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In-Plane Switching (IPS) Reflective LCDs, often found in digital watches and calculators, are illuminated by external light reflected by a (sometimes) diffusing reflector behind the display. This type of LCD can produce darker 'blacks' than the transmissive type since light must pass through the liquid crystal layer twice and thus is attenuated twice, however because the reflected light is also attenuated twice in the translucent parts of the display image contrast is usually poorer than a transmissive display. The absence of a lamp significantly reduces power consumption, allowing for longer battery life in battery-powered devices; small reflective LCDs consume so little power that they can rely on a photovoltaic cell, as often found in pocket calculators. A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices. * LCD screens occasionally suffer from image persistence, which is similar to screen burn on CRT displays. The Plasma display panel was invented at the University of Illinois at Urbana-Champaign by Donald L. Bitzer and H. Gene Slottow in 1964 for the PLATO Computer System. The original monochrome (usually orange or green) panels enjoyed a surge of popularity in the early 1970s because the displays were rugged and needed neither memory nor refresh circuitry. There followed a long period of sales decline in the late 1970s as semiconductor memory made CRT displays incredibly cheap. Nonetheless, plasma's relatively large screen size and thin profile made the displays attractive for high-profile placement such as lobbies and stock exchanges. In 1983, IBM introduced a 19" orange on black monochrome display (model 3290 'information panel') which was able to show four simultaneous 3270 virtual machine (VM) terminal sessions. In 1992, Fujitsu introduced the world's first 21-inch full color display. It was a hybrid based on the plasma display created at the University of Illinois at Urbana-Champaign and NHK STRL, achieving superior brightness.
The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can retain an image without power. The crystals may exist in one of two stable orientations (Black and "White") and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufacture both grayscale and colour ZBD devices. The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, on both sides of the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate. The Plasma display panel was invented at the University of Illinois at Urbana-Champaign by Donald L. Bitzer and H. Gene Slottow in 1964 for the PLATO Computer System. The original monochrome (usually orange or green) panels enjoyed a surge of popularity in the early 1970s because the displays were rugged and needed neither memory nor refresh circuitry. There followed a long period of sales decline in the late 1970s as semiconductor memory made CRT displays incredibly cheap. Nonetheless, plasma's relatively large screen size and thin profile made the displays attractive for high-profile placement such as lobbies and stock exchanges. In 1983, IBM introduced a 19" orange on black monochrome display (model 3290 'information panel') which was able to show four simultaneous 3270 virtual machine (VM) terminal sessions. In 1992, Fujitsu introduced the world's first 21-inch full color display. It was a hybrid based on the plasma display created at the University of Illinois at Urbana-Champaign and NHK STRL, achieving superior brightness.
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A diagram of the Pixel layout Before applying an electrical charge, the liquid crystal molecules are in a relaxed state. Charges on the molecules cause these molecules to align themselves in a helical structure, or twist (the "crystal"). In some LCDs, the electrode may have a chemical surface that seeds the crystal, so it crystallizes at the needed angle. Light passing through one filter is rotated as it passes through the liquid crystal, allowing it to pass through the second polarized filter. A small amount of light is absorbed by the polarizing filters, but otherwise the entire assembly is transparent. Kent Displays, [1], has also developed a "no power" display that uses Polymer Stabilized Cholesteric Liquid Crystals(ChLCD). The major drawback to the ChLCD display is slow refresh rate, especially with low temperatures. Zero-power displays To save cost in the electronics, LCDs are often multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together, and each group gets its own voltage source. On the other side, the electrodes are also grouped, with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink.
Quality control LCD panels are more likely to have defects than most ICs due to their larger size. In this example, a 12" SVGA LCD has 8 defects and a 6" wafer has only 3 defects. However, 134 of the 137 dies on the wafer will be acceptable, whereas rejection of the LCD panel would be a 0% yield. The standard is much higher now due to fierce competition between manufacturers and improved quality control. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. The location of defective pixels is also important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other. Manufacturers may also relax their replacement criteria when defective pixels are in the center of the viewing area. History