LCD DISPLAY TECHNOLOGY. Digital Images and Pixels

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1 LCD DISPLAY Figures are courtesy of 3M TECHNOLOGY Modified'by' Asst.Prof.Dr.'Surin'Ki6tornkun' Computer'Engineering,'KMITL' 1 Digital Images and Pixels A digital image is a binary (digital) representation of a two-dimensional pictorial data. Digital images may have a raster or vector representation. Raster Images defined over a 2D grid of picture elements, called pixels. A pixel is the basic items of a raster image and include intensity or color value. Pixels 2

2 LCD Display Structure 3 LCD (Liquid Crystal Display) LCD Panel is based on A light valve for each pixel that turn the light on, off, or an intermediate level. Grid of such light valve for the LCD display panel. A back light and display enhancement films create the illumination. 4

3 LCD-Display Applying voltage to the electrodes changes the level of illumination in each sub-pixel The panel is sandwiched between Front surface films to enhance display property Backlight 5 Linear Polarized Light Light usually vibrates in all direction A linear polarized light limit the vibration to one direction It absorbs the component of light that vibrate in all other direction. LCD require light to vibrate in one direction 6

4 Iodine Based Polarizer Is the most common polarizer It is made by Stretching a cast polyvinyl alcohol film (PVA) to align the iodine in turn. Staining it with iodine The stained PVA laminated between two slices of cellulose triacetate. The cellulose triacetate Provide physical rigidity Some degree of heat and humidity protection Cellulose Triacetate polyvinyl alcohol film Cellulose Triacetate polyvinyl alcohol film 7 About Liquid Crystal Liquid crystal molecules can move freely while maintaining their orientation. It align itself to a polyimide film to the inside of a panel glass. When the two glass panels are not aligned the liquid crystal twists accordingly. The liquid crystal will also align to electric field.`` 8

5 Light Path The light passes through the polarizer. The voltage applied to the electrodes controls the liquid crystal orientation The liquid crystal orientation controls the rotation of the incoming polarized light. Color filters are used in color LCD, where each color sub-pixel is controlled individually 9 Displays LED Direct Address Display Passive Matrix Display Active Matrix Display Twisted Nematic LCD Display 10

6 Direct Address Display When the display include limited variable components such as Watches Calculators Simple electronics is used to control the components 11 Passive Matrix Display Passive matrix display has Rows of electrodes on one piece of glass. Columns of electrodes on the opposing piece of glass. Complex electrical waveform control the voltage differential at the intersection of the electrodes. The intersection of the columns and rows are the pixels 12

7 Passive Matrix Display -disadvantages- As more rows and columns are added the range of the allowed voltage is reduced. At high range adjacent channels interferes Range limit reduces contrast Limit the types of useful liquid crystal. It is usually limited to about 50 rows Twisted nematic (TN) Display work best with large voltage variation. It can not be used in Passive Matrix Display 13 Active Matrix Display Allow very high resolution Each sub-pixel is individually controlled by an isolated thin-film transistor (TFT). It allows the electrical signal for each sub-pixel to avoid influencing adjacent elements. The TFT is patterned into the glass layer A display with 1024x768 resolution Include 1024x768x3 = 2,359,296 sub-pixels 14

8 Twisted Nematic (TN) Display Is the most common LCD Display. The two alignments layer for the liquid crystal material are orthogonal. The light entering the polarize panel rotates by the twist in the liquid crystal and allowing it to pass through the second polarize 15 Twisted Nematic (TN) Display The electric field is applied The liquid crystal loses its twist. Alight to the electric field. Prevents the rotation of the polarized light The second polarizer absorbs the light. The applied voltage control the absorbed and transmitted light 16

9 Twist Nematic Viewing Angle Light passes through the TN display from one angle may be blocked in other angles by the twist of the liquid crystal. To overcome this limitation different approaches have use various orientations for the polarize layers. 17 Back-Light The light generated by the backlight. The light is evenly distributed the light evenly over the LCD panel. Display enhancement films are placed between the light diffuser and the LCD panel. They aim to maximize the light reaching the observer. 18

10 Back-Light 19 3-D LCD Displays This technology aims to generate stereoscopic 3D images with the need for glasses. The idea is based on combining Active-matrix LCD with Lenticular lens: an array of magnifying lenses, designed to magnify different images when viewed from slightly different angles. Applications Industrial Visualization Medical imaging Entertainment 20

11 Our Color LCD Display TFT LCD Model KWH032GM02-F05 Display/datasheet/TFT/ KWH032GM02-F05.pdf 3.2 Inches 320 x 240 Pixels SPI (Serial Peripheral Interface) mode 21 Board Schematic 22

12 Read Command 23 Write Data 24

13 TFT#LCD# KWH032GM020F05! CS'GLCD'uses'P0.6'to'be'GPIO'Output.' SCL'GLCD'uses'P0.7'to'be'SCK1'of'SSP1.' SDO'GLCD'uses'P0.8'to'be'MISO1'of'SSP1' SDI'GLCD'uses'P0.9'to'be'MOSI1'of'SSP1.' BL'GLCD'uses'P4.28'to'be'GPIO'Output.'' 25 Color Assignment Up to 256*1024 colors per pixel Red = R5..R0 (6bits), Green = G5..G0, Blue = B5..B0 2^18 = 2^8 * 2^10 = 256*

14 Optical Specification 27 Back-Light Characteristic 28