Training Manual Principle of LCD Display
FILE NO.
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
REFERENCE NO. TI5110LCD
■ Construction of LCD Display
Training Manual Principle of LCD
1. Construction of LCD Display 1-1 Principle of LCD Display The LCD (Liquid Crystal Device) Display is used to display the electric signal, converted from picture data similar to a CRT display. The transistor (TFT) switched by the electric signal changes the transmission to light in small picture elements (pixels) of the LCD. The LCD display makes the picture by grouping these elements of each RGB color.
1-2 Construction of LCD Display 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 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 a glass 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 drive transistor) 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.
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Construction of LCD Display
Training Manual Principle of LCD
Backlight Polarized Board Glass Plate
Pixel (Picture Element) Transparent TFT Electrode (Pixel, TFT) Transparent Electrode (Common) Color Filter Glass Plate Polarized Board
Board Module (TFT side) LCD Layer
Board Module (Common side)
The light of each picture element is transmitted by switching the drive transistor (TFT) on and off.
Note: Alignment film is not shown in this figure.
Fig. 1 Construction
of LCD Display
(Transparent Type TFT LCD) -3-
Construction of LCD Display
Training Manual Principle of LCD
1-3 Main component of LCD Display 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 the backlight 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 arranged comparatively 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.
Color Filter It is a filter with three colors (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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Construction of LCD Display
Training Manual Principle of LCD
Backlight
Polarized Glass Board Plate Transparent Electrode (Pixel, TFT) Module (Back) LCD Shutter
Alignment Film Liquid Crystal Alignment Film Transparent Electrode (Common) Color Filter Glass Plate Polarized Board
LCD Layer Module (Front)
Fig. 2 Construction
of LCD Display
(Cross Section)
Backlight
LCD Panel (LCD Shutter)
LCD Display
LCD Module TFT Display Drive Circuit (with IC) -5-
Fig. 3 Assembly of LCD Display
â– Principle of Liquid Crystal
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 solids and liquids, and generally is a white turbid liquid. Its molecules are normally arranged comparatively opaque 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 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 axis for 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).
2-2 Rubbing-process After chemicals for arranging are put on the glass plate, they are hardened, and then the surface on the plate is rubbed with a cloth to fix the direction of the gaps that are made. The arranging direction of molecules is settled in the gaps. This process is used to change the characteristics so the molecules that touch the rubbed surface are arranged to the major axis of the rubbed direction. This thin film on the glass plate is called “Alignment film.�
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Principle of Liquid Crystal
Training Manual Principle of LCD
(a) Smectic
(b) Nematic
(c) Cholesteric
Fig. 4 Liquid Crystal
Liquid Crystal Molecule Natural Condition Arranging
Rubbing Direction Alignment Film
Fig. 5 Rubbing-Process
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Principle of Liquid Crystal
Training Manual Principle of LCD
2-3 Operation of Liquid Crystal The chemistry substance required for liquid crystal material is one that reacts so that the arrangement direction is changed according to an applied electric field. In the LCD display, 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 crystal molecules are moved and arranged. The Backlight applied to the liquid crystal is either passed or blocked according to the arrangement of the molecules. If an electric field from an external source is applied to liquid crystal, electric dipoles will be generated that will react to the intensity and direction of the electric field. Through the operation of these electric dipoles 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 direction from horizontal to vertical.
Transparent Electrode
Electric Field
Liquid Crystal
Electric Field
Liquid Crystal Molecule
Electric Dipole
Fig. 6 Operation of Liquid Crystal
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â– Principle of LCD
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, the oscillating directions of all light is mixed. A polarized board can let only the light in the specific direction pass from the light with which these various oscillating directions were mixed. Therefore, only the light of the same direction as the polarization direction of a polarized board can be taken out by letting the light pass through this polarized board. That is, if the oscillating direction of light and the direction of a polarized board are in agreement, the light will pass through a polarized board. Moreover, if the direction of a polarized board differs from the oscillating direction of light, the light cannot pass through a polarized board. When the oscillating direction of a polarized board and light are shifted 90Âş(right-angled), the light is blocked completely. The light passes and looks bright if the two boards are in the same direction when looking at two polarized boards in piles, however, if shifted at right-angles, the light is blocked and looks dark. Oscillating direction of light
Oscillating direction of light
Polarized Board
The direction of a polarized board differs from the oscillating direction of light
The oscillating direction of light and the direction of a polarized board are in agreement.
