2 The Tongue-in-Cheek Answer Why Worry about Power?The Tongue-in-Cheek AnswerTotal Energy of Milky Way Galaxy: 1059 JMinimum switching energy for digital gate (1 mV): J (limited by thermal noise)Upper bound on number of digital operations:Operations/year performed by 1 billion 100 MOPS computers:Energy consumed in 180 years, assuming a doubling of computational requirements every year (Moore’s Law).
3 Power the Dominant Design Constraint (1) Cost of large data centers solely determined by power bill …Google Data Center, The Dalles, OregonColumbia RiverNY Times, June 06450,000400 Millions of Personal Computers worldwide (Year 2000)- Assumed to consume 0.16 Tera (1012) kWh per yearEquivalent to 26 nuclear power plantsOver 1 Giga kWh per year just for coolingIncluding manufacturing electricity[Ref: Bar-Cohen et al., 2000]8,000100,000
4 Power the Dominant Design Constraint [Ref: R. Schmidt, ACEED’03]
5 Chip Architecture and Power Density Integration of diverse functionality on SoC causes major variations in activity (and hence power density)Today: steep gradientsThe past: temperature uniformityTemperature variations cause performance degradation – higher temperature means slower clock speed[Ref: R. Yung, ESSCIRC’02]
6 Temperature Gradients (and Performance) Copper hat (heat sink on top not shown)SiC spreader (chip underneath spreader)Glass ceramic substrateIBM Power PC 4 temperature mapHot spot:138 W/cm2(3.6 x chip avg flux)[Ref: R. Schmidt, ACEED’03]
9 Battery Storage a Limiting Factor Basic technology has evolved littlestore energy using a chemical reactionBattery capacity increases between 3% and 7 % per year (doubled during the 90’s, relatively flat before that)Energy density/size, safe handling are limiting factorFor extensive information on energy density of various materials, check
10 Battery EvolutionAccelerated since the 1990’s, but slower than IC power growth.
11 Battery Technology Saturating Battery capacity naturally plateaus as systems develop[Courtesy: M. Doyle, Dupont]
12 Need Higher Energy Density Fuel cells may increase stored energy more than a order of magnitudeExample: Methanol = 5 kWh/kgAnodeElectrolyteCathode+ ionsLoade -+-Fuel2H2 4H+ + 4e-OxidantO2 + 4H+ + 4e- 2H2OHOWe saw that the power consumption is gradually increasing. But is there any progress in energy sources? One such effort is found in the development of Direct Methanol Fuel Cell which increases the duration of a battery by an order of magnitude compared with currently widely used Lithium Ion Batteries, giving us a gleam of hope for long-operatable portable systems.[Ref: R. Nowak, SECA’01]
13 Fuel Cells Methanol fuel-cells for portable pc’s and mp3 players Portable mp3 fuel cell (300 mW from 10 ml reservoir)Fuel cell for pc (12 W avg – 24% effiency)[Ref: Toshiba, ]
14 Micro-batteries When Size is an Issue Using micro-electronics or thin-film manufacturing techniques to create integrate miniature (back-up) batteries on chip or on boardBattery printed on wireless sensor nodeStencil press for printing patterns[Courtesy: P. Wright, D. Steingart, UCB]
15 How much Energy Storage in 1 cm3? J/cm3mW/cm3/yearMicro Fuel cell3500110Primary battery288090Secondary battery108034Ultracapacitor1003.2ultracapacitorMicro fuel cellultracapacitor
16 Power The Dominant Design Constraint (3) Exciting emerging applications require “zero-power”Example: Computation/Communication Nodes for Wireless Sensor NetworksMeso-scale low-cost wireless transceivers forubiquitous wireless data acquisition thatare fully integratedSize smaller than 1 cm3are dirt cheapAt or below 1$minimize power/energy dissipationLimiting power dissipation to 100 mW enables energy scavengingand form self-configuring, robust, ad-hoc networks containing 100’s to 1000’s of nodes[Ref: J. Rabaey, ISSCC’01]
17 How to Make Electronics Truly Disappear? From 10’s of cm3 and 10’s to 100’s of mWTo 10’s of mm3 and 10’s of mW
18 Power the Dominant Design Constraint Exciting emerging applications require “zero-power”Real-time Health MonitoringSmart SurfacesArtificial SkinPhilips Sand moduleUCB mm3 radioUCB PicoCubeStill at least one order of magnitude away
19 How much Energy Can One Scavenge in 1 cm3? ThermalVibrationsmW/cm3Solar (outside)15,000Air flow380Human power330Vibration200Temperature40Pressure Var.17Solar (inside)10Air FlowSolar
20 A Side Note: What can one do with 1 cm3 A Side Note: What can one do with 1 cm3? Reference case: the human brainPavg(brain) = 20 W (20% of the total dissipation, 2% of the weight), Power density: ~15 mW/cm3Nerve cells only 4% of brain volumeAverage neuron density: 70 million/cm3
21 Power versus Energy Power in high performance systems Heat removalPeak power - power deliveryEnergy in portable systemsBattery lifeEnergy/power in “zero-power systems”Energy-scavenging and storage capabilitesDynamic (energy) vs. static (power) consumptionDetermined by operation modes
28 Power Density Increases Unsustainable in the long term10000Sun’s SurfaceRocket Nozzle1000Nuclear ReactorPower Density (W/cm2)100Upper Bound?808610Hot PlateP68008Pentium® proc808538640042864868080119701980199020002010Year[Courtesy: S. Borkar, Intel]
