A Low-Voltage、Rail-to-Rail And Constant Trans-conductance CMOS Operational Amplifier

The principle figures of input stage middle gain stage and output stage for a usual two stage low-voltage CMOS operational amplifier and their principal performance are presented in the paper.In the input stage the parallel supplementary differential input pair structure is applied by using NMOS tube and PMOS tube in oreder to enable the input common mode votage range to achieve rail-to-rail. To realize the contant transconductance of input stage, the proportional current mirror technlogy is used.In the middle gain stage ,the current mirror load of low voltage wide-swing cascade structure is adopted suitable to work in low voltage and increases output resistance, i.e. gain, and realizes rail-to-rail.In the output stage , in- order to enhance the efficiency and reaching rail-to-raip, the push-pull common soure pole amplifier is used. To design a norm current source, the differential amplifier with current mirror load is applied, which provides the stable bias current and bias voltage to the operational amplifier in order to guarant its stability and accuracy. For preventing OP-AMP oscillating, the Miller compensation technology with adjusting zero resistance is adopted. The simulation by using Hspice software the performance of the operational amplifier well meets the design requirement .