Crt display

CRT DISPLAY
Prepared by: Hinal Lunagariya

History
The earliest version of the CRT was known as the "Braun tube",
invented by the German physicist Ferdinand Braun in 1897.
In 1907, Russian scientist Boris Rosing used a CRT in the receiving
end of an experimental video signal to form a picture.
The first commercially made electronic television sets with cathode
ray tubes were manufactured by Telefunken in Germany in 1934.

• Emissive display  convert electrical energy into light
- Cathode ray tube (CRT)
- Flat panel CRT
- Plasma panels (gas-discharge display)
- Thin-film electroluminescent (EL) display
- Light-emitting diodes
• Non-Emissive display  optical effect: convert sunlight or light from other
source into graphic patterns.
- Liquid-crystal device (LCD) – flat panel
- Passive-matrix LCD
- Active-matrix LCD
Displays

Monitor Types
Monochrome
Grayscale
Color

Monochrome Monitor
A monochrome monitor is a type
of CRT computer display which was
very common in the early days of
computing.
They are still widely used in
applications such as computerized
cash register systems.
Green screen was the common
name for a monochrome monitor.

Grayscale Monitors
A special type of monochrome monitor
capable of displaying different shades of
gray.
They are also known as black-and-
white, are composed exclusively of
shades of gray, varying from black at the
weakest intensity to white at the strongest.
Early grayscale monitors can only show
up to sixteen different shades.

Color Monitors
A display monitor capable of displaying many colors.
Color Monitors works like a monochrome one, except that there are three
electron beams instead of one.
The three guns represent additive colors (red, green and blue) although the
beam they emit are colorless.
Each pixel includes three phosphors, red, green and blue, arranged in a
triangle.
When the beam of each of these guns are combined and focused on a pixel,
the phosphors light up.

Color Monitors
The monitors can display different colors by combining various intensities
of three beams.
Color CRTs are much more complicated. It requires manufacturing very
precise geometry.

It Consists of..
CRT
Anode
Cathode
Shadow mask
Focusing coil
Deflecting coil
Fluorescent screen

How It Works?
Cathode rays are emitted by an electron gun.
accelerated by a high positive voltage near the face of the tube
forced into a narrow stream by a focusing system
directed toward a point on the screen by the magnetic field generated by the
deflection coils
hit onto the phosphor-coated screen
phosphor emits visible light, whose intensity depends on the number of
electrons striking on the screen

How It Works?
Electrons travel through a vacuum sealed container from the cathode
(negative) to the anode (positive).
Because the electrons are negatively charged, they are repelled away from the
cathode, and move across the tube to the anode.
The ray can be affected by a magnet because of its relation to positive and
negative charges.
A CRT monitor contains millions of tiny red, green, and blue phosphor dots that
glow when struck by an electron beam. Electron beam travels across the screen to
create a visible image.
Dot mask ensures proper pixel is lit.

Phosphore
It is a semi-conducteur material which emits visible radiation in response
to the impact of electrons.
when it absorbs energy from some source such as an electron beam, it
releases a portion of this energy in the form of light.
In response to a sudden change in the electron beam(from on to off), the
light emission does not fall instantaneously, there is a gradual reduction
called ‘fluorescence’.

CRT Display Principles
Sample of Random-Scan displays principles.
Beam-penetration is used.

CRT Display Principles
Electron beam swept across screen one row at a time from top to bottom in
raster-scan.
Shadow mask.

Color CRT Monitors
Delta electron gun arrangement In-line electron gun arrangement

• Operation of delta-delta, shadow mask CRT
Color CRT Monitors

• Phosphor Persistence (PP)
- the light output decays exponentially with time.
- a phosphor’s persistence is defined as the time from the removal of
excitation to the moment of decaying the light to one-tenth of its
original intensity
- low persistence -> good for animation
- high persistence -> good for static picture with high complexity
- typical range: 10ms – 60ms
• Refresh rate (RR)
- number of times per second the image is redrawn (e.g., 60 or higher)
• Resolution
- the maximum number of points that can be displayed without overlap on
a CRT
- high-definition system, e.g. 1280 * 1024 pixels
- resolution depends on the type of phosphor, the intensity to be
displayed, focusing and deflection systems, size of video memory
• Horizontal scan rate
- the number of scan lines per second that the CRT is able to display
Properties of the CRT

Pros 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.

Cons 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 display

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Crt display