A fully on-chip 1-μW capacitor-free low-dropout regulator with adaptive output stage

Abstract

A fully on-chip 1-μW fast-transient response capacitor-free low-dropout regulator (LDO) using adaptive output stage (AOS) is presented in this paper in standard 0.13-μm CMOS process. The AOS circuit is proposed to deliver extra four times of output current of the operational amplifier at medium to heavy load to extend the bandwidth of the LDO and enhance the slew rate at the gate of the power transistor. And the AOS circuit is shut off at light load to reduce the quiescent current and maintain the stability without requiring area-consuming on-chip capacitor. Meanwhile, the proposed AOS circuit introduces VOUT offset at medium to heavy load to counteract the VOUT drop, which is caused by ILOAD increase. Hence, transient performances of LDO and VOUT drop between light load and full load are improved significantly with 1.1-μA quiescent current at light load. From the post simulation results, the LDO regulates the output voltage at 0.7 V from a 0.9-V supply voltage with a 100-mA maximum load current. The undershoot, the overshoot and the recovery time of the proposed LDO with ILOAD switching from 50 μA to 100 mA in 1 μs are about 130 mV, 130 mV and 1.5 μs, respectively. And the VOUT drop between light load and full load reduces to 0.16 mV.