A Seminar on

Cad Display DevicesAgnel Technical College

Mrinal D. Shah

042377

ACKNOWLEDGEMENT

It gives me great pleasure to create this seminar report on CAD DISPLAY DEVICES. It indeed goes without saying that success of the report is because of direct and indirect guidance of everybody in college. I take the opportunity to acknowledge their help for this valuable assistance, either by providing input required or by reviewing the project.

I am very thankful to Mr. Mangesh Mohan, for guiding me to get the require information needed to prepare the report.

Last but not the least I will like to thank all my friends.

MRINAL D. SHAH

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CONTENTS

Direct View Storage Tube History Direct View Storage Tube Display Direct View Storage Tube Terminal

Raster Scan Display Raster Raster Display Raster Scan Raster Scan Tracing Rasterize Raster Image Processing Rotatable Raster Scan Display

LCD TV’s History of TFT LCD What is TFT LCD TFT LCD - Electronic Aspects of LCD TVs and LCD Monitors TFT LCD - Precaution and Failure

Plasma TV’s What is Plasma? Another Version on How Plasmas Work Working of Plasma TV Inside the Display

DLP Technology What is DLP Technology for Video Projectors and TV? The DLP Light Engine How does DLP Technology work? Beautiful Picture Smarter Picture DLP Technology vs. LCD

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Direct View Storage Tube

History

Storage-tube display technology and costs will continue to attract new users and new applications, especially where verily high information density is needed.

The direct view storage tube was invented by Robert H. Anderson in the late 1950's' and first introduced in the model 564 oscilloscope. As computer display requirements matured, it was felt that a larger-screen version of the DVST might fulfill a need in the computing industry, and thus the 611 11-inch storage monitor was introduced in 1967.2 By 1970, Computek, Adage, and Tektronix all had graphics terminals on the market based on the 611 monitor. Even though these terminals represented a cost breakthrough at the time ($9000 as opposed to an IBM 2250 at $80,000), success was not assured and knowledgeable people were predicting a five-year life for the DVST technology. Then, in 1972, Tektronix introduced the 4010 DVST graphics terminal at $4000. This terminal launched the storage graphics revolution. Was cost the only important factor? Perhaps not, for in 1973 the 4014 19-inch storage terminal was introduced at $8995, and it became an even bigger success than the 4010, resulting in a new class of customers using storage graphics terminals. Knowledgeable people continued to predict a five-year life for the DVST technology and were now carefully watching the declining cost of RAM memory. Now, five years later, RAM costs are still being watched, and the 611 storage monitor is still selling. Complex interactions are evidently operating in the storage-terminal marketplace.

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Direct View Storage Tube Display

This CRT has a slightly different construction. Flood cathode produces free electrons. The electron beam now writes to (i.e. store a charge on) the storage grid: - this is semi-permanent. The resultant charge on the grid attracts the electrons produced by the flood cathode and these will pass the grid and hit the phosphor.

The finer the grid the higher the resolution of the DVST (Direct View Storage Tube). Resolutions up to 4096 x 4096 are currently available for monochrome displays. Colour displays are much more difficult but Tektronix, a leader in the field of DVST's, sells these also. The T4010 is a DVST. (This technology is pretty much dead now.)

To erase any part of the screen, we must erase the entire screen since we have to destroy the charge on the storage grid. Therefore no good for interactive work which requires selective erasure. But needs no memory nor computer power. Example:

  Direct View Storage Tube example

DVST Terminal

DVST terminals also use the stroke-writing approach to generate the image on the CRT screen. The term “storage tube” refers to the ability of the screen to retain the image, which has been projected against it, thus avoiding the need to rewrite the image constantly. What makes this possible is the use of an electron flood gun directed at the phosphor coated screen which keeps the phosphor elements illuminated once they have been energized by the stroke-writing electron beam. The resulting image on the CRT screen is flicker-free. Lines may be readily added to the image without concern over their effect on image density or refresh rates. However, the penalty associated with the storage tube is that individual lines cannot be selectively removed from the image.

Storage tubes have historically been the lowest-cost terminals and are capable of displaying large amounts of data, either graphical or textual. Because of these features, there are probably more storage tube terminals in service in industry at the time of this

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writing than any other graphics display terminal. The principal disadvantage of a storage CRT is that selective erasure is not possible. Instead, if the user wants to change the picture, the change will not be manifested on the screen until the entire picture is regenerated. Other disadvantages include its lack of color capability, the inability to use a light pen as a data entry device, and its lack of animation capability.

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Raster Scan Display

Raster

The horizontal lines (scan lines) displayed on a TV or computer monitor. This is the origin of the term "raster graphics," which is the major category that all bitmapped images and video frames fall into (GIF, JPEG, MPEG, etc.).

Raster Display

A TV or computer monitor that uses the raster scan method for creating the image on screen. Almost all displays use the raster method.

