A single-inductor 0.35µm CMOS energy-investing piezoelectric harvester

Although miniaturized piezoelectric transducers usually derive more power from motion than their electrostatic and electromagnetic counterparts, they still generate little power. The reason for this is that the electromechanical coupling factor is low, which means the damping force that tiny transducers impose on vibrations (when drawing power) is hardly noticeable. The single-inductor 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 power from the transducer, up to 79 μW from a 2.7-cm piezoelectric cantilever that is driven up to 0.25 m/s. Of the 79 μW drawn at 0.25 m/s 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 efficiency peaks at 69% when the harvester outputs 46 μW of the 67 μW it draws from the transducer at 0.25 m/s when investing 0.8 nJ of battery energy.