Sanyo TV LCD training manual

Training Manual Principle of LCD1-2 Construction of LCD Display LCD Display Liquid Crystal is packed between the board modules TFT and Common and the LCD panel or LCDshutter is construct

FILE NO.

Training Manual

Principle of LCD Display

CONTENTS

Pages

1 Construction of LCD Display - 2 - 5

1-1 Principle of LCD Display - 2

1-2 Construction of LCD Display - 2 - 3 1-3 Main Component of LCD Display - 4 - 5 2 Principle of Liquid Crystal - 6 - 8 2-1 Liquid Crystal - 6

2-2 Rubbing-process - 6 - 7 2-3 Operation of Liquid Crystal - 8

3 Principle of LCD - 9 - 11 3-1 Operation of Polarized Board for LCD Panel (Shutter) - 9

3-2 Operation of Alignment Film - 10

3-3 Operation of LCD Panel - 10 - 11 3-4 Transparent Electrode - 11

4 Type of LCD Display Construction - 12 - 13 4-1 Twisted Nematic (TN) Type - 12- 13 4-2 Super TN (STN) Type - 12- 13 4-3 Triple STN (TSTN) Type / Film STN (FSTN) Type - 12- 13 5 System of LCD Display - 14 - 20 5-1 Dot-Matrix System - 14

5-2 Colorization - 15

5-3 Drive System - 16

5-4 Passive Matrix System - 16 - 17 5-5 Active Matrix System - 18 - 19 5-6 Drive of Active Matrix System - 19 - 20 6 Improvement Technology of LCD Display - 21 - 27 6-1 Subject of LCD Display - 21

6-1-1 Angle of View - 21

6-1-2 Response Characteristic - 21

6-2 Angle of View - 22

6-3 Multi-Domain System - 23

6-4 MVA (Multi-domain Vertical Alignment) System - 24

6-5 IPS (In-Plain Switching) System - 25

6-6 Optically Compensated Film - 26

6-7 OCB (Optically Compensated Birefringence) System - 26

6-8 Improvement of Response Speed - 27

6-8-1 Inpulse System - 27

6-8-2 FFD (Feed Forward Driving) System - 27

7 Appendix - 28 - 31 7-1 Backlight - 28

7-2 LVDS Circuit - 29

7-3 Block Diagram Example - 30 - 31

Training Manual Principle of LCD

1-2 Construction of LCD Display

LCD Display

Liquid Crystal is packed between the board modules (TFT and Common) and the LCD panel (or LCDshutter) is constructed A back light is attached to the LCD panel for LCD Display

Board Module (Common Electrode)

The Common Electrode consists of a polarized board, a color filter, and a transparent electrode on aglass plate An alignment film is formed on the transparent electrode

Board Module (TFT Electrode)

The TFT Electrode consists of a polarized board and a transparent electrode (pixel electrode and drivetransistor) on a glass plate An alignment 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 for function

Training Manual Principle of LCD

Construction of LCD Display

Board Module (TFT side)

Board Module (Common side)

The light of each picture element is transmitted

by switching the drive transistor (TFT) on and off.

LCD Layer

Backlight

Polarized Board

Polarized Board

Pixel (Picture Element)

TFT

Transparent Electrode (Pixel, TFT)

Color Filter

Transparent Electrode (Common)

Glass Plate

Glass Plate

Note: Alignment film is not

shown in this figure

Fig 1Construction of LCD Display

(Transparent Type TFT LCD)

Training Manual Principle of LCD

Liquid Crystal

Liquid Crystal is a material whose state is between a solid and a liquid It has both characteristics ofsolids and liquids, and generally it is a white turbid liquid Its molecules are normally arranged compara-tively 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 usedfor its electrode

Training Manual Principle of LCD

Construction of LCD Display

Backlight

Polarized Board

Polarized Board

Glass Plate

Glass Plate

Alignment Film Alignment Film Liquid Crystal

Transparent Electrode (Pixel, TFT)

Transparent Electrode (Common)

Color Filter

Module (Back)

Module (Front)

LCD Layer

LCD

Shutter

TFT Display Drive Circuit (with IC)

LCD Display

Backlight

LCD

Module

LCD Panel (LCD Shutter)

Fig 2Construction of LCD Display

(Cross Section)

Fig 3Assembly of LCD Display

Training Manual Principle of LCD

2 Principle of Liquid Crystal

2-1 Liquid Crystal

What is Liquid Crystal?

Liquid Crystal is a material whose state is between a solid and liquid It has characteristics of both solidsand liquids, and generally is a white turbid liquid Its molecules are normally arranged comparativelyopaque and change to transparent with the application of voltage or heat

Almost all the materials consist of an organic compound taking the form of a slender stick or a flat plate.There are three types of liquid crystal as shown in Fig 4, and they depend on the construction andarrangement of molecules

Generally Nematic liquid crystal is used for the display apparatus

This process is used to change the characteristics so the molecules that touch the rubbed surface arearranged to the major axis of the rubbed direction

This thin film on the glass plate is called “Alignment film.”

