Contents of the Lecture

Name: Contents of the Lecture
Uploaded: 2017-08-13T04:26:18+00:00
Duration: PTM35S25
Channel: Dominick Roberts
Description: Contents of the Lecture

Contents of the Lecture
1. Introduction 2. Methods for I/O Operations 3. Buses 4. Liquid Crystal Displays 5. Other Types of Displays 6. Graphics Adapters 7. Optical Discs 12/04/2014 Input/Output Systems and Peripheral Devices (05)

5. Other Types of Displays
Plasma Displays Field Emission Displays OLED Displays 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Input/Output Systems and Peripheral Devices (05)
Plasma Displays Plasma Displays Principle of Plasma Displays Structure and Operation Advantages Disadvantages 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Principle of Plasma Displays (1)
Use a screen coated with phosphor dots  active displays Use a grill of electrodes to address individual pixels Principle: applying a voltage to an inert gas releases photons  ultraviolet domain The photons strike the phosphor particles  generate visible light 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Normally, the atoms of an inert gas contain an equal number of protons and electrons If a voltage is applied, free electrons are generated  collide with the atoms The atoms loose electrons  positive ions Plasma: gas consisting of free electrons, positive ions, and neutral particles The collisions between particles cause the gas atoms to release photons 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Original image © HowStuffWorks, Inc. 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Structure and Operation (1)
Two glass plates Electrodes for row and column selection Address electrodes (vertical) Display electrodes (horizontal): in a dielectric layer, covered with a protective layer (MgO) Phosphor particles: cover the rear plate Gas: neon mixed with argon or xenon 12/04/2014 Input/Output Systems and Peripheral Devices (05)

12/04/2014 Input/Output Systems and Peripheral Devices (05)

The gas inside the display is partitioned into cells  separators Sub-cells for the primary colors To ionize the gas cells, a priming voltage is applied between pairs of electrodes The cells are ionized in turn If an additional voltage is applied to a cell, the gas releases ultraviolet photons 12/04/2014 Input/Output Systems and Peripheral Devices (05)

The released photons interact with the phosphor coated on the cell’s inside wall The phosphor’s electrons release energy in the form of visible light photons To create colors, the intensity of each sub-pixel color is varied Pulse width modulation (PWM) of the addressing pulses: adjusting their widths in 256 steps  16.7 million colors 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Advantages The possibility to produce large-sized flat screens For multimedia presentations (60”..150”) For TV sets (32”..60”) High contrast ratio (10,000:1 static) Accurate color reproduction Wide viewing angles Faster response time (1 ms) compared to LCDs  superior performance for video images 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Disadvantages Relatively large pixel size Reducing the pixel size below 0.3 mm is difficult Luminosity decreases over time Lifespan: 60, ,000 hours Image retention problems may occur (screen burn-in) Average power consumption is higher than that of LCDs Higher weight compared to LCDs 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Field Emission Displays
Principle of Field Emission Displays Structure and Operation Advantages and Disadvantages 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Principle of Field Emission Displays
FED – Field Emission Display The screen is covered with phosphor dots, which are hit by electron beams Millions of miniature emitters and electron beams are used The emitters are at a small distance (fraction of mm) from the screen The electrons are emitted by a cold cathode 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Each R, G, and B sub-pixel is an emitter made as a miniature vacuum tube A large number of electron emitters are used for each pixel The emitters are made from a material based on molybdenum  emits electrons when a low voltage difference is applied Colors are generated sequentially: green, red, blue 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Advantages and Disadvantages (1)
Power consumption is lower than that of liquid crystal displays Consumption: dependent on the image With liquid crystal displays, the backlight is permanently on The viewing angle is wide: 160 There is a redundancy by construction The brightness is not affected even if 20% of the emitters fail 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Response time is lower than that of liquid crystal displays Color reproduction is of high quality, similar to that of cathode ray tubes Mass production is more difficult To withstand the difference of pressure, the display must be mechanically robust and sealed 12/04/2014 Input/Output Systems and Peripheral Devices (05)

