DISPLAY TECHNOLOGIES. Group 6: Steve Lenhart, Ryan King, Ramsey Akl, and Andrew Scheib

DISPLAY TECHNOLOGIES Group 6: Steve Lenhart, Ryan King, Ramsey Akl, and Andrew Scheib

Introduction First computers did not have monitors to display output information. These machines relied on volumes of paper or turn dials to display results.

Introduction In the 1960 s the first minicomputer was released. The PDP-1, by Digital Equipment, which retailed for a mere $120,000 and included a keyboard and CRT monitor. These early CRT monitors consisted of one electron beam and green phosphorus screens.

Introduction These monitors were only capable of handling text and had troubles with image burn-in. Image Quality and CRT technology didn t start advancing until IBM took the wheel in 1981

Introduction Video Adapter Timeline Year : Model: By: Max Pixels: Colors: Palette: Type: Refresh rate 1981 MDA Mono Display Adapter IBM 720x350 2 2 TTL 50 Hz 1981 CGA Color Graphics Adapter IBM 160x200 4 16 TTL 60 Hz 1981 RGBI Red Green Blue Intensity IBM 640x200 4 16 TTL 60 Hz 1982 HERC Hercules Display Adapter IBM 720x348 2 2 TTL 50 Hz 1984 PGA Professional Graphics Array IBM 640x480 Analog 1984 EGA Enhanced Graphics Adapter IBM 640x350 16 65536 TTL 60 Hz 1987 8514/A Video Standard for PCs IBM 1024x768 256 262,000 Analog 43.5 Hz 1987 MCGA MultiColor Graphics Array IBM 720x400 256 Analog 60Hz 1987 VGA Video Graphics Array IBM 320x200 256 262144 Analog 70Hz 1988 VGA Video Graphics Array VESA 1600x1200 DDC 85Hz 1990 XGA extended Graphics Array IBM 1024x768 16 256 DDC 70 Hz 1990 SVGA Super VGA VESA 1600x1200 256 DDC Analog 60 Hz 1991 EVGA Extended VGA VESA 1024x768 256 DDC Analog 70 Hz

Introduction However as of recently most monitors support the XUGA standard. This standard can support 16.8 million colors and resolutions of 1600x1200 pixels. Though these standards apply to both a compatibility with your monitor and the display adapter

Introduction On old monitor/adapter combinations the display adapter and monitor had to be matched. These monitors supported one resolution and only one color mode. Modern monitor technologies use a Multi-scanning technology.

Introduction About 10 years ago NEC introduced their MutiSync monitor. This monitor used a muti-scanning technology which allowed the monitor to accept any frequency within a certain bandwidth that was sent to it. This revolutionized the display market and now almost every monitor that is bought incorporates multi-scan technology.

Introduction 1: Red out 2: Green out 3: Blue out 5: Ground 6: Red return 7: Green return 8: Blue return 10: Sync return 11: Monitor ID 0 in 12: Monitor ID 1 in or data from display 13: Horizontal Sync out 15: Monitor ID 3 in or data clock Monitor pin out diagram

Introduction There are two basic types of connectors. We have just seen the standard monitor connector consisting of 15 pins. The signal travels in an analog form, which means that the digital signal from the computer has to be converted to analog, thus providing some loss. The 15 pin connectors are the standard for CRT monitors and many LCDs. The second connector is what most high end video adapters and LCD monitors support. The Digital Video Interface (DVI). These have a completely different connector and does not have to convert the signal from digital to analog. The monitor is digital, the computer is digital and now the connection is digital. There is no room for loss of signal. Thus as a result most DVI enhanced monitors produce a much better picture.

Introduction Monitors have many different characteristics that the common consumer may have heard about. These characteristics include, viewable area, maximum resolution, dot pitch, refresh rate and color depth.

Introduction Viewable Area: broken into two major parts, Aspect Ratio, and Screen size. Aspect Ratio: Most TVs and common computer display use a 4:3 aspect ratio. Which corresponds to the width of the display to the height of the display. Newer TVs and even laptop LCD panels use a 16:9 ratio, this yields a wide screen effect.

Introduction Screen Size: screen size refers to the viewable area available for which to display images on the screen. Common screen sizes are 15, 17, 19, and 21 inches. Maximum Resolution: this has to do with the number of pixels available on the display. A display with 1600x1200 pixels can support up to 1600x1200 resolutions.

Introduction Dot Pitch: dot pitch has to do with the amount of space between the pixels on the display. By placing the pixels closer together you can achieve higher resolutions and better image qualities. Refresh Rates: refer to the number of times a second the image is redrawn on the screen. This is often rated in Hertz. If you have to slow a refresh rate you might have flickering occur on your screen.

Introduction Bit-Depth Number of Colors Finally you have Color Depth: has to do with the number of bits used to describe the color of a single pixel. 1 2 4 2 4 16 (monochrome) (CGA) (EGA) 8 256 (VGA) 16 65,536 (High Color, XGA) 24 16,777,216 (True Color, SVGA) 32 16,777,216 (True Color + Alpha Channel)

Three Major Display Types Cathode Ray Tube (CRT) Liquid Crystal Display (LCD) Plasma

Cathode Ray Tube Usually shortened to simply CRT. Most people in class should know how CRTs work. CRTs, at least in there TV form, have been around for more then 60 years and the technology hasn t changed too much.

