High Performance Instrumentation Amplifier Design Based On CMOS Technology

The instrument amplifier is a circuit which can extract the weak signal from the sensor,it has the characteristics of low noise,high common mode rejection ratio,low offset voltage,low power consumption and so on.Instrumentation amplifier is generally used in the back of the sensor as the first step in the signal processing circuit,can also be used as a low noise amplifier in high precision,low noise analog to digital converter.With the development of CMOS technology,the development of instrument amplifier has been improved,but at the same time,more noise problems are introduced.As a weak signal processing circuit,the noise is the key problem to be solved.As the size of process is more and more small,the power consumption and the area of the circuit are also important factors to be considered.In this paper,the design of instrument amplifier is mainly around low noise and low power consumption.The design is based on the traditional instrument amplifier structure,using a combination of capacitance coupled amplifier and chopper mode to realize the stable structure of instrument amplifier.Due to the conventional instrumentation amplifier,resistor generally used as feedback element,will increase the power consumption,area and thermal noise.Therefore,capacitive coupling feedback circuit is used in this design.The chopper stabilized structure is mainly composed of MOS switches,The amplifier noise and offset can be modulated to high frequency,Then,through the filter to filter out.Finally,it can reduce the effect of low frequency noise.This paper studies and designs an instrument amplifier based on CMOS technology.The process of the design of the library is the standard CMOS process.The simulation software is Spectre under the Cadence.Supply voltage is 3.3 V,common mode voltage is 1.5 V and the overall power consumption is 64.68 ?W.Circuit simulation results are: When the input signal frequency is 50 Hz,the chopping signal frequency is 2 k Hz.At 50 Hz,the low frequency equivalent input noise has reached 12.77 n V/sqrt(Hz).The equivalent input noise in the range of 0.1Hz~100Hz is 8.945 ?V/sqrt(Hz).The common mode rejection ratio of the amplifier is 160 d B,the power supply rejection ratio PSRR+ is 147.13 d B,PSRR-is 122.52 d B.Meet the basic design requirements.On this basis,we conduct the whole circuit layout design.The overall layout of the area is 50×90 ?m2,and carry on the post layout simulation of function with the whole instrument amplifier and each module.At 50 Hz,the low frequency equivalent input noise has reached 19.77 n V/sqrt(Hz).The equivalent input noise in the range of 0.1 Hz~100 Hz is 12.65 ?V/sqrt(Hz).Achieve the requirements of low power consumption and low noise.