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Liquid Crystal Display

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  2. 2. INTRODUCTION <ul><li>A liquid crystal display ( LCD ) is an electro-optical amplitude modulator realized as a thin, flat display device . </li></ul><ul><li>It is made up of any number of color or monochrome pixels arrayed in front of a light source or reflector . </li></ul>
  3. 3. REFLECTIVE TWISTIVE LCD <ul><li>Polarize light with vertical axis as it enters. </li></ul><ul><li>Polarizing Filter film with Horizontal axis to block/pass light. </li></ul><ul><li>Reflective surface to send light back to viewers. </li></ul>
  4. 4. LCD ALARAM CLOCK <ul><li>Each pixel of an LCD typically </li></ul><ul><li>consists of a layer of </li></ul><ul><li>molecules aligned between </li></ul><ul><li>two transparent electrodes, </li></ul><ul><li>and two polarizing filters . </li></ul><ul><li>The axis of transmission of molecules which are perpendicular to each othe r. </li></ul>
  6. 6. <ul><li>With no liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. </li></ul><ul><li>The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction </li></ul>
  7. 7. <ul><li>Electrodes are made of a transparent conductor called Indium Tin Oxide (ITO). </li></ul><ul><li>When a voltage is applied across the electrodes , a torque acts to align the liquid crystal molecules parallel to the electric field . </li></ul><ul><li>By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray. </li></ul>
  8. 8. <ul><li>LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel. </li></ul>
  9. 9. SPECIFICATIONS <ul><li>RESOLUTION </li></ul><ul><li>RESPONSE TIME </li></ul><ul><li>DOT PITCH </li></ul><ul><li>REFRESH RATE </li></ul>
  10. 10. <ul><li>VIEWING ANGLE </li></ul><ul><li>BRIGHTNESS </li></ul><ul><li>CONTRAST RATIO </li></ul><ul><li>ASPECT RATIO </li></ul>
  11. 11. COLOR DISPLAY <ul><li>A typical LCD(Right) addresses groups of 3 locations as pixels. The XO-1(Left) display addresses each location as a separate pixel. </li></ul>
  12. 12. <ul><li>In color LCDs each individual pixel is </li></ul><ul><li>into three cells or subpixels . </li></ul><ul><li>These are colored red, green, and blue </li></ul><ul><li>respectively . </li></ul>
  13. 13. <ul><li>Color components may be arrayed in various pixel geometries , depending on the monitor's usage. </li></ul><ul><li>If software knows which type of geometry is being used in a given LCD, this can be used to increase the apparent resolution. </li></ul>
  14. 14. A general purpose alphanumeric LCD, with two lines of 16 characters <ul><li>LCDs with a small number of segments, such as those used in digital watches and pocket calculators </li></ul>
  15. 15. LCD DIGITAL COMPACT CAMERA <ul><li>High- resolution color displays such as modern LCD computer monitors , Camera and televisions use an active matrix structure. </li></ul><ul><li>A Matrix of thin-film transistors (TFTs) is added to the polarizing and color filters. </li></ul><ul><li>Each Pixel has its own dedicated transistor , to access one pixel </li></ul>
  16. 16. DEFACTS IN LCD <ul><li>Some LCD panels have defective transistors causing dead pixels. </li></ul><ul><li>It is also economically prohibitive to discard a panel with just a few defective transistor because LCD panels are much larger than ICs. </li></ul>
  17. 17. EXAMPLE <ul><li>LCD panels also have defects known as mura , which look like a small-scale crack with very small changes in luminance or color . </li></ul><ul><li>It is most visible in dark or black areas of displayed scenes. Defects in various LCD panel components can cause mura effect </li></ul>
  18. 18. APPLICATIONS <ul><li>PROJECTION TELEVISION </li></ul><ul><li>DIGITAL CLOCKS and WATCHES </li></ul><ul><li>COMPUTER MONITOR </li></ul><ul><li>LAPTOP COMPUTERS </li></ul><ul><li>MICROWAVE OWENS </li></ul><ul><li>CD Players </li></ul>
  19. 19. DrawBacks <ul><li>LCDs typically have longer response times than their plasma and CRT counterparts when image rapidly changes. </li></ul><ul><li>Some LCD TVs have slow video processing. </li></ul><ul><li>Dead pixels can occur when the screen is damaged or pressure is put upon the screen. </li></ul><ul><li>LCD panels using TN tend to have a limited viewing angle relative to CRT and plasma displays. This reduces the number of people able to conveniently view the same image – laptop screens are a prime example. </li></ul>
  20. 20. Comparision of LCD & CRT Display Technology   Screen Shape Largest known diagonal (in) Largest known diagonal (cm) Typical use Direct view CRT Spherical curve 24 61 Computer monitor , Radar display Direct view LCD Flat 108 74 Computer monitor
  21. 21. Other Display Technologies <ul><ul><li>Cathode ray tube (CRT) </li></ul></ul><ul><ul><li>Digital Light Processing (DLP) </li></ul></ul><ul><ul><li>Field emission display (FED) </li></ul></ul><ul><ul><li>Laser TV </li></ul></ul><ul><ul><li>Light-emitting diode (LED) </li></ul></ul>
  22. 22. THANKYOU