PHY 101: Mechanics
Topic: -LIQUID CRUSTAL DISPLAY

DOA: 28/08/2010
DOR: 28/09/2010
DOS: 10/11/2010

Submitted to: Submitted By:
Ms. Neeti Walia
Deptt. of Physics Roll. No. A13
Sec: E4001 Reg. No: 11007103

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. We are highly thankful to Miss NEETI WALIA for her active support, valuable time and advice, whole-hearted guidance, sincere cooperation and pains-taking involvement during the study and in completing the assignment of preparing the said project within the time stipulated. Lastly, We are thankful to all those, particularly the various friends , who have been instrumental in creating proper, healthy and conductive environment and including new and fresh innovative ideas for us during the project, their help, it would have been extremely difficult for us to prepare the project in a time bound framework.

TABLE OF CONTENTS:-

 INTRODUCTION
 WHAT IS LCD
 THEORY OF LCD
 TYPES OF LCD
 PASSIVE-MATRIX ADDRESSED LCD
 ACTIVE-MATRIX ADDRESED LCD
 ADVANTAGE N DISADVANTAGE
 COLOUR DISPLAY
 APPLICATIONS OF LCD
 BIBLIOGRAPHY

LIQUID CRYSTAL DISPLAY
INTRODUCTION:-

LCDs are super-thin displays that are used in laptop computer screens and flat panel monitors. Smaller LCDs are used in handheld TVs, PDAs, and portable video game devices. The image on an LCD screen is created by sandwiching an electrically reactive substance between two electrodes. This colour a type of display used in digital watches and many portable computers. LCD displays utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light of this substance can be changed by increasing or reducing the electrical current. Since LCD screens are based on the principle of blocking light (rather than emitting it), they use up much less power than standard CRT (Cathode-Ray Tube) monitors Monochrome LCD images usually appear as blue or dark gray images on top of a grayish-white background. Color LCD displays use two basic techniques for producing color. Passive matrix is the less expensive of the two technologies. The other technology, called thin film transistor (TFT) or active-matrix, produces color images that are as sharp as traditional CRT displays, but the technology is expensive. Recent passive-matrix displays using new CSTN and DSTN technologies produce sharp colors rivaling active-matrix displays.
WHAT IS LCD:- A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs.
THEORY:-
Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, 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. In most of the cases the liquid crystal has double refraction. The surfaces 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. This electric field also controls (reduces) the double refraction properties of the liquid crystal. 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.
TYPES OF LCD:-
Passive-matrix addressed LCD:- 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, electronic weighing scales, older laptop screens, and the original Gameboy have a passive-matrix structure. 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 addressed 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. Colour passive-matrix displays exist, although they are limited to 16 colours.
Active-matrix addressed LCD:- Monochrome passive-matrix LCDs were standard in most early laptops (although a few used plasma displays). The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an active-matrix display (though still monochrome), but passive-matrix was the norm until the mid-1990s, when colour active-matrix became standard on all laptops. High-resolution colour displays such as modern LCD computer monitors and televisions use an active matrix 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.
ADVANTAGES & DISADVANTAGES OF LCD:- Advantages:-
1. Sharpness
Image is perfectly sharp at the native resolution of the panel. LCDs using an analog input require careful adjustment of pixel tracking/phase (see Interference, below).
2. Geometric Distortion
Zero geometric distortion at the native resolution of the panel. Minor distortion for other resolutions because the images must be rescaled.
3. Brightness
High peak intensity produces very bright images. Best for brightly lit environments.
4. Screen Shape
Screens are perfectly flat.
5. Physical
Thin, with a small footprint. Consume little electricity and produce a little heat.
Disadvantages:-
1. Resolution
Each panel has a fixed pixel resolution format determined at the time of manufacture that can not be changed. All other image resolutions require rescaling, which generally results in significant image degradation, particularly for fine text and graphics. For most applications should only be used at the native resolution of the panel. If we need fine text and graphics at more than one resolution we will not get an LCD display.
2. Interference
LCDs using an analog input require careful adjustment of pixel tracking/phase in order to reduce or eliminate digital noise in the image. Automatic pixel tracking/phase controls seldom produce the optimum setting. Timing drift and jitter may require frequent readjustments during the day. For some displays and video boards we may not be able to entirely eliminate the digital noise.
3. Viewing Angle
Limited viewing angle. Brightness, contrast, gamma and color mixtures vary with the viewing angle. Can lead to contrast and color reversal at large angles. Need to be viewed as close to straight ahead as possible.
4. Black-Level, Contrast and Color Saturation
LCDs have difficulty producing black and very dark grays. As a result they generally have lower contrast than CRTs and the color saturation for low intensity colors is also reduced. Not suitable for use in dimly lit and dark environments.
5. White Saturation
The bright-end of the LCD intensity scale is easily overloaded, which leads to saturation and compression. When this happens the maximum brightness occurs before reaching the peak of the gray-scale or the brightness increases slowly near the maximum. Requires careful adjustment of the Contrast control.
6. Color and Gray-Scale Accuracy
The internal Gamma and gray-scale of an LCD is very irregular. Special circuitry attempts to fix it, often with only limited success. LCDs typically produce fewer than 256 discrete intensity levels. For some LCDs portions of the gray-scale may be dithered. Images are pleasing but not accurate because of problems with black-level, gray-scale and Gamma, which affects the accuracy of the gray-scale and color mixtures. Generally not suitable for professional image color balancing.
7. Bad Pixels and Screen Uniformity
LCDs can have many weak or stuck pixels, which are permanently on or off. Some pixels may be improperly connected to adjoining pixels, rows or columns. Also, the panel may not be uniformly illuminated by the backlight resulting in uneven intensity and shading over the screen.
8. Motion Artifacts
Slow response times and scan rate conversion result in severe motion artifacts and image degradation for moving or rapidly changing images.
9. Aspect Ratio
LCDs have a fixed resolution and aspect ratio. For panels with a resolution of 1280x1024 the aspect ratio is 5:4=1.25, which is noticeably smaller than the 4:3=1.33 aspect ratio for almost all other standard display modes. For some applications may require switching to a letterboxed 1280x960, which has a 4:3 aspect ratio.
10. Cost
Considerably more expensive than comparable CRTs.

