Cad Display Systems


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CATHODE RAY TUBE (CRT)


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IQUID CRYSTAL DISPLA(LCD)


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Polarized Filters• LCD monito! "!# $o%&i'#

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ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

7

Liquid crystal displays

The heart of all liquid crystal displays (LCDs) is a liquid crystal itself. A liquid

crystal is a substance that flows like a liquid, but its molecules orient themselvesin the manner of a crystal.

In the cholesteric crystals molecules form planes. A plane has nematic-likestructure, but with each plane molecules change their direction.

As a result the molecules display a helical twist through the material.

There are three basic types of ordering in liquid crystals which are termed nematic,cholesteric and smectic.


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When a nematic liquid crystal material comes into contact with a solid surface

molecules become aligned either perpendicular to the surface (homeotropicordering) or parallel to the surface (homogeneous ordering). These two formscan be produced by suitable treatment of the surface.

The most important electrical characteristic of liquid crystal materials is that thedirection of the molecules can be controlled by the electric field. Usually themolecules tend to be orientated along the electric field.


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10


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In the most common type of LCD cell based on twisted nematic field effect, two

sheets of glass form the main structure. Between the sheets of glass there is a verythin layer of liquid crystal material. The inner surface of each piece of glass iscoated with a transparent, conductive layer of metal oxide. The sandwich iscompleted with a polarizer on the outside of each piece of glass and a reflector onthe back of the display.

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Transmission LCD displays do not have the reflector and must be providedwith rear illumination. They operate in a very similar fashion to the reflectivedisplays.

Colour displays are possible by incorporating colour filters.

An LCD cell consumes only microwatts of power over a thousand times lessthan LED displays.

LCDs can operate on voltages as low as 2 to 3 V and are easily driven by MOSIC drivers.

LCDs also have their disadvantages. They cannot be seen in the dark, have alimited viewing angle and a limited temperature range.



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The left column electrode is at the same

potential level as the row electrode. To theright column electrode (red), a differentvoltage is applied. In this way, an electricfield is generated in the right pixel orientedperpendicular to the glass surfaces.On the picture one can see that the rubbingdirection of the alignment layers (green) ontop and bottom substrate are chosenperpendicular to each other. Due to thischoice, the director in the left pixel makes ahomogeneous turn of 90° from bottom to top.Therefore, this type of LCD is called a'Twisted Nematic LCD' (TN-LCD). If avoltage is applied to the electrode, thedirector reorients to become perpendicular tothe surfaces (right pixel).

http://www.elis.ugent.be/ELISgroups/lcd/lc/lc3.php



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LIGHT EMITTINGDIODES



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LED displays

Light emitting diodes are used in LED displays.

Operation of the LED displays is based on the injection luminescence.

LED displays are available in many different sizes and shapes.

Usually LED displays radiate red, orange, yellow or green light.

They have a wide operating temperature range, are inexpensive, easilyinterfaced to digital logic, easily multiplexed, do not require high voltagesand have fast response time.

The viewing angle is good and display of arbitrary numbers of digits is

easily assembled.



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The amazing new VAIO TX3 is the smallestand lightest fully featured notebook around.Developed for ultimate mobility using

advanced carbon-fibre materials, TX3 includesa range of brilliant design innovationsincluding a super-thin LED display panel andpostcard-sized motherboard.

LED displays


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What is Plasma?

Plasma is often called the "Fourth State ofMatter", the other three being solid, liquid andgas. A plasma is a distinct state of mattercontaining a significant number of electrically

charged particles, a number sufficient to affectits electrical properties and behavior. Inaddition to being important in many aspects ofour daily lives, plasmas are estimated to

constitute more than 99 percent of the visibleuniverse.


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Plasma display panels:

PLASMA display panels (PDPs) are one of theleadin !andidates in the !o"petition for #

large-size, high-brightness ,flat panel displayssuitable for high-definition television (HDTV)

monitors

Their advantages are:Fast response

Wide viewing angleLow weightSimple manufacturing processHigh resolution


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WORKING PRINCIPLE OF PLASMADISPLAY PANELS: Typical plasma displays

consist of two glass plates,each with parallelelectrodes deposited ontheir surfaces. Theelectrodes are coveredwith a dielectric film. Theplates are sealed togetherwith their electrodes atright angles, and the gap

between the plates is filledwith an inert gas mixture.A protective MgO layer is

deposited above thedielectric film. The role ofthis layer is to decrease the

breakdown voltage caused by the high secondaryelectron emission

coefficient of MgO.


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The discharge is initiated by applying a voltage pulse to

the electrodes. Xenon gasmixtures are used to efficientlygenerate UV photons. The UVphotonsemitted by the discharge hitthe phosphors deposited on

the walls of the PDP cell andare converted into visiblephotons. Each cell containsphosphor that emits oneprimary color—red,green, or blue.


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ORGANIC LIGHTEMITTINGDIODE


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ELEKTRONIKOS ĮTAISAI 2009 26


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Į


LED displays


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FUTURE

Cad Display Systems

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