Prepared By :- Kinjal Satasiya( ) (5 th sem) Guided By :- Dimple Agrawal

1. Cathode Ray Tube (CRT)

Cathode Ray Tube (CRT) 1. Electron guns 2. Electron beams 3. Focusing coils 4. Deflection coils 5.Anode connection 6.Mask for separating beams for RGB part of displayed image 7.Phosphor layer with RGB zones 8.Close-up of the phos- phor-coated inner side of the screen

Cathode Ray Tube (CRT) -Cathode rays are electron beams emitted by a cathode (negative terminal); the annode is number 5 -Emission is by heating the cathode in a vacuum tube – hence the name CRT -Cathode rays are electron beams emitted by a cathode (negative terminal); the annode is number 5 -Emission is by heating the cathode in a vacuum tube – hence the name CRT

CRT Imaging Process CRT Performance

Advantages of CRT The cathode rayed tube can easily increase the monitor’s brightness by reflecting the light. They produce more colours The Cathode Ray Tube monitors have lower price rate than the LCD display or Plasma display. The quality of the image displayed on a Cathode Ray Tube is superior to the LCD and Plasma monitors. The contrast features of the cathode ray tube monitor are considered highly excellent.

Disadvantages of CRT They have a big back and take up space on desk. The electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning of living cells. CRTs emit a small amount of X-ray band radiation which can result in a health hazard. Constant refreshing of CRT monitors can result in headache. CRTs operate at very high voltage which can overheat system or result in an implosion Within a CRT a strong vacuum exists in it and can also result in a implosion They are heavy to pick up and carry around

CRT Monitor

2. Liquid Crystal Display (LCD)

Specifying Color Color perception usually involves three quantities: – Hue: Distinguishes between colors like red, green, blue, etc – Saturation: How far the color is from a gray of equal intensity – Lightness: The perceived intensity of a reflecting object Sometimes lightness is called brightness if the object is emitting light instead of reflecting it. In order to use color precisely in computer graphics, we need to be able to specify and measure colors.

Liquid Crystal Display (LCD) LCD includes light source, liquid crystal, polarizer, color filter (CF), thin film tansistor (TFT), and so on. TFT controls orientation of liquid crystal, and Black Matrix fills in the gap between color filters.

TFT (Thin Film Transistor)

LCD Imaging Process Randomly arranged LCs pass light (“off” ) Aligned LCs block light (“on”) This effect is called “birefringence” Principle is the same for low-temperature and high- temperature polysilicon LCDs, and liquid crystal on silicon (LCoS) panels The principle of birefringence is nothing more than the ability of liquid crystals to pass or block polarized light. In nature, individual liquid crystals float in a random pattern, or ‘off’ state. When a voltage is applied to them, however, they will align in the same plane. In this ‘on’ state, polarized light will be blocked by the liquid crystals. Both large flat-panel LCD monitors and TVs and small LCD panels used in portable projectors control light with birefringenc e.

Output Light Intensity Depending on the Orientation of Liquid Crystal

Colorful Pixel The pixels are addressed in rows and columns, reducing the connection complexity. The column and row wires attach to transistor switches, one for each pixel. Controlling color filter to adjust the transmissions of three primary colors, one can obtain various colors.

Overall Descriptions of TFT- LCD

Back-Light The light generated by the backlight. The light is evenly distributed the light evenly over the LCD panel. Display enhancement films are placed between the light diffuser and the LCD panel. They aim to maximize the light reaching the observer.

Advantages of LCD The sharpness of a LCD display is at maximum tweak ness. High peak intensity produces very bright images. Best for brightly lit environments. Screens are perfectly flat. Thin, with a small footprint. Consume little electricity and produce little heat The LCD display unit is very light and can be put anywhere or moved anywhere in the house. Lack of flicker and low glare reduce eyestrain.

Disadvantages of LCD After a while the LCD display the some of the pixels will die you will see a discoloured spot on a black spot on the display. The cost of a LCD is considerably at a high price. The LCD display will have slow response times. The LCD display has a fixed resolution display and cannot be changed. The viewing angle of a LCD display is very limited.

3. Plasma display panel

Plasma Display

Structure of a PD

PD Rib Structure To make a plasma display panel, ribs are etched into one layer of special glass to form shallow channels, which are then filled with rare earth phosphors. Cross ribs on a second piece of glass then form pixels when bonded to the first layer. Addressing electrodes are attached to each pixel. The finished panel is then filled with a mixture of noble gases, typically neon and xenon.

Plasma Imaging Process Three-step charge/discharge cycle – Uses neon – xenon gas mixture – V AC discharge in cell stimulates ultraviolet (UV) radiation – UV stimulation causes color phosphors to glow and form picture elements – Considerable heat and EMI are released

PD Working Address electrode causes gas to change to plasma state. The plasma emits UV in discharge region which impinges on the phosphor Reaction causes each subpixel to produce red, green, and blue light.

4. Electroluminescent displays

Electroluminescent Source Electroluminescence  Excitation of electron by electric field + Dielectric with embedded phosphor

Electroluminescent -The structure consists of two thin layers of dielectric with phosphor sandwitched between them. - A thin Al layer on the top and thin ITO layer on the bottom completes EL.When voltage of order of 200V is applied the resultant high electric field (1MV/cm) tunnels electrons through dielectric on to phosphor. - The high energy of electrons impact the colour centres to emit visible light.

Advantages of Electroluminescent High brightness, high resolution, Blue phosphor improvement required High voltage switching High purity materials Small sizes Expensive