Raster Scan

Raster scan terminals operate by causing an electron beam to trace a zigzag pattern across the viewing screen, as described earlier. The operation is similar to that of a commercial television set. The difference is that a TV set uses analog signals originally generated by a video camera to construct the image on the CRT screen, while the raster scan ICG terminal uses digital signals generated by a computer. For this reason, the raster scan terminals used in computer graphics are sometimes called digital TVs.

The introduction of the raster scan graphics terminal using a refresh tube had been limited by the cost of computer memory. For example, the simplest and lowest-cost terminal in this category uses only two beam intensity levels, on or off. This means that each pixel in the viewing screen is either illuminated or dark. A picture tube with 223 lines of resolution and 223 addressable points per line to form the image would require 223 x 223 or over 32,000 bits of storage. Each bit of memory contains the on/off status of the corresponding pixel on the CRT screen. This memory is called the frame buffer or refresh buffer. The picture quality can be improved in two ways: by increasing the pixel density or adding a gray scale (or color).

Increasing pixel density for the same size screen means adding more lines of resolution and more addressable points per line. A 1021 x 1021 raster screen would require more than 1 million bits of storage in the frame buffer. A gray scale is accomplished by expanding the number of intensity levels, which can be displayed on each pixel. This requires additional bits for each pixel to store the intensity level. Two bits are required for four levels, three bits for eight levels, and so forth. Five or six bits would be needed to achieve an approximation of a continuous gray scale. For a color display, three times as many bits are required to get various intensity levels for each of the three primary colors: red, blue, and green. A raster scan graphics terminal with high resolution and gray scale can require a very large capacity refresh buffer. Until recent developments in memory technology, the cost of this storage capacity was prohibitive for a terminal with good picture quality. The capability to achieve color and animation was not possible except for very low-resolution levels. It is now possible to manufacture digital TV

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systems for interactive computer graphics at prices, which are competitive with the other two types. The advantages of the present raster scan terminals include the feasibility of use low-cost TV monitors, color capability, and the capability for animation of the image. These features, plus the continuing improvements being made in raster scan technology; make it the fastest-growing segment of the graphics display market.

Raster Scan Tracing

Starting at the top-left of the screen and going to the bottom-right, the electron beam is turned on a line at a time (1), then turned off to go back to the next line (2), then off once again to go back up to the top (3).

Rasterize

To prepare a page for display or printing, rasterization is performed by a raster image processor (RIP), which turns text and images into the matrix of pixels (bitmap) that will be displayed on screen or printed on the page. Various conversions may take place. For example, the mathematical coordinates of vector and outline fonts as well as vector drawings must be converted into bitmaps. Existing bitmaps may have to be scaled into different-sized bitmaps.

Unless output is printed on a vector graphics plotter, which literally draws the illustration with pens, all text and graphics must be rasterized into a bitmap for display or printing.

Raster Image Processing

The hardware and/or software that rasterizes an image for display or printing. RIPs are designed to rasterize a specific type of data, such as PostScript. As desktop computers became more powerful, software RIPs became more appealing than specialized

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hardware RIPs. Software can be upgraded more easily, and the operation is always speeded up by installing a faster CPU.

Rotatable Raster Scan Display

Apparatus for rotating a cathode ray tube (CRT) which is operated as a graphic display through 90 degrees such that different size pages of data may be displayed while minimizing the control circuitry required. The display deflection yoke is fixedly attached to a support frame for the display. The CRT is rotatably mounted within the yoke and held by annular thrust bearing which allows the CRT to be rotated 90 degrees. A switch is actuated by the rotation of the CRT to select between sets of control resistors to control the raster scan of the CRT in accordance with its orientation.

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LCD TV’s

History of TFT LCD

Liquid crystal was discovered by the Austrian botanist Fredreich Rheinizer in 1888. "Liquid crystal" is neither solid nor liquid (an example is soapy water).

In the mid-1960s, scientists showed that liquid crystals when stimulated by an external electrical charge could change the properties of light passing through the crystals.

The early prototypes (late 1960s) were too unstable for mass production. But all of that changed when a British researcher proposed a stable, liquid crystal material (biphenyl).

Today's color LCD TVs and LCD Monitors have a sandwich-like structure (see figure below).

What is TFT LCD?

TFT LCD (Thin Film Transistor Liquid Crystal Display) has a sandwich-like structure with liquid crystal filled between two glass plates.

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TFT Glass has as many TFTs as the number of pixels displayed, while a Color Filter Glass has color filter which generates color. Liquid crystals move according to the difference in voltage between the Color Filter Glass and the TFT Glass. The amount of light supplied by Back Light is determined by the amount of movement of the liquid crystals in such a way as to generate color. 

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TFT LCD - Electronic Aspects of LCD TVs and LCD Monitors

Electronic Aspects of AMLCDs

The most common liquid-crystal displays (LCDs) in use today rely on picture elements, or pixels, formed by liquid-crystal (LC) cells that change the polarization direction of light passing through them in response to an electrical voltage.

