1

Display Power Characteristics

Lin ZhongELEC518, Spring 2011

2

Display power

3

Display power (Contd.)

Basic idle; 244; 12%

Computing; 383; 19%

LCD; 82; 4%

Lighting; 444; 22%

Speaker; 367; 18%

Earphone; 65; 3%

Bluetooth; 470; 23%

Power profile of HP iPAQ 4350 (mW)

iPAQ 4350, 2004

4

Display power (Contd.)

Lighting: Keyboard; 72.937037227937; 3%

Lighting: Display I; 147.835647317401; 5%

Lighting: Display II; 61.2835089189648; 2%

LCD; 12.8726439856928; 0%

Speaker; 45; 2%

Bluetooth; 440; 16%

GPRS; 1600; 58%

Compute; 370; 13%

Cellular network; 17; 1%

Flight mode: Sleep; 3; 0%

Audiovox 5600, 2004

5

LCD principle

Luminance controller

Dot addressing

Lighting

DotElectrode: indium tin oxide (ITO)

Color filter

Lighting

• Cavity/direct backlight

• Edge-lit light-guide backlight6Abileah’08, Information Display

Edge-lit light-guide backlight• Reflector• Guide• Diffuser

7Abileah’08, Information Display

Edge-lit backlight (Contd.)

8

Backlighting

• Cold cathode fluorescent tube (CCFL)• LED (better white and brighter)

9

10

Addressing• Direct addressing

– Numeric LED display• Dot matrix: passive

– Slow response, poor contrast– Low-cost, low-power, small

displays• Dot matrix: active

– Higher power consumption

Common electrode

Switch for each pixel

Passive matrix addressing

• Cross talk between neighboring pixels

• Long latency due to scanning

11http://www.hitachi-displays-eu.com/doc/AN-002_Passive_and_Active_Matrix.pdf

Active matrix addressing• More expensive

12

13

Thin-film transistor (TFT) LCD

Cross-sectional diagram of an active-matrix LCD. The LC cell modulates light intensity according to the driving voltages. ITO = indium tin oxide

Flynn et al, 1999Switch

Storage capacitor

TFT ≈ Active Matrix

14

LCD power consumption• Liquid crystal cell

requires polarization• TFT panel must be on

– DRAM– Refreshing at 60Hz

15

Bistable display (Zero power)• Cholesteric liquid crystal cell stays polarized

without voltage• Long response time

– Fine for ebook, bulletin board, light interaction– Impossible for video

Kent display

Passive or Active addressing?

16

E-Ink: Electrophoretic ink

TFT on 75um-thick steel-foil substrateNature, 2003

L.G. Philips---E-Ink

http://www.eink.com/

17

E-Ink product

• No back light• Paper quality

– High contrast– High resolution

18

OLED display• LCD: filter white external light for colors• OLED: generate different colors

– Potential lower power• Luminance for each pixel can be changed

– Much larger view angle– Bright & high contrast– Broad color gamut (better colors)– Thin & light– Faster response

Commercial product

• Sony OLED TV– XEL-1, 11”, $2,500, 3mm-think Panel

– http://www.youtube.com/watch?v=FTEt5o_jt3019

Commercial products (Contd.)

• Samsung 12.1’’ OLED for laptops

20

21

Power efficiency

• Green is the most efficient

Color Power Model of OLED

0 0.2 0.4 0.6 0.8 10

2

4

6

8

sRGB Value

Pow

er (µ

W)

(a)

0 0.2 0.4 0.6 0.8 10

2

4

6

8

Linear RGB Value

Pow

er (µ

W)

(b)

0 0.2 0.4 0.6 0.8 10

2

4

6

sRGB Value

Pow

er (µ

W)

(c)

0 0.2 0.4 0.6 0.8 10

2

4

6

Linear RGB Value

Pow

er (µ

W)

(d)

0.0 0.2 0.4 0.6 0.8 1.00

1

2

sRGB Value

Pow

er (μ

W)

0.0 0.2 0.4 0.6 0.8 1.00

1

2

Linear RGB ValuePo

wer

(μW

)

uOLED N85

23

OLED display power management

• Darken unused areas

2.5 times power reduction

HP Labs, MobileHCI 2004

24

OLED display power management

• Luminance inversion

HP Labs, MobileHCI 2004

5 times power reduction

DarkR’ = λRG’ = λGB’ = λB

↓25%

GreenR’ = λRRG’ = λGGB’ = λBB

↓34%

ArbitraryR’ = R*G’ = G*B’ = B*

↓72%

InversionR’= λ(1-R)G’= λ(1-G)B’= λ(1-B)

↓66%

Original

Human visual system

Normalized response spectra of human cones, S, M, and L types, to monochromatic spectral stimuli, with wavelength given in nanometers.

http://en.wikipedia.org/wiki/Color_vision

Color sensitivity

Single color sensitivity diagram of the human eye.