Design Of Low Noise Instrumentation Amplifier

As an Analog Front End(AFE)circuit,instrumentation amplifier is used to detect and process the weak voltage signal output by the sensor.Both in the basic signal amplification,acquisition system and in the application of AI,telemedicine and other emerging fields,higher requirements are put forward for the performance of the instrumentation amplifier.Instrumentation amplifier is a kind of precise differential voltage amplifier,which meets the advantages of low noise,low offset,high linearity and high input impedance.The realization of high standard instrumentation amplifier is an important factor to improve the performance of the whole circuit,on the other hand,in order to guarantee that the instrumentation amplifier is applicable to the signal acquisition system with a wide input dynamic range and make full use of the effective resolution of the post ADC,the programmable gain function is added.This paper analyzed the research status of instrumentation amplifier domestically and abroad,then the influence factors of circuit offset and noise are introduced,and the key technologies of low noise circuit design are summarized.Based on the analysis of the working principle and application requirements of the main circuit module,a low noise instrumentation amplifier is designed to drive a high precision ?-? ADC.The main work of this paper is described as follows:1.The principle of offset and different types of noise in the circuit are summarized,through the theoretical analysis and calculation,the realization technology of low noise is introduced,especially the principle of the chopper stabilization topology.On the other hand,the influence of the offset-stabilized structure on the amplifier offset is analyzed and calculated2.The amplifier system and core circuit modules of the design are proposed.The instrumentation amplifier consists of two low noise amplifiers and a programmable gain block,the circuit offset and noise are reduced by offset-stabilized structure and chopper stabilization topology.The output impedance of the intermediate stage can be improved by using the gain-boost technique.The output stage of push-pull structure is adopted to ensure the strong driving capability of the circuit,at the same time,the power consumption can be saved.The programmable gain is achieved by switches and resistor array.The on resistance of switches is isolated from the feedback resistor,which reduces the gain error.With the multistage nested Miller compensation structure,the LHP zero introduced by the feedforward path can be used to cancel the secondary pole of the circuit and guarantee the stability of the circuit3.The layout and post-simulation of the instrumentation amplifier are completed,including the matching design of the amplifier input stage,current mirror and resistor.Finally,the layout of the low noise instrumentation amplifier is designed.Combined with the circuit layout,the post-simulation of noise,offset,circuit stability,programmable gain and linearity of the design is completed.The low noise instrumentation amplifier is simulated based on 0.18?m standard CMOS process with a supply voltage of 5V.The post-simulation results show that the equivalent input noise Power Spectral Density(PSD)of 4.24875nV/?Hz@200Hz is achieved when the close loop gain is 64.The mean value of the equivalent input offset voltage is 162.225nV and the variance is about 1.0183?V.The loop gain is 204.972dB with the phase margin is about 61.966�.The power consumption is 7.5mW.The Total Harmonic Distortion(THD)is less than-100dB,PSRR is 136.528dB,and CMRR is 132.34dB.Compared with similar instrumentation amplifiers,this design has better low noise characteristic.