DT-2011-Christmann - Asynchronous Design Bringing...

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Bringing Robustness and Power Efficiency to Autonomous Energy- Harvesting Microsystems Jean-Fre ´de ´ric Christmann, Edith Beigne, Cyril Condemine, Pascal Vivet, and Je ´ro ˆme Willemin CEA-Leti, MINATEC Nicolas Leblond Tiempo SAS Christian Piguet Swiss Center for Electronics and Microtechnology ĸ E XTENDING BATTERY LIFE or eliminating the battery altogether is a key issue in today’s autonomous wireless microsystems. 1 A proposed solution is to harvest en- ergy from the environment and thereby maximize the lifespan of autonomous communicating sensors to avoid any human maintenance. By extracting their en- ergy from the environment, autonomous devices can be self-powered over their full lifetimes, an essential property for applications such as ambient intelligence, active security, and monitoring. 2 In such devices and applications, energy availability and power dissipation are not constant over time, so energy management is crucial in determining the potential for information processing. A limited amount of extractable energy is indeed fixed by solar radiation, thermal gradients, or even device movements. Moreover, the harvester tech- nologies, such as photovoltaic, Seebeck-effect ± based thermo generators (or even piezoelectrical generators) provide low efficiencies and remain under development. For those reasons, the average harvested energy of these devices is extremely low. 3,4 Asynchronous circuits are well- suited for the implementation of energy-harvesting microsystems for sev- eral reasons. For implementing digital logic, the intrinsic standby-state and process-voltage-temperature (PVT) robustness provided by asynchronous data-driven de- sign techniques is promising. 5 Asynchronous circuits can be easily supplied at very low voltage levels, and their smooth current profile due to automatic speed regulation perfectly meets energy harvester and bat- tery requirements. Detecting and processing events is the fundamental behavior of asynchronous cir- cuits, and energy monitoring is among the main functions in applications based on energy harvesting. An energy-harvesting microsystem must indeed be aware of both available energy and system activity. By detecting environmental energy changes, the microsystem can configure the optimal power path within the architecture to reach the best trade-off be- tween power and efficiency. (The sidebar ‘‘Related Work’’ presents other approaches.) In this article, we propose an autonomous, recon- figurable, robust energy-harvesting microsystem. Asynchronous Design Editors’ note: Asynchronous circuits are well-suited to ultra-low-power design. This article presents a microsystem that is powered only by energy extracted from the en- vironment to implement an autonomous sensing application. Key to this appli- cation is the use of asynchronous logic, which not only provides greater energy efficiency due to its event-driven nature but, more importantly, allows graceful adaptation to highly variable power availability.
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This note was uploaded on 11/28/2011 for the course COMP 790 taught by Professor Staff during the Fall '08 term at UNC.

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DT-2011-Christmann - Asynchronous Design Bringing...

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