Low Power Design Thomas Ebi and Prof. Dr. J. Henkel Thomas Ebi and - - PowerPoint PPT Presentation
1 introduction Low Power Design Thomas Ebi and Prof. Dr. J. Henkel Thomas Ebi and Prof. Dr. J. Henkel CES CES - Chair for Embedded Systems Chair for Embedded Systems KIT, Germany KIT, Germany I. Introduction and Energy/Power Sources I.
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Thomas Ebi and Prof. Dr. J. Henkel Thomas Ebi and Prof. Dr. J. Henkel CES CES - Chair for Embedded Systems Chair for Embedded Systems KIT, Germany KIT, Germany
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Reason for Low Power Design: motivation Reason for Low Power Design: motivation Specific need for low power in embedded systems: Specific need for low power in embedded systems: examples examples Battery issues (re Battery issues (re-chargeable batteries) chargeable batteries) Power/energy sources Power/energy sources
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Portable Systems
Notebooks, smartphones, tablets, cameras, etc.
32% of PC market, and growing
Battery-driven - long battery life crucial
System cost, weight limited by batteries
40W, 10 hrs @ 20-35 W- hr/pound = 7-20 pounds
Slow growth in battery technology
Must reduce energy drain from batteries
Thermal Considerations
10 oC increase in operating temperature => component failure rate doubles
Packaging: ceramic vs. plastic
Cooling requirements
Increasing levels of integration / clock frequencies make the problem worse
10cm2, 500 MHz => 315Watts
Reliability Issues
Electro-migration
IR drops on supply lines
Inductive effects
Tied to peak/average power consumption
Environmental Concerns
EPA estimate: 80% of office equipment electricity is used in computers
“Energy Star” program to recognize power efficient PCs
Power management standard for desktops and laptops
Drive towards “Green PC”
LOW POWER (Src: A. Raghunathan, NEC)
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Pentium Crusoe
Pentium 4 Crusoe Processor
(source: www.transmeta.com)
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Large (100X Large (100X – – 1000X) gap in energy efficiency between 1000X) gap in energy efficiency between fully programmable and fully custom implementations fully programmable and fully custom implementations
Ample scope for tradeoffs Ample scope for tradeoffs
Source: Rabaey et. al., IEEE Computer, July 2000
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Technology Operations/Watt [MOPS/mW] 1 0.1 0.01 0.13µ Ambient Intelligence 0.07µ DSP-ASIPs µPs 10 0.25µ 0.5µ 1.0µ poor design generation techniques
(Src:[Marw03])
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t P E
Energy: 1 Ws = 1 VAs = 1 Joule = 1 Nm
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Minimizing the power consumption is important for
the design of the power supply the design of voltage regulators the dimensioning of interconnect short term cooling
Minimizing the energy consumption:
Limited availability of energy (mobile systems, try to maximize the amount of computation that can be accomplished with a given amount of energy) through: limited battery capacities (only slowly improving) very high costs of energy (solar panels, in space) cooling high costs limited space dependability long lifetimes, low temperatures
(Src:[Marw03])
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HW Power Consumption
Behavior level Register-transfer level Logic level Transistor level Power analysis iteration times seconds - minutes minutes - hours hours - days Decreasing design iteration times
High-level synthesis, RTL optimizations Architecture-level power analysis Logic synthesis Logic-level power analysis Transistor-level/ Layout synthesis Transistor-level power analysis Power models for macroblocks, control logic Power models for gates, cells, nets
