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					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
“X-Internet” Beyond the PC

    Internet Computers           500
                                Million                Today’s Internet
    Internet Users             1.5 Billion

                          Automobiles
                             700 Million

                           Telephones                            X-Internet
                                4 Billion


                        Electronic Chips
                                60 Billion


                                                         Forrester Research, May 2001
              CS 150 - Spring 2007 – Lec #28 – Power - 2 Revised 2007
“X-Internet” Beyond the PC

  Millions




                                     PC
                                  Internet

                                                         X
                                                      Internet


                                                                            Year

                                                          Forrester Research, May 2001
             CS 150 - Spring 2007 – Lec #28 – Power - 3
   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 +
Siemens SL45i   Ericsson T68               embedded cameras
                   CS 150 - Spring 2007 – Lec #28 – Power - 4
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
  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
                                                 Important (Wireless)
                                                   Technology Trends



“Spectral Efficiency”:
    More bits/m3
                                                                      Rapidly increasing
                                                                      transistor density



                              Rapidly declining
                                system cost




                         CS 150 - Spring 2007 – Lec #28 – Power - 7
In the Physical World: Sensor Devices




             CS 150 - Spring 2007 – Lec #28 – Power - 8
Important (Wireless)
Technology Trends




                                             Rapid Growth: Machine-to-
   Speed-Distance-Cost                            Machine Devices
       Tradeoffs                                  (mostly sensors)

                 CS 150 - Spring 2007 – Lec #28 – Power - 9
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
Basics
 Power supply provides energy for charging and discharging wires and
  transistor gates. The energy supplied is stored & then dissipated as
  heat.
                     Power: Rate of work being done wrt time
                             Rate of energy being used
  Units:                   Watts = Joules/seconds
 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:

                                                                       A very practical
                                                                       formulation!


                                                            If we would like
                               total energy                 to know total energy
                     CS 150 - Spring 2007 – Lec #28 – Power - 11
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
                         This is how electric tea pots work ...
                                 Heats 1 gram of water
                                     0.24 degree C
                                       0.24 Calories per Second
                                               1 Joule of Heat
         1A                                   Energy per Second



     +
1V
     -
                                  1 Ohm
                                 Resistor
                                              20 W rating: Maximum power
                                              the package is able to transfer
                                              to the air. Exceed rating and
                                              resistor burns.
              CS 150 - Spring 2007 – Lec #28 – Power - 13
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
Powering an iPod nano (2005 edition)
                                           Battery has 1.2 W-hour
                                           rating: Can supply
                                           1.2 W of power for 1 hour

                                    1.2 W / 5 W = 15 minutes

                                 More W-hours require bigger battery
                                 and thus bigger “form factor” --
                                 it wouldn’t be “nano” anymore!

                                 Real specs for iPod nano :
                                 14 hours for music,
                                 4 hours for slide shows

                                               85 mW for music
                                               300 mW for slides
             CS 150 - Spring 2007 – Lec #28 – Power - 15
                                              0.55 ounces

                                                  12 hour
                                              battery life

                                                  $79.00

                                                     1 GB




CS 150 - Spring 2007 – Lec #28 – Power - 16
      20 hour battery life for audio,
      6.5 hours for movies (80GB version)


                           24 hour           Up from 14
                           battery life hours for 2005
                           for audio           iPod nano
                            Thinner than 2005 iPod nano
                           5 hour             Up from 4
                           battery life hours for 2005
                           for photos          iPod nano



                                              12 hour
                                              battery life

CS 150 - Spring 2007 – Lec #28 – Power - 17
   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
   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
46x energy than iPod nano.                               battery life! And,
iPod lets you listen to music                            just for CPU!
for 14 hours!

Almost full 1 inch                                    At 1 GHz, CPU consumes
depth. Width and                                      13 Watts. “Energy saver”
height set by available                               option uses this mode ...
space, weight.       CS 150 - Spring 2007 – Lec #28 – Power - 19
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




                        Handspring
   Nokia 61xx -
                        PDA - 10%
      33%
                                                         Toshiba Portege
                                                         3110 laptop - 20%
                  CS 150 - Spring 2007 – Lec #28 – Power - 20
                                                            55 W-hour battery stores
                                                                        the energy of
                                                             1/2 a stick of dynamite.




If battery short-circuits,
catastrophe is possible ... - Spring 2007 – Lec #28 – Power - 21
                         CS 150
CPU Only Part of Power Budget
 2004-era notebook running a
        full workload.


    “other”
  GPU                                If our CPU took no power
                                     at all to run, that would
 LCD          CPU                    only double battery life!
 Backlight

    LCD




               CS 150 - Spring 2007 – Lec #28 – Power - 22
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
Reliability: running computers hot                             conditioners is a
makes them fail more often                                     big part of TCO

                 CS 150 - Spring 2007 – Lec #28 – Power - 23
 Thermal Image of Typical Cluster Rack



Rack
Switch




         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
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, MIPS 2/watt. Puts more weight on performance



                       CS 150 - Spring 2007 – Lec #28 – Power - 25
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
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
   Switching Power
  Gate power consumption:
     Assume a gate output is switching its output at a rate of:

                                                activity factor           clock rate
                                                (probability of switching on
                                                any particular clock period)




  Therefore:



   Chip/circuit power consumption:


number of nodes (or gates)
                            CS 150 - Spring 2007 – Lec #28 – Power - 28
Other Sources of Energy Consumption
 “Short Circuit” Current:                    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
Other Sources of Energy Consumption
  Consumption caused by “DC leakage current” (Ids leakage):




   Transistor s/d conductance
   never turns off all the way

   Low voltage processes much worse
  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



                       CS 150 - Spring 2007 – Lec #28 – Power - 30
Controlling Energy Consumption: What
Control Do You Have as a Designer?
 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?

  Our design projects do not optimize for power consumption
                     CS 150 - Spring 2007 – Lec #28 – Power - 31
    Scaling Switching Energy per Gate
                                                                               Moore’s Law
                                                                               at work …



                                                                              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


From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005.
                                CS 150 - Spring 2007 – Lec #28 – Power - 32
 Device Engineers Trade Speed and Power

We can reduce CV2 (Pactive)
by lowering Vdd


We can increase speed
by raising Vdd and
lowering Vt



We can reduce leakage
(Pstandby) by raising Vt


                             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
 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
Intel: Comparing 2 CPU Generations ...

                                                                      Find enough
                                                                      tricks, and you
                                                                      can afford to
                                                                      raise Vdd a
                                                                      little so that
                                                                      you can raise
                                                                      the clock
                                                                      speed!




Clock speed                                                  Design tricks:
unchanged ...   Lower Vdd, lower C,
                                                             architecture & circuits
                but more leakage
                    CS 150 - Spring 2007 – Lec #28 – Power - 35

				
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