LIQUID CRYSTAL DISPLAY

INTRODUCTIONINTRODUCTION

A A liquid crystal display ( (LCDLCD) is an ) is an electro-optical amplitude modulator realized as a thin, flat display device .

It is made up of any number of color or It is made up of any number of color or monochrome pixels arrayed in front of a light source or reflector.

REFLECTIVE TWISTIVE LCDREFLECTIVE TWISTIVE LCD

Polarize light with vertical axis Polarize light with vertical axis as it enters.as it enters.

Polarizing Filter film with Polarizing Filter film with Horizontal axis to block/pass Horizontal axis to block/pass light.light.

Reflective surface to send light Reflective surface to send light back to viewers.back to viewers.

LCD ALARAM CLOCKLCD ALARAM CLOCK

Each Each pixel of an LCD typically consists of a layer ofconsists of a layer ofmolecules aligned betweentwo two transparent electrodes,and two and two polarizing filters. The axis of transmission of The axis of transmission of

molecules which are molecules which are perpendicular to each otheperpendicular to each other.r.

POLARIZING FILTERSPOLARIZING FILTERS

With no With no 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 The surface of the electrodes that are in contact with the liquid crystal material are contact with the liquid crystal material are treated so as to align the liquid crystal treated so as to align the liquid crystal molecules in a particular direction molecules in a particular direction

Electrodes are made of a Electrodes are made of a transparent conductor called transparent conductor called Indium Tin Oxide (ITO).

When a When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field.

By controlling the voltage By controlling the voltage applied across the liquid applied across the liquid crystal layer in each pixel, light crystal layer in each pixel, light can be allowed to pass can be allowed to pass through in varying amounts through in varying amounts thus constituting different thus constituting different levels of gray. levels of gray.

LCD with top polarizer LCD with top polarizer removed from device removed from device and placed on top, and placed on top, such that the top and such that the top and bottom polarizers are bottom polarizers are parallel. parallel.

SPECIFICATIONSSPECIFICATIONS

RESOLUTIONRESOLUTION

RESPONSE TIMERESPONSE TIME

DOT PITCHDOT PITCH

REFRESH RATEREFRESH RATE

VIEWING ANGLEVIEWING ANGLE

BRIGHTNESSBRIGHTNESS

CONTRAST RATIOCONTRAST RATIO

ASPECT RATIOASPECT RATIO

COLOR DISPLAYCOLOR DISPLAYA typical LCD(Right) addresses groups of A typical LCD(Right) addresses groups of 3 locations as pixels. The XO-1(Left) 3 locations as pixels. The XO-1(Left) display addresses each location as a display addresses each location as a separate pixel. separate pixel.

• In color LCDs each individual pixel is into three cells or subpixels.

• These are colored red, green, and blue respectively.

Color components may be arrayed in Color components may be arrayed in various various pixel geometries, depending on the monitor's usage.

If software knows which type of geometry If software knows which type of geometry is being used in a given LCD, this can be is being used in a given LCD, this can be used to increase the apparent resolution. used to increase the apparent resolution.

A general purpose alphanumeric LCD, with two lines of 16

characters

LCDs with a small number of segments, such LCDs with a small number of segments, such as those used in as those used in digital watches and and pocket calculators

LCD DIGITAL COMPACT LCD DIGITAL COMPACT CAMERACAMERA

High-High-resolution color color displays such as modern displays such as modern LCD LCD computer monitors, , Camera and Camera and televisions use an use an active matrix structure.structure. A Matrix of A Matrix of thin-film transistors (TFTs) is added to the (TFTs) is added to the polarizing and color polarizing and color filters. filters. Each Pixel has its own Each Pixel has its own dedicated dedicated transistor, to , to access one pixel access one pixel

DEFACTS IN LCDDEFACTS IN LCD

Some LCD panels have defective Some LCD panels have defective transistors causing dead pixels.

It is also economically prohibitive to It is also economically prohibitive to discard a panel with just a few defective discard a panel with just a few defective transistor because LCD panels are much transistor because LCD panels are much larger than ICs. larger than ICs.

EXAMPLEEXAMPLE

LCD panels also have defects known as LCD panels also have defects known as mura, , which look like a small-scale crack with very which look like a small-scale crack with very small changes in small changes in luminance or or color..

It is most visible in dark or black areas of It is most visible in dark or black areas of displayed scenes. Defects in various LCD panel displayed scenes. Defects in various LCD panel components can cause mura effect components can cause mura effect

APPLICATIONSAPPLICATIONS

PROJECTION TELEVISIONPROJECTION TELEVISION DIGITAL CLOCKS and WATCHESDIGITAL CLOCKS and WATCHES COMPUTER MONITORCOMPUTER MONITOR LAPTOP COMPUTERSLAPTOP COMPUTERS MICROWAVE OWENSMICROWAVE OWENS CD PlayersCD Players

DrawBacksDrawBacksLCDs typically have longer LCDs typically have longer response times than than their plasma and CRT counterparts their plasma and CRT counterparts when image when image rapidly changes.rapidly changes.

Some LCD TVs have slow video processing.Some LCD TVs have slow video processing.

Dead pixels can occur when the screen is can occur when the screen is damaged or pressure is put upon the screen.damaged or pressure is put upon the screen.

LCD panels using LCD panels using TN tend to have a limited tend to have a limited viewing angle relative to CRT and plasma relative to CRT and plasma displays. This reduces the number of people displays. This reduces the number of people able to conveniently view the same image – able to conveniently view the same image – laptop screens are a prime example. laptop screens are a prime example.

Comparision of LCD & CRTComparision of LCD & CRTDisplay Display TechnologTechnology   y  

Screen Screen ShapeShape

Largest Largest knownknowndiagonal diagonal (in)(in)

Largest Largest knownknowndiagonal diagonal (cm)(cm)

Typical Typical useuse

Direct view Direct view CRT

Spherical Spherical curvecurve

2424 6161 Computer monitor,Radar display

Direct view Direct view LCD LCD

FlatFlat 108108 7474 Computer Computer monitormonitor

Other Display TechnologiesOther Display Technologies

– Cathode ray tube (CRT) Cathode ray tube (CRT) – Digital Light Processing (DLP) Digital Light Processing (DLP) – Field emission display (FED) Field emission display (FED) – Laser TV Laser TV – Light-emitting diode (LED) Light-emitting diode (LED)

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