CHAPTER THIRTEEN

DISPLAY TECHNOLOGY (II)PDP, & TOUCHSCREEN

CGMB113/ CITB 123: MULTIMEDIA TECHNOLOGY

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SARASWATHY SHAMINI

Adapted from Notes Prepared by:Noor Fardela Zainal Abidin

© UNITEN 2004/2005

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• identify the terms and concept related to display technology• state the different types of display technologies• understand how the various display technology works

At the end of this chapter, students should be able to:

Plasma Display Panels•Based on the principle that certain gases emit

light when subject to an electric current•The basic idea of a plasma display is to

illuminate tiny colored fluorescent lights to form an image.

•Each pixel is made up of three fluorescent lights -- a red light, a green light and a blue light.

• Just like a CRT television, the plasma display varies the intensities of the different lights to produce a full range of colors.

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What is Plasma?•The central element in a fluorescent light

is a plasma, a gas made up of free-flowing ions (electrically charged atoms) and electrons (negatively charged particles).

•In a plasma with an electrical current running through it, negatively charged particles are rushing toward the positively charged area of the plasma, and positively charged particles are rushing toward the negatively charged area.

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What is Plasma?•In this mad rush, particles are constantly

bumping into each other. These collisions excite the gas atoms in the plasma, causing them to release photons of energy.

•Xenon and neon atoms, the atoms used in plasma screens, release light photons when they are excited. Mostly, these atoms release ultraviolet light photons, which are invisible to the human eye. But ultraviolet photons can be used to excite visible light photons.

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What is Plasma?

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Inside the Display: Gas and Electrodes • The xenon and neon gas in a plasma television is

contained in hundreds of thousands of tiny cells positioned between two plates of glass.

• Long electrodes are also sandwiched between the glass plates, on both sides of the cells.

• The address electrodes sit behind the cells, along the rear glass plate.

• The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate.

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Inside the Display: Gas and Electrodes

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Inside the Display: Gas and Electrodes •Both sets of electrodes extend across the

entire screen. The display electrodes are arranged in horizontal rows along the screen and the address electrodes are arranged in vertical columns. As you can see in the next diagram, the vertical and horizontal electrodes form a basic grid.

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Inside the Display: Gas and Electrodes

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Inside the Display: Gas and Electrodes • To ionize the gas in a particular cell, the plasma

display's computer charges the electrodes that intersect at that cell. ▫ It does this thousands of times in a small fraction of

a second, charging each cell in turn. • When the intersecting electrodes are charged

(with a voltage difference between them), an electric current flows through the gas in the cell.

• The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons

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Inside the Display: Phosphors • The released ultraviolet photons interact with

phosphor material coated on the inside wall of the cell.

• Phosphors are substances that give off light when they are exposed to other light.

• When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons jumps to a higher energy level and the atom heats up.

• When the electron falls back to its normal level, it releases energy in the form of a visible light photon

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Inside the Display: Phosphors • The phosphors in a plasma display give off

colored light when they are excited. • Every pixel is made up of three separate

subpixel cells, each with different colored phosphors. ▫ One subpixel has a red light phosphor, one subpixel

has a green light phosphor and one subpixel has a blue light phosphor.

▫ These colors blend together to create the overall color of the pixel.

• By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel color to create hundreds of different combinations of red, green and blue.

• In this way, the control system can produce colors across the entire spectrum

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Inside the Display: Phosphors • The main advantage of plasma display

technology is that you can produce a very wide screen using extremely thin materials.

• And because each pixel is lit individually, the image is very bright and looks good from almost every angle.

• The image quality isn't quite up to the standards of the best cathode ray tube sets, but it certainly meets most people's expectations.

• The biggest drawback of this technology has to be the price.

• In the near future, setting up a new TV might be as easy as hanging a picture!

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TOUCHSCREEN•A touchscreen is any monitor, based

either on LCD (Liquid Crystal Display) or CRT (Cathode Ray Tube) technology, that accepts direct onscreen input.

• The ability for direct onscreen input is facilitated by an external (light pen) or an internal device (touch overlay and controller) that relays the X,Y coordinates to the computer.

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How Touch Screen Work

•A basic touchscreen has three main components: a touch sensor, a controller, and a software driver.

•The touchscreen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.

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How Touch Screen Work

1. Touch Sensor2. Controller3. Software Driver

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How Touch Screen Work1.Touch Sensor

• A touch screen sensor is a clear glass panel with a touch responsive surface.

• The touch sensor/panel is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen.

• There are several different touch sensor technologies on the market today, each using a different method to detect touch input. The sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. This voltage change is used to determine the location of the touch to the screen.

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How Touch Screen WorkController

• The controller is a small PC card that connects between the touch sensor and the PC. It takes information from the touch sensor and translates it into information that PC can understand.

• The controller is usually installed inside the monitor for integrated monitors or it is housed in a plastic case for external touch add-ons/overlays.

• The controller determines what type of interface/connection you will need on the PC. Integrated touch monitors will have an extra cable connection on the back for the touchscreen.

• Controllers are available that can connect to a Serial/COM port (PC) or to a USB port (PC or Macintosh). Specialized controllers are also available that work with DVD players and other devices.

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How Touch Screen WorkSoftware Driver

• The driver is a software update for the PC system that allows the touchscreen and computer to work together.

• It tells the computer's operating system how to interpret the touch event information that is sent from the controller.

• Most touch screen drivers today are a mouse-emulation type driver. This makes touching the screen the same as clicking your mouse at the same location on the screen.

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Resistive Touchscreen Technology

•Resistive LCD touchscreen monitors rely on a touch overlay, which is composed of a flexible top layer and a rigid bottom layer separated by insulating dots, attached to a touchscreen controller.

•The inside surface of each of the two layers is coated with a transparent metal oxide coating (ITO) that facilitates a gradient across each layer when voltage is applied.

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Resistive Touchscreen Technology

•Pressing the flexible top sheet creates electrical contact between the resistive layers, producing a switch closing in the circuit.

•The control electronics alternate voltage between the layers and pass the resulting X and Y touch coordinates to the touchscreen controller.

•The touchscreen controller data is then passed on to the computer operating system for processing.

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Touch screen

1. Polyester Film 2. Upper Resistive Circuit Layer 3. Conductive ITO (Transparent

Metal Coating) 4. Lower Resistive Circuit Layer 5. Insulating Dots 6. Glass/Acrylic Substrate 7. Touching the overlay surface

causes the (2) Upper Resistive Circuit Layer to contact the (4) Lower Resistive Circuit Layer, producing a circuit switch from the activated area.

8. The touchscreen controller gets the alternating voltages between the (7) two circuit layers and converts them into the digital X and Y coordinates of the activated area.

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Reference

•Jeff Tyson, How LCDs Works, http://www.stuffo.com. 1998-2005

•Lachlan L. Mackinnon. Notes: Multimedia Technology (F291G2). Heriot_Watt University. Edinburgh. Scotland

• What is a touchscreen? http://www.ftgdata.com/touchscreens/resistive-touchscreens.html. FastPoint Technologies Inc. 2001-2005

• How Does a Touchscreen Work? http://www.touchscreens.com/intro-anatomy.html

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