As the polarization direction changes, more or less of the light is able to pass through a polarizing layer on the face of the display. Change the voltage, and the amount of light is changed.

There are two ways to produce a liquid-crystal image with such cells: the segment driving method and the matrix driving method.

The segment driving method displays characters and pictures with cells defined by patterned electrodes.

The matrix driving method displays characters and pictures in sets of dots.

Direct vs. multiplex driving of LCD TVs.

The segment drive method is used for simple displays, such as those in calculators, while the dot-matrix drive method is used for high-resolution displays, such as those in portable computers and TFT monitors.

Two types of drive method are used for matrix displays. In the static, or direct, drive method, each pixel is individually wired to a driver. This is a simple driving method, but, as the number of pixels is increased, the wiring becomes very complex. An alternative method is the multiplex drive method, in which the pixels are arranged and wired in a matrix format.

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To drive the pixels of a dot-matrix LCD, a voltage can be applied at the intersections of specific vertical signal electrodes and specific horizontal scanning electrodes. This method involves driving several pixels at the same time by time-division in a pulse drive. Therefore, it is also called a multiplex, or dynamic, drive method.

Passive and Active Matrix LCD’s

There are two types of dot-matrix LCD’s.

Passive-matrix vs. active-matrix driving of LCD Monitors.

In passive-matrix LCDs (PMLCDs) there are no switching devices, and each pixel is addressed for more than one frame time. The effective voltage applied to the LC must average the signal voltage pulses over several frame times, which results in a slow response time of greater than 150 msec and a reduction of the maximum contrast ratio. The addressing of a PMLCD also produces a kind of crosstalk that produces blurred images because non-selected pixels are driven through a secondary signal-voltage path. In active-matrix LCDs (AMLCDs), on the other hand, a switching device and a storage capacitor are integrated at the each cross point of the electrodes.

The active addressing removes the multiplexing limitations by incorporating an active switching element. In contrast to passive-matrix LCDs, AMLCDs have no inherent limitation in the number of scan lines, and they present fewer cross-talk issues. There are many kinds of AMLCD. For their integrated switching devices most use transistors made of deposited thin films, which are therefore called thin-film transistors (TFTs).

The most common semiconducting layer is made of amorphous silicon (a-Si). A-Si TFTs are amenable to large-area fabrication using glass substrates in a low-temperature (300°C to 400°C) process.

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An alternative TFT technology, polycrystalline silicon - or polysilicon or p-Si-is costly to produce and especially difficult to fabricate when manufacturing large-area displays.

Nearly all TFT LCDs are made from a-Si because of the technology's economy and maturity, but the electron mobility of a p-Si TFT is one or two orders of magnitude greater than that of an a-Si TFT.

This makes the p-Si TFT a good candidate for an TFT array containing integrated drivers, which is likely to be an attractive choice for small, high definition displays such as view finders and projection displays.

Structure of Color TFT LCD TVs and LCD Monitors

A TFT LCD module consists of a TFT panel, driving-circuit unit, backlight system, and assembly unit.

Structure of a color TFT LCD Panel:

1. LCD Panel - TFT-Array Substrate - Color Filter Substrate

2. Driving Circuit Unit - LCD Driver IC (LDI) Chips - Multi-layer PCBs - Driving Circuits

3. Backlight & Chassis Unit - Backlight Unit - Chassis Assembly

It is commonly used to display characters and graphic images when connected a host system.The TFT LCD panel consists of a TFT-array substrate and a color-filter substrate.

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The vertical structure of a color TFT LCD panel.

The TFT-array substrate contains the TFTs, storage capacitors, pixel electrodes, and interconnect wiring. The color filter contains the black matrix and resin film containing three primary-color - red, green, and blue - dyes or pigments. The two glass substrates are assembled with a sealant, the gap between them is maintained by spacers, and LC material is injected into the gap between the substrates. Two sheets of polarizer film are attached to the outer faces of the sandwich formed by the glass substrates. A set of bonding pads are fabricated on each end of the gate and data-signal bus-lines to attach LCD Driver IC (LDI) chips

Driving Circuit Unit

Driving an a-Si TFT LCD requires a driving circuit unit consisting of a set of LCD driving IC (LDI) chips and printed-circuit-boards (PCBs).

The assembly of LCD driving circuits .

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A block diagram showing the driving of an LCD panel.

To reduce the footprint of the LCD module, the drive circuit unit can be placed on the backside of the LCD module by using bent Tape Carrier Packages (TCPs) and a tapered light-guide panel (LGP).

How TFT LCD Pixels Work  

A TFT LCD panel contains a specific number of unit pixels often called sub pixels. Each unit pixel has a TFT, a pixel electrode (IT0), and a storage capacitor (Cs). For example, an SVGA color TFT LCD panel has total of 800x3x600, or 1,440,000, unit pixels. Each unit pixel is connected to one of the gate bus-lines and one of the data bus-lines in a 3mxn matrix format. The matrix is 2400x600 for SVGA.