29 Projecting Into the Future FD-SOIDual GateCompute density: k3Leakage power density: k2.7Active power density: k1.9Power density (active and static) accelerating anew.Technology innovations help, but impact limited.2005 ITRS – Low operating power scenario2003 ITRS – Low operating power scenario
30 Complicating the Issue: The Diversity of SoCs Let’s take another look at the system level. These four pi charts show power distributions in different chips. As you can see, power distribution is very diverse. Before starting the power-aware design, we have to check what portion of the target system consumes power. Some chips consume lots of power at I/O’s as is the case in the lower right chart.Power budgets of leading general purpose (MPU) and special purpose (ASSP) processors[Ref: many combined sources]
31 Supply and Threshold Voltage Trends Slide 1.3010.90.80.7VDD/VTH = 2!VDD0.60.50.40.3VT0.20.12004200620082010201220142016201820202022Voltage reduction projected to saturateOptimistic scenario – some claims exist that VDD may get stuck around 1V[Ref: ITRS 05, Low power scenario]
32 A 20 nm Scenario Assume VDD = 1.2V FO4 delay < 5 ps Assuming no architectural changes, digital circuits could be run at 30 GHzLeading to power density of 20 kW/cm2 (??)Reduce VDD to 0.6VFO4 delay ≈ 10 psThe clock frequency is lowered to 10 GHzPower density reduces to 5 kW/cm2 (still way too high)[Ref: S. Borkar, Intel]
33 A 20 nm Scenario (cntd)Assume optimistically that we can design FETs (Dual-Gate, FinFet, or whatever) that operate at 1 kW/cm2 for FO4 = 10 ps and VDD = 0.6 V [Frank, Proc. IEEE, 3/01]For a 2cm x 2cm high-performance microprocessor die, this means 4kW power dissipation.If die power has to be limited to 200W, only 5% of these devices can switching at any time, assuming that nothing else dissipates power.[Ref: S. Borkar, Intel]
34 An Era of Power-Limited Technology Scaling Technology innovations offer some reliefDevices that perform better at low voltage without leaking too muchBut also are adding major grieveImpact of increasing process variations and various failure mechanisms more pronounced in low-power design regime.Most plausible scenarioCircuit and system level solutions essential to keep power/energy dissipation in checkSlow down growth in computational density, and use obtained slack to control power density increase.Introduce design techniques to operate circuit at nominal, not worst-case, conditions
35 Some Useful References … Selected Keynote PresentationsFred Boekhorst, ”Ambient intelligence, the next paradigm for consumer electronics: How will it affect Silicon?, ” Digest of Technical Papers ISSCC, pp. 28-31, Febr. 02.Theo A. C. M. Claasen, “High speed: Not the only way to exploit the intrinsic computational power of silicon,” Digest of Technical Papers ISSCC, pp. 22-25, Febr. 99.Hugo De Man, “Ambient intelligence: Gigascale dreams and nanoscale realities,” Digest of Technical Papers ISSCC, pp. 29-35, Febr. 05.Patrick P. Gelsinger, Microprocessors for the new millennium: Challenges, opportunities, and new frontiers,” Digest of Technical Papers ISSCC, pp. 22-25, Febr. 01.Gordon E. Moore, “No exponential is forever: But "Forever" can be delayed!,” Digest of Technical Papers ISSCC, pp. 20-23, Febr. 03.Yrjö Neuvo, ”Cellular phones as embedded systems,” Digest of Technical Papers ISSCC, pp. 32-37, Febr. 04.Takayasu Sakurai, ”Perspectives on power-aware electronics,” Digest of Technical Papers ISSCC, pp. 26-29, Febr. 03.Robert Yung, Stefan Rusu, and Ken Shoemaker, Future trend of microprocessor design, Proceedings ESSCIRC, SeptBooks and Book ChaptersS. Roundy, P. Wright and J.M. Rabaey, "Energy Scavenging for Wireless Sensor Networks," Kluwer Academic Publishers, 2003.F. Snijders, “Ambient Intelligence Technology: An Overview,” In Ambient Intelligence, Ed. W. Weber et al, pp , Springer, 2005.T. Starner and J. Paradiso, “Human-Generated Power for Mobile Electronics,” in “Low-Power Electronics”, C. Piguet, Editor, pp , CRC Press 05.
36 Some Useful References (cntd) PublicationsA. Bar-Cohen, S. Prstic, K. Yazawa, M. Iyengar. “Design and Optimization of Forced Convection Heat Sinks for Sustainable Development”, Euro Conference –New and Renewable Technologies for Sustainable, 2000.S. Borkar, numerous presentations over the past decade …R. Chu, “The Challenges of Electronic Cooling: Past, Current and Future,” Journal of Electronic Packaging, Vol 126, pp. 491, DecD. Frank, R. Dennard, E. Nowak, P. Solomon, Y. Taur, P. Wong, “Device scaling limits of Si MOSFETs and their application dependencies,” Proceedings of the IEEE, Volume 89, Issue 3, pp. 259 – 288 , March 2001.International Technology Roadmap for Semiconductors,J. Markoff and S. Hansell, “Hiding in Plain Sight, Google Seeks More Power”, NY Times, June 2006.R. Nowak, “A DARPA Perspective on Small Fuel Cells for the Military,” presented at Solid State Energy Conversion Alliance (SECA) Workshop, Arlington, March 2001.J. Rabaey et al. "PicoRadios for wireless sensor networks: the next challenge in ultra-low power design,” Proc IEEE ISSCC Conference, pp.200-1, San Francisco, February 2002.R. Schmidt, “Power Trends in the Electronics Industry – Thermal Impacts,” ACEED03, IBM Austin Conference on Energy-Efficient Design, 2003.Toshiba, “Toshiba Announces World's Smallest Direct Methanol Fuel Cell With Energy Output of 100 Milliwatts,” June 2004.