Direct-View Storage Tubes

This is the method for maintaining a screen

image by storing the picture information

inside the CRT. Similar to the standard CRT,

except that it does not need to be refreshed

because its stores picture information as a

charged distribution just behind the screen.

Flood Gun

Writing Beam Gun

Flood Electrons

Writing Beam

Collector

Storage mesh grid

PhosphorsScreen

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 the

flow of flood electron. Electon pass thru. Collector at

a low Velocity & attach to +vely charged portion of

mesh ,but rest are repelled. Others pass thru. Mesh &

strikes the phosphor. The flood electrons are still

continue to move slowly. In order to increase the

energy of these relatively slow moving electron &

thus create a bright picture, the screen is maintained

at 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 DisplaysRefers to a class of video devices that have

reduced volume, weight and power required

compared to a CRT. Currently used in TV

monitors, Calculators, pocket video games,

laptop computers & advertisement boards etc.

Two categories of Flat-panel displays are:

1.) Emissive Displays

2.) 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).