基于高摆率误差放大器的无片外电容LDO设计

Design of a capacitor-free LDO based on high slew-rate error amplifier

为了解决无片外电容低压差线性稳压器(LDO)的瞬态响应性能较差的问题,采用跨导提高技术设计了一种高摆率的误差放大器。在误差放大器的基础上,通过电容将LDO的输出端耦合至电流镜构建瞬态增强电路,提升LDO的瞬态响应能力,且瞬态增强电路可以引入两个左半平面零点,改善环路的稳定性。同时,误差放大器采用动态偏置结构,进一步减小下冲和过冲电压,缩短稳定时间。电路基于TSMC 0.18μm CMOS工艺设计。仿真结果表明,在片上负载电容为50 pF,压差为200 mV的条件下,LDO环路在100μA~100 mA的负载电流下保持稳定。负载电流在0.5μs内在100μA和100 mA之间跳变时,输出最大下冲和过冲电压均小于100 mV,稳定时间小于1μs。

To address the poor transient response of a capacitor-free LDO,a high slew-rate error amplifier was designed utilizing transconductance boosting technique.Based on the error amplifier,a transient enhancement circuit was constructed to improve the transient response of the LDO by coupling the output to the current mirrors through capacitors,and the transient enhancement circuit could introduce two left half-plane zeros to improve the stability of the loop.Meanwhile,a dynamic bias structure was adopted by the error amplifier to further reduce the undershoot and overshoot voltages and shorten the settling time.The circuit was designed using the TSMC 0.18μm CMOS technology.The simulation results show that by using a 50 pF on-chip load capacitor the LDO loop can achieve stability at 200 mV dropout voltage with load current from 100μA to 100 mA.When the load current jumps between 100μA and 100 mA within 0.5μs,the maximum undershoot and overshoot voltages of the output are both less than 100 mV with settling time of less than 1μs.