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See It Now: A Primer on LCD, DLP, LCoS, and Plasma Technologies Pete Putman, CTS, ISF Publisher, HDTVexpert.com Contributing Editor, Pro AV 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 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 CRT Imaging Process 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 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 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 > 500 nits • Power draw < plasma in same size • Weight < plasma in same size 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 LCD Imaging Process LCD Imaging Process Building a Better Mousetrap The Sharp Approach The Samsung Approach The LG Philips Approach Real-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 6hour interval (total of 1.726 kWh) 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 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 @ 37”) – Improved LC twist times (various) Emissive Imaging: Plasma Display Panels (PDPs) PDP 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 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 PDP Rib Structure (Simple) Deep Cell Structure (Advanced) • Waffle-like structure • Higher light output • Less light leakage between rib barriers • Developed by Pioneer 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 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 Benchmarks • Color Rendering – Gamut is smaller than REC 709 coordinates – Green somewhat undersaturated – Red, blue are very close to ideal coordinates Plasma 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 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 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 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 > OFF OFF > ON DLP Imaging – Single Chip DLP Imaging – Three-Chip Three-Chip Imaging • Uses Polarizing Beam Splitter (PBS) for highpower three-chip DLP projectors • Light travels in both directions through it • Red, green, and blue colors added in PBS Digital 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 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 LCoS Panel Cutaway LCoS Optical Engine LCoS 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 systems JVC 4096x2160 D-ILA Panel 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 Image Quality Parameters Brightness/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 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 • Short-arc mercury vapor lamps • UHP, UHE, SHE are common designations • Uneven spectral output • Life 1000–3000 hours 150W UHP Lamp 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 • 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 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 • 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 Pete Putman, CTS, ISF Publisher, HDTVexpert.com Contributing Editor, Pro AV