Cathode Ray Tube The CRT consists of a vacuum tube enclosure with an electron gun and several strong magnets. In it s basic sense the electron beam fires towards the front of the tube, striking a phosphorus layer. The magnets are used to bend the beam. When the beam hits the phosphorus it makes that area glow. Each spot is considered a pixel. By carefully adjusting voltage you can make the point glow brighter or dimmer

Cathode Ray Tube

Cathode Ray Tube The electron beam scans from left to right. The time it takes for the beam to reach the end of one line is called the horizontal refresh rate. This is measured in kilohertz, khz. When the beam gets to the end of a line the magnets reset and it goes back to the left and scans again. When it gets all the way to the bottom it goes back to the top and does it all again. The time it takes to draw vertically is called the vertical refresh rate or simply refresh rate, this is measured in Hertz, Hz.

Cathode Ray Tube Original CRTs had a problem. The phosphorus on the screen would not retain brightness long enough for the beam to hit it again. To overcome this CRT makers introduced a process known as interlacing. Interlacing works by drawing only the odd rows on the display then going back and drawing the even rows. This allows for the screen to not look dull or faded.

Cathode Ray Tube Technology has increased since those early days and interlacing is not needed anymore. Another problem was brought up when CRTs started to be used for computers. Most of the work required lines of text, which meant that the resolution and refresh rate had to be increased. Scientists were able to increase both, now monitors run above 60Hz, this is compared to the 30Hz of the TV. Computer monitors should be ran at as high of a refresh rate as possible. Lower rates lead to screen flicker and eye strains and possible vision problems. Even if you cannot pick up the flicker a lower refresh will still cause eye strain, so be careful.

Cathode Ray Tube In order to produce a color picture the CRTs use three electron beams, which strike a triad of color phosphorus, red, green, and blue. In order to produce higher resolutions and better picture qualities the triads of colors had to be placed closer together. This problem would then produce smearing or poor picture quality if the electron guns were not perfectly aimed.

Cathode Ray Tube To fix this the scientists created something called a shadow mask. The shadow mask is placed right before the phosphorus layer on the tube. This then only allows the beams which are perfectly aligned to strike the right spot. The mask is usually made of a material called invar.

Cathode Ray Tube

Cathode Ray Tube Because of the difficulty of painting the phosphorus dots on the tube, scientists invented a different type of way to put the color phosphorus on the screen. This process is called aperture grille. In this technique the phosphorus colors are painted vertically with a thin wire to block stray electrons.

Cathode Ray Tube

Cathode Ray Tube Both shadow mask and aperture grille have their advantages and draw backs. Shadow mask usually produces a better picture, while the aperture grille produces brighter and more accurate colors. However aperture grille has two damping wires which cast a shadow on the screen.

Cathode Ray Tube One last thing about CRTs Dot Pitch, or Stripe Pitch (AG) This has to do with how close the phosphorus dots (shadow mask) or lines (aperture grille) are to each other. This measurements is in mm. The closer they are the better the image quality will be.

Liquid Crystal Displays Also go by the abbreviation of LCD Technology used most often on laptops. Recently though LCD displays have become common on the desktop computer market and other types of portable devices.

Liquid Crystal Displays The journey to LCD display has been a long one. The liquid crystal was first discovered in 1888 by a botanist named Friedrich Reinitzer. Reinitzer melted cholesteryl benzoate and observed the substance became a cloudy liquid and then cleared as it heated up. When it cooled it turned blue before it crystallized.

Liquid Crystal Displays Nothing was done with LCDs for 80 years. Then RCA picked it up and made the first experimental LCD in 1968. Since then the rest is history. Many companies have joined in to produce the LCD panels we have today.

Liquid Crystal Displays Because of the liquid nature of the display, LCDs are very sensitive to temperature changes. Liquid crystals have many different varieties of substances. Most displays operated in the nematic phase.

Liquid Crystal Displays A very important feature of liquid crystals is that they are affected by current. One type of nematic crystal is twisted nematics (TN), which are naturally twisted. When an electric current is passed through them they untwist to a certain degree. Which depends on the current s voltage.

Liquid Crystal Displays Companies use the liquid crystals because they react in a predictable manner when an electric current is passed through it. There are four major assumptions that LCD panels use to produce their displays Light can be polarized Liquid crystals can transmit and change polarized light The structure of liquid crystals can be changed by electric current. There are transparent substances that can conduct electricity

Liquid Crystal Displays LCDs are constructed of several different layers. For the most basic LCD there is only 6 different layers. The layers are, starting in the back. Mirror to make it reflective. Then a piece of glass with a polarizing film on the bottom side. On top of that is a common electrode plane which covers the entire area of the LCD. This also has a layer of liquid crystals. Next is another piece of glass with an electrode in the shape of a rectangle on the bottom. On top of that is another polarizing film at a right angle to the first one.