OLED Displays OLED Displays Organic Materials Principle of Operation Manufacturing Technologies Passive-Matrix Displays Active-Matrix Displays Advantages and Disadvantages 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Organic Materials (1) OLED – Organic Light Emitting Diode Electroluminescent organic materials have been discovered in the 1950’s Materials based on conductive polymers have been developed in the 1970’s Examples: polyacetylene; polyaniline The first organic LED has been developed at Eastman Kodak company (1987) 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Organic Materials (2) Two types of materials, depending on the size of molecules: With small molecules: SM-OLED (Small Molecule OLED) With large molecules (polymers): LEP (Light Emitting Polymer) Both types generate light by forming electrons and holes, and then by their recombination 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Principle of Operation (1)
Organic LED: One or more layers of organic materials ( nm) Two electrodes (anode, cathode) Substrate (plastic, glass) Early OLEDs: a single organic layer Multilayer OLEDs: have improved efficiency Many OLEDs have two layers: conductive layer, emissive layer 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Concepts related to particle physics Spin Angular momentum carried by elementary and composite particles Vector quantity: it has magnitude and direction Spin magnitude: indicated by the spin quantum number (s) For fermions – particles that make all known matter: s = ½ 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Spin direction: direction in which the spin vector is pointing For spin-½ particles: two quantum states, with the spin pointing in the +z or –z direction Singlet state Obtained when two spin-½ particles are combined  they form an exciton If the particles have opposite spins, the total spin is s = 0  only one quantum state 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Triplet state Set of three quantum states of a particle or combination of particles Each state has a total spin of s = 1 Combination of two spin-½ particles: the spin directions are the same Formation of a triplet state is more probable Triplet  singlet transition: phosphorescence 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Structure of a typical OLED cell Two organic layers Two electrodes Cathode: metallic mirror Anode: transparent (ITO) Substrate: glass or plastic 12/04/2014 Input/Output Systems and Peripheral Devices (05)

When a voltage is applied: A current of electrons flows through the organic layers (cathode  anode) Electrons and holes are attracted towards each other by electrostatic forces An electron and a hole recombine  exciton in a singlet state or triplet state Decay of the singlet state  release of energy as a photon 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Efficiency of an OLED cell: limited by the ratio of singlet states to triplet states SM-OLED materials: The formation of the singlet state is three times less probable  efficiency limited to 25% Phosphorescent OLEDs: doping with compounds LEP materials: The singlet/triplet ratio can be > 1 Very high efficiency 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Structure of an OLED display (bottom emission) Other variant: with top emission 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Manufacturing Technologies (1)
Small-molecule LEDs Conductive (hole transport) layer: metal-phthalocyanine, triphenylamine Emissive layer: fluorescent dyes Process: thermal evaporation in vacuum Advantages: Homogeneous film layers can be formed Complex multi-layer structures can be achieved 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Disadvantages: Expensive process Not scalable to very large substrates 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Creating the pattern for the RGB subpixels: thermal evaporation using shadow masks A precise alignment of the masks is required for each of the R, G, and B emissive materials Disadvantages: the process is not scalable; not suitable for high-volume production Another method for creating the subpixel pattern: laser transfer The materials are transferred spot-by-spot Disadvantage: slow process 12/04/2014 Input/Output Systems and Peripheral Devices (05)

RGB subpixel definition by shadow masking 12/04/2014 Input/Output Systems and Peripheral Devices (05)

WOLED (White-emitting OLED) technology Uniform deposition of a white-emitting OLED material Color filters applied according to the subpixel pattern Color filter deposition: photolithographic methods  technology also used for LCDs Advantages: high speed; process scalable to large displays; no color balance problems Disadvantage: higher power consumption 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Polymer LEDs Conducting layer: polyaniline Emissive layer: polyphenylene vinylene (PPV), polyfluorene (PF) Spin coating: solution placed on the substrate, which is rotated at high speed Advantages: Scalable process for high-volume manufacturing Fewer vacuum deposition steps Inkjet printing can be used for the emissive layer 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Disadvantage: Multi-layer structures are difficult to form 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Passive-Matrix Displays (1)
PMOLED Drivers attached to each electrode The pixel rows are selected successively A certain voltage is applied to the columns of selected row  an electric current Advantage: manufacturing costs are low Disadvantages: relatively intensive currents are required  high power consumption; only suitable for small screens 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Passive-Matrix Displays (2)

Active-Matrix Displays (1)
AMOLED An array of thin film transistors (TFTs) At least two transistors and a storage capacitor are needed for each subpixel First TFT: charges the storage capacitor Second TFT: provides a correct voltage Advantages: higher refresh rates; higher brightness; reduced power consumption 12/04/2014 Input/Output Systems and Peripheral Devices (05)

