See It Now: A Primer on LCD, DLP, LCoS, and Plasma Technologies

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See It NowA Primer on LCD, DLP, LCoS, and
Plasma Technologies

• Pete Putman, CTS, ISF
• Publisher, HDTVexpert.com
• Contributing Editor, Pro AV

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The CRT is Getting Old

• Technology is over 100 years old
• Monochrome CRTs used from 1910s
• Color CRTs developed in early 1950s (RCA)
• Monochrome tubes were used in front projectors in
  1980s 90s (7, 8, 9)
• Manufacturing has largely moved to China
• High-volume, low-margin product
• Thomson TTE, TCL, and others make them

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CRT Imaging Process

• Low-voltage emission of electrons
• High-voltage anode attracts electrons
• Electrons strike phosphors, causing them to glow
  brightly
• Color CRTs use three electron guns
• Projection CRTs use single-color phosphors
• Response of CRT is linear for wide grayscales

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CRT Imaging Process
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CRT Performance

• Advantages
• CRTs can scan multiple resolutions
• Wide, linear grayscales are possible
• Precise color shading is achieved
• CRTs have no native pixel structure
• Drawbacks
• Brightness limited by tube size
• Resolution (spot size) linked to brightness
• Heavy, bulky displays for small screen sizes

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What Will Replace The CRT?

• Contenders for direct-view applications
• Liquid-crystal displays (LCDs)
• Plasma display panels (PDPs)
• Contenders for front/rear projection
  applications
• Liquid-crystal on silicon (LCoS)
• Silicon Xtal Reflective Device (SXRD)
• Digital Image Light Amplifier (D-ILA)
• Digital Light Processing (DLP)

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Transmissive Liquid-Crystal (LCD) Displays
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LCD Display Technology

• Liquid-crystal displays are transmissive
• LC pixels act as light shutters
• Current LCD benchmarks
• Sizes to 82 (prototypes)
• Resolution to 1920x1080 pixels
• Brightness gt 500 nits
• Power draw lt plasma in same size
• Weight lt plasma in same size

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LCD Imaging Process

• Randomly arranged LCs pass light (off )
• Aligned LCs block light (on)
• This effect is called birefringence
• Principle is the same for low-temperature and
  high-temperature polysilicon LCDs, and liquid
  crystal on silicon (LCoS) panels

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LCD Imaging Process
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LCD Imaging ProcessBuilding a Better Mousetrap
The Sharp Approach
The Samsung Approach
The LG Philips Approach
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Real-World LCD Benchmarks

• A review sample 45-inch LCD monitor delivered 304
  nits (89 foot-Lamberts) with ANSI (average)
  contrast measured at 2171 and peak contrast at
  2341
• Typical black level was 1.6 nits (8x CRT)
• Native resolution 1920x1080
• Power consumption 284.2 watts over a 6-hour
  interval (total of 1.726 kWh)

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Real-World LCD Benchmarks

• Color Rendering
• Test panel uses CCFLs
• Gamut is smaller than REC 709 coordinates
• Green way undersaturated
• Red, blue are closer to ideal coordinates

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LCD Display Technology

• Technology Enhancements
• Better color through corrected CCFLs, LEDs
• Improved black levels (compensating films)
• Higher contrast (pulsed backlights)
• Wider viewing angles (compensating films)
• Higher resolution (1920x1080 _at_ 37)
• Improved LC twist times (various)

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Emissive ImagingPlasma Display Panels (PDPs)
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PDP Technology

• Plasma displays are emissive
• Current PDP benchmarks
• Sizes to 103
• Resolution to 1920x1080
• Brightness gt100 nits (FW), 1000 nits peak
• Power draw 15-20 gt same size LCD
• Weight 20-25 gt same size LCD

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Plasma Imaging Process

• Three-step charge/discharge cycle
• Uses neon xenon gas mixture
• 160 - 250V AC discharge in cell stimulates
  ultraviolet (UV) radiation
• UV stimulation causes color phosphors to glow and
  form picture elements
• Considerable heat and EMI are released

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Plasma Imaging Process
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PDP Rib Structure (Simple)
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Deep Cell Structure (Advanced)

• Waffle-like structure
• Higher light output
• Less light leakage between rib barriers
• Developed by Pioneer

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Plasma Tube Structure (Future?)

