Paper Accepted in IEEE TCAS Special Issue on IoT

Research work from the “Energy Harvesting and Integrated Power Conversion for Micro-Scale Sensor Nodes” project was recently accepted for publication in IEEE Transactions on Circuits and Systems I, in a special issue on the Internet of Things (IoT) “From Sensing to Sensemaking”. The highly impactful special issue has topics spanning from sensing, processing, security and sensemaking with an emphasis on both “vertical” and “transversal” design methodologies and approaches that cross traditional design boundaries.

Energy harvesting IoT systems aim for energy neutrality, i.e., harvesting at least as much energy as is needed. This, however, is complicated by variations in environmental energy and application demands. Conventional systems use separate power converters to interface between the harvester and the storage, and then to the CPU system. Reciprocal power conversion has recently been proposed to perform both roles, eliminating redundancy and minimising losses. This paper proposed to enhance this topology with “selective direct operation,” which completely bypasses the converter when appropriate.

The integrated system, with 82% bidirectional conversion efficiency, was validated in the Pipistrelle-3 test chip in 65-nm CMOS with only the harvester, battery, and decoupling capacitors being off-chip. Optimized for operation with a cm² photovoltaic cell and a 32-bit sub-threshold processor, the scheme enables up to 16% otherwise wasted energy to be utilized to provide >30% additional compute cycles under realistic indoor lighting conditions. Measured results show 84% peak conversion efficiency and energy neutral execution of benchmark sensor software (ULPBench) with cold-start capability.

The full paper can be downloaded via the university’s institutional repository.