IOS-Displays-1

IOS-Displays-1

Contents of the Lecture 1. Introduction 2. Methods for I/O Operations 3. Computer Buses 4. Expansion Modules for Embedded Systems 5. Computer Displays 6. Graphics Adapters 7. Optical Discs 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 1 5. Computer Displays

Liquid Crystal Displays Organic LED Displays Electronic Paper Displays 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 2 Liquid Crystal Displays Liquid Crystals Twisted Nematic Technology Addressing Techniques Backlighting Types

Display Parameters Vertical Alignment Technology In-Plane Switching Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 3 Liquid Crystals (1) Liquid crystals: discovered in 1888 Changing the state of a material known as cholesteryl benzoate from solid into liquid Substances that exhibit anisotropy of properties variable depending on the

direction of measurement Equilibrium state mesomorphic State between solid crystalline and liquid 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 4 Liquid Crystals (2) Light passing through liquid crystals follows the alignment of the molecules Applying an electric or magnetic field changes the molecular alignment of liquid crystals Three types of liquid crystals:

Thermotropic Lyotropic Metallotropic 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 5 Liquid Crystals (3) Thermotropic liquid crystals Transition into several phases with temperature changes Lyotropic liquid crystals Present phase transitions determined primarily

by the concentration of molecules in a solvent Metallotropic liquid crystals Composed of organic and inorganic molecules Phase transitions also depend on the organic / inorganic composition ratio 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 6 Liquid Crystals (4) Phases of thermotropic liquid crystals High temperature: liquid (isotropic) phase Low temperature: solid (crystalline) phase

Nematic phase Smectic phase Cholesteric phase Types of ordering for the phases: Positional order of molecules Orientation order of molecules 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 7 Liquid Crystals (5) Nematic phase (N) Nema thread; nemato

threadlike (Greek) Threadlike molecules No positional order Approximately parallel orientation order director Can be easily aligned by an electric field 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 8 Liquid Crystals (6) Smectic phase (Sm)

Molecules maintain the orientation order They align in layers Positional order along one direction SmA (left) SmC (right) Other Sm phases exist 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 9 Liquid Crystals (7) Cholesteric phase

Typical for cholesterol esters cholesteric Chiral molecules: have no internal plane of symmetry Chiral nematic (N*) Structure similar to a stack of 2D nematic layers The director in each layer is twisted Twisted nematic (TN) 11/14/2019 Input/Output Systems and Peripheral Devices (05-1)

10 Liquid Crystal Displays Liquid Crystals Twisted Nematic Technology Addressing Techniques Backlighting Types Display Parameters Vertical Alignment Technology In-Plane Switching Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 11

Twisted Nematic Technology Twisted Nematic Technology Principle of Operation Display Structure Super-Twisted Nematic Technology Double Super-Twisted Nematic Technology Film Super-Twisted Nematic Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 12 Principle of Operation (1) Liquid crystal displays are passive

Use a light source (backlight) or a mirror (to reflect ambient light) The operation is based on the properties of polarized light The light waves are oriented in parallel with a specific direction Can be obtained with a polarizer 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 13 Principle of Operation (2) The polarized light passes through a TN liquid

crystal layer The light follows the alignment of molecules The polarizing direction is changed by the twisting of molecules 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 14 Principle of Operation (3) Single pixel: TN liquid crystals placed between two transparent electrodes The electrodes are provided with alignment layers to control molecule alignment grooves

The grooves on the two electrodes are perpendicular to each other This results in a 90 twist of the longitudinal axes of molecules on the two electrodes 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 15 Principle of Operation (4) Two polarizers Two glass plates Two transparent electrodes TN liquid crystal layer No voltage is applied:

The light is polarized by the first polarizer The polarizing direction is twisted with 90 The light will also pass through the second polarizer 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 16 Principle of Operation (5) Voltage is applied: The molecules realign

The direction of longitudinal axes tends to align in parallel to the field The light is not twisted is blocked by the second polarizer By controlling the voltage, different levels of gray can be obtained 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 17 Principle of Operation (6)

Displays for which the light is blocked in the areas with no voltage applied The polarizing directions are parallel The optical effect is more dependent on the thickness of display when no voltage is applied The eye is more sensitive to variations of brightness in the dark state spotted image This variant may also increase power consumption 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 18

