1. See It Now: A Primer on LCD, DLP, LCoS, and Plasma Technologies
Pete Putman, CTS, ISF
Publisher, HDTVexpert.com
Contributing Editor, Pro AV

2. 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
The only raster-imaging system in use today is the cathode-ray tube (CRT), developed in the early 20th century. Early CRTs were used in the first black-and-white television demonstrations in the 1920s, and in the first consumer TV sets in the 1940s. Color CRTs were developed in the early 1950s by RCA. Larger monochrome versions were developed in the 1980s for front projectors. Today, most CRTs are being built in China because there is little profit in manufacturing and selling them.

3. 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
In a CRT monitor or TV, a high voltage potential is used to attract electronics from the tube’s cathodes (guns) to the front of the CRT glass (anode). These electrons are deflected onto red, green, and blue color phosphors, causing them to glow brightly. There are three different electron guns in a CRT. In contrast, CRT projectors use individual red, green, and blue CRTs, and the images they produce are converged to form a full-color electronic image, traced by a high-speed scanning raster.

4. CRT Imaging Process
This diagram shows how the electron beams are directed through individual apertures in the CRT shadow mask and on to individual color phosphors. Without a shadow mask, it would be difficult to form the precise red, green, and blue dots that make up electronic images.

5. CRT Performance Advantages: Drawbacks:
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
Why use CRT imaging? First of all, every scan line is accounted for, regardless of the size of the projected image. If we need to project images of higher resolution, all the projector must do is scan more horizontal lines of detail (if it has fine enough pitch) and refresh the pictures within a specific interval.
Secondly, CRT displays will achieve a wide grayscale, which is critical for photorealism. Remember that each shade of gray that is displayed in any image represents several shades of color that can also be displayed. Third, CRT images have very precise color shading and saturation because they are mixing equal amounts of red, green, and blue light simultaneously.
Finally, CRT displays have no native resolution, or matrix of imaging pixels. The raster can simply trace fewer or greater scan lines as needed.

6. 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)

7. Transmissive Liquid-Crystal (LCD) Displays

8. 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
A liquid-crystal display (LCD) employs transmissive light and a shutter-like mechanism to form grayscale images. Individual liquid crystals within each pixel change their alignment in response to changes in control voltage and will pass or block polarized light to varying degrees. This variation in light intensity, or light shuttering, forms a grayscale image.
LCD monitors are capable of generating very bright images, suitable for viewing under low to moderate ambient light levels. Screens as large as 82 inches have been shown publicly, with resolutions of 1920x1080 pixels. Brightness levels are in excess of 500 nits (over 146 ft-L) on some models. Currently, a LCD monitor or TV requires 10% to 20% less power than a same-size plasma monitor or TV, and weighs about 20% to 25% less.

9. 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
The principle of birefringence is nothing more than the ability of liquid crystals to pass or block polarized light. In nature, individual liquid crystals float in a random pattern, or ‘off’ state. When a voltage is applied to them, however, they will align in the same plane. In this ‘on’ state, polarized light will be blocked by the liquid crystals. Both large flat-panel LCD monitors and TVs and small LCD panels used in portable projectors control light with birefringence.

10. LCD Imaging Process
This diagram shows the principles of liquid crystal twisting and birefringence as a voltage is applied to an individual liquid crystal pixel.

11. LCD Imaging Process Building a Better Mousetrap
The Sharp Approach
The Samsung Approach
The LG Philips Approach

12. 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 – watts over a 6-hour interval (total of kWh)
A typical late-model LCD monitor or TV will deliver as much as 350 nits brightness when adjusted for best grayscale, with average contrast at 130:1 and peak contrast at 170:1. Black levels on LCD displays, while still higher than CRTs, have dropped to as low as 1.2 nits in the past year – about 10 times that of the best CRT displays.

13. 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
A typical late-model LCD monitor or TV will deliver as much as 350 nits brightness when adjusted for best grayscale, with average contrast at 130:1 and peak contrast at 170:1. Black levels on LCD displays, while still higher than CRTs, have dropped to as low as 1.2 nits in the past year – about 10 times that of the best CRT displays.

