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INTRODUCTION TO LCD T.V. CIRCUITS - 1. Construction of LCD Display 1-1 Principle of LCD Display 1-2 Construction of LCD Display 1-3 Main Component of LCD Display 2. Principle of Liquid Crystal 2-1 Liquid Crystal 2-2 Rubbing-process 2-3 Operation of Liquid Crystal 3. Principle of LCD 3-1 Operation of Polarized Board for LCD Panel (Shutter 3-2 Operation of Alignment Film 3-3 Operation of LCD Panel 3-4 Transparent Electrode 4. Type of LCD Display Construction 4-1 Twisted Nematic (TN) Type 4-2 Super TN (STN) Type 4-3 Triple STN (TSTN) Type / Film STN (FSTN) Type 5. System of LCD Display 5-1 Dot-Matrix System 5-2 Colorization 5-3 Drive System 5-4 Passive Matrix System 5-5 Active Matrix System 5-6 Drive of Active Matrix System 6. Improvement Technology of LCD Display 6-1 Subject of LCD Display 6-1-1 Angle of View 6-1-2 Response Characteristic 6-2 Angle of View 6-3 Multi-Domain System 6-4 MVA (Multi-domain Vertical Alignment) System 6-5 IPS (In-Plain Switching) System 6-6 Optically Compensated Film 6-7 OCB (Optically Compensated Birefringence) System 6-8 Improvement of Response Speed 6-8-1 Inpulse System 6-8-2 FFD (Feed Forward Driving) System 7. HANDLING PRECAUTIONS FOR TFT-LCD MODULE

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1-1 Principle of LCD Display

1-2 Construction of LCD Display

1-3 Main Component of LCD Display

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The LCD (Liquid Crystal Device) Display isused to display the electric signal, convertedfrom picture data similar to a CRT display. The

transistor (TFT) switched by the electric signalchanges the transmission to light in smallpicture elements (pixels) of the LCD. The LCDdisplay makes the picture by grouping these

elements of each RGB color

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LCD Display Liquid Crystal is packed between the board modules (TFT and Common)

and the LCD panel (or LCD shutter) is constructed. A back light isattached to the LCD panel for LCD Display.

Board Module (Common Electrode)

The Common Electrode consists of a polarized board, a color filter, and atransparent electrode on a glass plate. An alignment film is formed on thetransparent electrode.

Board Module (TFT Electrode) The TFT Electrode consists of a polarized board and a transparent

electrode (pixel electrode and drive transistor) on a glass plate. Analignment film is formed on the transparent electrode.

Backlight

A fluorescent light is used for the Backlight. TFT: Thin Film Transistor LCD Panel and LCD Shutter: They are the same things, but in the

explanation LCD panel is used for structure and LCD shutter is used forfunction.

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LCD Shutter Supplying voltage to the transparent electrodes between the pixel and common sides changes the

arrangement of liquid crystal. By assembling two polarized boards, the transfer of light from thebacklight can be controlled by the transparent ratio of the LCD Shutter.

Liquid Crystal Liquid Crystal is a material whose state is between a solid and a liquid. It has both characteristics of

solids and liquids, and generally it is a white turbid liquid. Its molecules are normally arrangedcomparatively opaque and change to transparent with the application of voltage or heat.

Transparent Electrode (Film) An LCD shutter is operated by supplying voltage derived from the video signal. Transparent film is

used for its electrode. Alignment Film This is a film for arranging liquid crystal molecules and is made of Polymid resin. Polarized Board The light with a specified direction passes through a polarized board. Drive Transistor

The thin film transistor (TFT) is used to drive the LCD shutter of each pixel. Colour Filter It is a filter with three colours (R, G, B) arranged for each pixel. Backlight Liquid crystal does not emit light. A light source is needed for display. The light source placed on the

reverse side of the LCD panel is called Backlight.

