LCD PRSENTATION

8/8/2019 LCD PRSENTATION

http://slidepdf.com/reader/full/lcd-prsentation 1/27

By:NEELANSHUNIKITAPALLABI

NILESH



What are Liquid crystals? Examples of Liquid Crystals.

Introduction to liquid crystal displays. Types of LCDs. Working Principle. Construction.

Working procedure. Applications. Advantages. Disadvantages.



Intermediary substance between a liquid

and solid state of matter.

E.g. soapy water Light passes through liquid crystal

changes when it is stimulated by an

electrical charge.



1962: Richard Williams found that liquid

crystals had some interesting electro-optic

characteristics and he realized an electro-optical effect by generating stripe-patterns in

a thin layer of liquid crystal material by the

application of a voltage The f irst active-matrix liquid crystal display

panel was produced in 1972 in USA.



A photoresist composition for LCD lightdiff use reflecting f ilm is disclosed, which

comprises (a) 8 to 90% by weight of base-soluble resin; (b) 1 to 30% by weight of polyf unctional unit; (c) 0.1 to 20% by weightof photopolymerization initiator; (d) 0.1 to

20% by weight of thermosetting cross-linking reagent; (e) 0.01 to 10% by weight of ultraviolet absorber; and (f) 8 to 90% by weight of solvent.



Consists of an array of tiny segments (called pixels) that can be manipulated to present

information. Using polarization of lights to display objects. Use only ambient light to illuminate the

display.



Passive Matrix LCDs (AMLCD) and Active

Matrix LCDs (AMLCD)

Passive Twisted Nematic Displays (TNLCD) Super Twisted Nematic LCD (STNLCD)

Thin Film Transistor LCD (TFT LCD)

Reflective LCD

Rear Projection LCD



LCD works on the

principle of PolarizationOf Light.

When unpolarized lightpasses through polarizing f ilter, only one plane of polarization is

transmitted. Twopolarizing f ilters used together transmit lightdifferently depending on

their relative orientation.



Each pixel of an LCD typically consists of a layerof molecules aligned between two transparent

electrodes, and two polarizing f ilters, the axes of transmission of which are (in most of the cases)perpendicular to each other. With no actual

liquid crystal between the polarizing f ilters, light

passing through the f irst f ilter would be blocked by the second (crossed) polarizer.



Before applying an electric f ield, the orientation of the liquid crystal molecules is determined by

the alignment at the surfaces of electrodes. In atwisted nematic device (still the most common liquid crystal device), the surface alignmentdirections at the two electrodes areperpendicular to each other, and so themolecules arrange themselves in a helicalstructure, or twist. This reduces the rotation of the polarization of the incident light, and thedevice appears grey.



If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almostcompletely untwisted and the polarization of the

incident light is not rotated as it passes through theliquid crystal layer. This light will then be mainly polarized perpendicular to the second f ilter, 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.



In colour LCDs each individual pixel is divided into three cells, or subpixels, which are coloured

red, green, and blue, respectively, by additionalf ilters (pigment f ilters, dye f ilters and metaloxide f ilters). Each subpixel can be controlled independently to yield thousands or millions of possible colours for each pixel. CRT monitors employ a similar 'subpixel' structures viaphosphors, although the electron beamemployed in CRTs do not hit exact subpixels.



Resolution versusRange: Fundamentally resolution is the granularity (ornumber of levels) with which a performance feature of the display is divided.. Frequently the range is an inherent limitation of the display while the resolution is a f unction of the electronics that make the display work.

Spatial Performance LCDs come in a variety of sizes for a variety of applications and a variety of resolutions within each of thoseapplications. LCD spatial performance is also sometimes described in terms of "dot pitch". Later, when TVs went to a more square format, thesquare screens were measured diagonally to compare with the olderround screens

Aspect ratio:-The Aspect ratio is the ratio of the width to the height TheViewing Angle of an LCD may be important depending on its use or

location. The viewing angle is usually measured as the angle where thecontrast of the LCD falls below 10:1. At this point, the colours usually start to change and can even invert, red becoming green and so forth.



