An Ultra-Low Power Fully Integrated Energy Harvester Based on Self-Oscillating Switched-Capacitor Voltage Doubler. Jung, W., Oh, S., Bang, S., Lee, Y., Foo, Z., Kim, G., Zhang, Y., Sylvester, D., & Blaauw, D. IEEE Journal of Solid-State Circuits, 49(12):2800–2811, December, 2014.
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This paper presents a fully integrated energy harvester that maintains \textgreater35% end-to-end efficiency when harvesting from a 0.84 mm 2 solar cell in low light condition of 260 lux, converting 7 nW input power from 250 mV to 4 V. Newly proposed self-oscillating switched-capacitor (SC) DC-DC voltage doublers are cascaded to form a complete harvester, with configurable overall conversion ratio from 9× to 23×. In each voltage doubler, the oscillator is completely internalized within the SC network, eliminating clock generation and level shifting power overheads. A single doubler has \textgreater70% measured efficiency across 1 nA to 0.35 mA output current ( \textgreater10 5 range) with low idle power consumption of 170 pW. In the harvester, each doubler has independent frequency modulation to maintain its optimum conversion efficiency, enabling optimization of harvester overall conversion efficiency. A leakage-based delay element provides energy-efficient frequency control over a wide range, enabling low idle power consumption and a wide load range with optimum conversion efficiency. The harvester delivers 5 nW-5 μW output power with \textgreater40% efficiency and has an idle power consumption 3 nW, in test chip fabricated in 0.18 μm CMOS technology.
@article{jung_ultra-low_2014,
	title = {An {Ultra}-{Low} {Power} {Fully} {Integrated} {Energy} {Harvester} {Based} on {Self}-{Oscillating} {Switched}-{Capacitor} {Voltage} {Doubler}},
	volume = {49},
	issn = {0018-9200},
	doi = {10.1109/JSSC.2014.2346788},
	abstract = {This paper presents a fully integrated energy harvester that maintains {\textgreater}35\% end-to-end efficiency when harvesting from a 0.84 mm 2 solar cell in low light condition of 260 lux, converting 7 nW input power from 250 mV to 4 V. Newly proposed self-oscillating switched-capacitor (SC) DC-DC voltage doublers are cascaded to form a complete harvester, with configurable overall conversion ratio from 9× to 23×. In each voltage doubler, the oscillator is completely internalized within the SC network, eliminating clock generation and level shifting power overheads. A single doubler has {\textgreater}70\% measured efficiency across 1 nA to 0.35 mA output current ( {\textgreater}10 5 range) with low idle power consumption of 170 pW. In the harvester, each doubler has independent frequency modulation to maintain its optimum conversion efficiency, enabling optimization of harvester overall conversion efficiency. A leakage-based delay element provides energy-efficient frequency control over a wide range, enabling low idle power consumption and a wide load range with optimum conversion efficiency. The harvester delivers 5 nW-5 μW output power with {\textgreater}40\% efficiency and has an idle power consumption 3 nW, in test chip fabricated in 0.18 μm CMOS technology.},
	number = {12},
	journal = {IEEE Journal of Solid-State Circuits},
	author = {Jung, W. and Oh, S. and Bang, S. and Lee, Y. and Foo, Z. and Kim, G. and Zhang, Y. and Sylvester, D. and Blaauw, D.},
	month = dec,
	year = {2014},
	pages = {2800--2811}
}

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