14. 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 37”)
Improved LC twist times (various)
A liquid-crystal display (LCD) employs transmissive light and a shutter-like mechanism to form grayscale images. Individual liquid crystals within each pixel change their alignment in response to changes in control voltage and will pass or block polarized light to varying degrees. This variation in light intensity, or light shuttering, forms a grayscale image.
LCD monitors are capable of generating very bright images, suitable for viewing under low to moderate ambient light levels. Screens as large as 82 inches have been shown publicly, with resolutions of 1920x1080 pixels. Brightness levels are in excess of 500 nits (over 146 ft-L) on some models. Currently, a LCD monitor or TV requires 10% to 20% less power than a same-size plasma monitor or TV, and weighs about 20% to 25% less.

15. Emissive Imaging: Plasma Display Panels (PDPs)

16. 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 display technology is emissive, like a CRT. The technology scales well and affordably to larger screen sizes; a 102” prototype has been shown publicly. Resolution in smaller sizes ranges from 480 to 768 vertical rows of pixels, with 1920x080 resolution appearing in 70” and larger models. Compared to same-size LCD monitors and TVs, plasma monitors and TVs use 15%-20% more electricity and weigh 20%-25% more.

17. Plasma Imaging Process
Three-step charge/discharge cycle
Uses neon – xenon gas mixture
V 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
When the voltage potential across each pixel rises to a sufficiently high level, there is an electrical discharge through the pixel that ionizes the rare gas mixture. This ionizes gas changes into a ‘plasma’ state and conducts electricity, simultaneously emitting a burst of spectral energy including ultraviolet (UV) light.

18. Plasma Imaging Process
It is the UV energy that causes individual red, green, and blue phosphors to glow, and the mix of those color phosphors determines both the brightness and color shade of each pixel. Once the pixel is fired, a lower sustaining voltage is sufficient to keep it lit until the pixel is completely discharged and shut off.

19. PDP Rib Structure (Simple)
To make a plasma display panel, ribs are etched into one layer of special glass to form shallow channels, which are then filled with rare earth phosphors. Cross ribs on a second piece of glass then form pixels when bonded to the first layer. Addressing electrodes are attached to each pixel. The finished panel is then filled with a mixture of noble gases, typically neon and xenon.

20. Deep Cell Structure (Advanced)
Waffle-like structure
Higher light output
Less light leakage between rib barriers
Developed by Pioneer
Plasma panels are also being manufactured with formed cells instead of simple ribs. The advantage of this pixel design is that it reduces stray light leakage and achieves higher luminous efficiency for a given level of power. Pioneer originally developed this technique, which is being adopted by other plasma manufacturers.

21. Plasma Tube Structure (Future?)
Phosphors, electrodes, and Ne/Xe gas combined into long tubes
Reduces cost of larger screens
Flexible displays?
Developed by Fujitsu
Plasma can be made even larger by encasing the phosphors and electrodes into long tubes. This simplifies the construction of super-large plasma panels and reduces weight. It may be possible to construct flexible or curved plasma displays using tube technology.

22. 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 x768
Power consumption – watts over a 6-hour interval (total of kWh)
A representative 6th or 7th generation plasma monitor can develop 90 to 110 nits (26-32 ft-L) of brightness with a full white screen, and peak small-area brightness readings exceeding 400 nits. Contrast readings of 280:1 (average) and 500:1 (peak) are typical. The best plasma displays are capable of very low black levels, comparable to those of a CRT. Like LCD monitors and TVs, all plasma monitors and TVs being sold today have widescreen (16:9) aspect ratios.

23. Real-World Plasma Benchmarks
Color Rendering
Gamut is smaller than REC 709 coordinates
Green somewhat undersaturated
Red, blue are very close to ideal coordinates
A typical late-model LCD monitor or TV will deliver as much as 350 nits brightness when adjusted for best grayscale, with average contrast at 130:1 and peak contrast at 170:1. Black levels on LCD displays, while still higher than CRTs, have dropped to as low as 1.2 nits in the past year – about 10 times that of the best CRT displays.

