Digital Display System – The rapid growth of electronic handling of numerical data has bought with it a great demand for simple systems to display the data in a readily understandable form. Display devices provide a visual display of numbers, letters, and symbols in response to electrical input, and serve as constituents of an electronic display system.
Classification of Displays
Commonly used displays in the digital electronic field are as follows.
- Cathode ray tube (CRT)
- Light emitting diode (LED)
- Liquid crystal display (LCD)
- Gas discharge plasma displays (Cold cathode displays or Nixies)
- Electro-luminescent (EL) displays
- Incandescent display
- Bectrophoretic image displays (END)
- Liquid vapour display (LVD)
In general, displays are classified in a number of ways, as follows.
1.On methods of conversion of electrical data into visible light
(a) Active displays
(Light emitters – Incandescent, i.e. due to temperature, luminescence, i.e. due to non-thermal means or physio-thermal, and gas discharge-glow of light around the cathode.) CRTs, Gas discharge plasma, LEDs, etc.
(b) Passive displays
Light controllers, LCDs, EPIDs, etc.
2.On the applications
(a) Analog displays — Bar graph displays (CRT)
(b) Digital displays — Nixies, Alphanumeric, LEDs, etc.
3.According to the display size and physical dimensions
(a) Symbolic displays — Alphanumeric, Nixie tubes, LEDs, etc.
(b) Console displays — CRTs, LEDs, etc.
(c) Large screen display— Enlarged projection system
4.According to the display format
(a) Direct view type (Flat panel planar) — Segmental, dotmatrix —CRTs
(b) Stacked electrode non-planar type — Nixie
5.In terms of resolution and legibility of characters
(a) Simple single element indicator
(b) Multi-element displays
When displaying large quantities of alphanumeric data, the read out system employed most commonly is a familiar CRT. Conventionally, CRTs form the basis of CROs and TV systems. To generate characters on the CRT, the generation system of characters on CRTs requires relatively simple electronic circuitry.
A typical CRT display has easy facilities for the control of digit size by controlling the deflection sensitivity of the system (either electromagnetic or electrostatic deflection). The number of characters displayed can be changed with the help of time shared deflection and modulator circuits.
Importantly, the intensity and brightness can be realised. with different gray scales, and the display can have different colour depending on the phosphor used in the screen. Generally the phosphor is chosen to be white or green.
Storage type CRTs facilitate storing a stationary pattern on the screen without flickering display and it is possible to retain the pattern for a long time, independent of the phosphor persistence.