A 540-mA, 0.0487-ps-FOM Digital LDO based on Bi-directional Binary Search with Dual-loop Control

Abstract

A dual-loop digital low-dropout regulator based on the bi-directional binary search method is implemented in a 0.18-μm CMOS process in this paper. To improve the transient response, a bi-directional successive approximation register without initialization is proposed in coarse loop. To speed up fine adjustment during heavy loads, a two-dimensional MOSFET array is adopted to improve fine regulation step. Simulation results demonstrate that, during load current steps between 540 mA and 40 mA, the undershoot/overshoot is 364 mV/161 mV, and the digital LDO settles within 210 ns. For a supply voltage of 1.4 V with 200 mV dropout, the current efficiency is as high as 99.99% and the figure of merit is as low as 0.0487 ps.