Integrated Power Management for Battery-Indifferent Systems With Ultra-Wide Adaptation Down to nW

This article presents a power management unit (PMU) enabling ultra-wide power-performance tradeoff well beyond voltage scaling, and adaptation to the sensed power/energy availability in the harvester and battery. Gap-less power scaling by more than five orders of magnitude and down to nW permits continuous microcontroller unit (MCU) operation regardless of the battery energy availability, thanks to a sub-mm(2) on-chip harvester. Such battery-indifferent operation allows to considerably shrink the battery down, as battery discharge no longer has disruptive impact on operation. Battery-indifferent operation is enabled by introducing a purely harvested power mode in the PMU, and widely power-scalable circuits in critical blocks to maintain the power efficiency nearly constant down to nW level. To avoid pessimistic power/timing overdesign, a novel self-biasing comparator and a zero current switching scheme with fast convergence and circuit sharing across power modes are proposed. A 180-nm testchip shows MSP430-like MCU power scaling from sub-mW down to 1.85 nW, with at least 27 $\times $ power dynamic range extension compared to prior art. Self-start-up from 2-nW harvested power is demonstrated, corresponding to a 0.8-mm(2) on-chip solar cell with 100-lx illuminance (i.e., equivalent to a very dark overcast day).