Study On A Low Noise Low Offset And High Precision Operational Amplifier

Analog circuits are one of the most important branches in today's integrated circuit systems,and op amps,one of the most important basic units in analog circuits,have undergone several changes since invention.With the continuous development of Internet of Things,5G communication and artificial intelligence,newrequirements have been put forward for operational amplifiers.At the same time,due to the continuous reduction of process size,the design of operational amplifiers is becoming more and more difficult.Especially the development of consumer portable devices makes high-precision and low-power operational amplifiers become a hot field in the research of analog circuits.Its research has important significance for the development of operational amplifiers.Based on the significance of this research,the paper focuses on the design of high precision operational amplifiers.The paper first analyzes the physical meaning of the parameters of the operational amplifier and the trade-off relationship between them.Secondly,it analyzes the sources of noise and offset in the circuit,and compares the difference between noise and offset between BJT process and CMOS process.Next,the low-noise,low-offset high-precision operational amplifier designed by the paper is introduced in detail.The bias circuit realizes the bias current of low temperature drift through the high-order temperature compensation structure;the input stage adopts the differential pair with the common centroid structure to improve the matching,and the resistor is used as the load and the trimming circuit is added to adjust the offset voltage.The base current cancellation circuit uses one current source to reduce the noise while reducing the input bias current of the op amp;the intermediate stage adopts the folded cascode structure to obtain high gain,and the Miller compensation and feedforward compensation structure are used to stabilize the operational amplifier.Finally,the buffer output stage structure is used to improve the load capacity of the op amp to the load.The op amp designed by the paper uses Shanghai's advanced 40V 4μm bipolar process,and the simulation tool is based on the Cadence IC610 Spectre simulator.The simulation results show that the equivalent input noise voltage density of the op amp is 8.68nV/(?)at 10Hz,the equivalent input noise current is 0.43 pA/(?),the input bias current is 0.24nA,the large signal voltage gain is 138dB.The bandwidth product is 722KHz,the single-channel power supply currentis 432 μA,the slewrate is 0.18V/us,the bias current temperature drift coefficient is 103.2ppm/℃,and the maximum non-oscillatingload capacitance is 10nF.The circuit layout design was completed by Cadence software,and the final area was 5.18mm×3.38mm.The above results show that the circuit design achieves the expected design goals.The low-noise,low-offset high-precision operational amplifier designed in this paper is mainly used in high-precision instrumentation amplification systems,and can also be applied to portable devices with high precision requirements.