1 Power Cap Switching _Power Leakage/Static Power + … = ( . _ +
L dd
2 C V A f . . .
2
)
(src: A. Raghunathan, NEC)
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Some examples-
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Source: [Marc03]
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(source: Jan Madsen DTU)
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Manufacturing plants & Power distribution
Health care
rooms
cardiac attacks Energy-efficient buildings
US
Disaster Prevention & Emergency Response
Traffic control
by 15 min => $15B/year in California alone “Smart” environments
(source: A. Raghunathan, NEC)
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Banking & Money transfer Banking & Money transfer smart cards, …
smart cards, …
Consumer Consumer cell phone, MP3 player, PDA, …
cell phone, MP3 player, PDA, …
Clothing Clothing electronic textiles
electronic textiles
Environment Environment sensor networks
sensor networks
Healthcare Healthcare hearings aids, pace maker, …
hearings aids, pace maker, …
Telecom Systems Telecom Systems satellite, …
satellite, … …
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1 10 100 1000 10000 100000 1000000 10000000
Algorithmic Complexity (Shannon’s Law) Processor Performance (Moore’s Law) Battery Capacity 1G 2G 3G
(src: A. Cuomo, ST Micro, Stockholm, Sept.8, 2004)
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Primary batteries Primary batteries
+ availability + availability + no re + no re-charging required charging required + often higher density compared to secondary batteries (later) + often higher density compared to secondary batteries (later) - cannot be re cannot be re-charged (replacement of cartridge etc. instead) charged (replacement of cartridge etc. instead) -
user always needs to carry replacement batteries -
form-factor often unfavorable (not flat as desired) factor often unfavorable (not flat as desired)
Secondary batteries Secondary batteries
Ni Ni-Cd (nickel Cd (nickel-cadmium), NiMH (nickel cadmium), NiMH (nickel-metal metal-hydride, Lithium hydride, Lithium-Ion, Ion, Lithium Lithium-polymer polymer + can be re + can be re-charged charged -
lesser energy density compared to primary (it is constantly increasing but increasing but “plateauing plateauing” i.e. cannot be significantly improved i.e. cannot be significantly improved any more. Lithium any more. Lithium-Ion: has increased around 8 Ion: has increased around 8-10% in the last 10 10% in the last 10 years (every year) years (every year)
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1994 200 wh/kg 1996 1998 2000 2002 2004 2006 150 100 50 Sanyo Toshiba 1994 500 wh/l 1996 1998 2000 2002 2004 2006 300 100 200 400 Sanyo Toshiba
shown Lithium-Ion technology
Gravimetric: Wh/kg Gravimetric: Wh/kg -> Watt * hours / kg > Watt * hours / kg Volumetric: Wh/l Volumetric: Wh/l -> Watt * hours / liter > Watt * hours / liter
(src: [Blo04])
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Average cost of Average cost of Lithium Lithium-Ion Ion technology (currently technology (currently 2005) is ~0.5 2005) is ~0.5 USD/Wh USD/Wh Will decrease further Will decrease further but curve is predicted but curve is predicted to flatten in the near to flatten in the near future future
0,5 1 1,5 $0,55 $0,55 $0,45 $1,27 $ per Wh NiCd average price NiMH average price Li-ion cyl. average price Li-ion prism. average price
1 2 3 4 5 6 7 8 9 10 US $/cell 1999 2000 2002 2001 2003 2004 2005 2006 Li-ion (average) Li-ion Cylindrical Li-ion Prismatic Li-ion Polym r e
(src: [Blo04])
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Improving the gravimetric and/or volumetric by embedding Improving the gravimetric and/or volumetric by embedding part of the battery into the final device and obtain the part of the battery into the final device and obtain the
does not have to be carried by the user does not have to be carried by the user Example: metal Example: metal-air system. Basic idea: positive electrode is air system. Basic idea: positive electrode is the ambient air. the ambient air. Metal Metal-air system: air system: Reaction: Reaction: Negative electrode: Negative electrode:
Zn + 4 OH Zn + 4 OH-
> Zn(OH-)4
2- + 2 e
+ 2 e- E0 = = -1.266V 1.266V
Positive electrode: Positive electrode:
½ O ½ O2
2 + H
+ H2O +2 e O +2 e-
> 2 OH- E0 = 0.401V = 0.401V
Allover reaction: Allover reaction:
Zn + H Zn + H2O + ½ O O + ½ O2
> ZnO E0 = 1.667V = 1.667V
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Oxidation reaction of zinc with oxygen produces very high Oxidation reaction of zinc with oxygen produces very high energy density: 1370 Wh/kg (theoretical) energy density: 1370 Wh/kg (theoretical) Reaction begins by presence of air and continues until zinc Reaction begins by presence of air and continues until zinc has been used up has been used up
-
For continuous use only -
No re-charging (then energy density would drop) charging (then energy density would drop) + low cost + low cost + simple to use + simple to use + environmentally OK (no heavy or noble metals nor hazardous + environmentally OK (no heavy or noble metals nor hazardous compounds involved) compounds involved)
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Technologies: Technologies: Solid oxide fuel cells (SOFC): Solid oxide fuel cells (SOFC):
Needs 800 Needs 800-850 degrees centigrade 850 degrees centigrade
Polymer exchange membrane (PEM) Polymer exchange membrane (PEM)
Reaction positive electrode: Reaction positive electrode: ½ O ½ O2