Passage Light The two boards are the same directions.
White
Fig. 7 Operation of Polarized Board
Interception Light The two boards are shifted right-angled.
Black
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Fig. 8 Operation of Polarized Board
Principle of Liquid Crystal
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 of grooves shifted by 90ยบ on the LCD display. The liquid crystal molecules of upper alignment plate are arranged along with the upper alignment film. The liquid crystal molecules of lower alignment plate are arranged along with the lower alignment film. The liquid crystal layer between these alignment films is twisted little by little and is arranged so that a spiral is formed. Light entering through the first alignment plate will have its oscillating direction twisted 90ยบ 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.
Alignment Plate
Alignment Film
Direction of Groove
Liquid Crystal Molecule
By the upper-and-lower alignment films, spirally, a liquid crystal molecules are twisted 90ยบ and arranged.
Alignment Film
Direction of Groove
Fig. 9 Operation of Alignment Film
3-3 Operation of LCD Panel In the LCD panel, a liquid crystal is inserted and enclosed between two glass plates. The polarized board, transparent electrode, and the alignment film are formed on these glass plates. The light can be passed 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 90ยบ sideways and arranged spirally. The oscillating direction of the light that passed the upper polarized board is changed by the twisted liquid crystal molecule arrangement. Therefore, the direction of a polarized board and the oscillating direction of the light which is shifted 90ยบ 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. -10-
Principle of Liquid Crystal
Training Manual Principle of LCD
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 crystal molecules do not affect the oscillating direction of light, the light that passed the upper polarized board passes as it is without changing the oscillating direction. Since the oscillating direction of this light differs from direction of the lower polarized board which is shifted 90º and arranged, the light collides with this polarized board and cannot pass. 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 sandwich structure 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 when voltage 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.” In practice, 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 arrangement of the liquid crystal molecules.
Lig
Lig
ht
ht Polarized Board Transparent Electrode (Upper)
Polarized Board Transparent Electrode (Upper)
Alignment Film
Alignment Film Liquid Crystal
Liquid Crystal
Alignment Film Transparent Electrode (Lower) Polarized Board
Alignment Film Transparent Electrode (Lower) Polarized Board
Fig. 10 Operation of Passage
Interception
LCD Panel
3-4 Transparent Electrode In order to generate an electric field in liquid crystal, voltage is supplied to the upper-and-lower electrodes. If metal is used for these electrodes, the light is interrupted by this metal and cannot pass into the liquid crystal. Therefore, a transparent electrode that passes light is used for the electrode of the LCD shutter. -11-
■ Type of LCD Display Construction
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 and lower 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, cellular phones, etc. A liquid crystal material developed to improve visual characteristics, such as contrast ratio is used. In this STN type liquid crystal molecules are twisted 180º to 270º and arranged between upper and lower electrodes. 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 yellowish green and navy blue. (In TN type, they are white and black.) This is because light of a specific wavelength is reflected and scattered by the thickness of the LCD panel. Therefore, even if a color filter of RGB is attached to an STN type liquid crystal, bluish green is mixed with the colors from black, gray to white, and a natural color picture cannot be displayed. The triple STN type (TSTN type) and the film STN type (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 lower LCD panels are used. They compensate for the twist of the light crystal cell, and the display colors of yellowish green and navy blue are changed to the correct white and black. The “FSTN” type uses a single optically compensated film
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Type of LCD Display Construction
TN Type
Training Manual Principle of LCD
Module
LCD Layer
Module Twist of molecule (90ยบ)
STN Type Module
LCD Layer
Module Twist of molecule (180ยบ - 270ยบ)
TSTN Type Optically Compensated Film Module
LCD Layer
Module Optically Compensated Film Fig. 11 Type of LCD Display Construction -13-
■ System of LCD Display
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 LCD television 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 fine character or picture becomes possible. With the present liquid crystal manufacture technology, the number of pixels per inch has reached 200ppi*, and very high definition screen display is possible. Moreover, the number of pixels of an LCD display panel corresponding to bigger screen sizes can be specified and manufactured. For example, the number 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
R G B
In colorization of LCD panel, one pixel consists of 3 RGB dots (sub-pixels).