Structure of a color TFT LCD panel.

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Because each unit pixel is connected through the matrix, each is individually addressable from the bonding pads at the ends of the rows and columns.

The performance of the TFT LCD is related to the design parameters of the unit pixel, i.e., the channel width W and the channel length L of the TFT, the overlap between TFT electrodes, the sizes of the storage capacitor and pixel electrode, and the space between these elements.

The design parameters associated with the black matrix, the bus-lines, and the routing of the bus lines also set very important performance limits on the LCD.

In a TFT LCD's unit pixel, the liquid crystal layer on the ITO pixel electrode forms a capacitor whose counter electrode is the common electrode on the color-filter substrate.

Vertical structure of a unit pixel and its equivalent circuit

A storage capacitor (Cs) and liquid-crystal capacitor (CLC) are connected as a load on the TFT. Applying a positive pulse of about 20V peak-to-peak to a gate electrode through a gate bus-line turns the TFT on. Clc and Cs are charged and the voltage level on the pixel electrode rises to the signal voltage level (+8 V) applied to the data bus-line.

The voltage on the pixel electrode is subjected to a level shift of DV resulting from a parasitic capacitance between the gate and drain electrodes when the gate voltage turns from the ON to OFF state. After the level shift, this charged state can be maintained as the gate voltage goes to -5 V, at which time the TFT turns off. The main function of the Cs is to maintain the voltage on the pixel electrode until the next signal voltage is applied.

Liquid crystal must be driven with an alternating current to prevent any deterioration of image quality resulting from dc stress. This is usually implemented with a frame-reversal drive method, in which the voltage applied to each pixel varies from frame to frame. If

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the LC voltage changes unevenly between frames, the result would be a 30-Hz flicker. (One frame period is normally 1/60 of a second.) Other drive methods are available that prevent this flicker problem.

Polarity-inversion driving methods.

In an active-matrix panel, the gate and source electrodes are used on a shared basis, but each unit pixel is individually addressable by selecting the appropriate two contact pads at the ends of the rows and columns.

Active addressing of a 3x3 matrix

By scanning the gate bus-lines sequentially, and by applying signal voltages to all source bus-lines in a specified sequence, we can address all pixels. One result of all this is that the addressing of an AMLCD is done line by line.

Virtually all AMLCDs are designed to produce gray levels - intermediate brightness levels between the brightest white and the darkest black a unit pixel can generate. There can be either a discrete numbers of levels - such as 8, 16, 64, or 256 - or a continuous gradation of levels, depending on the LDI.

The optical transmittance of a TN-mode LC changes continuously as a function of the applied voltage. An analog LDI is capable of producing a continuous voltage signal so that a continuous range of gray levels can be displayed. The digital LDI produces

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discrete voltage amplitudes, which permits on a discrete numbers of shades to be displayed. The number of gray levels is determined by the number of data bits produced by the digital driver.

Generating Colors

The color filter of a TFT LCD TV consists of three primary colors - red (R), green (G), and blue (B) - which are included on the color-filter substrate.

How an LCD Panel produces colors.

The elements of this color filter line up one-to-one with the unit pixels on the TFT-array substrate. Each pixel in a color LCD is subdivided into three sub pixels, where one set of RGB sub pixels is equal to one pixel. (Each sub pixel consists of what we've been calling a unit pixel up to this point.)

Because the sub pixels are too small to distinguish independently, the RGB elements appear to the human eye as a mixture of the three colors. Any color, with some qualifications, can be produced by mixing these three primary colors.

The total number of display colors using an n-bit LDI is given by 23n, because each sub pixel can generate 2n different transmittance levels.

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TFT LCD - Precaution and Failure

Temperature / Humidity

It is recommended to use the product at room temperature and humidity in order to maintain its optimum performance.

1. Product lifetime can be shortened when it is used under conditions of high temperature and humidity.

2. When it is used at low temperature of 10°C or lower, response time and brightness are affected in such a way that the proper display may not be obtained.

3. When exposed to drastic fluctuation of temperature (hot to cold or cold to hot), the product may be affected; specifically, drastic temperature fluctuation from cold to hot, produces dew on the surface which may affect the operation of the polarizer and product.

 Environmental Consideration

It is recommended to use the product in a clean place and to exercise caution to ensure it is not affected by dust or liquids, etc.

1. If used in dusty place, dust may cause an electrical short inside the product resulting in malfunction

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2. If the product is contaminated by humid or liquid substance, polarizer may be discolored. If the liquid enters may enter the product to cause electrical failure or corrosion which, in turn, may lead to malfunction

 Handing

As LCD is a product made of glass, caution must be exercised in using it. It is recommended to handle it with care since shock, vibration, and careless handling may seriously affect the product.

1. The LCD surface is made of a soft film that is vulnerable to scratch and thus to damage by a sharp article.

2. Since the LCD is made of glass, it may be damaged if it is bent. If it falls from a high place or receives a strong shock, the glass may be broken.

