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Active matrix technologies TFT LCDs are a variant of liquid crystal display which use thin-film transistor technology to improve their image quality. TFT LCDs are one type of active matrix LCD, though this is usually synonymous with them. They are used in both flat panel displays and projectors. In computing, TFT monitors are rapidly displacing competing CRT technology, and are commonly available in sizes from 30 to 77 cm (~12 to 30 inches). As of 2005, they have also made inroads on the television market. The layout of the circuit is very similar to the one used in DRAM computer memory but rather than being built using silicon wafers, the whole structure needs to be created on glass. Many of the processing techniques used in creating circuits on silicon require temperatures in excess of the melting point of glass. The silicon substrate of normal semiconductors is grown from liquid silicon to produce a large single crystal with excellent properties for transistors. The silicon layer for TFT LCDs is deposited from Silane gas to produce an amorphic or polycrystalline silicon layer which is far less suitable for producing high grade transistors. In a monochrome plasma panel, control circuitry charges the electrodes that cross paths at a cell, causing the plasma to ionize and emit photons between the electrodes. The ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.
The layout of the circuit is very similar to the one used in DRAM computer memory but rather than being built using silicon wafers, the whole structure needs to be created on glass. Many of the processing techniques used in creating circuits on silicon require temperatures in excess of the melting point of glass. The silicon substrate of normal semiconductors is grown from liquid silicon to produce a large single crystal with excellent properties for transistors. The silicon layer for TFT LCDs is deposited from Silane gas to produce an amorphic or polycrystalline silicon layer which is far less suitable for producing high grade transistors. Zero-power displays Contrast ratio claims Construction TN+Film Many LCDs are driven to darkness by an alternating current, which disrupts the twisting effect, and become faint or transparent when no current is applied. General characteristics
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Passive-matrix and active-matrix Quality control Due to the immense cost of building TFT factories, the number of major OEM panel vendors probably does not exceed four or five. Several of the most well-known are Samsung, LG.Philips LCD and AU Optronics. Drawbacks During the 1970s and early 1980s, LCD technology was not yet mature. However, during the early 80's timeframe, a tabletop video game called Popeye was made with a color LCD, a device with technology ahead of it's time. Technologies used for portable devices made prior to the 1990s to use color graphics include tabletop video games that use Vacuum fluorescent displays and also, before modern laptop computers that used color graphics, the so-called luggable computer, Commodore SX-64 used color graphics on a mini-CRT. The Commodore SX-64 was however bulky hence the aforementioned term luggable. Construction A general purpose alphanumeric LCD, with two lines of 16 characters.
The TN display suffers from limited viewing angles, especially in the vertical direction, and some are unable to display the full 16.7 million colors (24-bit truecolor) available from modern graphics cards. These particular panels, with 6 bits per color channel as opposed to 8, can approach true 24-bit color using a dither method which quickly cycles pixels to simulate a given shade, which are noticeable to some and discomforting to others. Overall, color reproduction and linearity on TN panels is poor. Shortcomings in display color gamut (often referred to as a percentage of the NTSC color gamut) can also be attributed to backlighting technology. It is not uncommon for displays with CCFL (Cold Cathode Fluorescent Lamps) based lighting to range from 40% to 76% of the NTSC color gamut, whereas displays utilizing white LED backlights may extend past 100% of the NTSC color gamut -a difference quite perceivable by the human eye. 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. To ionize the gas in a color panel, the plasma display's computer charges the electrodes that intersect at that cell thousands of times in a small fraction of a second, charging each cell in turn. When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons. Some LCD panels have defective transistors, causing permanently lit or unlit pixels. Unlike integrated circuits, LCD panels with a few defective pixels are usually still usable. It is also economically prohibitive to discard a panel with just a few bad pixels because LCD panels are much larger than ICs. Manufacturers have different standards for determining a maximum acceptable number of defective pixels. The following table presents the maximum acceptable number of defective pixels for IBM's ThinkPad laptop line.