X
A character or a figure is displayed by making the pixel of each X and Y intersection turn on (or off).
Y Fig. 12 Dot-Matrix System
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System of LCD Display
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 picture is made by mixing the three colors of RGB (three primary colors of light) respectively, like the CRT color television. The color LCD panel has a color filter of RGB attached to the monochrome panel. See Fig. 13. In this color LCD panel, by controlling the voltages and the waveforms that are supplied at each RGB pixel, the transparent ratio is controlled and hue and brightness are adjusted. Therefore, smaller pixels and more numbers of pixels are required for the color LCD Display. For example, although the SXGA panel described before has about 1,300,000 pixels, in colorization, there are about 4 million dots (sub-pixels).
Backlight
Backlight
ite
ite
Wh
Wh r
lo Co
e
R G B
m hro c o
n
Mo
Color Filter LCD Shutter
LCD Shutter
Color Panel
Monochrome Panel Fig. 13 Colorization of LCD Display
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System of LCD Display
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.
Drive System
Static Drive System Dynamic Drive System
Passive Matrix System
Classification of LCD Drive System
Active Matrix 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 glass plate as a matrix. The liquid crystal molecules are sandwiched between these electrodes. By supplying voltage between the Y electrode and the X electrode in sequence, at a certain time, an electric field is generated in the liquid crystal where the selected Y electrode and X electrode cross. Therefore, the liquid crystal molecules of this pixel address (X, Y electrode intersection) change arrangement and an LCD shutter is turned On or Off.
Y Electrode Y0
Y1
Y2
Y3
Y4
Glass Plate X0 X1 X2 X3
Liquid Crystal Layer
X4 Glass Plate
X Electrode
These electrodes are transparent electrodes.
Fig. 14 Passive Matrix System
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System of LCD Display
Training Manual Principle of LCD
Y1 Y0
Y1
Y2
LCD shutter is turned on or turned off in this address (X2, Y1).
X0 X1 X2
Liquid Crystal
X3 X2 Fig. 15 Passive Matrix System
In the dynamic drive system, since the electric signal (voltage) is supplied to the Y electrode and the X electrode in sequence, the number of pixels which makes all pixels (the total number of pixels are “X x Y”) turn on or off becomes “X+Y”. Therefore, compared with the static drive system that has an independent electrode for each pixel, the number of electrodes of the dynamic drive system is very few. However, with this dynamic drive system, since the electrode itself is the wiring, it has resistance that cannot be disregarded in the big screens. This resistance causes the speed of the shutter to become slower. Therefore, when displaying moving pictures etc., an afterimage is generated. This passive matrix system is not suitable for LCD televisions with big screens that require moving pictures and high resolution. The active matrix system was developed in order to overcome these faults.