3. The LCD product is composed of sensitive electronic parts and components. Therefore it must be grounded by ESD protection equipment (wrist band, etc.) before it is directly handled.

4. It is recommended that the product be handled with soft gloves during Assembly, etc. The LCD surface is made of soft film, vulnerable to scratches and thus to damage by a sharp articles.

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5. Do not bend or stretch the back light wire.

6. It is recommended that the product surface be cleaned it is dirty by using IPA (Isopropyl Alcohol) or Hexane. Keytone type material (Acetone), Ethyl or Methyl chloride must not be used as they can cause damage to the Polarizer.

7. The Driver IC of the TFT LCD for a Notebook PC is exposed on the back of the screen. If mechanical stress is applied to this area, it can cause failure. Do not hold or press this part with your hands.

 Usage

As LCD is sensitive electronic equipment, it is urged to comply with following precautions.

1. Never disassemble LCD product under any circumstances. If unqualified operators or users assemble the product after disassembling it, it may not function or its operation may be seriously affected.

2. When it is not in use, the screen must be turned off or the pattern must be frequently changed by a screen saver. If it displays the same pattern for a long period of time, brightness down/image sticking may develop due to the LCD structure.

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3. It is recommended that the product be stored in a cool and dry place in its original product box.

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Plasma TV’s

What is Plasma?

Plasma is often called the "Fourth State of Matter", the other three being solid, liquid and gas. Plasma is a distinct state of matter containing a significant number of electrically charged particles, a number sufficient to affect its electrical properties and behavior. In addition to being important in many aspects of our daily lives, plasmas are estimated to constitute more than 99 percent of the visible universe.

In an ordinary gas each atom contains an equal number of positive and negative charges; the positive charges in the nucleus are surrounded by an equal number of negatively charged electrons, and each atom is electrically "neutral". A gas becomes plasma when the addition of heat or other energy causes a significant number of atoms to release some or all of their electrons. The remaining parts of those atoms are left with a positive charge, and the detached negative electrons are free to move about. Those atoms and the resulting electrically charged gas are said to be "ionized". When enough atoms are ionized to significantly affect the electrical characteristics of the gas, it is plasma.

In many cases interactions between the charged particles and the neutral particles are important in determining the behavior and usefulness of the plasma. The type of atoms in a plasma, the ratio of ionized to neutral particles and the particle energies all result in a broad spectrum of plasma types, characteristics and behaviors. These unique behaviors cause plasmas to be useful in a large and growing number of important applications in our lives.

Another Version on How Plasmas Work

Plasma Display Panels (PDPs) are like CRTs in that they are emissive and use phosphor, and like LCDs in their use of an X and Y grid of electrodes separated by an MgO dielectric layer and surrounded by a mixture of inert gases - such as argon, neon or xenon - to address individual picture elements.

They work on the principle that passing a high voltage through a low-pressure gas generates light. Essentially, a PDP can be viewed as a matrix of tiny fluorescent tubes which are controlled in a sophisticated fashion. Each pixel, or cell, comprises a small capacitor with three electrodes. An electrical discharge across the electrodes causes the rare gases sealed in the cell to be converted to 24 | P a g e

plasma form as it ionizes. Plasma is an electrically neutral, highly ionized substance consisting of electrons, positive ions, and neutral particles. Being electrically neutral, it contains equal quantities of electrons and ions and is, by definition, a good conductor. Once energized, the cells of plasma release ultraviolet (UV) light which then strikes and excites red, green and blue phosphors along the face of each pixel, causing them to glow.

Within each cell, there are actually three sub cells, one containing a red phosphor, another blue phosphor, and the third a green phosphor. To generate colour shades, the perceived intensity of each RGB colour must be controlled independently. While this is done in CRTs by modulating the electron beam current, and therefore also the emitted light intensities, PDPs accomplish shading by pulse code modulation (PCM). Dividing one field into eight sub-fields, with each pulse weighted according to the bits in an 8-bit word, makes it possible to adjust the widths of the addressing pulses in 256 steps. Since the eye is much slower than the PCM, it will integrate the intensity over time. Modulating the pulse widths in this way translates into 256 different intensities of each colour - giving a total number of colour combinations of 256x256x256 = 16,777,216.

The fact that PDPs are emissive and use phosphor means that they have an excellent viewing angle and colour performance. Initially, PDPs had problems with disturbances caused by interference between the PCM and fast moving pictures. However, this problem has been eliminated by fine-tuning the PCM scheme. Conventional plasma screens have traditionally suffered from low contrast. This is caused by the need to "prime" the cells, applying a constant low voltage to each pixel. Without this priming, plasma cells would suffer the same poor response time of household fluorescent tubes, making them impractical. The knock-on effect, however, is that pixels which should be switched off still emit some light, reducing contrast. In the late 1990s Fujitsu alleviated this problem with new driver technology which improved contrast ratios from 70:1 to 400:1. By 2000 some manufacturers claimed as much as 3000:1 image contrast; albeit before the anti-glare glass is added to the raw panels.

