1. A 12-μW to 1.1-mW AIM Piezoelectric Energy Harvester for Time-
Varying Vibrations With 450-nA
Abstract:
Continuing advancements in low power VLSI systems have enabled the
use of self-powered wirelesssensor nodes (WSNs) for many industrial
applications. Toalleviate WSN battery maintenance requirements,
piezoelectric devices are implemented to harvest vibration energy.
However, significant challenges remain unresolved with regard to
harvesting from time-varying vibrations in environments where
harvestable energy is unpredictable. This paper presents a new integrated
piezoelectric energy harvesting system. An adaptive impedance matching
maximum power point tracking technique is proposed to improve
harvesting efficiency. An adaptive on-time dc-dc controller with pulse
skipping modulation is also employed. Toretain reasonable efficiency in
such low power applications, the controller is designed with ultralow
power analog circuits and zero bias current dynamic circuits, with a total
quiescent current of only 450 nA. The design is fabricated and verified on a
0.25-μmCMOS process. It is capable of harvesting time-varying
piezoelectric energy ranging of 12 μW to 1.1 mW. In comparison with
quasi-resistive impedance matching, a harvesting improvement of more

2. than two times is achieved. Thanks to the low power design effort, it
achieves greater than 70% efficiency from 80 μW to 1.1 mW.