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2-1 Liquid Crystal

2-2 Rubbing-process

2-3 Operation of Liquid Crystal

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What is Liquid Crystal? Liquid Crystal is a material whose state is between a solid and liquid. It has

characteristics of both solids and liquids, and generally is a white turbid liquid. Itsmolecules are normally arranged comparatively opaque and change to transparent withthe application of voltage or heat. Almost all the materials consist of an organiccompound taking the form of a slender stick or a flat plate. There are three types ofliquid crystal as shown in Fig. 4, and they depend on the construction and arrangement

of molecules. Generally Nematic liquid crystal is used for the display apparatus. (a) Smectic Molecules are in layers and arranged parallel to each other. The center of gravity is

arranged at random in the layer. (b) Nematic Molecules are not in layers. They are arranged parallel. The center of gravity is able to

move freely to the major axis. (c) Cholesteric

Molecules are in layers and arranged parallel. The arranging direction of the major axisfor the neighboring layers is shifted gradually. In order to use liquid crystal for display,it is necessary to regularly arrange the molecules of Nematic (Rubbing-process).

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After chemicals for arranging are put on theglass plate, they are hardened, and then thesurface on the plate is rubbed with a cloth to fix

the direction of the gaps that are made. Thearranging direction of molecules is settled inthe gaps. This process is used to change thecharacteristics so the molecules that touch the

rubbed surface are arranged to the major axisof the rubbed direction. This thin film on theglass plate is called Alignment film.

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The chemistry substance required for liquid crystal materialis one that reacts so that the arrangement direction ischanged according to an applied electric field. In the LCDdisplay, a liquid crystal is placed between two electrodes.When the voltage is supplied between them, an electric field

is generated in the liquid crystal, and liquid crystalmolecules are moved and arranged. The Backlight appliedto the liquid crystal is either passed or blocked according tothe arrangement of the molecules. If an electric field from anexternal source is applied to liquid crystal, electric dipoleswill be generated that will react to the intensity and

direction of the electric field. Through the operation of theseelectric dipoles and the electric field, the power changingdirection of liquid crystal molecules is generated. Therefore,according to an external electric field, liquid crystalmolecules move and change direction from horizontal tovertical.

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3-1 Operation of Polarized Board for LCDPanel (Shutter)

3-2 Operation of Alignment Film

3-3 Operation of LCD Panel

3-4 Transparent Electrode

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Light is an electromagnetic wave that is oscillating at right anglesto the direction of advance. In fact, the oscillating directions of alllight is mixed. A polarized board can let only the light in thespecific direction pass from the light with which these variousoscillating directions were mixed. Therefore, only the light of the

same direction as the polarization direction of a polarized boardcan be taken out by letting the light pass through this polarizedboard. That is, if the oscillating direction of light and the directionof a polarized board are in agreement, the light will pass througha polarized board. Moreover, if the direction of a polarized boarddiffers from the oscillating direction of light, the light cannot passthrough a polarized board. When the oscillating direction of a

polarized board and light are shifted 90(right-angled), the light isblocked completely. The light passes and looks bright if the twoboards are in the same direction when looking at two polarizedboards in piles, however, if shifted at right-angles, the light isblocked and looks dark.

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Liquid crystal is inserted into alignment films of anupper and lower plate that have the direction ofgrooves shifted by 90 on the LCD display. The liquidcrystal molecules of upper alignment plate are

arranged along with the upper alignment film. Theliquid crystal molecules of lower alignment plate arearranged along with the lower alignment film. Theliquid crystal layer between these alignment films istwisted little by little and is arranged so that a spiral is

formed. Light entering through the first alignmentplate will have its oscillating direction twisted 90 bythe liquid crystal layer between the alignment films.Now the direction of oscillation is aligned with thesecond alignment plate and the light will pass through

