Display Devices – Refresh Cathode Ray Tube (CRT)

1. Display Devices

Display devices are output hardware components that present visual information to users. They convert digital signals into visible images.

• CRT monitors
• LCD and LED displays
• Plasma panels

2. What is a Cathode Ray Tube (CRT)?

A CRT is a vacuum tube containing an electron gun that emits electrons. These electrons strike a phosphor screen to form images.

• Invented for early television and monitors
• Used extensively before flat displays

3. Components of CRT

• Electron Gun: Produces electron beam
• Deflection System: Controls beam direction
• Phosphor Screen: Emits light when struck
• Glass Vacuum Tube: Encloses components

4. Working Principle of CRT

The electron gun emits a focused beam that is guided across the screen by the deflection system. When the beam hits the phosphor coating, light is produced.

Electron Gun
     |
     v
Deflection System
     |
     v
Phosphor Screen
     |
     v
Visible Image

5. Refresh CRT

In a refresh CRT, the image is redrawn many times per second to maintain brightness, as phosphor light fades quickly.

• Requires periodic refreshing
• Refresh rate measured in Hz
• Common rates: 60Hz, 75Hz

6. Raster Scan in CRT

Raster scan displays draw images line by line from the top-left to bottom-right of the screen.

• Horizontal scan lines
• Uses frame buffer
• Widely used in monitors

7. Advantages of CRT

• High refresh rate
• Good color accuracy
• Wide viewing angle

8. Disadvantages of CRT

• Large and heavy
• High power consumption
• Radiation emission

9. Applications of CRT

• Early computer monitors
• Television displays
• Oscilloscopes

Practice Questions

1. What is a CRT?
2. Explain the working of a refresh CRT.
3. List components of CRT.
4. What is raster scan?
5. Write advantages and disadvantages of CRT.

Practice Task