Digital LDO regulator with analogue-assisted loop using source follower

Abstract

A digital low-dropout regulator (DLDO) with an analogue-assist (AA) loop using a source follower has been proposed to improve the drawbacks of the DLDO. The proposed AA loop, which uses a source follower structure to generate the compensation current without additional passive components, mitigates the voltage droop and accelerates the transient response by complementing a slow digital control loop. Additionally, the boost loop enhances the deceleration of the compensation speed owing to the size of the power transistors. This ultimately results in the improvement of the transient response to the voltage droop side. Also, this can facilitate in reducing the amount of the output capacitance (C-OUT) closely associated with the output voltage droop (Delta V-OUT). The proposed DLDO occupying an area of 0.015 mm(2) is designed in a 28-nm CMOS process. The Delta T-s of 14 ns with C-OUT of 10 pF is achieved under the load step of 1.5-30 mA with edge time of 2 ns. The consumed quiescent current is 35 mu A, and the figure-of-merit of 0.008 ps is achieved.