Principle of Operation (7) Response of a TN cell to an applied voltage 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 19 Principle of Operation (8) Percent transmission of light for a TN cell 11/14/2019 Input/Output Systems and Peripheral Devices (05-1)

20 Principle of Operation (9) Color displays Intermediate levels of brightness are required Changing the voltage applied to the cells The white backlight contains all the wavelengths The color components are obtained through filtering of the white light Each pixel is composed of three subpixels for the primary R, G, and B colors additive synthesis 11/14/2019 Input/Output Systems and Peripheral Devices (05-1)

21 Twisted Nematic Technology Twisted Nematic Technology Principle of Operation Display Structure Super-Twisted Nematic Technology Double Super-Twisted Nematic Technology Film Super-Twisted Nematic Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 22

Display Structure 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 23 Twisted Nematic Technology Twisted Nematic Technology Principle of Operation Display Structure Super-Twisted Nematic Technology Double Super-Twisted Nematic Technology Film Super-Twisted Nematic Technology

11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 24 Super-Twisted Nematic Technology (1) STN Super-Twisted Nematic The difference between the voltages for which a cell is ON/OFF must be very small The TN technology is impractical for large sizes with conventional addressing STN technology: the direction of the polarized light is rotated with an angle of 180 .. 270 The diagram representing the light

transmission becomes more abrupt 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 25 Super-Twisted Nematic Technology (2) Percent transmission of light for an STN cell with a twist angle of 270 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 26

Super-Twisted Nematic Technology (3) Advantages of STN technology compared to the TN technology: Higher contrast ratio Wider viewing angle Simpler control for the percent transmission of light through the liquid crystal cells Enables to increase the number of rows that can be displayed simultaneously 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 27

Super-Twisted Nematic Technology (4) Disadvantages of STN technology: Slower response time compared to the TN technology Lower brightness level Higher manufacturing costs Early STN displays presented an undesirable coloration shifted transmission spectrum In the ON state: yellow In the OFF state: bluish 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 28

Twisted Nematic Technology Twisted Nematic Technology Principle of Operation Display Structure Super-Twisted Nematic Technology Double Super-Twisted Nematic Technology Film Super-Twisted Nematic Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 29 Double Super-Twisted Nematic

Technology (1) DSTN Double Super-Twisted Nematic Solved the coloration problem of the STN technology by adding a second STN layer Without electrodes or polarizers The twisting direction of the polarized light is opposite to that of the first layer In the OFF state, the phase shift due to the first layer is compensated by the second layer black cell 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 30

Double Super-Twisted Nematic Technology (2) DSTN cell in OFF state (left) and ON state (right) 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 31 Double Super-Twisted Nematic Technology (3) The ON state of the pixel is not affected by the second STN layer white pixel Both layers consist of the same type of

liquid crystal the characteristics are constant Disadvantages: More intense backlight is required Higher cost Higher thickness and weight 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 32 Twisted Nematic Technology Twisted Nematic Technology Principle of Operation Display Structure

Super-Twisted Nematic Technology Double Super-Twisted Nematic Technology Film Super-Twisted Nematic Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 33 Film Super-Twisted Nematic Technology FSTN Film Super-Twisted Nematic Color compensation is achieved with a thin polymer film instead of a glass layer Advantages compared to DSTN technology: Lower cost

Lower thickness and weight Lower-power backlight Disadvantage: Reduced contrast 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 34 Liquid Crystal Displays Liquid Crystals Twisted Nematic Technology Addressing Techniques Backlighting Types

Display Parameters Vertical Alignment Technology In-Plane Switching Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 35 Addressing Techniques Addressing Techniques Direct and Multiplexed Addressing Passive-Matrix Displays Active-Matrix Displays Defective Pixels

11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 36 Direct and Multiplexed Addressing (1) Direct addressing Used for displays with a small number of display elements Each element (segment or pixel) can be addressed or driven separately A voltage should be

applied to each element to change orientation of the molecules 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 37 Direct and Multiplexed Addressing (2) Multiplexed addressing Used for displays with a large number of pixels The pixels can be addressed by a matrix of rows and columns

