Content: LCD types Working - PowerPoint Presentation

Content:LCD typesWorking principle of LCD TVAlternative displays LED displayOLED displayPlasma displayField Emission displayHDTV3D TV Large-screen Television Vision Technology

Type of LCDTN displays are suitable for calculators, simple electronic organizers, andany other numerical displays. STN displays are suitable for mono color word processors. Lastly, FSTN displays can produce black/white or full color, are thin, light weight, can handle large capacity, have high contrast and can respond fast to changes. FSTN displays are suitable for word processors and low-end color displays.(TN) (STN) (FSTN)

Passive matrix displayIn the passive matrix liquid crystal displays, row and column signals are used to input information into the display matrix. There are no non-linear elements (switches) at the individual cells so that the signal applied to each pixel for a small fraction of the refresh cycle. A typical passive matrix display is shown in figure belowPassive Matrix – a simple grid supplies is used to charge a particular pixel on the display. Slow response time and imprecise voltage control .

If the number of multiplexed lines increased the contrast ratio decreased. This is due to the ratio of voltage at a selected point (for example a pixel) and an unselected point is a decreasing function of the number of rows being multiplexed. The relation is shown below:Crosstalk occurContrast reduces Twisted Nematic (TN) Poor contrast ratio due to slower voltage/transmission curve Lower multiplexing of LC cell Suitable for calculators, Simple electronic organizers, and any other numerical displays.

Use another STN cell on the top of the first one. Reduce the brightness of the display. Add a polymer film retardation layer.This new structure was named film compensated STN or FSTNColor shift took place. Characters to appear yellow on a blue background Problem of producing black and white screens Super Twisted Nematic (STN)

In case of active matrix display a switching device is used at each pixel. This switch allows the signal voltage to be applied to the liquid crystal cell for the entire cycle time between refreshes. This leads to better overall performance and most importantly allows one to use a 900 twist in the liquid crystal.Active matrix display

Different elements of LCDMain parts of LCD: Backlight Polarizer Glass Substrate Pixel electrodes (ITO) Thin film transistors (TFTs) Liquid crystal layer Top electrode Black matrix RGB color filter array Glass Polarizer

Light transmission modes in LCDReflective technology includes a diffuser attached to the lower polarizer; this layer reflects incoming light evenly back through the display. Reflective technology is commonly found in calculators and digital wristwatches.Transmissive technologies have backlights attached to the lower polarizer. Instead of reflecting ambient light, the backlight supplies a light source directly to the display. Transmissive devices can be found in medical devices, electrical test and measurement instruments, and laptop computers.

Light transmission modes in LCDTransflective devices are a hybrid of the reflective and transmissive schemes. The construction is similar to transmissive displays except a partially reflective layer is added between the backlight and the liquid crystal. Since it is a hybrid, transflective screens perform in both indoor and outdoor conditions, but are not as effective as the previous two. Transflective displays are used in devices such as cell phones, PDAs and GPS receivers.

How does a TV screen make its picture?Each one of the pixels is effectively a separate red, blue, or green light that can be switched on or off very rapidly to make the moving color picture. The pixels are controlled in completely different ways in plasma and LCD screens. In a plasma screen, each pixel is a tiny fluorescent lamp switched on or off electronically . In an LCD television, the pixels are switched on or off electronically using  liquid crystals  to rotate  polarized light . How pixels are switched off: Light travels from the back of the TV toward the front from a large bright light. A horizontal polarizing filter in front of the light blocks out all light waves except those vibrating horizontally. Only light waves vibrating horizontally can get through. A transistor switches off this pixel by switching  on  the electricity flowing through its liquid crystal. That makes the crystal straighten out (so it's completely untwisted), and the light travels straight through it unchanged. Light waves emerge from the liquid crystal still vibrating horizontally. A vertical polarizing filter in front of the liquid crystal blocks out all light waves except those vibrating vertically. The horizontally vibrating light that travelled through the liquid crystal cannot get through the vertical filter. No light reaches the screen at this point. In other words, this pixel is dark.

SDHow pixels are switched ON: The bright light at the back of the screen shines as before. The horizontal polarizing filter in front of the light blocks out all light waves except those vibrating horizontally. Only light waves vibrating horizontally can get through. A transistor switches on this pixel by switching  off  the electricity flowing through its liquid crystal. That makes the crystal twist. The twisted crystal rotates light waves by 90° as they travel through it. Light waves that entered the liquid crystal vibrating horizontally emerge from it vibrating vertically. The vertical polarizing filter in front of the liquid crystal blocks out all light waves except those vibrating vertically. The vertically vibrating light that emerged from the liquid crystal can now get through the vertical filter. The pixel is lit up. A red, blue, or green filter gives the pixel its color. How does a TV screen make its picture?

