TERM PAPER

Topic:LCD (LIQUED CRYSTAL DISPLAY)

DOA: 22/02/2010

DOS: 06/05/2010

Submitted to: Submitted by: Bindu

ABSTRACT

LCD projectors are becoming smaller and less expensive, and are starting to incorporate built-in light sources and speakers. LCD panels are also improving in resolution and response. An LCD panel is fairly light and thin, but require a separate overhead projector. The LCD projector contains its own light source, so no overhead projector is required. These have more multimedia features than LCD panels, and usually include speakers and multiple inputs and outputs. Polysilicone LCDs are smaller, and allow more light to pass through than thin-film transistor LCDs. LCD projectors typically weigh between 10 to 50 pounds. Heavier ones are also available that can achieve movie screen quality, although these are more costly, and better suited to permanent installations. Most LCD panel devices have a screen of between 8.4 and 10.4 inches diagonally. A good panel or projector will also provide on-screen adjustment, remote control and a hard shell carrying case.

ACKNOWLEDGEMENT

I take this opportunity to present my votes of thanks to all those guidepost who really acted as lightening pillars to enlighten our way throughout this project that has led to successful and satisfactory completion of this study.

Name-Rahul Rawat

Regd.No-10908461

Rollno-RC66903B65

TABLE OF CONTENTS

LCD (LIQUED CRYSTAL DISPLAY)

OVERVIEW

HISTORY

WORKING

USES

COLOR DISPLAY

PASSIVE AND ACTIVE MATRIX LCD’S

QUALITY CONTROL

APPLICATIONS

FUTURE SCOPE

LCD (LIQUED CRYSTAL DISPLAY)

A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystal (LCs). LCs do not emit light directly. LCDs therefore need a light source and are classified as "passive" displays. Some types can use ambient light such as sunlight or room lighting. There are many types of LCDs that are designed for both special and general uses. They can be optimized for static text, detailed still images, or dynamic, fast-changing, video content.

OVERVIEW

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparentelectrodes, and two polarizingfilters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer.
The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes are made of a transparent conductor called Indium Tin Oxide (ITO).
Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This reduces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.
LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel.The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device.
Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).
When a large number of pixels are needed in a display, it is not technically possible to drive each directly since then each pixel would require independent electrodes. Instead, the display is multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together (typically in columns), and each group gets its own voltage source. On the other side, the electrodes are also grouped (typically in rows), 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.

History of Liquid Crystal Displays - LCD

In 1888, liquid crystals were first discovered in cholesterol extracted from carrots by Austrian botanist and chemist, Friedrich Reinitzer.

In 1962, RCA researcher Richard Williams generated stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what is now called “Williams domains” inside the liquid crystal.

According to the IEEE, "Between 1964 and 1968, at the RCA David Sarnoff Research Center in Princeton, New Jersey, a team of engineers and scientists led by George Heilmeier with Louis Zanoni and Lucian Barton, devised a method for electronic control of light reflected from liquid crystals and demonstrated the first liquid crystal display. Their work launched a global industry that now produces millions of LCDs."

Heilmeier's liquid crystal displays used what he called DSM or dynamic scattering method, wherein an electrical charge is applied which rearranges the molecules so that they scatter light.

The DSM design worked poorly and proved to be too power hungry and was replaced by an improved version, which used the twisted nematic field effect of liquid crystals invented by James Fergason in 1969.

Inventor, James Fergason holds some of the fundamental patents in liquid crystal displays filed in the early 1970's, including key US patent number 3,731,986 for "Display Devices Utilizing Liquid Crystal Light Modulation"

WORKING

[pic]