Colour display:- In colour LCDs each individual pixel is divided into three cells, or subpixels, which are coloured 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 colours for each pixel. CRT monitors employ a similar 'subpixel' structures through phosphors, although the electron beam employed in CRTs do not hit exact subpixels.

APPICATION OF LCD:- Telecomms / Mobile Phone:- Selectronic offers a unique total solution service, combining the design requirement of keypads, LCDs and backlights. This package includes the ability to support production demand.

Datacoms:- The new demands of network hub producers cannot be met by the off the shelf packages. Selectronic's total custom LED concept is flexible enough to offer optimum display performance in production quantities. As well as LED assemblies, further packaging will include LCD and VFD options to ensure perfect hub performance and differentiation. Selectronic supply the world's leading network producers.

Consumer ElectronicsL:- Market pressures for enhanced display and product performance at the right price require suppliers to offer design benefits, and front panel and display options can provide these. Selectronic can make the difference with strategic design experience in the set top box, audio, energy metering and controls sectors. Custom solutions that visibly enhance product performance and stock/service support to maximise production effectiveness come together at Selectronic.

Security + CCTV :- The UK security market was one of the first to spot Selectronic's potential. Technology that can be optimised for assembly and user understanding has always been a key requirement in the industry, backed by the most rigorous QA standards and the ability to support rapid growth. From alarm panels to detectors, only Selectronic has the proven ability to meet these demands . Like these lcd is used in a wide range of application

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, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in. Most LCD screens used in notebook computers are backlit, or transmissive , to make them easier to read.

Bibiliography :

1. www.google.com
2. www.yahoo.com
3. www.answers.com
4. www.plc.case.edu