| With the rapid development of AI and 5G technology,intelligent hardware has also ushered in a new round of evolution,and amplifiers,as an indispensable part of sensors in the use of intelligent hardware,also need to further improve their own accuracy.The offset voltage is an important indicator to measure the accuracy of the operational amplifier.If it is too high,it will cause a huge error in the output of the operational amplifier,which will affect the sensor’s judgment of reality.Therefore,the current intelligent hardware industry needs amplifiers that can achieve a series of indicators such as low input offset voltage and high input impedance.To this end,this paper designs an auto-zero instrumentation amplifier with extremely low offset voltage,and requires the outp t of the op amp to be close to the power rail to rail to ensure that the op amp has a wider range of use scenarios.This paper firstly elaborates the role of low-offset operational amplifiers in the new generation of intelligent hardware,introduces the development of operational amplifiers and the research status of low-offset technology,and then introduces the basic theory and important parameters of operational amplifiers,and then focuses on The low-offset technology and implementation principle used by the current op amp are studied.Finally,the auto-zero technology of the Ping-Pong structure is selected to design and complete an op-amp chip,in order to achieve extremely low offset voltage.The overall chip is composed of main operational amplifier,auxiliary operational amplifier,PTAT reference source,sequential circuit and switch logic circuit.The main op amp is a two-stage op amp.The first stage adopts a folded cascode structure to achieve high output impedance and wide output swing.The second stage is used to provide greater load capacity and rail-to-rail output.Class AB output structure,in order to improve the PSRR of the output stage,additionally use MOS tube coupled feedforward bias technology,and finally use Miller compensation to ensure the stability of the op amp.The auxiliary operational amplifier is a fully differential connection structure with Gain-Boosting technology.This structure can provide a relatively large gain,and a larger gain can better calibrate the offset voltage of the main operational amplifier.In addition,the main and auxiliary op amps have additional inputs for receiving calibration signal inputs.The PTAT reference source can provide bias for each MOS tube in the op amp.The principle is that the voltages of two negative temperature coefficients are superimposed.Because in the use of auto-zero technology,multiple MOS switches are needed to realize the switching of the circuit,so it is necessary to design a sequential circuit and a logic control circuit to control its on-off.Based on 0.5μm characteristic CMOS process,this paper uses EDA tools to design and simulate the circuit.After continuous testing and iteration,the auto-zero op amp designed in this paper can achieve an offset voltage of 3.756 n V at standard temperature,the maximum offset voltage does not exceed 24 n V,the unity gain bandwidth can reach1.848 MHz,and the output voltage is close to rail-to-rail. |
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