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System of LCD Display
Training Manual Principle of LCD
5-5 Active Matrix System In the active matrix system, a switch element is attached for every pixel at the intersection of the X and Yelectrodes of a passive matrix system. Each pixel is now controlled by the switch element (active element). Since the switch for each pixel is turned On and Off independently, the response speed is increased. Thin Film Transistor (TFT) is used for the switch element and is attached on the glass board. The LCD display using this TFT is called “TFT LCD display”. The upper electrode for the whole pattern is formed on the upper glass plate and is called the “Common Electrode”. A pixel electrode (pixel pattern), TFT (switch element) which drives a pixel electrode, and X electrode for gate input and Y electrode for source input of TFT are formed on the lower glass plate. In this structure, the electric field is generated in the area between the pixel electrode and the common electrode, and the LCD shutter for 1 pixel is operated. When an electric signal (voltage) is supplied to the Y and X electrode of TFT, TFT is turned On, and the liquid crystal molecules are operated as a light switch. Refer to Fig. 17 (Address X1 and Y0). Glass Plate (Upper)
COMMON Electrode
Pixel Electrode (Pixel Pattern)
Liquid Crystal Layer
X Electrode Glass Plate (Lower)
Y Electrode
Equivalent Circuit (TFT)
Liquid Crystal
Y0
Y Electrode Y1
COMMON Electrode
Matrix System
Equivalent Circuit (Switch) COMMON
COMMON COMMON Electrode
Fig. 16 Structure of Active
TFT (Switch Element)
Liquid Crystal
Pixel Electrode
Drain
Drain
X1 X Electrode X1 X2 TFT
Pixel Electrode
X1 Gate
Gate
Source
Source Y0
TFT
By TFT, the shutter of a pixel at the address (X1, Y0) is turned On or Off.
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Y0
Switch (On / Off)
Fig. 17 Equivalent Circuit of Active Matrix System
System of LCD Display
Y0
Y1
Training Manual Principle of LCD
Y2
Y3 X0
TFT (Switch) Liquid Crystal COMMON Electrode
X1 X2 X3
The LCD shutter is operated by TFT at the address (X1, Y0).
Fig. 18 Structure of TFT Matrix The amplification operation of a transistor is used for the TFT switch in the active matrix system. In this system, switching speed is unified over the whole display, increasing drive response speed as compared with the passive matrix system. Therefore, TFT LCD display (active matrix system) is adopted for the highly efficient display, which can provide the response speed required for big screens or quickly moving pictures. However, further response speed is needed for high definition LCD television. This will be described later.
5-6 Drive of Active Matrix System
Voltage to liquid crystal
The TFT LCD display consists of a matrix of n lines of X direction (X0 - Xn-1) and of n rows of Y direction (Y0 - Yn-1). The line of X direction is called the “gate line” and the line (row) of Y direction is called the “data line.” First, the scan is started from the pixel address Since the time for the drive voltage to reach its required value is shorter in the active matrix system, (X0, Y0), and when the address (X0, Yn-1) is the response time of the display becomes quicker. selected the scan of X0 line is completed. Next, all the pixels from X1 line to Xn-1 line are scanned in Active Matrix System sequence, and the final address is (Xn-1, Yn-1). The operation of selected pixel address (X1, Y2) is explained below. First, (signal) voltage is supplied to X1 line (gate of TFT), next voltage is supplied to Y2 row (source of TFT), and the address of the intersection of X1 Passive Matrix System line and Y2 row is selected and its TFT is turned On or Off. However, just switching the TFT on and off will not change the brightness of the screen. The brightness of a screen is changed by controlTime ling the voltage of a data line (Y row). Fig. 19 shows the voltage characteristic of the matrix sysFig. 19 Voltage Characteristic of Matrix System tem. -19-
System of LCD Display
Training Manual Principle of LCD
In Fig. 20, the voltage of the data line (Y2) is supplied in the positive direction to a common electrode (DC drive). In practice a uniform AC voltage is supplied to the common electrode (AC drive) to prolong the life of the liquid crystal.