The biggest obstacle that plasma panels have to overcome is their inability to achieve a smooth ramp from full white to dark black. Low shades of grey are particularly troublesome, a noticeable posterised effect often being present during the display of movies or other video programming with dark scenes. In technical terms, this problem is due to insufficient quantization, or digital sampling of brightness levels. It's an indication that the display of black remains an issue with PDPs.

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Manufacturing is simpler than for LCDs and costs are similar to CRTs at the same volume. Compared to TFTs, which use photolithographic and high-temperature processes in clean rooms, PDPs can be manufactured in less clean factories using low-temperature and inexpensive direct printing processes. However, with display lifetimes of around 30,000 hours, a factor not usually considered with PC displays - cost per hour - comes into play. For boardroom presentation use this isn't a problem, but for hundreds of general-purpose desktop PCs in a large company it's a different matter.

However, the ultimate limitation of the plasma screen has proved to be pixel size. At present manufacturers can't see how to get pixels sizes below 0.3mm, even in the long term. For these reasons PDPs are unlikely to play a part in the mainstream desktop PC market. For the medium term they are likely to remain best suited to TV and multi-viewer presentation applications employing large screens, from 25in up to 70in.For a number of years Fujitsu and Hitachi were the leading manufacturers of plasma displays. However, the number of patents issued for plasma display technology has surged in the last few years and now many large electronics companies believe PDPs are set to become a significant consumer product by 2005.

Working of Plasma TV

For the past 75 years, the vast majority of televisions have been built around the same technology: the cathode ray tube (CRT). In a CRT television, a gun fires a beam of electrons (negatively-charged particles) inside a large glass tube. The electrons excite phosphor atoms along the wide end of the tube (the screen), which causes the phosphor atoms to light up. The television image is produced by lighting up different areas of the phosphor coating with different colors at different intensities

Cathode ray tubes produce crisp, vibrant images, but they do have a serious drawback: They are bulky. In order to increase the screen width in a CRT set, you also have to increase the length of the tube (to give the scanning electron gun room to reach all parts of the screen). Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable chunk of a room.

Recently, a new alternative has popped up on store shelves: the plasma flat panel display. These televisions have wide screens, comparable to the largest CRT sets, but they are only about 6 inches (15 cm) thick. Based on the information in a video signal, the television lights up thousands of tiny dots (called pixels) with a high-energy beam of electrons. In most systems, there are three pixel colors -- red, green and blue -- which are evenly distributed on the screen. By combining these colors in different proportions, the television can produce the entire color spectrum.

The basic idea of a plasma display is to illuminate tiny colored fluorescent lights to form an image. Each pixel is made up of three fluorescent lights -- a red light, a green light and a blue light. Just like a CRT television, the plasma display varies the intensities of the different lights to produce a full range of colors.

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The central element in a fluorescent light is plasma, a gas made up of free-flowing ions (electrically charged atoms) and electrons (negatively charged particles). Under normal conditions, a gas is mainly made up of uncharged particles. That is, the individual gas atoms include equal numbers of protons (positively charged particles in the atom's nucleus) and electrons. The negatively charged electrons perfectly balance the positively charged protons, so the atom has a net charge of zero.

If you introduce many free electrons into the gas by establishing an electrical voltage across it, the situation changes very quickly. The free electrons collide with the atoms, knocking loose other electrons. With a missing electron, an atom loses its balance. It has a net positive charge, making it an ion.

In plasma with an electrical current running through it, negatively charged particles are rushing toward the positively charged area of the plasma, and positively charged particles are rushing toward the negatively charged area.

In this mad rush, particles are constantly bumping into each other. These collisions excite the gas atoms in the plasma, causing them to release photons of energyXenon and neon atoms, the atoms used in plasma screens, release light photons when they are excited. Mostly, these atoms release ultraviolet light photons, which are invisible to the human eye. But ultraviolet photons can be used to excite visible light photons, as we'll see in the next section.

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Inside the Display

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.

Both sets of electrodes extend across the entire screen. The display electrodes are arranged in horizontal rows along the screen and the address electrodes are arranged in vertical columns. As you can see in the diagram below, the vertical and horizontal electrodes form a basic grid.

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To ionize the gas in a particular cell, the plasma display's computer charges the electrodes that intersect at that cell. It does this 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. As we saw in the last section, the current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.

The released ultraviolet photons interact with phosphor material coated on the inside wall of the cell. Phosphors are substances that give off light when they are exposed to other light. When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons jumps to a higher energy level and the atom heats up. When the electron falls back to its normal level, it releases energy in the form of a visible light photon.

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The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate sub pixel cells, each with different colored phosphors. One sub pixel has a red light phosphor, one sub pixel has a green light phosphor and one sub pixel has a blue light phosphor. These colors blend together to create the overall color of the pixel.

By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each sub pixel color to create hundreds of different combinations of red, green and blue. In this way, the control system can produce colors across the entire spectrum.

