Integrated Reciprocal Conversion With Selective Direct Operation for Energy Harvesting Systems

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 s...

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Bibliographic Details
Published in:IEEE transactions on circuits and systems. I, Regular papers Regular papers, 2017-09, Vol.64 (9), p.2370-2379
Main Authors: Savanth, Anand, Weddell, Alex S., Myers, James, Flynn, David, Al-Hashimi, Bashir M.
Format: Article
Language:English
Subjects:
Batteries
Bypasses
Central Processing Unit
Clocks
CMOS
Cold starts
cold-start
Decoupling
Energy consumption
Energy conversion efficiency
Energy harvesting
Energy measurement
Impedance
Microprocessors
MPPT
Power conversion
Power converters
Redundancy
Sensor systems
sub-threshold
switched capacitor converters
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Summary: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 minimizing losses. This paper proposes 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 65-nm CMOS with only the harvester, battery, and decoupling capacitors being off-chip. Optimized for operation with cm 2 photo-voltaic cell and a 32-b 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.
ISSN:1549-8328
1558-0806
DOI:10.1109/TCSI.2017.2707304