0.5-V Input Digital Low-Dropout Regulator (LDO) with 98.7% Current Efficiency in 65nm CMOS

In this paper, Digital Low Dropout Regulator (LDO) is proposed to provide the low noise and tunable power supply voltage to the 0.5-V near-threshold logic circuits. Because the conventional LDO feedback-controlled by the operational amplifier fail to operate at 0.5V, the digital LDO eliminates all analog circuits and is controlled by digital circuits, which enables the 0.5-V operation. The developed digital LDO in 65nm CMOS achieved the 0.5-V input voltage and 0.45-V output voltage with 98.7% current efficiency and 2.7-µA quiescent current at 200-µA load current. Both the input voltage and the quiescent current are the lowest values in the published LDO's, which indicates the good energy efficiency of the digital LDO at 0.5-V operation.