The main advantage of plasma display technology is that you can produce a very wide screen using extremely thin materials. And because each pixel is lit individually, the image is very bright and looks good from almost every angle. The image quality isn't quite up to the standards of the best cathode ray tube sets, but it certainly meets most people's expectations. The biggest drawback of this technology has to be the price. With prices starting at $4,000 and going all the way up past $20,000, these sets aren't exactly flying off the shelves. But as prices fall and technology advances, they may start to edge out the old CRT sets. In the near future, setting up a new TV might be as easy as hanging a picture!

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DLP Technology

What is DLP Technology for Video Projectors and TV?

DLP technology is a revolutionary display solution for video projectors that uses an optical semiconductor to manipulate light digitally. It’s also a proven and dependable technology preferred by leading electronics manufacturers worldwide, with more than 1 million systems shipped since 1996.

DLP technology is in use wherever visual excellence is in demand. In fact, it’s the only display solution that enables movie video projectors, televisions, home theater systems and business video projectors to create an entirely digital connection between a graphic or video source and the screen in front of you.

The result is maximum fidelity: a picture whose clarity, brilliance and color must be seen to be believed.

The DLP Light Engine

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How does DLP Technology work?

The story begins with a breakthrough in micro engineering-and ends with the best picture quality money can buy.

1. The semiconductor that changed everything 2. Digital Light Processing I: the grayscale image 3. Digital Light Processing II: adding color 4. Applications and configurations

1. THE SEMICONDUCTOR THAT CHANGED EVERYTHING

At the heart of every DLP projection system is an optical semiconductor known as the Digital Micro mirror Device, or DMD chip, which was invented by Dr. Larry Hornbeck of Texas Instruments in 1987. The DMD chip is probably the world's most sophisticated light switch. It contains a rectangular array of up to 1.3 million hinge-mounted microscopic mirrors; each of these micro mirrors measures less than one-fifth the width of a human hair, and corresponds to one pixel in a projected image. When a DMD chip is coordinated with a digital video or graphic signal, a light source, and a projection lens, its mirrors can reflect an all-digital image onto a screen or other surface. The DMD and the sophisticated electronics that surround it are what we call Digital Light Processing technology.

2. DIGITAL LIGHT PROCESSING I: THE GRAYSCALE IMAGE

A DMD panel's micro mirrors are mounted on tiny hinges that enable them to tilt either toward the light source in a DLP projection system (ON) or away from it (OFF)-creating a light or dark pixel on the projection surface.

The bit-streamed image code entering the semiconductor directs each mirror to switch on and off up to several thousand times per second. When a mirror is switched on more frequently than off, it reflects a light gray pixel; a mirror that's switched off more frequently reflects a darker gray pixel.

In this way, the mirrors in a DLP projection system can reflect pixels in up to 1,024 shades of gray to convert the video or graphic signal entering the DMD into a highly detailed grayscale image.

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3. DIGITAL LIGHT PROCESSING II: ADDING COLOR

The white light generated by the lamp in a DLP projection system passes through a color wheel as it travels to the surface of the DMD panel. The color wheel filters the light into red, green, and blue, from which a single-chip DLP projection system can create at least 16.7 million colors. And the 3-DMD chip system found in DLP Cinema projection systems is capable of producing no fewer than 35 trillion colors.

The on and off states of each micro mirror are coordinated with these three basic building blocks of color. For example, a mirror responsible for projecting a purple pixel will only reflect red and blue light to the projection surface; our eyes then blend these rapidly alternating flashes to see the intended hue in a projected image.

4. APPLICATIONS AND CONFIGURATIONS

1-CHIP DLP PROJECTION SYSTEM

Televisions, home theater systems and business video projectors using DLP technology rely on a single DMD chip configuration like the one described above.

White light passes through a color wheel filter, causing red, green and blue light to be shone in sequence on the surface of the DMD. The switching of the mirrors and the proportion of time they are 'on' or 'off' is coordinated according to the color shining on them. The human visual system integrates the sequential color and sees a full-color image.

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3-CHIP DLP PROJECTION SYSTEM

DLP technology-enabled video projectors for very high image quality or high brightness applications such as cinema and large venue displays rely on a 3-DMD-chip configuration to produce stunning images, whether moving or still.

In a 3-chip system, the white light generated by the lamp passes through a prism that divides it into red, green and blue. Each DMD chip is dedicated to one of these three colors; the colored light that each micro mirror reflects is then combined and passed through the projection lens to form a single pixel in the image.

BEAUTIFUL PICTURE

CLARITY

DLP technology comes closer than any other display solution to reproducing the exact mirror image of its source material. That's why images projected by DLP technology are always crystal clear.

The thousands of mirrors making up the Digital Micro mirror Device at the heart of DLP technology are spaced less than one micron apart, resulting in a very high "fill factor." By minimizing the gaps between pixels in a projected image, DLP projection systems create a seamless digital picture that's sharp at any size-without the pixilation or "screen door" effect apparent in other technologies.

