Research And Design Of High Gain Low Offset Rail-to-Rail Operational Amplifier

As the basic building block of analog circuits and digital-analog mixed circuits,operational amplifiers are widely used in various electronic devices,and have a positive technical support for other ciricuit systems.With the rapid development of the integrated circuit industry,The size of semiconductor manufacturing process continues to shrink,and the supply voltage of electronic products continues to decrease.The trend of the industry places higher requirements on the performance of operational amplifiers.Rail-to-rail operational amplifiers can provide a wide range of input and output voltage,effectively improving the power supply voltage utilization.High-gain low-offset characteristic meet the application requirements of high-precision equipment such as precision mechanism and medical devices,Therefore,researching and designing a high gain low offset rail-to-rail operational amplifier has important theoretical significance and application value.Based on the research of the input and output range of the operational amplifier,the complementary differential pair with alternating conduction is selected as input stage,and the Class AB amplifier is selected as the output stage to realize the rail-to-rail input and output.By studying the realization method of high gain characteristics of operational amplifier,a dual-channel structure in which a three-stage high-gain channel and a two-stage high-speed channel are connected in parallel is adopted,so that the operational amplifier can simultaneous achieve high gain and wide bandwidth in the entire operating frequency range.On the basis of researching the circuit structure of classic intermediate summing stage,a folded cascode summing circuit scheme with an embedded level shift circuit is designed to generate the dual driving voltage of output stage while realizing the current summing function.In order to ensure the reliability of the signal transmission and the safety of the electronic load,the DC negative feedback loop is appointed and the overcurrent protection circuit of output stage is designed to accurately control the output stage quiescent current while stabilizing the output stage driving voltage.By analysing the properties of the offset voltage,deriving the expression of the total offset voltage.and the suppression method is studied from the two aspects includes layout design and circuit design.Finally,adopting the digital fuse trimming scheme to complete the suppression of the offset voltage.Based on the 0.18μm BCD simulation file of Dongbu Hitek,and the design and functional verification of the whole circuit are completed on the Cadence Spectre software platform.The simulation results show that the input and output voltage range of the operational amplifier can basically achieve rail-to-rail,the low-frequency gain of small signals can reach 137.5dB,the bandwidth is about 6MHz,the power supply rejection ratio can reach 137dB,the common mode rejection ratio can reach 128.1dB,and the slew rate is greater than 4.5V/μs,the input offset voltage after trimming is lower than 30μV,and all the indicators meet the expected design goals.Based on Virtuoso software to complete the circuit layout drawing and overall layout and routing,after continuous optimization and finally passed LVS and DRC verification.