24. Plasma Display Technology
Technology Enhancements:
Wider color gamuts (films, phosphors)
Improved lifetime (gas mixtures)
Higher resolution 50”)
Resistance to burn-in (change in gas mixture)
A liquid-crystal display (LCD) employs transmissive light and a shutter-like mechanism to form grayscale images. Individual liquid crystals within each pixel change their alignment in response to changes in control voltage and will pass or block polarized light to varying degrees. This variation in light intensity, or light shuttering, forms a grayscale image.
LCD monitors are capable of generating very bright images, suitable for viewing under low to moderate ambient light levels. Screens as large as 82 inches have been shown publicly, with resolutions of 1920x1080 pixels. Brightness levels are in excess of 500 nits (over 146 ft-L) on some models. Currently, a LCD monitor or TV requires 10% to 20% less power than a same-size plasma monitor or TV, and weighs about 20% to 25% less.

25. Reflective Imaging: Digital Light Processing (DLP) Displays

26. 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
DLP displays use reflected light to form images, rather than transmissive light. At the heart of DLP technology is a custom-made semiconductor chip with an array of tiny digital micromirror devices, or DMDs. Each individual mirror device can be independently commanded to tilt at a rapid, repeatable rate towards or away from a light source.

27. 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
The small angle of tilt and its repeatability makes it possible to form grayscale images on each DMD. The mirrors cycle between their ‘on’ and ‘off’ positions, thousands of times per second. This technique is known as ‘pulse-width modulation’. In such a system, there are no in-between positions for the mirrors. Rather, a grayscale image is produced by the ratio of ‘on’ positions to ‘off’ positions in a given time interval.

28. 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
The technique of pulse width modulation is not new. It has also been used to control motors, lighting, and even to conserve power in portable communications equipment. In a display system, the rapid on-off cycling can produce images with no apparent flicker. In a given time interval, if there are more ‘on’ cycles than ‘off’, the image will appear to be brighter. If there are more ‘off’ cycles than ‘on’, the image will appear darker.
ON > OFF
OFF > ON

29. DLP Imaging – Single Chip
In a single chip DLP light engine, the optical path is very simple. Light from the lamp passes through a condenser and a sequential color wheel. The colored beams of light then strike the surface of the DMD and are reflected at an angle back to the projection lens.

30. DLP Imaging – Three-Chip
The second approach uses three DMDs and a set of dichroic filters and mirrors. Red, green, and blue light is reflected off each DMD, and each color beam is then precisely converged inside the projector using a polarizing beam splitter. The result is once again a full-color image, with a greater degree of color saturation than the single DMD and color wheel can provide. Three-chip DMD projectors are used for projection in large spaces as well as electronic cinema.

31. 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
This slide shows a polarizing beam splitter for a digital cinema projection system. Light travels in two different directions through the mirrors inside this prism as images are being formed.

32. 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
DMDs are manufactured in a wide range of sizes and aspect ratios, from 800x600 (SVGA) and 1024x768 (XGA) chips with 4:3 aspect ratios to 16:9 1280x720 and 2048x1080 arrays. DLP imaging in the single-chip mode employs a simple light path from lamp to mirror to screen. DMDs are 100% digital light modulators, the only imaging system that can make that claim at present.
SXGA (left) and XGA (right) DMDs

33. Reflective Imaging: Liquid-Crystal on Silicon (LCoS) Displays

34. 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 and LCD devices have a lot in common. Both have a fixed-pixel structure, and both contain tiny liquid crystals that change position in response to varying control voltages. But that's where the similarity ends.
LCOS devices shutter light as it is reflected off their mirrored rear surface, or backplane. While this makes things a bit more complicated optically, it does improve the efficiency of the LCOS device.

35. LCoS Panel Cutaway
The controlling transistors are now part of the backplane of the LCOS chip, and not in the path of reflected light. The available imaging area on each pixel (known as the fill factor) is now greater, further improving illumination efficiency. As a result, the resolution of LCOS panels can be higher for a given panel size than in high-temperature polysilicon LCD panels.

36. LCoS Optical Engine
This image shows the complex optical path inside an LCoS imaging engine. Note that rays of light are traveling in two different directions through some of the mirror surfaces.

