Research And Design Of Low Noise Instrumentation Amplifier

Instrumentation amplifiers are precision differential amplifiers that feature low noise,low offset,high linearity,and high common-mode rejection.They are widely used in the fields of sensor signal conditioning,data acquisition and energy exploration.As a key part of the sensor signal readout circuit,the instrumentation amplifier not only needs to detect the output signal of the front-end sensor,but also usually drives the analog-to-digital converter of the latter stage.As the accuracy of analog-to-digital converters in application scenarios increases,there is a greater demand for high-performance instrumentation amplifier circuits.The paper firstly summarizes the research status of instrumentation amplifiers at home and abroad,introduces the noise and offset sources of the circuit,and focuses on the chopper stabilization and correlated double sampling technology in low-frequency error suppression.Then,based on the four commonly used topologies of instrumentation amplifiers,the advantages and disadvantages of different structures are summarized and compared.In order to weaken the influence of temperature change on the performance of instrumentation amplifier,a bandgap reference current generating circuit with lower temperature coefficient is designed in this paper.In addition,the offset-stabilized operational amplifier can further reduce the circuit’s offset.This paper analyzes the technical principle and stability of the structure.On this basis,two different types of low-noise instrumentation amplifiers are designed at the end of the thesis.In the continuous time domain,a high precision chopper type instrumentation amplifier is designed in this paper.Offset and noise are greatly reduced by applying chopper stabilization techniques in the circuit.Combined with the buffer module,the input impedance of the instrumentation amplifier is further enhanced.Then the paper completes the layout design and post-simulation of the instrumentation amplifier based on the 0.18μm 1P4M BCD process.Under 5V supply voltage and 5.1mA quiescent current,the equivalent input noise power spectral density of the instrumentation amplifier at 10Hz is 19.05 nV/√Hz;the average equivalent input offset voltage is 0.8μV.By programming the feedback resistance,the circuit can achieve an adjustable gain of 1 to 64 times.The input and output voltage ranges can reach 3.9V and 5V respectively,and when the input signal is in a fullscale state,the THD of the amplified output signal is below-115dB.In the discrete time domain,an improved switched capacitor instrumentation amplifier is designed in this paper.To reduce noise and offset,the amplifier applies predictive correlated double sampling at the input and oversamples the input signal.By optimizing the MO S switch and control clock,the linearity of the circuit is further improved.Then the thesis completes the design and pre-simulation of the instrumentation amplifier circuit based on the 0.18μm 1P4M BCD process.Under the condition of 5V supply voltage and 6.6mA quiescent current,the equivalent input noise power spectral density of the instrumentation amplifier at 100Hz is 29.27nV/(?)Hz,and the equivalent input integrated noise value of 0.1～10Hz is below 0.54μVrms;the average equivalent input offset voltage is 1.28μV.By programming the sampling capacitor and the feedback resistor,the circuit also achieves an adjustable gain of 1 to 64 times.Both the input and output voltage ranges can reach the power supply voltage of 5V,and when the input signal is in a full-amplitude state,the THD of the amplified output signal is below-100dB.In summary,the high-precision chopper type instrumentation amplifier can achieve lower noise and offset at low power consumption,but the input signal range is limited,and the resistance error in the process is relatively large,which leads to unstable circuit performance.Relatively speaking,switched-capacitor instrumentation amplifiers can handle a wider range of input signals and are not limited by the input common-mode voltage,but the linearity is limited by the performance of switches and clocks;in the process of manufacturing,the capacitance accuracy is higher,and the circuit has a stable frequency response.