A high current efficiency rail-to-rail buffer for low drop-out regulators with load regulation-enhanced

A 1.8-V 250-mA CMOS low-dropout regulator (LDO) with a current-efficiency rail-to-rail buffer to enhance load regulation is presented. The proposed buffer provides a push-pull output stage for driving pass device and pushes the parasitic pole far beyond the unity-gain frequency to improve phase margin of the LDO loop response. The proposed LDO has been implemented in a 0.35-μm CMOS process technology and occupies area of 0.735-mm2. The measurement results show that the LDO with the proposed buffer dissipates 40-μA quiescent current and a maximum drop-out voltage of 200-mV at 250-mA output load. The output voltage drop with a 1-μF off chip capacitor for a 250-mA load step is less than 25-mV. The proposed LDO is able to provide excellent agreement between theoretical and measurement results.