All-Digital Low-Dropout Regulator With Adaptive Control and Reduced Dynamic Stability for Digital Load Circuits

Digitally implementable LDOs embedded within digital functional units augment their analog counterparts for ultrafine-grained power management in digital ICs. Digital load circuits represent load currents with large and in frequent current transients and require a wide voltage range of operation, preferably down to the threshold voltage (V
_TH
) of the transistor. This paper presents a discrete-time, fully digital, scan-programmable LDO macro in a low-power 0.13-μm technology operating down to 1.07×, the transistor V
_TH
, and featuring greater than 90% current efficiency across a 50× current range through fine-grained clock gating and adaptive control. An 8× improvement in transient response time to large load steps is achieved through switched mode control. Both transient and steady-state operation models and measurements of the LDO are presented.