You probably use items containing an LCD (liquid crystal display) every day. They are all around us -- in laptop computers, digital clocks and watches, microwave ovens, CD players and many other electronic devices. LCDs are common because they offer some real advantages over other display technologies. They are thinner and lighter and draw much less power than cathode ray tubes (CRTs), for example.
But just what are these things called liquid crystals? The name "liquid crystal" sounds like a contradiction. We think of a crystal as a solid material like quartz, usually as hard as rock, and a liquid is obviously different. How could any material combine the two?
We learned in school that there are three common states of matter: solid, liquid or gaseous. Solids act the way they do because their molecules always maintain their orientation and stay in the same position with respect to one another. The molecules in liquids are just the opposite: They can change their orientation and move anywhere in the liquid. But there are some substances that can exist in an odd state that is sort of like a liquid and sort of like a solid. When they are in this state, their molecules tend to maintain their orientation, like the molecules in a solid, but also move around to different positions, like the molecules in a liquid. This means that liquid crystals are neither a solid nor a liquid. That's how they ended up with their seemingly contradictory name.
So, do liquid crystals act like solids or liquids or something else? It turns out that liquid crystals are closer to a liquid state than a solid. It takes a fair amount of heat to change a suitable substance from a solid into a liquid crystal, and it only takes a little more heat to turn that same liquid crystal into a real liquid. This explains why liquid crystals are very sensitive to temperature and why they are used to make thermometers and mood rings. It also explains why a laptop computer display may act funny in cold weather or during a hot day at the beach.

USES

They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube(CRT) displays in most applications. They are usually more compact, lightweight, portable, and lower cost. They are available in a wider range of screen sizes than CRT and other flat panel displays.
LCDs are more energy efficient, and offer safer disposal, than CRTs. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in color or monochrome. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from 1888. By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units.

COLOR DISPLAY

[pic]

In color LCDs each individual pixel is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters (pigment filters, dye filters and metal oxide filters). Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel. CRT monitors employ a similar 'subpixel' structures via phosphors, although the electron beam employed in CRTs do not hit exact 'subpixels'. Because they utilize red, green and blue elements, both LCD and CRT monitors are direct applications of the RGB color model and give the illusion of representing a continuous spectrum of hues as a result of the trichromatic nature of human vision.
Color components may be arrayed in various pixel geometries, depending on the monitor's usage. If the software knows which type of geometry is being used in a given LCD, this can be used to increase the apparent resolution of the monitor through subpixel rendering. This technique is especially useful for text anti-aliasing.
To reduce smudging in a moving picture when pixels do not respond quickly enough to color changes, so-called pixel overdrive may be used.

PASSIVE AND ACTIVE MATRIX LCD’S

LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.
Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive-matrix structure employing super-twisted nematic (STN) or double-layer STN (DSTN) technology—the latter of which addresses a color-shifting problem with the former—and color-STN (CSTN)—wherein color is added by using an internal filter. Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called passive matrix because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow response times and poor contrast are typical of passive-matrix addressed LCDs.
High-resolution colour displays such as modern LCD computer monitors and televisions use an active matrix structure. A matrix of thin-film transistors (TFTs) is added to the polarizing and color filters. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is activated, all of the column lines are connected to a row of pixels and the correct voltage is driven onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the row lines are activated in sequence during a refresh operation. Active-matrix addressed displays look "brighter" and "sharper" than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images.

QUALITY CONTROL

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective pixels are usually still usable. It is claimed that it is economically prohibitive to discard a panel with just a few defective pixels because LCD panels are much larger than ICs, but this has never been proven. Manufacturers' policies for the acceptable number of defective pixels vary greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea. Currently, though, Samsung adheres to the less restrictive ISO 13406-2 standard. Other companies have been known to tolerate as many as 11 dead pixels in their policies. Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard. However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways.

[pic]

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective pixels are usually still usable. It is claimed that it is economically prohibitive to discard a panel with just a few defective pixels because LCD panels are much larger than ICs, but this has never been proven. Manufacturers' policies for the acceptable number of defective pixels vary greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea. Currently, though, Samsung adheres to the less restrictive ISO 13406-2 standard. Other companies have been known to tolerate as many as 11 dead pixels in their policies. Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard. However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways.
LCD panels are more likely to have defects than most ICs due to their larger size. For example, a 300 mm SVGA LCD has 8 defects and a 150 mm 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. Due to competition between manufacturers quality control has been improved. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. Some manufacturers, notably in South Korea where some of the largest LCD panel manufacturers, such as LG, are located, now have "zero defective pixel guarantee", which is an extra screening process which can then determine "A" and "B" grade panels. Many manufacturers would replace a product even with one defective pixel. Even where such guarantees do not exist, the location of defective pixels is 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.
LCD panels also have defects known as clouding (or less commonly mura), which describes the uneven patches of changes in luminance. It is most visible in dark or black areas of displayed scene.

