14.6 A 745pA Hybrid Asynchronous Binary-Searching and Synchronous Linear-Searching Digital LDO with 3.8×10 5 Dynamic Load Range, 99.99% Current Efficiency, and 2mV Output Voltage Ripple

Voltage regulators for emerging nW-to-$\mu \mathrm {W}$ Internet-of-Things (IoT) systems-on-chip (SoCs) require ultra-low quiescent power to enhance lifetime, a large dynamic load range to support multiple components and applications, and fast transient performance to support duty-cycled loads. Switching regulators [1], [2] can achieve sub-nW operation, but suffer from slow settling time and large output voltage ripple that deteriorate analog and RF performance. Digital low-dropout regulators (DLDOs) offer faster transient response, low-voltage operation, and flexible control schemes [3]–[6]. However, conventional synchronous DLDOs that use a high frequency clock for fast response consume too much power [3], and asynchronous DLDOs can achieve lower current consumption and fast response, but suffer from larger steady-state error [4]. Also, previous DLDOs do not target load current in the $\lt 10 \mu \mathrm {A}$ range. To achieve ultra-low-current consumption, a wide dynamic load range down to nA loads, and good transient and steady-state performance, we propose a hybrid asynchronous binary-searching (ABS) and synchronous linear-searching (SLS) DLDO that achieves $3.8 \times 10 ^{5}$ dynamic load range, 99.99% current efficiency, and 2mV output voltage ripple, while consuming 745pA quiescent current.