Temporal/Timing Performance: Contrary to spatialperformance, temporal performance is a featurewhere smaller is better. Specif ically, the range is the

pixel response time of an LCD, or how quickly you can change a sub-pixels brightness from one level toanother

Colour Depth or colour support is sometimes expressed in bits, either as the number of bits per sub-

pixel or the number of bits per pixel. Brightness and Contrast ratio: Contrast Ratio is theratio of the brightness of a f ull-on pixel to a f ull-off pixel and, as such, would be directly tied to brightness if not for the invention of the blinking backlight



A)Thin FilmTransistor (TFT) Constructed on a glass surface using a

photolithographic process.

B) Alpha-numeric display Digital letters can be displayed by blocking the

lights in different plates we place. For applications such as digital watches and

calculators, a mirror is used under the bottompolarizer. With no voltage applied, ambient lightpasses through the cell, reflects off the mirror, reverses its path, and re-emerges from the topof the cell, giving it a silvery appearance.



C) Back lighting systems Alpha-numeric displays are not very bright because the

light must pass through multiple polarizers whichseverely cut down on the intensity of the light, in addition to the various layers of the display which areonly semi-transparent. Therefore a more intensesource is employed in the form of a back lighting

system.



D) Military Use

LCD monitors have been adopted by the

United States of America military instead of CRT displays because they are smaller, lighter

and more eff icient, although monochromeplasma displays are also used, notably for

their M1 Abrams tanks.



SharpnessImage is perfectly sharp at the native resolution of the panel. LCDs using an analog input require caref ul ad justment of pixeltracking/phase.

Geometric DistortionZero geometric distortion at the native resolution of the panel. Minor distortion for other resolutions because the images mustbe rescaled.

BrightnessHigh peak intensity produces very bright images. Best forbr

ightl

ylit e

nviro

nme

nts.

Screen Shape

Screens are perfectly flat. Physical

Thin, with a small footprint. Consume little electricity and produce little heat.



ResolutionEach panel has a f ixed pixel resolution format determined at the time of manufacture that can not be changed. All other image resolutions require rescaling, which generally results in signif icant imagedegradation, particularly for f ine text and graphics

InterferenceLCDs using an analog input require caref ul ad justment of pixeltracking/phase in order to reduce or eliminate digital noise in the image. Automatic pixel tracking/phase controls seldom produce the optimumsetting. Timing drift and jitter may require frequent read justments

during the day. Viewing Angle

Limited viewing angle. Brightness, contrast, gamma and color mixtures vary with the viewing angle. Can lead to contrast and color reversal atlarge angles. Need to be viewed as close to straight ahead as possible.



Black-Level, Contrast and Color SaturationLCDs have diff iculty 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 alsoreduced. Not suitable for use in dimly lit and darkenvironments.

White SaturationThe 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 thebrightness increases slowly near the maximum. Requires caref ul ad justment of the Contrast control.



Color andGray-Scale AccuracyThe internal Gamma and gray-scale of an LCD is very irregular. LCDs typically produce fewer than 256 discrete intensity levels. For some LCDs portions of the

gray-scale may be dithered. Images are pleasing butnot accurate because of problems with black-level, gray-scale and Gamma, which affects the accuracy of the gray-scale and color mixtures.

Bad Pixels and Screen UniformityLCDs can have many weak or stuck pixels, which arepermanently on or off . Some pixels may be improperly connected to ad joining pixels, rows or columns.



Motion ArtifactsSlow response times and scan rate conversion result in severe motion artifacts and image degradation formoving or rapidly changing images.

Aspect RatioLCDs have a f ixed 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 someapplications may require switching to a letterboxed 1280x960, which has a 4:3 aspect ratio.

Cost

Considerably more expensive than comparable CRTs.



THANKS.!!!!!!!!!!

LCD PRSENTATION

Documents

Transcript of LCD PRSENTATION