Alternative DisplaysDisplay technology must evolve to keep pace with advances in other areas of technology. This evolution in display technology will produce displays that are faster, brighter, lighter, and more power-efficient. Technologies that have emerged to meet this challenge are OLEDs, DLP technology, Plasma, FEDs, and Electronic PaperOrganic Light Emitting Diodes (OLEDs):One of the next trends in display technology is Organic Light Emitting Diodes (OLEDs). Polymer Light Emitting Diodes (PLEDs), Small Molecule Light Emitting Diodes (SMOLEDS) and dendrimer technology are all variations of OLEDs. With all variations being made by electroluminescent substances (substances that emit light when excited by an electric current), OLED displays are brighter, offer more contrast, consume less power, and offer large viewing angles –all areas where LCDs fall short.

OLED StructureOLED Structure OLEDs work in a similar way to conventional diodes and LEDs, but instead of using layers of n-type and p-type semiconductors, they use organic molecules to produce their electrons and holes. A simple OLED is made up of six different layers. On the top and bottom there are layers of protective  glass  or  plastic . The top layer is called the  seal  and the bottom layer the  substrate . In between those layers, there's a  negative terminal  (sometimes called the cathode) and a  positive terminal  (called the anode). Finally, in between the anode and cathode are two layers made from organic molecules called the  emissive layer  (where the light is produced, which is next to the cathode) and the  conductive layer  (next to the anode). Here's what it all looks like:

To make an OLED light up, we simply attach a voltage (potential difference) across the anode and cathode. As the electricity starts to flow, the cathode receives electrons from the power source and the anode loses them (or it "receives holes," if you prefer to look at it that way). Now we have a situation where the added electrons are making the emissive layer negatively charged (similar to the n-type layer in a junction diode), while the conductive layer is becoming positively charged (similar to p-type material). Positive holes are much more mobile than negative electrons so they jump across the boundary from the conductive layer to the emissive layer. When a hole (a lack of electron) meets an electron, the two things cancel out and release a brief burst of energy in the form of a particle of light—a  photon , in other words. This process is called  recombination , and because it's happening many times a second the OLED produces continuous light for as long as the current keeps flowing. We can make an OLED produce colored light by adding a colored filter into our plastic sandwich just beneath the glass or plastic top or bottom layer. If we put thousands of red, green, and blue OLEDs next to one another and switch them on and off independently, they work like the pixels in a conventional LCD screen, so we can produce complex, hi-resolution colored pictures. How an OLED emits light How does this sandwich of layers make light?

Plasma displayA plasma screen is similar to an LCD, but each pixel is effectively a microscopic fluorescent lamp  glowing with plasma. A plasma is a very hot form of gas in which the  atoms  have blown apart to make negatively charged electrons and positively charged ions (atoms minus their electrons). These move about freely, producing a fuzzy glow of light whenever they collide. Plasma screens can be made much bigger than ordinary cathode-ray tube televisions, but they are also much more expensive. Much like the picture in an LCD screen, the picture made by a plasma TV is made from an array (grid) of red, green and blue pixels (microscopic dots or squares). Each pixel can be switched on or off individually by a grid of horizontally and vertically mounted electrodes (shown as yellow lines). Suppose we want to activate one of the red pixels (shown hugely magnified in the light gray pullout circle on the right). The two electrodes leading to the pixel cell put a high voltage across it, causing it to ionize and emit ultraviolet light (shown here as a turquoise cross, though it would be invisible in the TV itself). The ultraviolet light shines through the red phosphor coating on the inside of the pixel cell. The phosphor coating converts the invisible ultraviolet into visible red light, making the pixel light up as a single red square.

Advantages & Disadvantages of plasma displayAdvantages:Every single pixel generates its own light and as a result viewing angles are large, approximately 1600, and. image quality is superior and it is not affected as the display area becomes larger; plasma displays can be built in dimensions nearing 2m . plasma displays are able to provide image quality and display size without the disadvantage of being bulky and blurry around the edges; It can generally be built with a depth of 15-20 cm and as a result can be mounted or used in space limited areas. Disadvantages: Due to the fragile nature of plasma screens (it utilizes glass panels as a substrate), professional installation is required. PDPs are susceptible to burn-in from static images and as a result they are not suitable for billboard-type displays, or channels that broadcast the same image constantly, i.e. news station logos. Ionizing the plasma requires a substantial amount of power; consequently, a 38-inch color plasma display can consume up to 700 W (power levels generally used by appliances such as vacuum cleaners) where the same sized CRT would only require 70 W. many other high quality display technologies can replace plasma displays and hence render it useless in the future .

Field Emission Displays (FEDs)Field emission displays (FEDs) function much like CRT technology. Instead of using one electron gun to emit electrons at the screen, FEDs use millions of smaller ones. The result is a display that can be as thin as an LCD, reproduce CRT-quality images, and be as large as a plasma display. Initial attempts in making emissive, flat-panel displays using metal tipped cathodes occurred nearly 20 years ago, however, with reliability, longevity, and manufacturing issues, these types of FEDs do not seem commercially viable .

