MONITORS
DEFINATION OF MONITOR
A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. Monitors generally conform to one or more display standards.
CLASSIFICATIONS OF MONITORS
monochrome : Monochrome monitors actually display two colors, one for the background and one for the foreground . The colors can be black and white, green and black, or amber and black.
gray-scale : A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray.
color: Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals -- red, green, and blue.
Types of monitors
** PLASMA
** LCD (LIQUID CRYSTAL DISPLAY)
** CRT (CATHODE RAY TUBE)
** TFT (THIN FILM TRANSISTER)
** FLAT PANNEL DISPLAY
** TOUCH SCREEN MONITORS
** WIRELESS MONITORS
CRT DISPLAY THEORY
A CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam that travels across the screen to create a visible image. The illustration below shows how this works inside a CRT.
The terms anode and cathode are used in electronics as synonyms for positive and negative terminals. For example, you could refer to the positive terminal of a battery as the anode and the negative terminal as the cathode.
In a cathode ray tube, the "cathode" is a heated filament. The heated filament is in a vacuum created inside a glass "tube." The "ray" is a stream of electrons generated by an electron gun that naturally pour off a heated cathode into the vacuum.
Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. This screen is coated with phosphor, an organic material that glows when struck by the electron beam.
Working theory of plasma
Plasma is a flat, lightweight surface covered with millions of tiny glass bubbles. Each bubble contains a gas-like substance, the plasma, and has a phosphor coating. Think of the bubbles as the pixels.Now, think of each pixel-bubble as having three sub-pixels - one red, one green, one blue. When it is time to display an image signal (RGB or video), a digitally controlled electric current flows through the flat screen, causing the plasma inside designated bubbles to give off ultraviolet rays. This light in turn causes the phosphor coatings to glow the appropriate color.
Millions of RGB bubbles glow and dim to make a rich, vivid image on your plasma TV.
HOW LCD EMIT LIGHT ?
A typical twisted nematic (TN) liquid crystal display consists of two polarising filters with their lines arranged perpendicular (at 90 degrees) to each other, which, as described above, would block all light trying to pass through.
But in-between these polarisers are the twisted liquid crystals. Therefore light is polarised by the first filter, twisted through 90 degrees by the liquid crystals, finally allowing it to completely pass through the second polarising filter.
However, when an electrical voltage is applied across the liquid crystal, the molecules realign vertically, allowing the light to pass through untwisted but to be blocked by the second polariser.
Consequently, no voltage equals light passing through, while applied voltage equals no light emerging at the other end.
TFT WORKING THEORY
Think of two glass substrates sandwiching a layer of liquid crystal. The front glass substrate is fitted with color filter while glass substrate behind has transistors.
This is basic structure of TFT lcd panel
When voltage is applied to transistor,liquid crystal is bent,allowing light to pass through to form a pixel.
A light source is located at the back of of the pannel is called as backlight unit.
The front glass substrate is fitted with a color filter,so that each pixel gets its own color
Combination of these pixels in different colors form the image on the panel.
TFT screens are active-matrix LCDs which contains thin film transistors which are added to polarizing and color filters
Wireless & touch screen monitors
Touch screen monitors
Displays with touch-screen technology let you input information or navigate applications by touching the surface of the display. The technology can be implemented through a variety of methods, including infrared sensors, pressure-sensitive resistors or electronic capacitors.
Wireless monitors
Similar in looks to a tablet PC, wireless monitors use technology such as 802.11b/g to connect to your computer without a cable. Most include buttons and controls for mousing and web surfing, and some also
include keyboards. The displays are battery-powered and relatively lightweight. Most also include touch-screen capabilities.