and Power Efficiency
to Autonomous Energy-
´ric Christmann, Edith Beigne,
Cyril Condemine, Pascal Vivet, and
Swiss Center for Electronics and Microtechnology
XTENDING BATTERY LIFE
or eliminating the battery
altogether is a key issue in today’s autonomous wireless
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.
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
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.
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
robustness provided by asynchronous data-driven de-
sign techniques is promising.
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 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.