Data Line Drive Circuit (Y row)
Y0 Y1 Y2 Y3 • • • Yn-1 X0 X1 X2 X3
Pixel Electrode Glass Plate (Common)
•••
Liquid Crystal
Xn-1
Glass Plate (TFT)
Gate Line Drive Circuit (X line)
TFT
COMMON X Direction
Variable Voltage
Video Data Processor Y Direction
Timming Controller (Scan Converter)
Power Circuit COMMON
X1 Y2 TFT: On (X1, Y2) Brightness of Screen
Y2
COMMON
TFT: On
Y2 In practice, driven by AC signal to COMMON. (AC Drive)
Y2 TFT: Off
Y2
Fig. 20 LCD Drive Circuit (Normally White Type)
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■ Improvement Technology of LCD Display
Training Manual Principle of LCD
6 Improvement Technology of LCD Display 6-1 Subject of LCD Display 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 a CRT or PDP (Plasma Display Panel). The viewing angle of the typical TN type LCD display is about 100º. However with the new improved technology that has been developed the angle of view for LCD display has increased to 160º or 170º. This improved system will be described later. (The angle of view for a CRT or PDP is 180º.)
Vertical
Angle of View
Horizontal Angle of View Fig. 21 Angle of View 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 data signal). If this response characteristic is slow, an afterimage will appear on the screen. Therefore, in large screen LCD television, improving this response characteristic becomes very important.
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Improvement Technology of LCD Display
Training Manual Principle of LCD
6-2 Angle of View (TN Type) The principle of optical penetration and the interception of the LCD shutter by the arranged direction of cylindrical liquid crystal molecules controls the direction of light. Therefore, brightness, hue, and contrast depend on the direction of view of the LCD display. The range (angle) where these look normal is called the “angle of view.� The fault of the TN LCD display is that this angle of view is narrow. Fig. 22 shows that brightness changes depending on the angle the screen with a gray picture is viewed. In this figure, the liquid crystal molecule leans diagonally. Therefore, the amount of optical penetration will change depending on the angle when watching the screen from the front or the side.
The brightness becomes different depending on the angle of view.
Polarized Board Transparent Electrode (Common) Alignment Film
Glass Plate
Liquid Crystal Molecule
Alignment Film Transparent Electrode (Pixel, TFT) Polarized Board
Glass Plate
Fig. 22 Angle of View (TN type)
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Improvement Technology of LCD Display
Training Manual Principle of LCD
6-3 Multi-Domain System The arrangement of the TN LCD display is one directional. In this Multi-Domain System, one pixel is divided into two or more different arranged domains. Fig. 23 shows the example of Multi-Domain System with two domains. The quantity of the light per pixel from various angles is equalized by this system. Moreover, the angle of view becomes even wider by increasing the number of divisions. However, manufacturing is difficult in the rubbing process*.
� Refer to 2-2 Rubbing-process.
The brightness of a screen is equalized as macro view.
Polarized Board Transparent Electrode (Common) Alignment Film
Glass Plate
Liquid Crystal Molecule
Glass Plate Alignment Film Alignment Film (Left) (Right)
Transparent Electrode (Pixel, TFT) Polarized Board Fig. 23 Multi-Domain System
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Improvement Technology of LCD Display
Training Manual Principle of LCD
6-4 MVA (Multi-domain Vertical Alignment) System In the MVA system, the (alignment) film is arranged so that the liquid crystal molecules are stood vertically. The MVA system combines vertical alignment with the Multi-domain system. 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 used that causes the liquid crystal molecules to become vertical to the glass plate without supplying voltage. (Nega-Nematic liquid crystal*) In the MVA system, attaching the boss by resin and making the liquid crystal molecules stand diagonally on the transparent electrode make multiple alignment domains. Therefore, since the rubbing process can be skipped at the alignment film production, manufacturing becomes easier compared with the multidomain system.
� Generally, a Posi-Nematic system is used that aligns the liquid crystal molecules by supplying voltage.