Electron emission in FED The emitted current, or moving electrons, depends on the electric field strength, the emitting surface, and the work function. In order for field emission to function, the electric field has to be extremely high: up to 3x V/cm . This value, though large, is accessible by the fact that field amplification increases with a decreasing curvature radius indicating that the pointier the object, the more charge it will have at its tip, and hence the larger the electric field. As a result, if such a material can be found, a moderate voltage will cause the tunneling effect, and hence allow electrons to escape into free space without the heating of the cathode like the traditional Cathode Ray Tube (CRT) technology .   Electric field concentration around a pointy object The basic structure of the first FED was comprised of millions of vacuum tubes, called micro-tips . Each tube was red, green, or blue and together, formed one pixel. These micro-tips were sharp cathode points made from molybdenum from which electrons, under a voltage difference, would be emitted towards a positively charged anode where red, blue, and green phosphors were struck, and as a result emit light through the glass display. Unlike CRTs, color was displayed sequentially, meaning the display processed all the green information first, then refreshed the screen with red information , and finally blue.

Merits and demerits of FEDMerits:The FED only produced light when the pixels are “on”, and as a result power consumption is dependent on the display content. A FED generates light from the front of the pixel, providing an excellent viewing angle of 160 degrees both vertically and horizontally. The FED does not suffer no brightness loss even if 20% of the emitters failed. Demerits: One problem being the metal molybdenum, used to make the micro-tips , would become so heated that local melting would result and consequently deform its sharp tips needed to form the electric field used for electron emission . Another problem caused by the electrical environment is the hot cathodes would react with the residual gases in the vacuum consequently reducing the field emission even more. A carbon nanotube structure CNTs are chemically stable therefore they only react under extreme conditions such as extremely high temperatures (2500°C) with oxygen or hydrogen; consequently, the problems of reacting with resident gases, overheating, or tip deformation are solved with CNTs.

Display Technology Comparison Chart

High-definition television (HDTV)High-definition television (HDTV) provides a resolution that is substantially higher than that of standard-definition TV (SDTV) or Conventional TV . HDTV is a  digital TV  broadcasting format where the broadcast transmits   widescreen  pictures with more detail and quality than found in a standard  analog television , or other digital television formats. HDTV essentially means the picture is much more detailed, a bit wider, and it doesn't flicker, even when it's shown on really big screens . Large-screen resolutions Resolution name Horizontal x vertical pixels Other names Devices 8K 7,680x4,320 8K UHD TVs UHD 3,840x2,160 4K, Ultra HD, Ultra-High Definition TVs, monitors 1080p 1,920x1,080 Full HD, FHD, HD, High Definition TVs, monitors 720p 1,280x720 HD, High Definition TVs

ParticularsHDTVSDTVConventional TVAspect ratio (W:H)16:916:94:3Sharpness and clarity6 times of conventional TVResolution1920x1080= 2M pixels1280x720= 0.9M Pixels 720x480= 0.3M pixels Color resolution 2 times of conventional TV Sound quality Surround sound Signal quality Very high (digitally transmitted) Affected by noise ( analog transmission) Performance comparison of different TVs

24How does a 3D TV work?Our brains generate a 3D picture largely by having two eyes spaced a short distance apart. Each eye captures a slightly different view of the world in front of it and, by fusing these two images together, our brains generate a single image that has real depth. This trick is called stereopsis (or stereoscopic vision). The basic principle of 3D TV working is that there are 2 images being shown on the TV screen simultaneously, one for the right eye and the other for the left eye. When the viewer sees the two separate images, he thinks that he is seeing a 3D image . There are several different ways of making a 3D TV, but all of them use the same basic principle: they have to produce two separate, moving images and send one of them to the viewer's left eye and the other to the right. To give the proper illusion of 3D, the left eye's image mustn't be seen by the right eye, while the right eye's image mustn't be seen by the left.

Here's a quick summary of the four most common 3D TV technologies. In these diagrams, we're looking down on a person's head from above and comparing how two different images enter their two eyes in each case:Anaglyph: We have to wear eye glasses with colored lenses so our brain can fuse together the partly overlapping red and cyan pictures on the screen. Polarizing : We wear lenses that filter light waves in different ways so each eye sees a different picture. Active-shutter : The left and right lenses of our glasses open and close at high speed, in rapid alternation, to view separate images (frames) shown on the screen. Lenticular : We don't need glasses with this system. Instead, a row of plastic lenses in front of the screen bends slightly different, side-by-side images so they travel to your left and right eyes. We must sit in the right place to see a 3D image. 3D technologies

3D TV with active glassesIn a 3D TV with active glasses, the pictures for the right and left eye are shown one after the other. The active 3D glasses for watching 3D TV have electronic shutters that blind vision to one eye while the picture meant for the other eye is on the TV. This process is repeated very fast at a rate of about 60 TV images per second. The left and right side lenses of the active 3D glasses opens and shuts synchronizing with signals emitted by the 3D TV to the 3D glasses.3D TV with passive glassesIn 3D TV with passive glasses there is a polarising screen on the passive type 3D TV which polarizes the light coming out from the TV image. Thus the light from the images on the passive 3D TV are polarized either horizontally or vertically and the special passive 3D glasses have lenses to see horizontally polarized light in one side, say the left lens and the other right side lens can only see vertically polarized light. Thus each eye gets the correct 3D picture frame through the different polarizing effect given to passive 3D TV images. Passive 3D glasses are very reliable unlike the complicated active 3D glasses which require to be powered by batteries to open and close each side of the lens according to signals received from the 3D TV.3D technologies