1

Display technologies

Lin ZhongELEC424, Fall 2010

2

Outline

• Liquid crystal displays (LCD)• Organic light-emitting diode (OLED) display• Flexible display• Administration

3

Mobile displays: Trend

• Brighter, clearer with probably the same size

CIF: Common Intermediate Format

Chung & Lee, 2005

iPhone 4: 326 ppi960x640

Human retina has a resolution of 477ppi

Trend

• 2005

4

5

Display power

6

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

7

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

8

LCD principle

Luminance controller

Dot addressing

Lighting

DotElectrode: indium tin oxide (ITO)

Color filter

9

Light and light guideMicroLenTM white LED light guide for cell phones

Lighting

• Cavity/direct backlight

• Edge-lit light-guide backlight10Abileah’08, Information Display

Laptop backlighting

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

11

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

12Abileah’08, Information Display

Edge-lit backlight (Contd.)

13

14

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

15http://www.hitachi-displays-eu.com/doc/AN-002_Passive_and_Active_Matrix.pdf

Active matrix addressing• More expensive

16

17

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

18

LCD power consumption• Liquid crystal cell

requires polarization• TFT panel must be on

– DRAM– Refreshing at 60Hz

19

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?

20

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– Flexible display

Commercial product

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

– http://www.youtube.com/watch?v=FTEt5o_jt30

21

Commercial products (Contd.)

• Samsung 12.1’’ OLED for laptops

22

23

Power efficiency

• Green is the most efficient

Our measurement

24

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Red Green

Blue

Intensity level

Pow

er (m

W)

http://www.4dsystems.com.au: uOLED-3208-PMD3T

25

OLED display power management

• Darken unused areas

2.5 times power reduction

HP Labs, MobileHCI 2004

26

OLED display power management

• Luminance inversion

HP Labs, MobileHCI 2004

5 times power reduction

27

Flexible display

• LCD impossible

Organic electronics (TFT)

Lighting?

Color filter panel?

28

OLED-based flexible display• Organic electronics (TFF) on plastic or foil• No need for color filter panel• No need for back lighting

Sony Flexible OLED displayhttp://www.youtube.com/watch?v=9OvTLg4i2_U

29

E-Ink: Electrophoretic ink

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

L.G. Philips---E-Ink

http://www.eink.com/

30

E-Ink product: Sony Reader

• No back light• Paper quality

– High contrast– High resolution

E-Ink product: Amazon Kindle

31

3D Displays

• Autostereoscopic 3D– Sony RayModeler

• http://www.youtube.com/watch?v=h5QSclrIdlE

• Virtual reality 3D• http://www.youtube.com/watch?v=h5QSclrIdlE

32

Autostereoscopic 3D

Lenticular display

Parallax barrier display

N. Dodgson, “Autostereoscopic 3D displays,” IEEE Computer Magazine, August 2005

Challenges

Head tracking