Direct-View Storage TubesThis is the method for maintaining a screenimage by storing the picture informationinside the CRT. Similar to the standard CRT,except that it does not need to be refreshedbecause its stores picture information as acharged distribution just behind the screen.
Two electron guns are used in DVST.One, used to store the picture pattern.Second, the flood gun, maintains the picture display.The electron beam is designed not to writedirectly on the phosphors but on a fine-meshwire grid, coated with dielectric and mounted justbehind the screen. A pattern of +ve charge isdeposited on the grid & this pattern is transferred tophosphors by continuous flood of electrons issuingfrom the flood.
Just behind the storage mesh a second grid,Collector, whose main purpose is to smooth out theflow of flood electron. Electon pass thru. Collector ata low Velocity & attach to +vely charged portion ofmesh ,but rest are repelled. Others pass thru. Mesh &strikes the phosphor. The flood electrons are stillcontinue to move slowly. In order to increase theenergy of these relatively slow moving electron &thus create a bright picture, the screen is maintainedat a high +ve potential.
Advantage: Very complex pictures can be displayed at a very high resolution without flicker, because no refreshing is needed. It is an inexpensive device.Disadvantage: Ordinarily they do not display colors. Some selected part of a picture could not be erased.
Flat-Panel Displays Refers to a class of video devices that havereduced volume, weight and power requiredcompared to a CRT. Currently used in TVmonitors, Calculators, pocket video games,laptop computers & advertisement boards etc.Two categories of Flat-panel displays are:1.) Emissive Displays2.) Nonemissive Displays.
Emissive Displays: are devices that convert electrical energy into light. Examples are Plasma panels, thin-film electroluminescent displays and Light-emitting diodes(LED).Nonemissive Displays: Use optical effects to convert sunlight or light from some other source into graphics patterns. Example is Light-crystal device(LCD).