APPLICATIONS

1. Technological improvements to liquid crystal display (LCD) screens have seen them become more popular in the high definition television market. With the improvement of broadcasting pictures moving quickly from analogue to digital television so too is the television market moving from regular Cathode Ray Tube (CRT) to large flat panel LCD or Plasma screens. 2. While liquid crystal display television (LCD TV) is new technology, we have been using liquid crystal display for many years in other household items such as digital clocks, oven timers and home computers. 3. LCD technology is not restricted to just large flat screen TVs with LCD projectors available for corporations to display video, images or data in much the same way that the old overhead projector once did. 4. LCD technology provides a cheaper alternative to large Plasma screens. Historically the LCD screens have been smaller but new technology is increasing the size of these large flat screen TVs to be more competitive than ever before. 5. While the size of LCDs has increased the advantage one has in price comparison with a Plasma screen has seen the LCD screens enjoy their fair share of high definition large flat screen sales in the home entertainment market. 6. LCD screens also need less power to function giving the consumers considerable savings on their electricity bills. 7. LCD technology is not restricted to just large flat screen TVs with LCD projectors available for corporations to display video, images or data in much the same way that the old overhead projector once did. 8. An LCD projector works by sending light from a halogen lamp through three LCD panels (one for red, blue and green). The individual pixels then open to allow light to pass or close to block the light producing our image. 9. We also use LCD technology in the world of computers with a LCD computer monitor the most popular display device for computers. An LCD monitor is the popular choice amongst consumers because of the flat panel screen taking up very little space. 10. Having replaced the bulky computer monitors the LCD monitor is here to stay with all new computer purchases going hand in hand with a LCD computer monitor. The advantages in buying an LCD monitor is not only restricted to the size but also the savings with LCD monitors using very little of your power supply to work. 11. Liquid crystal display television (LCD TV) provides the viewer with a far greater experience watching television. With the LCD TV set you don’t have to close the curtains because the screen is too bright to see the picture properly like you do with a normal CRT television. 12. One major advantage an LCD screen has is that it is not only a capable of displaying high-definition TV, video, dvd or normal television but it can also be used as a computer monitor. Just like your everyday PC monitor you can play games on your LCD screen, your just going to have a bigger, better view of your screen playing on your large screen TV mounted on the wall.

FUTURE SCOPE

In the midst of discussions and debates on the choice of an innovative television in the contemporary market environment, the question about the future of existing technologies arises. The days of CRT are over and the craze is for LCD or plasma technology. Both are sophisticated products which offer high definition television. Each of the above has many positive factors in the context of consumer satisfaction. Experts on the subject and experienced viewers make loud thinking on the respective advantages of both these modern television products.
At a time when plasma technology appears to have an edge over LCD, efforts are being taken to improve the features and performance level of the Liquid Crystal Display screens. The manufacturers are contemplating on the introduction of more sophisticated and consumer friendly products in the near future. It is imperative for them to offer more innovative products in order to survive in the competitive market. Size of the screen alone cannot make a television acceptable to the consumer. Performance is the keyword. Improving the screen resolution is essential. Contrast ratio is also required to be improved. Even though LCD screens do not suffer from burn-in problems, individual pixels on LCD can burn to cause black and white dots.
The Manufacturers are now undertaking technological up gradation to effect qualitative changes in the next generation LCD screens. Bright colours and infinite contrast ratio will bring in new experience to the users. Applications of new technology are expected to make LCD screens capable for high end performance in home theatre or satellite picture reproduction. With 95 percent uniformity in luminance throughout the display, LCD will attain more perfection than its competitors.
The innovative natural light technology is poised to lift LCD to new heights. The dynamic contrast ratio will be enhanced to 50,000:1. Eye protection and energy conservation are also getting priorities in the agenda for the future LCD products. Ultra thin screens will be featured with shorter response time and improved color depths. Blurring will be completely eliminated. It is also expected that the next generation LCD screens will be the thinnest one available in the market. LCD is already enjoying the advantage of longevity.
Efforts will be taken to enhance the lifespan further. Enhanced productivity in the manufacturing process will extend further cost benefits to the consumer. With comparatively lesser CO2 emission than plasma, the LCD will be more environment friendly than its competitor.
In a competitive environment, the technological up gradations has become inevitable for market survival of the products. The LCD manufacturers have noted the writings on the wall and are preparing to meet the challenges with no holds barred attitude.