A Research On A CMOS Operational Amplifier Based On Digital Trimming Technology

Since the first integrated circuit was invented in 1985,integrated circuit technology has begun to develop at an alarming rate.As a member of the integrated circuit,because of the engineers' pursuit of operational amplifiers with different functions and the limitation of the octagon rule,operational amplifiers can be divided into general-purpose operational amplifiers and functional operational amplifiers.First,this article introduces the basic concept and design flow of the op amp,and analyzes the definition of some common performance indicators in the circuit,such as common mode input range,input offset voltage,open loop gain,input impedance,etc.Subsequently,the offset classification and the principle of the offset of the operational amplifier are introduced,and some trimming techniques for op amps commonly used in engineering are given.Then introduced a kind of low offset operational amplifier based on digital trimming technology,which is mainly used in instrumentation and some systems with high requirements on processing accuracy.The amplifier in this paper uses a two-stage structure.The input stage of the op amp uses the cross-conduction method to achieve the constant trans-conductance input from rail to rail.A folding cascode structure is connected to ensure the high gain of the op amp.The output stage is a feedforward type AB output stage.Compared with the ordinary AB output stage,it can not only provide a rail-to-rail output,but also perform well in high frequency bands.The bias circuit uses a zero temperature drift voltage reference source to ensure the stability of the bias current.In the digital trimming module,we reduce the offset voltage of the op amp by tracking the current of the N differential pair and then using the trimming signal generation circuit and the fuse array circuit.This design uses Hua Hong's 0.35?m CMOS process,and uses Cadence's spectre simulation software to design and simulate the op amp.This design circuit has completed the tape-out and test verification.The test results show that the common-mode rejection ratio of the amplifier is 117.04 dB,the unity-gain bandwidth is 8.78 MHz,the bias current is 0.46 pA,the offset voltage is 81.13?V,and the slew rate is 3.93 V / ?s.All the indicators meet the expected requirements.