Design And Realization Of Low Noise Voltage Amplifier Chip

The measurement of weak signals is widely used in fields such as biomedicine,aerospace,ocean exploration,and semiconductor measurement.In these fields,the source under test is likely to be high impedance,so the voltage signal of the source under test is very weak.In order to reduce the difficulty of detection,it is necessary to amplify the weak signal before detecting the signal.However,the noise and offset in the circuit often directly affect the quality of the weak signal to be measured.Measures must be taken to suppress or eliminate the noise and offset in the circuit.That is,the weak signal amplifier must have the characteristics of low noise while having the amplification gain.Since the performance of the weak signal amplifying circuit determines the accuracy of the entire weak signal measurement to a certain extent,it is of great significance to design a weak signal amplifying circuit with superior performance.This article proposes a low-noise weak voltage signal amplifier circuit.In terms of noise suppression,chopper modulation technology is used to separate signal from noise and offset,which lays the foundation for the subsequent low-pass filtering to eliminate noise.Compared with the autozero technology,the chopping modulation technology can better suppress the noise in the circuit without increasing the noise floor,and is more suitable for the low-noise design of this article.In terms of amplifying the input signal,a differential difference amplifier is used to amplify the input signal,which has a high input impedance and a high common-mode rejection ratio.The circuit designed in this article uses a single-ended input signal method,but because this method will cause input common-mode fluctuations.If the input common mode fluctuation is not considered,the voltage at the positive and negative input terminals of the amplifier cannot be consistent,which results in distortion of the output signal of the amplifier;In order to suppress input common-mode fluctuations,an input common-mode feedback circuit is introduced into the system circuit,so that the voltage at the end of the amplifier not connected to the system input can follow the voltage at the end connected to the system input,that is,the voltage at the positive and negative input ends are consistent,thus ensuring the linearity of the overall circuit.The input common mode point voltage needs to calculate the average value of the two input terminal voltages of the differential difference amplifier,so it is necessary to introduce a resistance network.In order to drive the resistance network,an input impedance conversion circuit is introduced into the system circuit,which increases the input impedance of the system circuit.This article adopts SMIC's 180 nm CMOS process.The circuit design and layout design of the overall circuit have been completed on the virtuoso software,and the performance simulation of the circuit has been performed.The simulation results show that the circuit designed in this paper is less affected by the three factors of PVT,and its performance is stable;The equivalent input noise of the designed circuit is 1.32?Vrms within 1Hz?100Hz,the input impedance of the circuit reaches3.378G?,the common mode rejection ratio reaches 153 d B,and the power supply rejection ratio reaches 126 d B.All indicators meet the design requirements of this article.Finally,the performance parameters of this article are compared with other documents,and the results show that the circuit designed in this article has more advantages in terms of input impedance,common-mode rejection ratio,and power supply rejection ratio.After the circuit's post-simulation results meet the index requirements,the circuit is taped out and tested.The test results show that the voltage resolution of the chip can reach 100 n V.