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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?. 500 Million. Internet Computers. Today’s Internet. Internet Users. 1.5 Billion. Automobiles 700 Million. Telephones 4 Billion.

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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?

CS 150 - Spring 2007 – Lec #28 – Power - 1

x internet beyond the pc

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

x internet beyond the pc1

Millions

PC

Internet

X

Internet

Year

“X-Internet” Beyond the PC

CS 150 - Spring 2007 – Lec #28 – Power - 3

Forrester Research, May 2001

cell phones

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

shape of things
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
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 increasingtransistor density

Rapidly decliningsystem cost

Important (Wireless) Technology Trends

CS 150 - Spring 2007 – Lec #28 – Power - 7

in the physical world sensor devices
In the Physical World: Sensor Devices

CS 150 - Spring 2007 – Lec #28 – Power - 8

important wireless technology trends1

Rapid Growth: Machine-to-Machine Devices (mostly sensors)

Speed-Distance-CostTradeoffs

Important (Wireless)Technology Trends

CS 150 - Spring 2007 – Lec #28 – Power - 9

why worry about power
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

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

basics1
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

slide13

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

cooling an ipod nano
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

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

slide16

0.55 ounces

12 hour

battery life

$79.00

1 GB

CS 150 - Spring 2007 – Lec #28 – Power - 16

slide17

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

notebooks now most of the pc market
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

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

battery technology

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

slide21

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

cpu only part of power budget

“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

servers total cost of ownership tco
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

thermal image of typical cluster rack

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

how do we measure and compare power consumption
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

metrics
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
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

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

other sources of energy consumption
“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

other sources of energy consumption1
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

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?

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

scaling switching energy per gate

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.

device engineers trade speed and power

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

customize processes for product types
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

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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