Each pixel sits at the intersection of a row electrode and a column electrode 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 38 Direct and Multiplexed Addressing (3) Advantage: Reduced complexity of the circuits For a matrix of 1000 x 1000 pixels, 2000 drivers are needed (compared to 1,000,000

with direct addressing) Disadvantage: Reduced contrast TN displays have been improved through various techniques 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 39 Addressing Techniques Addressing Techniques Direct and Multiplexed Addressing

Passive-Matrix Displays Active-Matrix Displays Defective Pixels 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 40 Passive-Matrix Displays (1) Use a set of multiplexed transparent electrodes A transistor is connected to each row electrode or each column electrode

The liquid crystal layer is placed between the electrodes The electrodes are composed of indium tin oxide (ITO) 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 41 Passive-Matrix Displays (2) A pixel addressed when a voltage is applied across it

The pixel becomes opaque when it is addressed When the voltage is removed, the pixel deactivates slowly 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 42 Passive-Matrix Displays (3) The display controller scans across the matrix of pixels Delay since the voltage is applied to a pixel

until it is turned on response time Inertia of the pixels after the voltage is removed The time to scan the entire matrix must be shorter than the time needed for the pixels to deactivate 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 43 Passive-Matrix Displays (4) Disadvantages: Crosstalk interference between neighboring pixels

Causes the occurrence of shadows for bright objects Viewing angle is limited Response time is relatively slow The current image is still maintained on the screen after a new image is displayed 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 44 Addressing Techniques Addressing Techniques

Direct and Multiplexed Addressing Passive-Matrix Displays Active-Matrix Displays Defective Pixels 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 45 Active-Matrix Displays (1) The front glass plate of the display is coated with a continuous electrode The rear glass plate is

coated with electrodes divided into pixels Each pixel is connected in series with a thin film transistor (TFT) Also called TFT displays A storage capacitor can also be connected in series 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 46 Active-Matrix Displays (2)

A pixel of the active matrix display Active element: field effect transistor (FET) Semiconductor material: silicon Crystalline silicon (c-Si) Expensive High mobility of charge carriers enable to integrate the drivers 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 47

Active-Matrix Displays (3) Amorphous silicon (a-Si) Simple manufacturing process Mobility of electrons is relatively low Hydrogenated a-Si (a-SI:H) increases the mobility of electrons Polysilicon (p-Si) Consists of small silicon crystals High mobility of charge carriers Semiconducting metal oxides Indium gallium zinc oxide (IGZO) 11/14/2019

Input/Output Systems and Peripheral Devices (05-1) 48 Active-Matrix Displays (4) 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 49 Active-Matrix Displays (5) An image is created by scanning the matrix A row of pixels is selected by applying voltage to the row electrode connected to

the transistor gates on that row Voltages corresponding to the image are applied to the column electrodes connected to the transistor sources The operations are repeated for each row Refresh rate of the screen: 50 or 60 Hz 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 50 Active-Matrix Displays (6) Advantages (compared to passive matrix displays): Faster response time

Higher contrast Higher brightness level Wider viewing angle Disadvantages: More intense backlight is required Higher cost 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 51 Addressing Techniques Addressing Techniques

Direct and Multiplexed Addressing Passive-Matrix Displays Active-Matrix Displays Defective Pixels 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 52 Defective Pixels (1) For high resolutions, a large number of transistors are needed 4K resolution: 3840 x 2160 x 3 24.9 million transistors

Defective transistors due to impurities Lit pixel (permanently on) Black pixel (permanently off) Stuck pixel (one or two sub-pixels on or off) Manufacturers set limits for an acceptable number of defective pixels 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 53 Defective Pixels (2) ISO standards: ergonomic requirements for

flat panel displays ISO 13406, Part 2 (2001) ISO 9241, Part 303 (2008, 2011) Image-quality requirements: Three types of defective pixels Four display classes (Class II: common) Maximum number of defective pixels of each type per million pixels for each class Maximum number of defective pixels within a block of 5x5 pixels 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 54

Liquid Crystal Displays Liquid Crystals Twisted Nematic Technology Addressing Techniques Backlighting Types Display Parameters Vertical Alignment Technology In-Plane Switching Technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 55 Backlighting Types (1) Fluorescent lamp backlighting

