基于单一PMOS差分对的轨到轨输入运算放大器设计

Design of a rail-to-rail input operational amplifier based on a single PMOS differential pair

基于国内某CMOS工艺设计了一种单一PMOS差分对的轨到轨输入、恒跨导CMOS运算放大器。输入级电路采用折叠共源共栅结构,通过体效应动态调节输入管的阈值电压扩展共模输入范围到正负电源轨,恒定共模输入范围内的跨导,自级联电流镜有源负载将差分输入转换为单端输出;输出级电路采用AB类结构实现轨到轨输出,线性跨导环确定输出管的静态偏置电流。在5 V电源电压,2.5 V共模电压,1 MΩ负载条件下,经Spectre仿真验证,该运算放大器开环增益为119 dB,相位裕度为58°,共模输入范围为0.0027~4.995 V,共模范围内跨导变化小于3%,实现了轨到轨输入共模范围内的跨导恒定。

A rail-to-rail input and constant transconductance CMOS operational amplifier was designed with a single PMOS differential pair based on a domestic CMOS process.The input stage circuit adopted folded cascode structure to dynamically adjust the threshold voltage of the input transistors by body effect,which could extend the common-mode input range from positive to negative supply rails.This structure made transconductance stable within common-mode input range.The selfcascaded current mirror,as active-load of input stage,converted differential input signal to an output signal that was referenced to ground.The output stage circuit adopted class AB structure to achieve the rail-to-rail output.Meanwhile,the translinear loop in output stage determines the quiescent bias current of output transistor.The Spectre simulation results show that the open-loop gain is 119 dB,the phase margin is 58°,the common-mode input range is 0.0027-4.995 V and the transconductance variation among common-mode range is less than 3%at the control of 5 V supply voltage,2.5 V commonmode voltage and 1 MΩload.The op-amp achieves constant transconductance within rail-to-rail common-mode input range.