Polarized Board Transparent Electrode (Common) Alignment Film
Glass Plate
Liquid Crystal Molecule (Nega-Nematic) Alignment Film Boss (Left)
(Right)
Glass Plate
Transparent Electrode (Pixel, TFT) Polarized Board
Fig. 24 MVA (Multi-domain Vertical Alignment) System
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Improvement Technology of LCD Display
Training Manual Principle of LCD
6-5 IPS (In-Plain Switching) System The structure of an IPS system is shown in Fig. 25. The pixel and common electrodes are mounted to the transparent film (drive transistor) side and the electric field is generated horizontally to the glass plate. With this electric field, the alignment direction of liquid crystal molecules is rotated 90ยบ in parallel to the glass plate. In the IPS system, liquid crystal molecules rotate all at once in the horizontal direction. Since these liquid crystal molecules do not lean like the TN type, there is little change in the picture characteristics (contrast, brightness, hue, etc.) and the angle of view becomes wider. However, there are a few problems. The quantity of transparent light is reduced, slower response speed, and a white picture becomes a little bluish or yellowish depending on the viewing direction. The S-IPS (Super-IPS) type was developed to improve upon these problems. In the S-IPS type, the structure of the electrode for driving the liquid crystal molecules becomes a zigzag form, which reduces the change of color, increases the viewing angle to about 160ยบ and has high definition equivalent to a CRT.
Polarized Board
Basic Structure of IPS System
Glass Plate (Without Transparent Electrode) Alignment Film
Electric Field
Transparent Electrode (Pixel)
Alignment Film Transparent Electrode (Common)
Glass Plate Liquid Crystal Molecule (Vertical)
Polarized Board Polarized Board
Normally Black Mode
Alignment Film Liquid Crystal Molecule (Vertical)
Dark (Switch Off)
Bright (Switch On)
Fig. 25 IPS (In-Plain Switching) System -25-
Improvement Technology of LCD Display
Training Manual Principle of LCD
6-6 Optically Compensated Film By using the optically compensated film, the phase shift of the STN type of LCD display is corrected, and the angle of view and contrast are improved. (Refer to 4-3 Triple STN Type.) Three methods for attaching the optically compensated film are shown in Fig. 26. 1 sheet / 1 side
Polarized Board Compensated Film
Liquid Crystal
Polarized Board
2 sheets / 1 side
2 sheets / 2 sides
Polarized Board Compensated Film 1 Compensated Film 2
Polarized Board Compensated Film 1
Liquid Crystal
Polarized Board
Liquid Crystal
Polarized Board
Compensated Film 2
Fig. 26 Optically Compensated Film
6-7 OCB (Optically Compensated Birefringence) System The OCB system combines the bend-alignment system where the liquid crystal molecules are bent and aligned between the upper and lower boards and optically compensation film. This system has the features of increased angle of view and quicker response speeds. However, bend-alignment is difficult to make uniform and stable.
Polarized Board Optically Compensated Film Transparent Electrode (Common)
Glass Plate
Alignment Film Liquid Crystal Molecule
Alignment Film Transparent Electrode (Pixel, TFT) Polarized Board
Glass Plate
Fig. 27 OCB System -26-
Improvement Technology of LCD Display
Training Manual Principle of LCD
6-8 Improvement of Response Speed 6-8-1 Inpulse System In order to reduce afterimage and dim outline, there is the system that has the backlight blinked for every writing of one picture or an all black picture in inserted in the fixed cycle. It is called the “Inpulse System.” For example, with the system called “Super Inpulse System,” the black data is written in every 1/60 second, and the afterimage and the ghosts are reduced. With the usual LCD panel, since the picture is displayed continuously, the front picture becomes dim as the afterimage. In the inpulse system, by inserting black data between the picture data, the afterimage is reduced and the high-speed response is improved.
Black Data
Fig. 28 Inpulse System
Picture Data
6-8-2 FFD (Feed Forward Driving) System
Over-Shoot
Waveform (Normal)
Voltage
Voltage
The response speed of LCD brightness can be improved by adding over-shoot characteristic to the data line voltage. Fig. 29 shows the actual overdrive circuit used in a digital drive system.
Waveform with Over-Shoot
Time
Time
Response Time Brightness
Brightness
Response Time
(By Overdrive Circuit)
Time Voltage
Voltage
Time
Time
Time
Overdrive Circuit
Drive Circuit (Normal)
Fig. 29 Overdrive Circuit
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â– Appendix
Training Manual Principle of LCD
7 Appendix 7-1 Backlight An LCD panel does not emit light itself. For the display, a light source is required, and normally fluorescent lights are used for the backlight of the LCD television. The backlight consists of fluorescent lights, a reflective plate, and a diffusion sheet (or board). Fig. 30 shows the structure and photograph of 30V and 15V LCD televisions backlights.
