Crt display

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CRT DISPLAY Prepared by: Hinal Lunagariya

Transcript of Crt display

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CRT DISPLAY

Prepared by: Hinal Lunagariya

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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.

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• 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

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Monitor Types

Monochrome

Grayscale

Color

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Monochrome MonitorA 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.

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Grayscale MonitorsA 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.

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Color MonitorsA 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.

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Color MonitorsThe monitors can display different colors by combining various intensities

of three beams. Color CRTs are much more complicated. It requires manufacturing very

precise geometry.

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Mixing of Colors

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It Consists of..

CRTAnodeCathodeShadow mask

Focusing coilDeflecting coilFluorescent screen

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How It Works?

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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

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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.

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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’ .

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

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CRT Display Principles Electron beam swept across screen one row at a time from top to bottom in

raster-scan.Shadow mask.

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Color CRT Monitors

Delta electron gun arrangement In-line electron gun arrangement

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• Operation of delta-delta, shadow mask CRT

Color CRT Monitors

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• 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

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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.

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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

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