Training Manual Principle of LCD

Principle of Liquid Crystal

Alignment Film

Arranging

Rubbing Direction

Natural Condition

Liquid Crystal Molecule

Fig 4Liquid Crystal

(a) Smectic

(c) Cholesteric (b) Nematic

Fig 5Rubbing-Process

Training Manual Principle of LCD

Principle of Liquid Crystal

2-3 Operation of Liquid Crystal

The chemistry substance required for liquid crystal material is one that reacts so that the arrangementdirection is changed according to an applied electric field

In the LCD display, a liquid crystal is placed between two electrodes When the voltage is suppliedbetween them, an electric field is generated in the liquid crystal, and liquid crystal molecules are movedand arranged The Backlight applied to the liquid crystal is either passed or blocked according to thearrangement of the molecules

If an electric field from an external source is applied to liquid crystal, electric dipoles will be generatedthat will react to the intensity and direction of the electric field Through the operation of these electricdipoles and the electric field, the power changing direction of liquid crystal molecules is generated.Therefore, according to an external electric field, liquid crystal molecules move and change directionfrom horizontal to vertical

Electric Dipole

Liquid Crystal Molecule

Liquid Crystal

Electric Field

Electric Field

Transparent Electrode

Fig 6Operation of Liquid Crystal

Training Manual Principle of LCD

3 Principle of LCD

3-1 Operation of Polarized Board for LCD Panel (Shutter)

Light is an electromagnetic wave that is oscillating at right angles to the direction of advance In fact, theoscillating directions of all light is mixed A polarized board can let only the light in the specific directionpass from the light with which these various oscillating directions were mixed Therefore, only the light ofthe same direction as the polarization direction of a polarized board can be taken out by letting the lightpass through this polarized board That is, if the oscillating direction of light and the direction of a polar-ized board are in agreement, the light will pass through a polarized board Moreover, if the direction of apolarized board differs from the oscillating direction of light, the light cannot pass through a polarizedboard When the oscillating direction of a polarized board and light are shifted 90º(right-angled), the light

is blocked completely The light passes and looks bright if the two boards are in the same direction whenlooking at two polarized boards in piles, however, if shifted at right-angles, the light is blocked and looksdark

Polarized Board

Oscillating direction of light Oscillating direction of light

The oscillating direction

of light and the direction

of a polarized board are

in agreement.

The direction of a polarized board differs from the oscillating direction of light

Training Manual Principle of LCD

3-2 Operation of Alignment Film

Liquid crystal is inserted into alignment films of an upper and lower plate that have the direction ofgrooves shifted by 90º on the LCD display The liquid crystal molecules of upper alignment plate arearranged along with the upper alignment film The liquid crystal molecules of lower alignment plate arearranged along with the lower alignment film The liquid 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 90º by the liquid crystal layer between the alignment films.Now the direction of oscillation is aligned with the second alignment plate and the light will pass through

Principle of Liquid Crystal

Alignment Film

Alignment

Film

Alignment Plate

3-3 Operation of LCD Panel

In the LCD panel, a liquid crystal is inserted and enclosed between two glass plates The polarizedboard, transparent electrode, and the alignment film are formed on these glass plates The light can bepassed or blocked by supplying voltage or not to this LCD panel

In the condition (Switch-Off) that the voltage is not supplied, the liquid crystal molecules are twisted 90ºsideways and arranged spirally The oscillating direction of the light that passed the upper polarizedboard is changed by the twisted liquid crystal molecule arrangement Therefore, the direction of a polar-ized board and the oscillating direction of the light which is shifted 90º and arranged 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

Training Manual Principle of LCD

Principle of Liquid Crystal

Transparent Electrode (Lower)

Transparent Electrode (Upper)

Alignment Film

Liquid Crystal

Alignment Film

elec-On the contrary, in the condition (Switch-elec-On) that voltage is supplied, the liquid crystal molecules arearranged in a line at right angles to a glass plate Since vertical liquid crystal molecules do not affect theoscillating direction of light, the light that passed the upper polarized board passes as it is without chang-ing the oscillating direction Since the oscillating direction of this light differs from direction of the lowerpolarized board which is shifted 90º and arranged, the light collides with this polarized board and cannotpass This is the liquid crystal shutter-off condition and the LCD panel (LCD shutter) blocks the light.This is the basic structure (On—Off of the light by the LCD shutter) of an LCD panel It is a sandwichstructure of the upper and lower sides of transparent electrodes, alignment films, and polarized boards,with an enclosed liquid crystal material between them