• Phosphors, electrodes, and Ne/Xe gas combined
  into long tubes
• Reduces cost of larger screens
• Flexible displays?
• Developed by Fujitsu

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Real-World Plasma Benchmarks

• A review sample 50-inch plasma monitor measured
  from 93 nits (full white) to 233 nits (small
  area), with ANSI (average) contrast measured at
  5721 and peak contrast at 6681
• Typical black level .21 nits (closer to CRT)
• Native Resolution - 1366x768
• Power consumption 411.3 watts over a 6-hour
  interval (total of 2.089 kWh)

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Real-World Plasma Benchmarks

• Color Rendering
• Gamut is smaller than REC 709 coordinates
• Green somewhat undersaturated
• Red, blue are very close to ideal coordinates

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Plasma Display Technology

• Technology Enhancements
• Wider color gamuts (films, phosphors)
• Improved lifetime (gas mixtures)
• Higher resolution (1920x1080 _at_ 50)
• Resistance to burn-in (change in gas mixture)

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Reflective ImagingDigital Light Processing
(DLP) Displays
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DLP Imaging

• Digital micromirror device (DMD) used
• Rapid on-off cycling of mirrors (pulse-width
  modulation) builds grayscale image
• Color added and blended
• With color wheel (single chip)
• With polarizing beam splitter (3-chip)
• Lens projects image to screen

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Pulse-Width Modulation

• Technique to re-create grayscale intensities
  digitally with DMD
• DMD mirror positions are ON (1) and OFF (0)
• Rapid cycling between ON and OFF mirror positions
  produces grayscale values
• Total mirror tilt is 12o

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Pulse-Width Modulation

• PWM grayscale values related to on/off ratios
• In a given interval
• If more ON DMD tilt positions than OFF, lighter
  value results
• If more OFF DMD tilt positions than ON, darker
  value results

ON gt OFF
OFF gt ON
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DLP Imaging Single Chip
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DLP Imaging Three-Chip
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Three-Chip Imaging

• Uses Polarizing Beam Splitter (PBS) for
  high-power three-chip DLP projectors
• Light travels in both directions through it
• Red, green, and blue colors added in PBS

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Digital Micromirror Devices

• DMDs can be made in many sizes
• 43 - 169 aspect ratios are supported
• Simple light path with single chip
• Pure digital light modulator

SXGA (left) and XGA (right) DMDs
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Reflective ImagingLiquid-Crystal on Silicon
(LCoS) Displays
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LCoS Imaging

• LCoS is a reflective imaging system
• Switching transistors are on backplane
• Greater imaging surface available higher fill
  factor than HTPS LCD
• Easier to achieve high pixel density in small
  panels than with HTPS LCD

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LCoS Panel Cutaway
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LCoS Optical Engine
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LCoS Panels

• JVC Direct Drive Digital Light Amplifier (D-ILA)
  is LCoS technology
• Resolutions to 4K
• High fill factor (gt90)
• Used in front and rear projection systems

JVC 4096x2160 D-ILA Panel
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LCoS Panels

• Sony Silicon Xtal Reflective Device (SXRD) also
  LCoS technology
• Panels made with both 2K and 4K resolution
• Used in front/rear projection systems

Sony 4096x2160 SXRD panel
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Image Quality Parameters
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Brightness/Contrast/Grayscale

• Pixel-based imaging breaks the link between
  brightness and resolution
• Peak brightness levels to 1000 nits in LCD and
  plasma achieved, gt 10,000 lumens in LCoS and DLP
  projectors
• Average contrast to 5001 (LCD, LCoS)
• Average contrast gt 10001 (DLP, plasma)

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Color and White Balance

• CRT offers pure RGB color blending and clean
  white balance
• Plasma color balance affected by gas mixture and
  UV emissions
• LCD, LCoS, DLP projectors dependent on light
  source (short-arc lamps)
• UHP/UHE less expensive, color is tricky
• Xenon more costly, color quality is superior

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IlluminantsProjection Lamps

• Short-arc mercury vapor lamps
• UHP, UHE, SHE are common designations
• Uneven spectral output
• Life 10003000 hours

• 150W UHP Lamp

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IlluminantsProjection Lamps

• Short-arc xenon lamps
• Higher wattage than comparable UHP lamps
• Evenly-distributed spectral output
• Life 500-2000 hours

• 325W Xenon Lamp

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IlluminantsCold-Cathode Backlights

• Compact design
• Uneven spectral energy high in green/blue
• Bright sources of diffuse lighting
• Life 50,000 60,000 hrs
• Not green! (contains Hg)

Two CCFL Lamps
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Illuminants LED Backlights

• Compact design
• Evenly-distributed spectral energy
• LED matrix is weighted
• LED life estimated at 50,000 100,000 hours
• LEDs are current hogs

GRB LED Array
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IlluminantsPlasma Phosphors

• Rare earth formulations similar to CRT
• Red, blue easy to saturate green is tougher
• Ne/Xe mixture affects color balance and life
  (estimated 40,000 60,000 hrs)

Close-up of RGB Phosphors
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See It NowA Primer on LCD, DLP, LCoS, and
Plasma Technologies

• Pete Putman, CTS, ISF
• Publisher, HDTVexpert.com
• Contributing Editor, Pro AV