5.11 Electronic displays

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5.11 Electronic displays

  1. 1. Module 5: Digital Techniques and Electronic Instrument Systems 5.11 Electronic Displays
  2. 2. CRT  Cathode Ray Tube  Monochrome:  A heated cathode emits electron beams, accelerated by magnetic fields and collide in a phosphor coating screen. The collision emits light.  Color:  Three cathodes emit one electron beam for each color (RGB). Each pixel of the screen contains 1 phosphor dot for each color. Each beam collides only with the corresponding phosphor dot of each pixel.  The CRT contains:  A heated cathode  Accelerating magnetic field  A phosphor coating
  3. 3. Monochrome CRT  The input of each plate is a combination of the input signal and a sawtooth wave.  The refresh rate is around 70Hz.
  4. 4. Color CRT  By controlling the intensity of each beam, various colors can be obtained.
  5. 5. LCD  Liquid Crystal Displays.  The polarization of light:  Liquid crystals are organic compounds that exhibit both solid and liquid properties.  A property of liquid crystals is that they can be reoriented by an electric field.  2 polarization filters are placed with 90 degrees angle with each other.  The polarized light that exits the first polarization filter is reoriented by the liquid crystals by 90 degrees and passes through the second polarization filter.  If an electric filed is applied to the liquid crystals, the light is not reoriented and does not pass the second filter.
  6. 6. Color LCD  Each pixel is divided to three sub-pixels: RGB.  A color filter is placed in front of each sub- pixel.
  7. 7. TFT LCD Screens  Thin-film-transistor LED technology (1 transistor switching each sub-pixel) enables higher resolutions and fast response time.
  8. 8. (O)LED displays  (Organic) LED displays use the LCD technology, but the backlight provided by a LED panel.  Each LED emits light when supplied with 1.7 to 3V.
  9. 9. CRTs vs. LCDs.  CRTs:  Low resolutions  Generate magnetic fields  Heavy, require depth behind the front panel  Heating problems  Excellent viewing angle  Response time: 1msec.  LCDs:  Higher resolutions and image quality  Power efficient  Thinner, lighter than CRTs  Poor viewing angle, but better in newer models and excellent in OLEDs.  Response time: 1-8msec for LED and sub-ms for OLED. Sluggish in low temperatures.

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