CRT Display Subtitle Cathode Ray Tube Display • Most common output device in earlier monitors Parts of a CRT Display 1. A source of electrons • A cathode (an oxide coated metal) heated by a filament 2. An evacuated glass tube enclosing a source of electrons 3. A control grid to accelerate the electron beam (controls the brightness of the display). 4. A focusing system to focus the electrons streaming from the cathode. 5. A deflection system to move the beam from left to right and from top to bottom 6. A phosphor coated screen which glows when the electron beam strikes it. Working of CRT Display • The cathode emits electrons when heated. • Emitted electrons are accelerated by a grid. • They are focused on the phosphor coated screen by a focusing system. • The focused spot is a pixel. • The screen becomes bright when the electron beam hits it. • Two types of displays • Monochrome display • Color Display • In monochrome display, a single phosphor coating is there which produces white light • In color displays, each pixel on the screen is coated with three different phosphors as patterns of three dots or triads covering the whole screen. • Each phosphor emits one of the three colors red, green or blue. • Variation in the intensity of the dots produces varying colors. Display Method • All current CRT displays are called raster displays. • In these displays an electron beam of CRT sweeps and draws a line from left edge of the screen to right edge of the screen. • During the return sweep the beam is blanked. • This scanning is repeated 30 times per second. • A VGA card in a computer controls a video display.