30V Type LCD Panel
Fluorescent Lights (30V: 16pcs)
Diffusion Sheet (Board)
Reflective Plate
15V Type LCD Panel
Fluorescent Lights (15V: 2pcs, 20V:3pcs)
Diffusion Sheet
Reflective Plate
Fig. 30 Backlight
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Appendix
Training Manual Principle of LCD
7-2 LVDS Circuit (1) LVDS Interface For transmitting the video signal information, an interface circuit with an LVDS (Low Noise Differential Signaling) standard is used, which has the merit of low noise, high speed operation by a small amplitude, and low power consumption. The LVDS cable connects the transmitter in the driving circuit and the receiver in the module.
Fig. 31 LVDS Interface
Transmitter (Driving Circuit)
100â„Ś Terminated
3.5mA
Receiver (LCD Panel)
LVDS Cable
1.2V
345/200mV
(2) Driving Circuit Fig. 32 shows the block diagrams of a panel driving circuit. The final video information (signal) from the video processor (for example pixelworks) is transmitted to the LCD panel module through an LVDS cable.
Fig. 32 Block Diagrams of Panel Driving Circuit
Video Processor (pixelworks)
LVDS Transmitter TxOUT TxIN
Part of Panel Display (in the module) DATA (LVDS)
LVDS Receiver RxIN
RxOUT
R
8
R
8
G
8
G
8
B
8
B
8
Vsync
Vsync
Hsync
Hsync
BLANK
BLANK
PARITY
PARITY PDWN
DCLK
TxCLKIN
DCLK
CLOCK (LVDS)
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LVDS
RxCLKOUT
LCD Module
Part of (Panel) Driving Circuit
Appendix
Training Manual Principle of LCD
7-3 Block Diagram Example (1) CLT-1583 R
Speaker (R)
U45 R
Audio AMP
3
LA4263
1
10
Tuner Board
1 30
S_CLK / SIN_OUT/ ENABLE_IN / ENABLE_OUT V33D
DRO [0-7]
Video Decoder
VY [0-7]
V L R
L_PC 11
L2
GBE [0-7]
VCPU 33 37
Flash ROM
U30
8Mbits
V33D
AVDD PVDD
R
V L R Y Cb Cr
G H
Component AV2 Input
B_PC
Red_PC
9
AV1 Input
THC63LVDM83A
54 30 48 31 43
R2
8
CVBS2
4 R1
2
V L R
S
Monitor Output
1
CVBS1
SY1
5
DBO [0-7]
MENORY DATA
Graphic A/D AD9883
R_PC
16
L1
3
SC1
7 S1
R_OUT
L_OUT
CVBS_OUT
AV Switch U46 CXA2089Q 33 30 32
LVDS Interface
DGO [0-7]
U6 18
34
V33
5 4 6
GGE [0-7]
74 71
Main Scaler / (Main)CPU PW113-10Q PIXELWORKS
VUV [0-7]
VPC3230D
40 43 45
41 39
IC1
U36
INPUT_Y INPUT_Cb/Pb INPUT_Cr/Pr
CVBS
47 48 46
VCPU 33/18
U19
SELECTED_C
72
AUDIO_L
AUDIO_R
L_TV
R_TV
3 2 1
SELECTED_Y
CC_R CC_G CC_B
7 6
V_TV
Main Board
NJW1138M
Tuner / IF TMQJ8
+9V
LCD Panel
Audio Processor
IIC +CONTROL
17
Speaker (L)
GRE [0-7]
