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Power

Power. Motivation for design constraints of power consumption Power metrics Power consumption analysis in CMOS How can a logic designer control power?. 500 Million. Internet Computers. Today’s Internet. Internet Users. 1.5 Billion. Automobiles 700 Million. Telephones 4 Billion.

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Power

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  1. Power • Motivation for design constraints of power consumption • Power metrics • Power consumption analysis in CMOS • How can a logic designer control power? CS 150 - Spring 2007 – Lec #28 – Power - 1

  2. 500 Million Internet Computers Today’s Internet Internet Users 1.5 Billion Automobiles 700 Million Telephones 4 Billion X-Internet Electronic Chips 60 Billion “X-Internet” Beyond the PC Forrester Research, May 2001 Revised 2007 CS 150 - Spring 2007 – Lec #28 – Power - 2

  3. Millions PC Internet X Internet Year “X-Internet” Beyond the PC CS 150 - Spring 2007 – Lec #28 – Power - 3 Forrester Research, May 2001

  4. Siemens SL45i Ericsson T68 Cell Phones • Phone w/voice command, voice dialing, intelligent text for short msgs • MP3 player + headset, digital voice recorder • “Mobile Internet” with a built-in WAP Browser • Java-enabled, over the air programmable • Bluetooth + GPRS • Enhanced displays + embedded cameras CS 150 - Spring 2007 – Lec #28 – Power - 4

  5. Shape of Things • Phone + Messenger + PDA Combinations • E.g., Blackberry 5810 Wireless Phone/Handheld • Integration of PDA + Telephone • PLUS Gateway to Internet and Enterprise applications • 1900 MHz GSM/GPRS (Euroversion at 900 Mhz) • SMS Messaging, Internet access • QWERTY Keyboard, 20 line display • JAVA applications capable • 8 MB flash + 1 MB SRAM CS 150 - Spring 2007 – Lec #28 – Power - 5

  6. Shape of Things to Come • Danger “Hiptop” • Full-featured mobile phone w/Internet Access • Email + attachments/instant messaging + PIM • Digital camera accessory • End-to-end integration of voice + data apps • Media-rich UI for graphics + sound • Large screen + QWERTY keyboard • Data nav: keyboard or push wheel • Affordable (under $200) • MIDI synthesizer for quality sound • Multi-tasking of user actions • Customizable ring tones and alerts to personalize hiptop experience CS 150 - Spring 2007 – Lec #28 – Power - 6

  7. “Spectral Efficiency”: More bits/m3 Rapidly increasingtransistor density Rapidly decliningsystem cost Important (Wireless) Technology Trends CS 150 - Spring 2007 – Lec #28 – Power - 7

  8. In the Physical World: Sensor Devices CS 150 - Spring 2007 – Lec #28 – Power - 8

  9. Rapid Growth: Machine-to-Machine Devices (mostly sensors) Speed-Distance-CostTradeoffs Important (Wireless)Technology Trends CS 150 - Spring 2007 – Lec #28 – Power - 9

  10. Why Worry About Power? • Portable devices: • Handhelds, laptops, phones, MP3 players, cameras, … all need to run for extended periods on small batteries without recharging • Devices that need regular recharging or large heavy batteries will lose out to those that don’t. • Power consumption important even in “tethered” devices • System cost tracks power consumption: • Power supplies, distribution, heat removal • Power conservation, environmental concerns • In 10 years, have gone from minimal consideration of power consumption to (designing with power consumption as a primary design constraint! CS 150 - Spring 2007 – Lec #28 – Power - 10

  11. total energy Basics • Power supply provides energy for charging and discharging wires and transistor gates. The energy supplied is stored & then dissipated as heat. • If a differential amount of charge dq is given a differential increase in energy dw, the potential of the charge is increased by: • By definition of current: Power: Rate of work being done wrt time Rate of energy being used Watts = Joules/seconds Units: A very practical formulation! If we would like to know total energy CS 150 - Spring 2007 – Lec #28 – Power - 11