CCFL Cold Cathode Fluorescent Lamp Placed at the edges of the display For uniform distribution of light: light guide plate (LGP) and diffuser panel Disadvantage: low energy efficiency For portable devices, the voltage needs to be converted to a high voltage It is not possible to build thin displays 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 56 Backlighting Types (2) LED backlighting

Most used type of backlighting Displays and TV sets with LED backlighting (LED displays, LED TVs) use an active-matrix LCD technology improper names Advantages compared to CCFL backlighting: Reduced power consumption (35..40%) LED lifetime is longer Very thin displays can be built (< 1 cm) Higher contrast and brightness 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 57 Backlighting Types (3)

Disadvantages of LED backlighting: More difficult to maintain the uniformity of brightness in the long term brighter or darker areas The color range (gamut) is slightly narrower compared to that of CCFL lit displays Edge-Lit White LED (EL-WLED) backlighting Rows of white LEDs placed at the edges of the display Variants with the LEDs placed on four sides, two sides, or one side 11/14/2019 Input/Output Systems and Peripheral Devices (05-1)

58 Backlighting Types (4) Local Dimming feature: changing the brightness separately in different regions 11/14/2019 Dividing the rows of LEDs into zones and controlling independently the brightness Improves the apparent contrast ratio Input/Output Systems and Peripheral Devices (05-1) 59

Backlighting Types (5) White LED array backlighting Array of white LEDs uniformly distributed behind the display panel Full-Array Local Dimming (FALD) feature: setting the backlight intensity differently in different zones 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 60 Backlighting Types (6) The FALD feature enables better control of the

brightness than local dimming A much higher dynamic contrast ratio can be achieved Mostly used in TV sets Few computer displays with the FALD feature: 384 zones (27-inch), 512 zones (35-inch) Mini LED backlighting Size of a Mini LED: 100 .. 200 m Enables to increase the number of zones used by the FALD feature 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 61

Backlighting Types (7) First displays with Mini LED backlighting: ASUS ProArt PA32UCX (32-inch, >1000 zones), ASUS ProArt PA27UCX (27-inch, 576 zones) Input/Output Systems and Peripheral Devices (05-1) ASUS ProArt PA32UCX display ( ASUSTeK Computer Inc.)62 11/14/2019 Backlighting Types (8) RGB LED backlighting Similar to white LED array backlighting, but uses an array of RGB LED triads

An extended color range can be achieved Pure and saturated colors Used in professional-grade displays for graphics editing, photography, video/film post-production, visual effects, animation High cost 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 63 Backlighting Types (9) Example of professional-grade display: HP DreamColor Z31x Studio Display Built-in colorimeter: automatically performs

the color calibration process HP Development Company, L.P. 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 64 Summary (1) Liquid crystals have properties of the liquid matter and of the crystalline solid matter Types of liquid crystals: thermotropic, lyotropic, metallotropic Thermotropic liquid crystals present several phases depending on temperature

Twisted Nematic (TN) has been the first technology used for liquid crystal displays It is based on the properties of polarized light, which follows the alignment of molecules 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 65 Summary (2) Improvements of the TN technology: Super TN (STN), Double STN (DSTN), Film STN (FSTN) There are two addressing methods of the display elements: direct and multiplexed Displays with multiplexed addressing may use

a passive-matrix or an active-matrix Active-matrix displays have important advantages compared to passive-matrix displays Generating the backlight with an array of RGB LEDs is the most advantageous method 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 66 Concepts, Knowledge (1) Types of liquid crystals Phases of thermotropic liquid crystals Nematic phase

Smectic phase Cholesteric phase Principle of operation of Twisted Nematic (TN) liquid crystal displays Super TN (STN) technology Double STN (DSTN) technology 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 67 Concepts, Knowledge (2) Film STN (FSTN) technology Multiplexed addressing Principle of passive-matrix displays

Principle of active-matrix displays Fluorescent lamp backlighting Advantages/disadvantages of LED backlighting Edge-lit white LED backlighting White LED array backlighting RGB LED backlighting 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 68 Questions 1. How does the polarized light pass through a TN liquid crystal layer? 2. What is the difference between TN and

STN technologies? 3. What are the disadvantages of passivematrix displays? 4. What are the advantages of LED backlighting compared to fluorescent lamp backlighting? 11/14/2019 Input/Output Systems and Peripheral Devices (05-1) 69

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