Piezoelectric CMOS Charger: Highest Output-Power Design

Wireless microsensors and internet of things that add intelligence to the surroundings need ambient energy to extend life and expand functionality. Piezoelectric transducer can turn vibrations into electrical charge, and with the recycling bridge power stage, it can keep the highest voltage across the transducer and output the most power into the battery. This paper examines how to design the optimum recycling bridge power stage. Specifically, this paper theorizes the optimum size of the switches, the optimum inductor, and how to operate the circuit so that it losses the least power. The ohmic loss should equal charge loss to yield the lowest total loss on a MOSFET switch. The loss on the switches and the inductor are co-optimized. The switched inductor charger is optimized for discontinuous conduction mode. The resulting optimized power stage is 92% efficient.