Sub CPU M37272M6
16
HS_PC G_PC VS_PC
+9V
U101 TU201
L
U44
8 23
RX CLK+/-
R
8
Headphone (J26)
L
RX IN+/-[0-3]
4
L
+12V
B V
D-SUB
Fig. 33 Block Diagram: CLT-1583
PC Input
(2) CLT-2053 R
Speaker (R)
U45 R 4
Audio AMP
3
LA4263
1
10
R
8
+9V
Sub CPU M37272M6
16
Audio Processor
1 30
Tuner / IF TMQJ8
47 48 46 41 39
74 71
5
Main Scaler / (Main)CPU PW113-10Q PIXELWORKS
VUV [0-7]
VPC3230D
DGO [0-7] DBO [0-7]
LCD Panel
4 6
U36
MENORY DATA
U30
VCPU 33 37
Flash ROM 8Mbits
40 43 45
V L R Monitor Output
S
V L R
AV1 Input
9
11
V L R AV2 Input
R3
8
R2
4
L2
2
CVBS2
1
16
R1
CVBS1
5
L1
3
SC1
7
SY1
R_OUT
33 30 32
S1
AV Switch U46 CXA2089Q
L3
34
CVBS_OUT
VY [0-7]
18
L_OUT
+9V
DRO [0-7]
Video Decoder
INPUT_Y INPUT_Cb/Pb INPUT_Cr/Pr
CVBS
72
VCPU 33/18
U19
SELECTED_C
AUDIO_R
3 2 1
SELECTED_Y
CC_R CC_G CC_B
L_TV
R_TV
S_CLK / SIN_OUT/ ENABLE_IN / ENABLE_OUT V33D
7 6
V_TV
17
Speaker (L)
Main Board
NJW1138M
IIC +CONTROL
AUDIO_L
U101 TU201
L
U44
8 23
Tuner Board
Headphone (J26)
L
L
+14V
L R
Y Cb Cr
Audio Board
Component
Fig. 34 Block Diagram: CLT-2053 AV3 Input
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Appendix
Training Manual Principle of LCD
(3) CLT1554 / CLT2054 AV1 AV1_Y 3
S Video Composite Video Audio
AV1_CV 1
IC1001
IC801
TV_CV 5
Video SW
CPU
7 AV1/TV_Y/CV 5
AV2
AV2_V 1 AV3_Y 3
Composite Video Audio
IC1002
36 37 22 23 OSD_HD VD (For Caption) 12 10 5V
13 11 OSD_HD VD 154 153
85
IC2001
AD_Y 48
Audio
AD_Cr 54
IC301
IC4101
AD_HS
IP Converter Screen Controller
(Y/UV)
38
AD_VS
IIC Bus
IC361 SDRAM
Sync Separation 15
R: 1
Tuner IF Sound Multiplex
AV3_L/R L: 28
R: 3
R: 4 TV_L/R L: 27
IIC Bus
LCD PANEL (15V)
AD_CLAMP
28
AV1_L/R L: 30 R: 2 AV2_L/R L: 29
IC781 LVDS Transmitter
IC1701
TV (A201)
R/G/B (0-7)
31
16 AD_Y 26
LCD PANEL (20V) (For 15V)
IIC Bus
AD_Cb 43 A/D Converter 30
(For 20V) R/G/B (0-7)
IIC Bus AD_R/G (0-7)
(480p)
152 151 150 148 149 R G B Y I
DEC_Y/C (0-7)
with AV3_Cb 94 Y/C Separation (480i)
Component Video
OSD_CC
DD Converter 3.3V
AV3_Cr 92 Digital Decoder
AV3
18 19 20 21 16 R G B Y I
IC871
7 SEL_Y/CV
Video SW
AV1_C 90
IIC Bus
IC001
10 SEL_R
16 R-OUT (+)
13
Audio SW Audio Control 21 SEL_L Surround
IC101
15 R-OUT (-)
SPEAKER (Right)
Audio AMP 9
24 L-OUT (+) 25 L-OUT (-)
IIC Bus
SPEAKER (Left)
Fig. 35 Block Diagram: CLT1554 / CLT2054
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SEP / 2004
Printed in Japan
SANYO Electric Co., Ltd.