A Single-Inductor 0.35 µm CMOS Energy-Investing

Abstract

Although miniaturized piezoelectric transducers usu- ally derive more power from motion than their electrostatic and electromagnetic counterparts, they still gener ate little power. The reason for this is that the electromechanical coupling factor is low, which means the damping force that tiny transducers impose on vi- brations (when drawing power) is hardly n oticeable. The single-in- ductor 0.35 µm CMOS piezoelectric harvester proposed in this paper counters this deficiency by investing energy from the battery into the transducer. The idea is to strengthen the electrostatic force against which vibrations work. This way, the circuit draws more p o w e rf r o mt h et r a n s d u c e r ,u pt o7 9µ Wf r o ma2 . 7c mp i e z o e l e c - tric cantilever that is driven up to 0 .25 m/s 2. Of the 79 µW drawn at 0.25 m/s 2 when investing 91 nJ of battery energy, the system outputs 52 µW, which is 3.6 times more output power than the 14.5 µW that a full-wave bridge rectifier with zero-volt diodes at its maximum power point can deliver from the same source. With 630 nW lost to the controller, power-conversion ef ficiency peaks at 69% when the harvester outputs 46 µW of the 67 µW it draws from the transducer at 0.25 m/s 2 when investing 0.8 nJ of battery energy.