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In the LCD panel, a liquid crystal is inserted and enclosed between two glass plates. Thepolarized board, transparent electrode, and the alignment film are formed on these glassplates. The light can be passed or blocked by supplying voltage or not to this LCD panel. In thecondition (Switch-Off) that the voltage is not supplied, the liquid crystal molecules are twisted90 sideways and arranged spirally. The oscillating direction of the light that passed the upperpolarized board is changed by the twisted liquid crystal molecule arrangement. Therefore, thedirection of a polarized board and the oscillating direction of the light which is shifted 90 andarranged become the same, and this light can now pass through a polarized board. This is the

liquid crystal shutter-on condition and an LCD panel (LCD shutter) passes the light. On the contrary, in the condition (Switch-On) that voltage is supplied, the liquid crystal

molecules are arranged in a line at right angles to a glass plate. Since vertical liquid crystalmolecules do not affect the oscillating direction of light, the light that passed the upperpolarized board passes as it is without changing the oscillating direction. Since the oscillatingdirection of this light differs from direction of the lower polarized board which is shifted 90and arranged, the light collides with this polarized board and cannot pass. This is the liquidcrystal shutter-off condition and the LCD panel (LCD shutter) blocks the light. This is the basicstructure (OnOff of the light by the LCD shutter) of an LCD panel. It is a sandwich structureof the upper and lower sides of transparent electrodes, alignment films, and polarized boards,with an enclosed liquid crystal material between them.

voltage is not supplied between the upper-and-lower polarized boards that are arranged at 90.This type of panel has the advantage that black contrast is improved, and it usually works well.This mode is called Normally White Mode.

An LCD panel that passes light when voltage is not supplied is referred to as Normally BlackMode. In practice, with this type (when the upper-and-lower polarized boards are arranged inthe same direction), is playing perfect black becomes difficult due to the leakage of light causedby variations in the arrangement of the liquid crystal molecules..

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4-1 Twisted Nematic (TN) Type

4-2 Super TN (STN) Type

4-3 Triple STN (TSTN) Type / Film STN(FSTN) Type

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A Nematic type of LCD Display where the liquidcrystal molecules are twisted 90 between upper andlower boards is called a Twisted Nematic type (TNtype) liquid crystal. Most LCD displays are of this typeand feature high contrast (ratio) under low voltage andpower.

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Super TN type (STN type) LCD Displays are usedfor LCD televisions, personal computer monitors,cellular phones, etc. A liquid crystal materialdeveloped to improve visual characteristics, such

as contrast ratio is used. In this STN type liquidcrystal molecules are twisted 180 to 270 andarranged between upper and lower electrodes. Bysupplying voltage to this liquid crystal, thetransparent ratio of light changes more steeply.

Therefore, with the STN type as compared to theTN type, contrast and rise characteristic of thevoltage (response of switch On and Off) areimproved, and a clearer picture on larger screensbecomes possible.

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A fault of the STN type is that the display colors during Onand Off of the LCD shutter become yellowish green andnavy blue. (In TN type, they are white and black.) This isbecause light of a specific wavelength is reflected andscattered by the thickness of the LCD panel. Therefore, even

if a color filter of RGB is attached to an STN type liquidcrystal, bluish green is mixed with the colors from black,gray to white, and a natural color picture cannot bedisplayed. The triple STN type (TSTN type) and the filmSTN type (FSTN type) have been developed as an advancedtype of STN. In the TSTN type, optically compensated films

(high polymer films) which sandwich the upper and lowerLCD panels are used. They compensate for the twist of thelight crystal cell, and the display colors of yellowish greenand navy blue are changed to the correct white and black.The FSTN type uses a single optically compensated film

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5-1 Dot-Matrix System

5-2 Colorization

5-3 Drive System

5-4 Passive Matrix System

5-5 Active Matrix System

5-6 Drive of Active Matrix System

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LCD displays have two drive systems, Segment and Dot-Matrix.The Dot-Matrix system is used for LCD television displays.

The picture elements (pixels) of the display unit are arrangedhorizontally (X line) and vertically (Y row) by this Dot-Matrixsystem, and various characteristics and figures can be displayed.