PenTile Matrices Set of subpixel layout methods  Samsung Display Inspired by peculiarity of the human retina  fewer sensors for perceiving blue colors Use proprietary algorithms for subpixel rendering Any input pixel is mapped to a logical pixel Compatibility with conventional RGB layout 12/04/2014 Input/Output Systems and Peripheral Devices (05)

PenTile RG-BG Matrix G subpixels, alternating R and B subpixels The input image is mapped to subpixels  1:1 mapping only for G subpixels Only two subpixels are used for a pixel  the subpixel density can be reduced Resolution of the luminance information is not affected significantly Disadvantage: the pixel structure may be more visible 12/04/2014 Input/Output Systems and Peripheral Devices (05)

PenTile RG-BG pixel layout – Google/HTC Nexus One (800480) 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Integrated touch panels The capacitive sensor array is integrated during the AMOLED manufacturing process Manufacturers: Samsung Display AU Optronics Super AMOLED (Samsung Display) Integrated touch panel PenTile matrix 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Super AMOLED Plus Conventional RGB layout Higher brightness and energy efficiency Example: Samsung Galaxy S II (800480) 12/04/2014 Input/Output Systems and Peripheral Devices (05)

HD Super AMOLED Higher resolution (1280720) With PenTile RG-BG matrix (e.g., Samsung Galaxy S III) With RGB matrix (e.g., Samsung Galaxy Note II, image on the right) 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Full HD Super AMOLED Full HD resolution (19201080) PenTile matrix, with a different pixel arrangement Example: Samsung Galaxy S4 441 pixels/inch Color gamut: 97% of Adobe RGB color space 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Example: Samsung Galaxy S5 Full HD resolution 432 pixels/inch (ppi) Samsung Galaxy Prime (LTE-A): QHD resolution (25601440, 560 ppi) New organic materials Modified subpixel structure Higher brightness (up to 698 cd/m2) 12/04/2014 Input/Output Systems and Peripheral Devices (05)

High contrast ratio (>1,000,000:1), both static and dynamic Wide viewing angles  no color shifting Wide color gamut Fast response time (0.01 ms .. 1 ms) On average, power consumption is lower compared to LCDs (40% .. 80%) The plastic substrate is lightweight Flexible and transparent displays can be built 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Currently, the cost of the manufacturing process is high The lifetime of some organic materials (blue OLEDs) is limited (e.g., 14,000 hours) Color balance may change in time Biasing the color balance towards blue Optimizing the size of R, G, and B subpixels  larger blue subpixels 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Image persistence may occur The display may be damaged by prolonged exposure to ultraviolet rays The organic materials can be damaged by water Readability in outdoor conditions may be limited Circular polarizer; anti-reflective coating Power consumption is increased when displaying images on white background 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Summary (1) Plasma displays are based on applying a voltage to an inert gas The gas releases ultraviolet photons The photons are transformed into visible light by phosphor particles coated on the screen Advantages: accurate color reproduction; wide viewing angles; fast response time Field emission displays use a large number of miniature emitters and electron beams Advantage: redundancy by construction 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Summary (2) There are two types of electroluminescent organic materials: SM-OLED and LEP The operation of OLED displays is based on forming electrons and holes, and then recombining them to form excitons Decay of the singlet state: releases photons Manufacturing technology for SM-OLED materials: thermal evaporation in vacuum Creating the subpixel pattern: shadow masks; laser transfer; white-emitting OLED technology 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Summary (3) Manufacturing technologies for LEP materials: spin coating; inkjet printing Active-matrix OLED displays require two transistors and a capacitor for each pixel Advantages: higher brightness; reduced power consumption Advantages of OLED displays: high contrast; wide viewing angles; fast response time Disadvantages: limited lifetime of blue OLEDs; color balance may change in time 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Concepts, Knowledge (1) Principle of plasma displays Structure and operation of plasma displays Advantages of plasma displays Disadvantages of plasma displays Principle of field emission displays Advantages of field emission displays Types of electroluminescent organic materials Structure and operation of an OLED cell 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Concepts, Knowledge (2) Manufacturing technologies for small-molecule LEDs White-emitting OLED technology Manufacturing technologies for polymer LEDs Active-matrix OLED displays PenTile matrices Advantages of OLED displays Disadvantages of OLED displays 12/04/2014 Input/Output Systems and Peripheral Devices (05)

Questions What are the advantages and disadvantages of plasma displays? What is the operating principle of field emission displays? What is the difference between SM-OLED and LEP organic materials considering the efficiency of light emission? What are the advantages of OLED displays? 12/04/2014 Input/Output Systems and Peripheral Devices (05)

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