Transcript 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
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Plasma Displays
Field Emission Displays
OLED Displays
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Plasma Displays
Principle of Plasma Displays
Structure and Operation
Advantages
Disadvantages
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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
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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
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Plasma Displays
Principle of Plasma Displays
Structure and Operation
Advantages
Disadvantages
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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
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Original image © HowStuffWorks, Inc.
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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
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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 subpixel color is varied
Pulse width modulation (PWM) of the
addressing pulses: adjusting their widths in
256 steps  16.7 million colors
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Plasma Displays
Principle of Plasma Displays
Structure and Operation
Advantages
Disadvantages
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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
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Plasma Displays
Principle of Plasma Displays
Structure and Operation
Advantages
Disadvantages
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Relatively large pixel size
Reducing the pixel size below 0.3 mm is
difficult
Luminosity decreases over time
Lifespan: 60,000 .. 100,000 hours
Image retention problems may occur
(screen burn-in)
Average power consumption is higher than
that of LCDs
Higher weight compared to LCDs
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Plasma Displays
Field Emission Displays
OLED Displays
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Field Emission Displays
Principle of Field Emission Displays
Structure and Operation
Advantages and Disadvantages
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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
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Field Emission Displays
Principle of Field Emission Displays
Structure and Operation
Advantages and Disadvantages
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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
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Field Emission Displays
Principle of Field Emission Displays
Structure and Operation
Advantages and Disadvantages
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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
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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
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Plasma Displays
Field Emission Displays
OLED Displays
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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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)
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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
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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Organic LED:
One or more layers of organic materials
(100..500 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
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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
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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
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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
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Structure of a typical
OLED cell
Two organic layers
Two electrodes
Cathode: metallic
mirror
Anode: transparent
(ITO)
Substrate: glass or
plastic
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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
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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
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Structure of an OLED display (bottom emission)
Other variant: with top emission
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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Small-molecule LEDs
Conductive (hole transport) layer: metalphthalocyanine, triphenylamine
Emissive layer: fluorescent dyes
Process: thermal evaporation in vacuum
Advantages:
Homogeneous film layers can be formed
Complex multi-layer structures can be
achieved
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Disadvantages:
Expensive process
Not scalable to very large substrates
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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
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RGB subpixel definition by shadow masking
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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
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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
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Disadvantage:
Multi-layer structures are difficult to form
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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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
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Original image © HowStuffWorks, Inc.
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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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
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Original image © HowStuffWorks, Inc.
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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
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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
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PenTile RG-BG pixel layout – Google/HTC Nexus One
(800480)
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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
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Super AMOLED Plus
Conventional RGB layout
Higher brightness and energy efficiency
Example: Samsung Galaxy S II (800480)
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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)
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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
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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)
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OLED Displays
Organic Materials
Principle of Operation
Manufacturing Technologies
Passive-Matrix Displays
Active-Matrix Displays
Advantages and Disadvantages
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Advantages
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
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Disadvantages
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
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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
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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
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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
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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
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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
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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
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1. What are the advantages and
disadvantages of plasma displays?
2. What is the operating principle of field
emission displays?
3. What is the difference between SM-OLED
and LEP organic materials considering the
efficiency of light emission?
4. What are the advantages of OLED
displays?
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