  12. Basics • Warning! In everyday language, the term “power” is used incorrectly in place of “energy” • Power is not energy • Power is not something you can run out of • Power can not be lost or used up • It is not a thing, it is merely a rate • It can not be put into a battery any more than velocity can be put in the gas tank of a car CS 150 - Spring 2007 – Lec #28 – Power - 12

  13. 1A 1 Joule of Heat Energy per Second 20 W rating: Maximum power the package is able to transfer to the air. Exceed rating and resistor burns. 1 Watt This is how electric tea pots work ... Heats 1 gram of water 0.24 degree C 0.24 Calories per Second + 1V - 1 Ohm Resistor CS 150 - Spring 2007 – Lec #28 – Power - 13

  14. Cooling an iPod nano ... Like a resistor, iPod relies on passive transfer of heat from case to the air Why? Users don’t want fans in their pocket ... To stay “cool to the touch” via passive cooling, power budget of 5 W If iPod nano used 5W all the time, its battery would last 15 minutes ... CS 150 - Spring 2007 – Lec #28 – Power - 14

  15. Real specs for iPod nano : 14 hours for music, 4 hours for slide shows Battery has 1.2 W-hour rating:Can supply 1.2 W of power for 1 hour 85 mW for music 300 mW for slides Powering an iPod nano (2005 edition) 1.2 W / 5 W = 15 minutes More W-hours require bigger battery and thus bigger “form factor” -- it wouldn’t be “nano” anymore! CS 150 - Spring 2007 – Lec #28 – Power - 15

  16. 0.55 ounces 12 hour battery life $79.00 1 GB CS 150 - Spring 2007 – Lec #28 – Power - 16

  17. 20 hour battery life for audio, 6.5 hours for movies (80GB version) Up from 14 hours for 2005 iPod nano Up from 4 hours for 2005 iPod nano 24 hour battery life for audio 5 hour battery life for photos Thinner than 2005 iPod nano 12 hour battery life CS 150 - Spring 2007 – Lec #28 – Power - 17

  18. Notebooks ... now most of the PC market Apple MacBook -- Weighs 5.2 lbs 8.9 in 1 in 12.8 in Performance: Must be “close enough” to desktop performance ... many people no longer own a desktop Size and Weight: Ideal: paper notebook Heat: No longer “laptops” -- top may get “warm”, bottom “hot”. Quiet fans OK CS 150 - Spring 2007 – Lec #28 – Power - 18

  19. Almost full 1 inch depth. Width and height set by available space, weight. Battery: Set by size and weight limits ... Battery rating: 55 W-hour At 2.3 GHz, Intel Core Duo CPU consumes 31 W running a heavy load - under 2 hours battery life! And, just for CPU! 46x energy than iPod nano. iPod lets you listen to music for 14 hours! At 1 GHz, CPU consumes 13 Watts. “Energy saver” option uses this mode ... CS 150 - Spring 2007 – Lec #28 – Power - 19

  20. Toshiba Portege 3110 laptop - 20% Handspring PDA - 10% Nokia 61xx - 33% Battery Technology • Battery technology has developed slowly • Li-Ion and NiMh still the dominate technologies • Batteries still contribute significantly to the weight of mobile devices CS 150 - Spring 2007 – Lec #28 – Power - 20

  21. 55 W-hour battery stores the energy of 1/2 a stick of dynamite. If battery short-circuits, catastrophe is possible ... CS 150 - Spring 2007 – Lec #28 – Power - 21

  22. “other” GPU CPU LCD Backlight LCD CPU Only Part of Power Budget 2004-era notebook running a full workload. If our CPU took no power at all to run, that would only double battery life! CS 150 - Spring 2007 – Lec #28 – Power - 22

  23. Servers: Total Cost of Ownership (TCO) Machine rooms are expensive … removing heat dictates how many servers to put in a machine room. Electric bill adds up! Powering the servers + powering the air conditioners is a big part of TCO Reliability: running computers hot makes them fail more often CS 150 - Spring 2007 – Lec #28 – Power - 23

  24. Rack Switch Thermal Image of Typical Cluster Rack M. K. Patterson, A. Pratt, P. Kumar, “From UPS to Silicon: an end-to-end evaluation of datacenter efficiency”, Intel Corporation CS 150 - Spring 2007 – Lec #28 – Power - 24