Liquid Crystal Displays The electrodes are then connected to a power source. When the source is off and there is no current flowing, light entering from the front hits the mirror in the back and reflects. When current is applied to the liquid crystals between the two electrode planes they untwist and block the light coming in making the rectangular area show as a black area. This is the most simple design. By adding more electrodes in different configurations you can produce a more complex display.

Liquid Crystal Displays Liquid crystals emit no light, therefore in the basic example, all the light is reflected from outside light sources. Hence the name given to this type of panel, Reflective. In another type of panel, backlit, the light comes from florescent tubes organized all around the display. They then use a white diffusing panel behind the display to make sure the light is evenly distributed to the whole display.

Liquid Crystal Displays Two main types on LCDs used in computers today, Passive Matrix and Active Matrix.

Liquid Crystal Displays Passive Display: Use a simple grid to bring current to a pixel on the display Grid rather difficult to produce. The process starts with two pieces of glass called substrates. The substrates (made of indium-tin oxide, are oriented with one having columns, while the other has rows. These are then connected to integrated circuits that control when a charge is sent to a column or row. The liquid crystal material is then placed between the two substrates and a polarizing film is placed on the outside of the two substrates

Liquid Crystal Displays Passive Displays (cont.): In order to turn a pixel on the IC has to send a charge to the correct column and a ground activated for the row. This causes a voltage to flow to the pixel and untwist the liquid crystal.

Liquid Crystal Displays Passive Displays (cont.): The passive display is simple but it has drawbacks. Two biggest ones are slow response time and imprecise voltage control. The response time has to do with the refresh capabilities of the LCD. The slow response time often leaves ghost effects on the screen. The imprecise voltage control has to do with the matrix s ability to influence only one pixel at a time. Being imprecise the pixels around the target pixel slightly untwist causing a fuzzy or blurry image.

Liquid Crystal Displays Active Displays: Uses a technology called thin film transistors (TFT). TFTs are little switching transistors and capacitors. They are arranged in a matrix on the glass substrate. In order for a particular pixel to be lit up the display actives a row and then sends a charge down the column. The capacitor in the pixel holds the charge until the next refresh rate. Using careful voltage regulation the amount of light transmitted through the pixel can be controlled by only untwisting the liquid crystal to a certain degree. Today's displays can offer 256 levels of brightness.

Liquid Crystal Displays Color: LCDs that handle color have 3 different sub pixels, each with a different color filter, red, green, or blue. As mentioned before carefully controlling the voltage can produce up to 256 shades. All of these combined can produce up to 16.8 million colors. More than the human eye can register. (About 10 million). To make these displays a very large amount of transistors are used. A typical modern display supporting 1024x768 resolution will have 2,359,296 transistors etched into the glass. If a transistor goes bad it produces a dead spot or bad pixel. Most panels have a few dead pixels.

Liquid Crystal Displays One last point: Quality control for LCDs is a problem. As the screens get bigger and more complex, more transistors and more dead pixels exists. With this in mind, most manufacturers reject up to 40% of the panels that are produced. This helps to drive up the price on the displays, but technology keeps progressing so advances may help that number.

In the Future Display technologies are a very important part of computing. Several different types of display technology are currently in the research process. Just to look at three we have Lightemitting Polymer, Electronic Paper, and Plasma Displays

In the Future Perhaps the most recognizable and farthest along is the plasma display. Plasma displays are currently used in high resolution televisions. They haven t moved over to computer displays but might in the near future.

In the Future The basic layout of the plasma display is to light up many tiny fluorescent lights. Each pixels contains lights for red, green, and blue. By varying voltage one can control exactly what color to produce. Florescent lights are made up plasma. Plasma is a gas made up of free flowing ions and electrons.

In the Future When free electrons are introduced the whole system goes crazy and electrons and ions are flying everywhere. These excited states cause the electrons to release photons. When the photons are released they interact with phosphorus of the different colors in the individual cell and produce a color. This technology allows for large wide screen displays to be made without a lot of bulk and thickness.

In the Future

In the Future Light Emitting Polymers (LEP) are creating new flat panel displays which are lighter and thinner then before. LEPs are designed in the same manner as LCDs. The major difference is that after the polymer is put on the substrates, the substrates have a transparent layer of electrodes and another layer is evaporated onto the top of the polymer.

In the Future The polymer then emits light when an electric field between the two electrodes in created. This provides for ultra fast response time and the polymer is not affected by temperature. These panels can also be made smaller then LCDs by only needing one piece of glass. It is also made of flexible plastic substrates which allow it to be bent or shaped to any desired shape, while also making it practically indestructible.

In the Future The last new display is still in its infancy and progress is moving slowly. This technology is known as electronic paper. E-paper uses a thin display surface and has ink injected onto it in order to produce an image. Right now though, there is now way to easily erase the display and keep reusing. However, the device requires hardly any power consumption which makes it ideal for PDAs and cell phones. Currently companies like Phillips are working on research for this type of display technology.

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