2 + 2 H
+ 2 H3O+
+ + 2e
+ 2e- -> 3 H > 3 H2O Reaction negative electrode: Reaction negative electrode: H2 + 2 H + 2 H2O O -> 2H > 2H3O+ + 2 e + 2 e- Overall reaction: Overall reaction: H2 + ½ O + ½ O2
> H2O E O E0 = 1.229V = 1.229V
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Functionality: Functionality:
Core parts are two electrodes separated by an ion separated by an ion-conducting conducting polymeric membrane (electrolyte) polymeric membrane (electrolyte)
Fuel (i.e. H2) is transformed on catalytic sites at the negative catalytic sites at the negative electrode and form protons (H+) electrode and form protons (H+) which cross the membrane and which cross the membrane and electrons on the other hand which electrons on the other hand which produce a current outside the cell produce a current outside the cell
electrical energy is obtained when electrons recombine at the positive electrons recombine at the positive electrode with protons (H+) coming electrode with protons (H+) coming from the negative electrode and from the negative electrode and
chemical reaction results in: electricity, water heat electricity, water heat
a whole system is shown on the next page next page
H*
EME
Heat O (air)
2
H O + O
2 2
Cathode Solid Polymer Elektrolyte Anode H
2
H O + H
2 2
Current collector Bipolar plate
Proton exchange membrane fuel cell principle (PEM)
Proton exchange membrane fuel cell principle (PEM) (src: [Blo04])
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Whole system contains besides the core (stack): a) electrical, b) Whole system contains besides the core (stack): a) electrical, b) thermal, c) and fluidic management systems thermal, c) and fluidic management systems
Methanol Methanol Reformer Humidi- fication water PEMFC Stack H Loop
2
Water pump Heat exchanger Water condenser exhaust Cooling Loop
DC DC
Air + H O
2
Regulation Compressor Air H
2
Buffer battery
DC DC
Electric device
(src: [Blo04])
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Estimated to be more energy efficient in converting Estimated to be more energy efficient in converting chemical energy to work (via electrical and afterwards chemical energy to work (via electrical and afterwards mechanical energy conversion) mechanical energy conversion) Environmentally clean (byproduct is water) Environmentally clean (byproduct is water) Efficiency of 50% (globally) is claimed to be achievable Efficiency of 50% (globally) is claimed to be achievable (incl. peripherals like water/heat/fuel management and fuel (incl. peripherals like water/heat/fuel management and fuel storage) storage)
Ex: H Ex: H2
2 heating value: 33.3 Wh/g , 600g H2
heating value: 33.3 Wh/g , 600g H2 600g * 33.3 Wh/g * 50% = 10,000 Wh (e.g. 10kW for 1 hour) 600g * 33.3 Wh/g * 50% = 10,000 Wh (e.g. 10kW for 1 hour)
However: large However: large-power fuel cells are not likely to be mass power fuel cells are not likely to be mass- produced before probably 2020 produced before probably 2020 But: miniature fuel cells are on their way … But: miniature fuel cells are on their way …
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Application domain: portable electronic devices (PDA, cell Application domain: portable electronic devices (PDA, cell ph, cameras, etc.) ph, cameras, etc.) Two approaches: Two approaches:
A) A) “bipolar bipolar” technology technology Built with bipolar plates forming the fuel cell stack Built with bipolar plates forming the fuel cell stack Typically 20 Typically 20-500W 500W Smaller stacks seem not to be competitive with Lithium Smaller stacks seem not to be competitive with Lithium-Ion Ion batteries batteries www.smartfuelcell.de www.smartfuelcell.de and many others and many others B) Various approaches with new concepts e.g. micro fabrication B) Various approaches with new concepts e.g. micro fabrication techniques techniques Typically 0.1 Typically 0.1-25W 25W substrate (thin substrate (thin-film) film)-based based
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Current Collector Positive electrode Elektrolyte Diffusion layer Catalyst layer Hydrogen or methanol Air H O
2
e- e- H+
O 2 H 2
Silicon wafer; grown and treated Silicon wafer; grown and treated with lithographic techniques with lithographic techniques Often less than a centimeter Often less than a centimeter wide wide By various By various companies/institutions like: companies/institutions like: Neah Power; Integrated Fuel Neah Power; Integrated Fuel Cell Technologies, French Cell Technologies, French Atomic Energy Commission, Atomic Energy Commission, Case Western University Case Western University
(src: [Blo04])
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Source: [StaPa04] Source: [StaPa04]
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Improvement multiple since 1990
1990 1992 1994 1996 1998 2000 2002 1 10 100 1000 Year Disk capacity CPU speed Available RAM Wireless transfer speed Battery erargy density
(Note: different physical (Note: different physical units for different units for different components are given) components are given) Battery capacity only Battery capacity only grew by 3x since 1990 grew by 3x since 1990 On contrary: storage On contrary: storage size, as an example, size, as an example, grew by 4000x during grew by 4000x during same time frame same time frame Problem Problem: how can these : how can these largely increased system largely increased system components components appropriately fed with appropriately fed with electrical energy? electrical energy?
