Low Power Design
Due to power scarcity, necessary to preferred Low Power Design techniques. Energy conservation refers
to reducing energy through using less of an energy service. Energy conservation
differs from efficient
energy use, which refers to using less energy for a
constant service. For example, driving less is an example of energy
conservation. Driving the same amount with a higher mileage vehicle is an
example of energy efficiency. Energy conservation and efficiency are both
energy reduction techniques.
Low Power electronics are electronics that have been designed to
use less electric power, e.g. notebook processors.
Some features of
low power design are: portability, isolation, battery power, and low heat
dissipation. Power is a function of frequency, load capacitance, and voltage:
reduction in any of these will reduce the consumption of power by our system.(
this really applies only to complementary metal oxide semiconductor [CMOS]
components, the most prevalent in law power device, not to certain other logic
families such as emitter –coupled logic[ ECL].
P= f C V2
Where P = power
f = frequency
C = load
capacitance
V = DC supply
voltage
Thanks to integrated circuit
technology, electronic devices have greatly decreased in size and mass over the
past few decades. Most of us routinely carry or wear electronics every day. The
formula above is most convenient for low power design. While VLSI (Very Large
Scale Integration) technology, particularly CMOS, has enjoyed the rapid
exponential growth characterized by Moore’s
Law, energy storage Technology
(mainly batteries) has grown much more slowly.
Application
Areas for Low-Power Electronics
Portable computing,
communication, and multimedia devices
-
Laptops
-
Palmtops
-
Cell
phones
-
Pagers
-
Video
Recorders
-
Cameras
-
Watches
(Power < 500nW @ 1.5V)
Remote sensing
-
Long-term
environmental monitoring in wilderness areas or the ocean
-
Mobile
robots
-
Satellites
and space probes
Implantable biomedical
devices
-
Pacemakers
-
Defibrillators
-
Muscle
stimulators
-
Neuro
prosthetic devices
Low power systems are usually
smaller and cheaper to manufacture (smaller heat sinks, no cooling fans,
smaller power supplies, smaller batteries).
Power Sources for Low-Power Devices
Batteries
– Most Common Power Source for Portable
Electronics. Batteries convert chemical energy into electrical energy by means
of a reduction-oxidation (redox) reaction.
Example:
Alkaline cell operation.
anode reaction (oxidation): Zn + 2OH– ______ Zn(OH)2 + 2e–
cathode reaction (reduction): 2MnO2
+ H2O + 2e– ________ Mn2O3 + 2
OH–
electrolyte: KOH
(K+, OH– in solution)
overall
reaction: Zn + 2MnO2 + H2O _________Zn(OH)2 + Mn2O3
Electron
flow (i.e., current) external to the battery balances internal ionic flow.
Battery Types Grouped by Application
General
consumer electronics ( portable audio equipment, toys, etc.)
-
Alkaline
(Duracell, Energizer, etc.) – Standard AAA, AA, C, D, 9V cells
-
Zinc-Carbon
(old technology, but cheap) – Standard AAA, AA, C, D, 9V cells
Film
cameras and flash units
-
Alkaline
-
Lithium
Wristwatches
-
Silver – “Button” batteries
Hearing
aids
-
Zinc-Air – “Button” or “coin” batteries
Smoke
detectors
-
Mercury
-
Lithium
CMOS
memory backup
-
Lithium
Medical
implants (pacemakers, etc.)
-
Mercury – Used in implants before 1972
-
Zinc-Air – Used in many modern implants
-
Lithium-SVO (silver vanadium oxide) –
Used in implantable defibrillators, where they can supply microamps for years
and occasional amp-level pulses.
General guidelines for Low Power Design
-
Lower clock frequency
-
Lower supply voltage to digital logic
-
Shut down unused circuits
-
Put controller into sleep mode when not
needed
-
Terminates all unused inputs. Don’t
allow any to float.
-
Avoid slow signal transition
-
Make normal states use the lowest
current etc.
References:
-
K. R. Fowler, “Electronic Instrument
Design: Architecting for the life cycle” Oxford university Press.
-
D. V. Hall “ Microprocessor &
interfacing, Programming and Hardware” , Tata McGraw Hill
-
Dr. Harrision “Low Power Circuit
Design” 2012.
-
Many other “Research Articles on
Internet”.
