Transcript Cathode Ray Tube (CRT)

Prepared By :- Kinjal Satasiya(130770111047)
(5th sem)
Guided By :- Dimple Agrawal
1.Cathode Ray Tube (CRT)
Cathode Ray Tube (CRT)
1.
2.
3.
4.
Electron guns
Electron beams
Focusing coils
Deflection coils
5.
6.
7.
8.
Anode
connection
Mask for
separating
beams for
RGB part of
displayed
image
Phosphor
layer with
RGB zones
Close-up of
the phosphor-coated
inner side of
the screen
Cathode Ray Tube (CRT)
- Cathode rays are electron beams emitted by a
cathode (negative terminal); the annode is number 5
- Emission is by heating the cathode in a vacuum tube
– hence the name CRT
- Cathode rays are electron beams emitted by a
cathode (negative terminal); the annode is number 5
- Emission is by heating the cathode in a vacuum tube
– hence the name CRT
CRT Imaging Process
CRT Performance
Advantages of CRT
• The cathode rayed tube can easily increase the
monitor’s brightness by reflecting the light.
• They produce more colours
• The Cathode Ray Tube monitors have lower price
rate than the LCD display or Plasma display.
• The quality of the image displayed on a Cathode Ray
Tube is superior to the LCD and Plasma monitors.
• The contrast features of the cathode ray tube
monitor are considered highly excellent.
Disadvantages of CRT
• They have a big back and take up space on desk.
• The electromagnetic fields emitted by CRT monitors
constitute a health hazard to the functioning of living cells.
• CRTs emit a small amount of X-ray band radiation which can
result in a health hazard.
• Constant refreshing of CRT monitors can result in headache.
• CRTs operate at very high voltage which can overheat system
or result in an implosion
• Within a CRT a strong vacuum exists in it and can also result in
a implosion
• They are heavy to pick up and carry around
CRT Monitor
2.Liquid Crystal Display (LCD)
Specifying Color
• Color perception usually involves three quantities:
– Hue: Distinguishes between colors like red, green,
blue, etc
– Saturation: How far the color is from a gray of
equal intensity
– Lightness: The perceived intensity of a reflecting
object
• Sometimes lightness is called brightness if the object
is emitting light instead of reflecting it.
• In order to use color precisely in computer graphics,
we need to be able to specify and measure colors.
Liquid Crystal Display (LCD)
• LCD includes light source, liquid crystal, polarizer, color filter
(CF), thin film tansistor (TFT), and so on.
TFT controls orientation of liquid
crystal, and Black Matrix fills in the
gap between color filters.
TFT (Thin Film Transistor)
LCD Imaging Process
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Randomly arranged LCs pass light (“off” )
Aligned LCs block light (“on”)
This effect is called “birefringence”
Principle is the same for low-temperature and hightemperature polysilicon LCDs, and liquid crystal on silicon
(LCoS) panels
• The principle of birefringence is nothing more than the
ability of liquid crystals to pass or block polarized light. In
nature, individual liquid crystals float in a random pattern,
or ‘off’ state. When a voltage is applied to them, however,
they will align in the same plane. In this ‘on’ state,
polarized light will be blocked by the liquid crystals. Both
large flat-panel LCD monitors and TVs and small LCD panels
used in portable projectors control light with
birefringence.
Output Light Intensity Depending
on the Orientation of Liquid Crystal
Colorful Pixel
The pixels are addressed in rows and
columns, reducing the connection
complexity. The column and row wires
attach to transistor switches, one for each
pixel.
Controlling color filter to adjust the
transmissions of three primary colors, one
can obtain various colors.
Overall Descriptions of TFT- LCD
Back-Light
• The light
generated by the
backlight.
• The light is evenly
distributed the
light evenly over
the LCD panel.
• Display
enhancement
films are placed
between the light
diffuser and the
LCD panel. They
aim to maximize
the light reaching
the observer.
Advantages of LCD
• The sharpness of a LCD display is at maximum tweak ness.
• High peak intensity produces very bright images. Best for brightly lit
environments.
• Screens are perfectly flat.
• Thin, with a small footprint. Consume little electricity and produce
little heat
• The LCD display unit is very light and can be put anywhere or
moved anywhere in the house.
• Lack of flicker and low glare reduce eyestrain.
Disadvantages of LCD
• After a while the LCD display the some of the pixels will die
you will see a discoloured spot on a black spot on the display.
• The cost of a LCD is considerably at a high price.
• The LCD display will have slow response times.
• The LCD display has a fixed resolution display and cannot be
changed.
• The viewing angle of a LCD display is very limited.
3.Plasma display panel
Plasma Display
Structure of a PD
PD Rib Structure
To make a plasma display
panel, ribs are etched into
one layer of special glass
to form shallow channels,
which are then filled with
rare earth phosphors.
Cross ribs on a second
piece of glass then form
pixels when bonded to
the first layer. Addressing
electrodes are attached
to each pixel. The finished
panel is then filled with a
mixture of noble gases,
typically neon and xenon.
Plasma Imaging Process
• Three-step charge/discharge cycle
– Uses neon – xenon gas mixture
– 160 - 250V AC discharge in cell
stimulates ultraviolet (UV)
radiation
– UV stimulation causes color
phosphors to glow and form
picture elements
– Considerable heat and EMI are
released
PD Working
Address electrode
causes gas to
change to plasma
state.
The plasma emits UV
in discharge region
which impinges on
the phosphor
Reaction causes each
subpixel to produce red,
green, and blue light.
4. Electroluminescent displays
Electroluminescent Source
Electroluminescence  Excitation of electron by electric field
+ Dielectric with embedded phosphor
Electroluminescent
-The structure consists of two thin layers of dielectric with
phosphor sandwitched between them.
- A thin Al layer on the top and thin ITO layer on the
bottom completes EL.When voltage of order of 200V is
applied the resultant high electric field (1MV/cm) tunnels
electrons through dielectric on to phosphor.
- The high energy of electrons impact the colour centres to
emit visible light.
Advantages of Electroluminescent
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High brightness, high resolution,
Blue phosphor improvement required
High voltage switching
High purity materials
Small sizes
Expensive