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Sleeping Lying quietly Sitting Standing at case Conversation Eating a meal Strolling Driving a car Playing the violin or piano Housekeeping Carpentry Hiking, 4 mph Swimming Mountain climbing Long-distance run Sprinting 70 80 100 110 110 110 140 140 140 150 230 350 500 600 900 1400 81 93 116 128 128 128 163 163 163 175 268 407 582 698 1048 1630 Activity Kilocal/hr Watts Human Energy Expenditures for Selected Activities
Source: Derived from D. Morton. Human Locomotion and Body Form. Williams & Wilkens, Baltimore, MD.1952
A span of ~20x !
not be easily harvested
the power/energy stored, converted (DC/DC, impedance, etc)
harvesting needs to be completely non-obtrusive
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Body Heat 2.4 - 4.8 W (Carnot efficiency) Blood pressure 0.37W (0.93 W) Arm motion 0.33 W (60 W) Footfalls 5.0 - 8.3 W (67 W) Exhalation 0.40 W (1.0 W) Breathing band 0.42 W (0.83 W) Finger motion 0.76 - 2.1 mW (6.9 - 19 mW)
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Body heat: Body heat:
(T_body (T_body-T_ambient)/T_body = 310K T_ambient)/T_body = 310K-293K)/310K = 5.5% 293K)/310K = 5.5% -
> little efficient
From breath From breath
Principle: uses diff. in from breath pressure and atmospheric Principle: uses diff. in from breath pressure and atmospheric pressure pressure -> only 2% > only 2%
From blood pressure From blood pressure Capturing energy from vibrations, motion etc. Capturing energy from vibrations, motion etc.
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Power from typing Power from typing
Ex: 50g key pressure, depress by 0.5cm Ex: 50g key pressure, depress by 0.5cm (0.05kg/key (0.05kg/key-stroke) / (9.8m/s stroke) / (9.8m/s2) * 0.005m * (7.5 key ) * 0.005m * (7.5 key-strokes / sec) = strokes / sec) = = 19 mW = 19 mW -> too less to power a whole portable system; plus, user > too less to power a whole portable system; plus, user is not continuously typing is not continuously typing Idea: keyboard can at least announce its character to the rest of Idea: keyboard can at least announce its character to the rest of the system through own energy the system through own energy
Inertial micro systems Inertial micro systems
Used for hundred of years in watches Used for hundred of years in watches
Electrical version (next slide) Electrical version (next slide)
Functionality: Functionality: the mass winds a spring the mass winds a spring when enough mech. (spring) energy is accumulated, a micro when enough mech. (spring) energy is accumulated, a micro generator is driven at 15,000 rpm (rotations per minute) generator is driven at 15,000 rpm (rotations per minute) yields 6mA and 16V for 50ms yields 6mA and 16V for 50ms
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Walking (68kg human, 3.5mph) costs ~324Watt of power Walking (68kg human, 3.5mph) costs ~324Watt of power
Most of this power is used to move legs Most of this power is used to move legs
Power through the fall of the heel: Power through the fall of the heel:
68kg * (9.8m/sec 68kg * (9.8m/sec2) * 0.05m * (2 steps/sec) = 67W ) * 0.05m * (2 steps/sec) = 67W This power cannot simply converted in electrical power w/o significant This power cannot simply converted in electrical power w/o significant intrusion intrusion Converting to electrical power: e.g. via piezoelectric device (e.g. Quartz) Converting to electrical power: e.g. via piezoelectric device (e.g. Quartz)
M e c h a n i c a l l y s t r e s s e d a x i s d u r i n g f a b r i c a t i
Piezoelectric Material
Electrostatic Poling Direction (across electrodes)
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Energy Source Power/Energy Density Batteries (Zinc-Air, primary) 1050-1560 mWh/cm3 Batteries (Li, rechargeable) 300 mWh/cm3 Solar (outdoors) 15 mW/cm2 (direct sun) 1 mW/cm2 (24 hour avg) Solar (indoors) 0.006 mW/cm2 (office desk) 0.57mW/cm2 (<60W desk lamp) Vibrations 0.01-0.1 mW/cm3 Acoustic (noise) 3 e-6 mW/cm2 @ 75dB 9.6 e-4 mW/cm2 @ 100dB Miniature Fuel cells 0.1-500W Nuclear Reaction 80 mW/cm3, 1 e+6 mWh/cm3
(Src.(modified): A. Raghunathan, NEC)
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[Src: Hande, Dallas]
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[Piguet04] Ch. Piguet (Ed.), “Low Power Electronics Design”, CRC Press, ISBN 0-8493-1941-2, 2004. {Marc03], Marculescu, D.; Marculescu, R.; Park, S.; Jayaraman, S.; “Ready to ware”, Spectrum, IEEE ,Volume: 40 , Issue: 10 , Oct. 2003, Pages:28 – 32. [StaPa04] Th. Starner, J. Paradiso, “Human-generated power for mobile electronics”, appeared in “Low Power Electronics Design”, CRC Press, 2004. [Blo04] D. Bloch, “Miniature fuel cells for portable applications”, appeared in “Low Power Electronics Design”, CRC Press, 2004. [Marw03] P. Marwedel, “Embedded System Design”, Kluwer, 2003. [Raghunathan] A. Raghunathan, Tutorial on low power design, held at various CAD conferences