Fig. 12 shows a matrix of X x Y = 10 (pixels) with the characterY displayed. In this Dot-Matrix system, by making the size of apixel smaller and increasing the whole number of pixels, the bigscreen with fine character or picture becomes possible. With thepresent liquid crystal manufacture technology, the number ofpixels per inch has reached 200ppi*, and very high definitionscreen display is possible. Moreover, the number of pixels of an

LCD display panel corresponding to bigger screen sizes can bespecified and manufactured. For example, the number of pixels ofthe SXGA* panel is about 1,300,000 (1,280 x 1,024 = 1,310,720pixels).

ppi: pixel per inch SXGA: Super eXtended Graphics Array

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Since an LCD shutter only passes or blocks light, initself it cannot display a color picture. The color pictureis made by mixing the three colors of RGB (threeprimary colors of light) respectively, like the CRT color

television. The color LCD panel has a color filter ofRGB attached to the monochrome panel. See Fig. 13. Inthis color LCD panel, by controlling the voltages andthe waveforms that are supplied at each RGB pixel, thetransparent ratio is controlled and hue and brightness

are adjusted. Therefore, smaller pixels and morenumbers of pixels are required for the color LCDDisplay. For example, although the SXGA paneldescribed before has about 1,300,000 pixels, incolorization, there are about 4 million dots(sub-pixels).

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The drive systems for LCD display are dividedinto the following classifications:

The Static Drive System, which is seldom

used;

The Passive Matrix System, which is used forstill pictures, such as calculators and notebookPCs;

The Active Matrix System, which is suitablefor high definition and the high-speed responseneeded for big screen LCD television.

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In the structure of a passive matrix system, Yelectrodes of the vertical direction (Y-direction) areformed in upper glass plate, and X electrodes ofthe horizontal direction (X direction) are formed in

lower glass plate as a matrix. The liquid crystalmolecules are sandwiched between theseelectrodes. By supplying voltage between the Yelectrode and the X electrode in sequence, at acertain time, an electric field is generated in the

liquid crystal where the selected Y electrode and Xelectrode cross. Therefore, the liquid crystalmolecules of this pixel address (X, Y electrodeintersection) change arrangement and an LCDshutter is turned On or Off.

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In the active matrix system, a switch element is attached for every pixel atthe intersection of the X and Yelectrodes of a passive matrix system. Eachpixel is now controlled by the switch element (active element). Since theswitch for each pixel is turned On and Off independently, the responsespeed is increased. Thin Film Transistor (TFT) is used for the switchelement and is attached on the glass board.

The LCD display using this TFT is called TFT LCD display. The upperelectrode for the whole pattern is formed on the upper glass plate and iscalled the Common Electrode. A pixel electrode (pixel pattern), TFT(switch element) which drives a pixel electrode, and X electrode for gateinput and Y electrode for source input of TFT are formed on the lowerglass plat e. In this structure, the electric field is generated in the areabetween the pixel electrode and the common electrode, and the LCDshutter for 1 pixel is operated. When an electric signal (voltage) issupplied to the Y and X electrode of TFT, TFT is turned On, and the liquidcrystal molecules are operated as a light switch. Refer to Fig. 17 (AddressX1 and Y0).

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6-1 Subject of LCD Display6-1-1 Angle of View6-1-2 Response Characteristic

6-2 Angle of View 6-3 Multi-Domain System 6-4 MVA (Multi-domain Vertical Alignment) System 6-5 IPS (In-Plain Switching) System 6-6 Optically Compensated Film

6-7 OCB (Optically Compensated Birefringence)System 6-8 Improvement of Response Speed

6-8-1 Inpulse System6-8-2 FFD (Feed Forward Driving) System

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6-1-1 Angle of View Angle of view means the normal visible range (angle) of a screen.

In an LCD display, the angle of view is narrow compared with aCRT or PDP (Plasma Display Panel).

The viewing angle of the typical TN type LCD display is about

100. However with the new improved technology that has beendeveloped the angle of view for LCD display has increased to 160or 170. This improved system will be described later. (The angleof view for a CRT or PDP is 180.)

