle of the GMR magnetic field sensor,on the basis of studying the characteristics of the magnetic field sensor,a instrument amplifier is designed for the output signal of the GMR magnetic field sensor to achieve the amplification of the weak magnetic signal.After comparing and analyzing the common structure and working principle,main performance indicators,circuit noise and offset of the instrumentation amplifier,it is given that the design uses a capacitive coupling structure and a chopping stable structure to realize the instrumentation amplifier circuit.Chopper technology is used to reduce the noise and offset of the amplifier.The instrumentation amplifier is mainly composed of a main amplifier,a chopper and a buffer.This subject uses the standard TSMC 0.18μm CMOS process to design the instrumentation amplifier circuit,based on the Cadence platform for Spectre circuit simulation and Virtuoso for layout drawing.Simulation results show that the power supply operating voltage is 3.3 V,the chopping frequency is 10 k Hz,closed-loop gain is40 d B,overall power consumption is 35.15μW,the common mode rejection ratio of the instrumentation amplifier is 149 d B,and the power supply rejection ratio of the instrumentation amplifier is 156 d B,and at 1 k Hz,the equivalent input noise is 39n V/sqrt(Hz).Compared with the amplifier without chopping,low noise characteristics are achieved,The overall layout of the instrumentation amplifier has passed DRC and LVS verification.The total area of the final layout is 0.075 mm~2,and the simulation results meet the expected indicators. |
