See It Now:A Primer on LCD, DLP, LCoS, and
Plasma Technologies
See It Now:A Primer on LCD, DLP, LCoS, and
Plasma Technologies
Pete Putman, CTS, ISF
Publisher, HDTVexpert.comContributing Editor, Pro AV
The CRT is Getting OldThe 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
CRT Imaging ProcessCRT 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
CRT Imaging ProcessCRT Imaging Process
CRT PerformanceCRT 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
What Will Replace The CRT?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)
Transmissive Liquid-Crystal (LCD) Displays
Transmissive Liquid-Crystal (LCD) Displays
LCD Display TechnologyLCD 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 > 500 nits
• Power draw < plasma in same size• Weight < plasma in same size
LCD Imaging ProcessLCD 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
LCD Imaging ProcessLCD Imaging Process
LCD Imaging ProcessBuilding a Better Mousetrap
LCD Imaging ProcessBuilding a Better Mousetrap
The Sharp Approach
The LG Philips Approach
The Samsung Approach
Real-World LCD BenchmarksReal-World LCD Benchmarks• A review sample 45-inch LCD monitor delivered 304 nits (89 foot-Lamberts)
with ANSI (average) contrast measured at 217:1 and peak contrast at 234:1• 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)
Real-World LCD BenchmarksReal-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
LCD Display TechnologyLCD 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 @ 37”)– Improved LC twist times (various)
Emissive Imaging:Plasma Display Panels (PDPs)
Emissive Imaging:Plasma Display Panels (PDPs)
PDP TechnologyPDP Technology• Plasma displays are emissive • Current PDP benchmarks:
– Sizes to 103” – Resolution to 1920x1080– Brightness >100 nits (FW), 1000 nits peak
• Power draw 15%-20% > same size LCD• Weight 20%-25% > same size LCD
Plasma Imaging ProcessPlasma 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
Plasma Imaging Process Plasma Imaging Process
PDP Rib Structure (Simple)PDP Rib Structure (Simple)
Deep Cell Structure (Advanced)Deep Cell Structure (Advanced)
• Waffle-like structure • Higher light output• Less light leakage
between rib barriers• Developed by Pioneer
Plasma Tube Structure (Future?)Plasma Tube Structure (Future?)
• Phosphors, electrodes, and Ne/Xe gas combined into long tubes
• Reduces cost of larger screens
• Flexible displays?• Developed by Fujitsu
Real-World Plasma BenchmarksReal-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 572:1 and peak contrast at 668:1
• 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)
Real-World Plasma BenchmarksReal-World Plasma Benchmarks
• Color Rendering– Gamut is smaller than
REC 709 coordinates– Green somewhat
undersaturated– Red, blue are very
close to ideal coordinates
Plasma Display TechnologyPlasma Display Technology
• Technology Enhancements:– Wider color gamuts (films, phosphors)– Improved lifetime (gas mixtures)– Higher resolution (1920x1080 @ 50”)– Resistance to burn-in (change in gas mixture)
Reflective Imaging:Digital Light Processing (DLP)
Displays
Reflective Imaging:Digital Light Processing (DLP)
Displays
DLP ImagingDLP 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
Pulse-Width ModulationPulse-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
Pulse-Width ModulationPulse-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 > OFF OFF > ON
DLP Imaging – Single ChipDLP Imaging – Single Chip
DLP Imaging – Three-ChipDLP Imaging – Three-Chip
Three-Chip ImagingThree-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
Digital Micromirror DevicesDigital Micromirror Devices
• DMDs can be made in many sizes
• 4:3 - 16:9 aspect ratios are supported
• Simple light path with single chip
• Pure digital light modulator
SXGA (left) and XGA (right) DMDs
Reflective Imaging:Liquid-Crystal on Silicon (LCoS)
Displays
Reflective Imaging:Liquid-Crystal on Silicon (LCoS)
Displays
LCoS ImagingLCoS 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
LCoS Panel CutawayLCoS Panel Cutaway
LCoS Optical EngineLCoS Optical Engine
LCoS PanelsLCoS Panels
• JVC Direct Drive Digital Light Amplifier (D-ILA) is LCoS technology
• Resolutions to 4K • High ‘fill factor’ (>90%)• Used in front and rear
projection systemsJVC 4096x2160 D-ILA Panel
LCoS PanelsLCoS 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
Image Quality ParametersImage Quality Parameters
Brightness/Contrast/GrayscaleBrightness/Contrast/Grayscale
• Pixel-based imaging breaks the link between brightness and resolution
• Peak brightness levels to 1000 nits in LCD and plasma achieved, > 10,000 lumens in LCoS and DLP projectors
• Average contrast to 500:1 (LCD, LCoS)• Average contrast > 1000:1 (DLP, plasma)
Color and White BalanceColor 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
Illuminants:Projection Lamps
Illuminants:Projection Lamps
• Short-arc mercury vapor lamps
• UHP, UHE, SHE are common designations
• Uneven spectral output• Life 1000–3000 hours
150W UHP Lamp
Illuminants:Projection Lamps
Illuminants:Projection Lamps
• Short-arc xenon lamps• Higher wattage than
comparable UHP lamps• Evenly-distributed
spectral output• Life 500-2000 hours
325W Xenon Lamp
Illuminants:Cold-Cathode Backlights
Illuminants:Cold-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
Illuminants: LED BacklightsIlluminants:
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
Illuminants:Plasma Phosphors
Illuminants:Plasma 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
See It Now:A Primer on LCD, DLP, LCoS, and
Plasma Technologies
See It Now:A Primer on LCD, DLP, LCoS, and
Plasma Technologies
Pete Putman, CTS, ISF
Publisher, HDTVexpert.comContributing Editor, Pro AV