The LCD panel shown in Fig 10 is a type of panel that changes the light into a passage condition whenvoltage is not supplied between the upper-and-lower polarized boards that are arranged at 90º 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 Black Mode.” Inpractice, with this type (when the upper-and-lower polarized boards are arranged in the same direction),displaying perfect black becomes difficult due to the leakage of light caused by variations in the arrange-ment of the liquid crystal molecules

Training Manual Principle of LCD

4 Type of LCD Display Construction

4-1 Twisted Nematic (TN) Type

A Nematic type of LCD Display where the liquid crystal molecules are twisted 90º between upper andlower boards is called a Twisted Nematic type (TN type) liquid crystal

Most LCD displays are of this type and feature high contrast (ratio) under low voltage and power

4-2 Super TN (STN) Type

Super TN type (STN type) LCD Displays are used for LCD televisions, personal computer monitors, lular phones, etc A liquid crystal material developed to improve visual characteristics, such as contrastratio is used

cel-In this STN type liquid crystal molecules are twisted 180º to 270º and arranged between upper and lowerelectrodes By supplying voltage to this liquid crystal, the transparent ratio of light changes more steeply.Therefore, with the STN type as compared to the TN type, contrast and rise characteristic of the voltage(response of switch On and Off) are improved, and a clearer picture on larger screens becomes possible

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

A fault of the STN type is that the display colors during On and Off of the LCD shutter become yellowishgreen and navy blue (In TN type, they are white and black.) This is because light of a specific wave-length is reflected and scattered by the thickness of the LCD panel Therefore, even if a color filter ofRGB is attached to an STN type liquid crystal, bluish green is mixed with the colors from black, gray towhite, and a natural color picture cannot be displayed The triple STN type (TSTN type) and the film STNtype (FSTN type) have been developed as an advanced type 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 the light crystal cell, and the display colors of yel-lowish green and navy blue are changed to the correct white and black The “FSTN” type uses a singleoptically compensated film

Training Manual Principle of LCD

Type of LCD Display Construction

Film

Module

Optically Compensated

TSTN Type

STN Type

TN Type

Training Manual Principle of LCD

5 System of LCD Display

5-1 Dot-Matrix System

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

The picture elements (pixels) of the display unit are arranged horizontally (X line) and vertically (Y row)

by this Dot-Matrix system, and various characteristics and figures can be displayed

Fig 12 shows a matrix of “X x Y = 10 (pixels)” with the character “Y” displayed In this Dot-Matrix system,

by making the size of a pixel smaller and increasing the whole number of pixels, the big screen with finecharacter or picture becomes possible

With the present liquid crystal manufacture technology, the number of pixels per inch has reached200ppi*, and very high definition screen display is possible Moreover, the number of pixels of an LCDdisplay panel corresponding to bigger screen sizes can be specified and manufactured For example, thenumber of pixels of the SXGA* panel is about 1,300,000 (1,280 x 1,024 = 1,310,720 pixels)

✐ppi: pixel per inch

✐SXGA: Super eXtended Graphics Array

A character or a figure is displayed by making the pixel of each X and Y inter- section turn on (or off).

Training Manual Principle of LCD

5-2 Colorization

Since an LCD shutter only passes or blocks light, in itself it cannot display a color picture The color ture is made by mixing the three colors of RGB (three primary colors of light) respectively, like the CRTcolor television The color LCD panel has a color filter of RGB attached to the monochrome panel SeeFig 13 In this color LCD panel, by controlling the voltages and the waveforms that are supplied at eachRGB pixel, the transparent ratio is controlled and hue and brightness are adjusted Therefore, smallerpixels and more numbers of pixels are required for the color LCD Display For example, although theSXGA panel described before has about 1,300,000 pixels, in colorization, there are about 4 million dots(sub-pixels)

pic-System of LCD Display

Fig 13Colorization of LCD Display

LCD Shutter Color Filter

Training Manual Principle of LCD

5-3 Drive System

The drive systems for LCD display are divided into the following classifications:

The Static Drive System, which is seldom used;

The Passive Matrix System, which is used for still pictures, such as calculators and notebook PCs; The Active Matrix System, which is suitable for high definition and the high-speed response needed for

big screen LCD television

System of LCD Display

Active Matrix System

Classification of LCD Drive System

5-4 Passive Matrix System

In the structure of a passive matrix system, Y electrodes of the vertical direction (Y-direction) are formed

in upper glass plate, and X electrodes of the horizontal direction (X direction) are formed in lower glassplate as a matrix The liquid crystal molecules are sandwiched between these electrodes By supplyingvoltage between the Y electrode and the X electrode in sequence, at a certain time, an electric field isgenerated in the liquid crystal where the selected Y electrode and X electrode cross Therefore, the liquidcrystal molecules of this pixel address (X, Y electrode intersection) change arrangement and an LCDshutter is turned On or Off

Glass Plate

Y Electrode

X Electrode

Glass Plate

Fig 14Passive Matrix System

These electrodes are transparent electrodes.