6-1-2 Response Characteristic The response characteristic of the LCD display is the speed at

which the display is refreshed by the input signal (video datasignal).

If this response characteristic is slow, an afterimage will appear onthe screen. Therefore, in large screen LCD television, improvingthis response characteristic becomes very important.

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The principle of optical penetration and theinterception of the LCD shutter by the arrangeddirection of cylindrical liquid crystal moleculescontrols the direction of light. Therefore, brightness,hue, and contrast depend on the direction of view ofthe LCD display. The range (angle) where these looknormal is called the angle of view. The fault of theTN LCD display is that this angle of view is narrow.

shows that brightness changes depending on the anglethe screen with a gray picture is viewed.

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The arrangement of the TN LCD display is onedirectional. In this Multi-Domain System, one pixel isdivided into two or more different arranged domains.shows the example of Multi-Domain System with twodomains. The quantity of the light per pixel fromvarious angles is equalized by this system. Moreover,the angle of view becomes even wider by increasingthe number of divisions. However, manufacturing is

difficult in the rubbing process*.

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In the MVA system, the (alignment) film is arranged so thatthe liquid crystal molecules are stood vertically. The MVAsystem combines vertical alignment with the Multi-domainsystem. By vertically aligning the liquid crystal molecules,the influence of optical interception is lost, and the angle of

view and contrast are improved. A type of material is usedthat causes the liquid crystal molecules to become vertical tothe glass plate without supplying voltage. (Nega-Nematicliquid crystal*) In the MVA system, attaching the boss byresin and making the liquid crystal molecules standdiagonally on the transparent electrode make multiple

alignment domains. Therefore, since the rubbing process canbe skipped at the alignment film production, manufacturingbecomes easier compared with the multidomain system.

Generally, a Posi-Nematic system is used that aligns theliquid crystal molecules by supplying voltage.

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The pixel and common electrodes are mounted to the transparentfilm (drive transistor) side and the electric field is generatedhorizontally to the glass plate. With this electric field, thealignment direction of liquid crystal molecules is rotated 90 inparallel to the glass plate. In the IPS system, liquid crystalmolecules rotate all at once in the horizontal direction. Since theseliquid crystal molecules do not lean like the TN type, there is littlechange in the picture characteristics (contrast, brightness, hue,etc.) and the angle of view becomes wider. However, there are afew problems. The quantity of transparent light is reduced, slowerresponse speed, and a white picture becomes a little bluish oryellowish depending on the viewing direction. The S-IPS (Super-IPS) type was developed to improve upon these problems. In theS-IPS type, the structure of the electrode for driving the liquidcrystal molecules becomes a zigzag form, which reduces thechange of color, increases the viewing angle to about 160 and hashigh definition equivalent to a CRT.

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By using the optically compensated film, the phaseshift of the STN type of LCD display is corrected,andthe angle of view and contrast are improved.(Referto 4-3 Triple STN Type.)

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The OCB system combines the bend-alignment systemwhere the liquid crystal molecules are bent and alignedbetween the upper and lower boards and opticallycompensation film. This system has the features ofincreased angle of view and quicker response speeds.However, bend-alignment is difficult to make uniformand stable.

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6-8-1 Inpulse System

In order to reduce afterimage and dim outline, there isthe system that has the backlight blinked for every

writing of one picture or an all black picture in insertedin the fixed cycle. It is called the Inpulse System. Forexample, with the system called Super InpulseSystem, the black data is written in every 1/60second, and the afterimage and the ghosts are

reduced. 6-8-2 FFD (Feed Forward Driving) System

The response speed of LCD brightness can beimproved by adding over-shoot characteristic to the

data line voltage.the actual overdrive circuit used in a

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1. ASSEMBLY PRECAUTION

2. OPERATING PRECAUTIONS

3. PRECAUTFONSWITHELECTROSTATICS

4. STORAGE PRECAUTIONS