  25. How Do We Measure and Compare Power Consumption? • One popular metric for microprocessors is: MIPS/watt • MIPS, millions of instructions per second • Typical modern value? • Watt, standard unit of power consumption • Typical value for modern processor? • MIPS/watt reflects tradeoff between performance and power • Increasing performance requires increasing power • Problem with “MIPS/watt” • MIPS/watt values are typically not independent of MIPS • Techniques exist to achieve very high MIPS/watt values, but at very low absolute MIPS (used in watches) • Metric only relevant for comparing processors with a similar performance • One solution, MIPS2/watt. Puts more weight on performance CS 150 - Spring 2007 – Lec #28 – Power - 25

  26. Metrics • How does MIPS/watt relate to energy? • Average power consumption = energy / time • MIPS/watt = instructions/sec / joules/sec = instructions/joule • Equivalent metric (reciprocal) is energy per operation (E/op) • E/op is more general - applies to more that processors • also, usually more relevant, as batteries life is limited by total energy draw. • This metric gives us a measure to use to compare two alternative implementations of a particular function. CS 150 - Spring 2007 – Lec #28 – Power - 26

  27. Power in CMOS Switching Energy: energy used to switch a node Calculate energy dissipated in pullup: Energy supplied Energy stored Energy dissipated An equal amount of energy is dissipated on pulldown CS 150 - Spring 2007 – Lec #28 – Power - 27

  28. activity factor number of nodes (or gates) clock rate Switching Power • Gate power consumption: • Assume a gate output is switching its output at a rate of: (probability of switching on any particular clock period) Therefore: • Chip/circuit power consumption: CS 150 - Spring 2007 – Lec #28 – Power - 28

  29. “Short Circuit” Current: Other Sources of Energy Consumption • Junction Diode Leakage : Transistor drain regions “leak” charge to substrate. 10-20% of total chip power ~1nWatt/gate few mWatts/chip CS 150 - Spring 2007 – Lec #28 – Power - 29

  30. Consumption caused by “DC leakage current” (Ids leakage): This source of power consumption is becoming increasing significant as process technology scales down For 90nm chips around 10-20% of total power consumption Estimates put it at up to 50% for 65nm Other Sources of Energy Consumption Transistor s/d conductance never turns off all the way Low voltage processes much worse CS 150 - Spring 2007 – Lec #28 – Power - 30

  31. Largest contributing component to CMOS power consumption is switching power: Factors influencing power consumption: n: total number of nodes in circuit : activity factor (probability of each node switching) f: clock frequency (does this effect energy consumption?) Vdd: power supply voltage What control do you have over each factor? How does each effect the total Energy? Controlling Energy Consumption: What Control Do You Have as a Designer? Our design projects do not optimize for power consumption CS 150 - Spring 2007 – Lec #28 – Power - 31

  32. Due to reduced V and C (length and width of Cs decrease, but plate distance gets smaller) Recent slope reduced because V is scaled less aggressively Scaling Switching Energy per Gate Moore’s Lawat work … CS 150 - Spring 2007 – Lec #28 – Power - 32 From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005.

  33. We can reduce leakage (Pstandby) by raising Vt We can increase speed by raising Vdd andlowering Vt We can reduce CV2 (Pactive) by lowering Vdd Device Engineers Trade Speed and Power From: Silicon Device Scaling to the Sub-10-nm Regime Meikei Ieong,1* Bruce Doris,2 Jakub Kedzierski,1 Ken Rim,1 Min Yang1 CS 150 - Spring 2007 – Lec #28 – Power - 33

  34. Customize processes for product types ... From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005. CS 150 - Spring 2007 – Lec #28 – Power - 34

  35. Find enough tricks, and you can afford to raise Vdd a little so that you can raise the clock speed! Clock speed unchanged ... Design tricks: architecture & circuits Lower Vdd, lower C, but more leakage Intel: Comparing 2 CPU Generations ... CS 150 - Spring 2007 – Lec #28 – Power - 35

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