Research And Design Of Rail-to-Rail Output Operational Amplifier Based On Auto-Zero Technology

As the cornerstone of analog circuits Op amps is very meaningful.They can perform kinds of different functions,such as I-V conversion,meter measurements.However,op amp products cannot achieve the same zero input offset voltage and zero output impedance compared to an ideal op amp.Moreover,some parameter indicators have been proved to be conflicting,which requires the designer to compromise on this.The input offset voltage especially in high-precision applications and will cause serious errors or even make system unusable.In addition,in some areas,the output voltage of the operational amplifier is required to be close to the rail-to-rail output voltage range.Therefore,this article designs a rail-to-rail output operational amplifier with very low offset voltage.This paper first introduces the background and basic knowledge framework of op amps,then focuses on the low offset voltage strategy and rail-to-rail outputs of today's op amps.This paper uses autozeroing technique to eliminate low-pass filters and construct op amps with extremely low offset voltages and rail-to-rail outputs.The complete op amp consists of a main op amp,two offset compensation modules,a reference current source,an oscillator and a logic shutdown switch.The chopper input stage consists of two choppers and a folded cascode structure.The output stage uses class AB to get rail-to-rail output.Trans linear loop technology is used to have a specific quiescent current.In addition,to achieve input offset voltages of 10 microvolts or less than 3 microvolts,additional offsets introduced by the intermediate gain steps and offset compensation modules are taken into account and additional Auto-zeroing techniques are used to eliminate the offset voltage contributions of these modules do it.The reference current source is obtained by superimposing a current that has a negative correlation with temperature over a current that has a positive correlation with temperature.Since both the auto-zeroing technology and the chopper need a square wave signal to control the switching MOS tube,an oscillator is needed.This paper builds a circuit using the0.35 BCD process,builds the circuit using Cadence's Virtuoso,and simulates the circuit using Specter.The designed op amp offset is as low as 1.3 ?V,the low frequency gain exceeds 150 d B,and the phase margin is 61°.The GBW can reach 1.1 MHz.