1 display power characteristics lin zhong elec518, spring 2011
TRANSCRIPT
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Display Power Characteristics
Lin ZhongELEC518, Spring 2011
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Display power
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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
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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
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LCD principle
Luminance controller
Dot addressing
Lighting
DotElectrode: indium tin oxide (ITO)
Color filter
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Lighting
• Cavity/direct backlight
• Edge-lit light-guide backlight6Abileah’08, Information Display
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Edge-lit light-guide backlight• Reflector• Guide• Diffuser
7Abileah’08, Information Display
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Edge-lit backlight (Contd.)
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Backlighting
• Cold cathode fluorescent tube (CCFL)• LED (better white and brighter)
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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
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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
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Active matrix addressing• More expensive
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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
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LCD power consumption• Liquid crystal cell
requires polarization• TFT panel must be on
– DRAM– Refreshing at 60Hz
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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?
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E-Ink: Electrophoretic ink
TFT on 75um-thick steel-foil substrateNature, 2003
L.G. Philips---E-Ink
http://www.eink.com/
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E-Ink product
• No back light• Paper quality
– High contrast– High resolution
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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
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Commercial product
• Sony OLED TV– XEL-1, 11”, $2,500, 3mm-think Panel
– http://www.youtube.com/watch?v=FTEt5o_jt30
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Commercial products (Contd.)
• Samsung 12.1’’ OLED for laptops
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Power efficiency
• Green is the most efficient
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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 Value
Pow
er (μ
W)
uOLED N85
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OLED display power management
• Darken unused areas
2.5 times power reduction
HP Labs, MobileHCI 2004
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OLED display power management
• Luminance inversion
HP Labs, MobileHCI 2004
5 times power reduction
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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
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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
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Color sensitivity
Single color sensitivity diagram of the human eye.