BRIGHTNESS

DLP projection systems outshine the alternatives because, being mirror-based, they use light more efficiently.

While other technologies lose a certain amount of light in transit, the microscopic mirrors in a DLP projection system bring more light from lamp to screen.

The difference is plain to see. With DLP technology, home entertainment becomes the visually stunning experience it should be. Business presentations have maximum impact-whether the lights are on or off. And large venue displays captivate their audiences with outputs of up to a whopping 15,000 lumens.

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COLOR

DLP technology reproduces a range of colors up to eight times greater than that of analog projection systems.

In televisions and home theater systems, DLP projection creates rich blacks and darker shades than is possible with other technologies. At the movies, DLP Cinema technology projects no fewer than 35 trillion colors-over eight times more than is possible with film.

DLP color is becoming even more brilliant as we introduce Sequential Color Recapture or SCR, an innovation that will enable DLP projection systems (video projectors) to bring up to 40 percent more lumens to the screen than was previously possible.

SMARTER PRODUCT

DESIGN

The Digital Micro mirror Device at the core of DLP technology can modulate light much more quickly than other display ingredients. That means a DLP projection system only requires one panel, while other technologies require three.

The result is a projection subsystem that is smaller and lighter, leaving ample room for innovative design. So product designers can focus on making their products lighter, slimmer, and more elegant.

Think wide-screen televisions that don't eat up the living room. A new generation of cabinet-sized, 40-inch tabletop TVs. And portable projectors weighing as little as two pounds that are bright enough for lights-on presentations.

RELIABILITY

DLP technology makes video projectors, home theater systems, and televisions more robust and more reliable.

The digital nature of DLP technology means that, unlike other display solutions, it's not susceptible to heat, humidity, or vibration-environmental factors that can cause an image to degrade over time.

DLP projection systems display an original-quality picture time and time again with zero hassle and minimal maintenance. And with more than one million systems shipped since 1996, DLP technology has a proven track record for outstanding dependability.

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VERSATILITY

DLP projection brings the same peerless visual standard to entertainment, work, and play.Innovation and flexibility: As far as we're concerned, you can't have one without the other. DLP technology fits into your life wherever visual experience is important. DLP technology delivers stunning images in your home, while DLP Cinema technology delivers unmatched image quality in the movie theater. The video projector you use for presentations also works its magic in your living room-or even doubles as the ultimate PC game enhancer for your kids (if they're lucky). And the all-digital nature of televisions and home theater systems featuring DLP technology makes them ideal for enjoying television programming, the Internet, and gaming applications all in one place.

Digital Micro Mirror Device (DMD)

Digital Micro Mirror Device or DMD consists of hundreds-of-thousands of tiny actuated mirrors, each of which is responsible for directing a single pixel to the screen. This direct pixel-for-pixel relationship ensures a sharp, highly-accurate picture.

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DLP Technology vs. LCD

From the classroom to the boardroom and everywhere in between, DLP ® projectors give you a picture that lasts.

DLP® proves itself again in a 3rd round of testing. Projectors equipped with DLP® technology continue to shine bright – something to keep in mind when selecting a projector. Of course color, clarity and brightness should be top-of-mind concerns when buying a projector; but you must also consider the longevity of that picture. After all, what good is a beautiful picture if it doesn't last?

So just what does picture reliability mean?

Put simply, picture reliability is how the images from your projector will look over time. When looking at a projected image, if you see an unusual amount of yellow or greenish hues in your images, that's what we call Color Decay. Projectors that use DLP® technology are virtually immune to Color Decay. However, LCD projectors can't make that same claim.

Color deterioration chart

After 1771 hours of continuous operation. The LCD projectors started to show signs of visual deterioration

Watch as DLP® outperforms.

DLP ® shines bright again and again and again.

According to tests done by Intertek, an impartial global leader in product testing, images on LCD projectors may permanently degrade over time. Not only do these tests validate

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the results of two previous studies, it's also important to note all of the steps that were taken to ensure fairness and accuracy. For example, all 54 of the test samples were acquired on the open market, all test equipment was calibrated to the proper NTSC standards, and all the manufacturers' recommended maintenance was performed on the projectors.

Intertek's test was made up of three different runtime cycles, each one representing a different type of user.

The 24/7 user – leaving the projector on continuously. The classroom user – leaving the projector on for 5.5 hours at a time. The business user – turning the projector on for 1.5 hours at a time.

In the first two test cycles, projectors with DLP® showed no significant change in luminance, uniformity, contrast ratio or color reproduction. Meanwhile, the LCD projectors lost half their contrast ratio and their color uniformity deteriorated substantially. And in the ongoing third test cycle, the LCD projectors are expected to show similar signs of decay.

DLP® projectors provide stunning picture quality, and vibrant, rich, lifelike colors. However, the beauty of digital DLP® technology is more than an incredible picture. It's the ability to maintain that picture for years to come. That is true beauty.

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