37. 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
The largest manufacturer of LCOS panels is Japan Victor Corporation, otherwise known as JVC. Their implementation of LCOS is called the Direct Drive Image Light Amplifier, or D-ILA for short. It was introduced in 1997.
The original D-ILA measured .9" diagonally and had a native pixel count of 1365x1024 (SXGA), sufficient to show 1280x720 HDTV at full resolution in a letterbox presentation. JVC also offers .7-inch 1400x1050 (SXGA+) and .9-inch 1920x1080 D-ILA panels.
JVC 4096x2160 D-ILA Panel

38. 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 also manufactures a variation of LCOS, which goes by the name Silicon Xtal Reflective Device or SXRD. At present, there are two SXRD panel designs in use. The first measures .78 inches diagonally and offers 1920x1080 pixel resolution, while the second measures 1.55 inches diagonally and offers 4096x2160 pixels of resolution. Other companies currently manufacturing LCOS imaging panels include Brillian, SpatiaLight, and Hitachi.
Sony 4096x2160 SXRD panel

39. Image Quality Parameters

40. 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)
Light output and image resolution are permanently linked in a CRT display. Increasing the brightness of a CRT image also "spreads" the electron beam's dot, sacrificing resolution. LCD and DLP projectors have no such limitation, as their resolution is independent of image brightness. LCD and plasma displays also have a fixed resolution, with their brightness limited only by user choice.
Until recently, only CRT-based imaging systems could generate the widest possible grayscales and high contrast ratios while holding a very dense "black" on the screen. Now, LCOS and LCD projectors routinely achieve peak contrast levels approaching 500:1, while DLP projectors are pushing the 1000:1 barrier. The best plasma displays can exceed 800:1 peak contrast, while LCD monitors are still in the 200:1 range.

41. 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
White balance is an area where CRT projectors and monitors still hold an edge over flat-screen displays. Because a CRT projector generates equal amounts of red, green, and blue energy, we can dial in a precise color temperature and expect it to remain constant over a wide grayscale.
Color temperature works hand-in-hand with white balance. CRT displays (as well as the new SED and OLED displays) have no inherent color bias. Red, green, and blue light are simply mixed until the desired color temperature value is arrived at.

42. Illuminants: Projection Lamps
Short-arc mercury vapor lamps
UHP, UHE, SHE are common designations
Uneven spectral output
Life 1000–3000 hours
The most common lamp type is the short-arc mercury vapor lamp, which is sold under different brands including Ultra High Performance (UHP) and Ultra High Efficiency (UHE). This lamp has good luminous efficiency, but produces an excess of blue-green light that must be filtered. Lamp life varies, but is typically between 1000 to 4000 hours to half brightness.
150W UHP Lamp

43. Illuminants: Projection Lamps
Short-arc xenon lamps
Higher wattage than comparable UHP lamps
Evenly-distributed spectral output
Life hours
Another compact, high-output short-arc lamp is the xenon type. The spectral energy from xenon lamps is more evenly distributed across the color spectrum. Xenon lamps are commonly used in movie theaters. In projectors, they have a life expectancy of 500 to 2000 hours to half-brightness.
325W Xenon Lamp

44. 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)
LCD monitors also have an inherently high color temperature, due to their use of cold-cathode fluorescent lamps as backlights.
Cold-cathode fluorescent lamps are relatively inexpensive to manufacture and have high luminous efficiency. Their use enables the thin form factor of LCD TVs and monitors. The life expectancy of a CCFL is about 50,000 to 60,000 hours to half-brightness.
Two CCFL Lamps

45. 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”
Some manufacturers of LCD monitors are experimenting with light-emitting diode (LED) backlights to achieve more even spectral energy and precise color balancing. This is a must if LCD monitors are to replace CRT technology in professional-grade monitors.
GRB LED Array

46. 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)
Plasma monitors and TVs do not suffer from an inherent color bias, other than the nominal spectral output of stimulated neon and xenon gases. Filters built in to the front screen can easily correct for this slight tint. However, the red, green, and blue color points from plasma phosphors do not necessarily match those from a CRT display.
Typically, red as rendered on a plasma display has more orange in it, while green appears to have more yellow in it. This is a natural by-product of the UV stimulation of the phosphors. It is possible to correct for the excessive blue and UV energy with a tinted front glass filter. As is the case with projectors, using such a filter does reduce light output.
Close-up of RGB Phosphors

47. See It Now: A Primer on LCD, DLP, LCoS, and Plasma Technologies
Pete Putman, CTS, ISF
Publisher, HDTVexpert.com
Contributing Editor, Pro AV