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Unformatted text preview: Lecture 13 6.111 Flat Panel Display Devices Outline Overview Flat Panel Display Devices How do Displays Work? Emissive Displays Light Valve Displays Addressing Schemes Display Timing Generator Gray Scale / Color Schemes Display Drivers For more info take graduate course, 6.987 on flat panel displays Tayo Akinwande Applications of Flat-Panel Displays SMALL FORMAT Medical Defibrillator MP3 Player LARGE FORMAT Personal Digital Assistant Car Navigation & Entertainment Courtesy of PixTech Desktop Monitor (color) Electronic Book Large Screen Television (color) Some Display Terminologies Term Pixel Pixel Matrix Aspect Ratio Resolution (ppi) Frame Rate (Hz) Viewing Angle () Diagonal Size Contrast Ratio Definition Picture elementThe smallest unit that can be addressed to give color and intensity Number of Rows by the Number of Columns of pixels that make up the deisplay Ratio of display width to display height; for example 4:3, 16:9 Number of pixels per unit length (ppi=pixels per inch) Number of Frames displayed per second Angular range over which images from the display could be viewed without distortion Length of display diagonal Ratio of the highest luminance (brightest) to the lowest luminance (darkest) Information Capacity of Displays (Pixel Count) Resolution Pixel Ratio Video Graphic Array 640 x 480 x RGB 4:3 (VGA) Super Vedio Graphic Array 800 x 600 x RGB 4:3 (SVGA) eXtended Graphic Array 1,024 x 768 x RGB 4:3 (XGA) Super eXtended Graphic Array 1,280 x 1,024 RGB 5:4 (SXGA) Super eXtended Graphic Array plus 1,400 x 1,080 x RGB 4:3 (SXGA+) Ultra eXtended Graphic Array 1,600 x 1,200 x RGB 4:3 (UXGA) Quad eXtended Graphics Array 2048 x 1536 x RGB 4:3 (QXGA) Quad Super eXtended Graphics Array 2560 x 2048 x RGB 4:3 (QSXGA) Display Devices, No. 21, Spring 2000, p. 41 How Do Displays Work? Pankove "Time Sequential Electrical Signals" converted into images. Signals routed to the display elements (similar to memory addressing) Pixels convert the electrical signal into light of color and intensity (inverse of image capture) Human Eye-- Spectral Response 1.20 1.00 Relative Sensistivity 0.80 0.60 0.40 Blue Green Violet 0.20 Yellow Orange 550 600 0.00 400 450 500 650 70 Wavelength (nm) Red Classifications of Displays by Technology Displays could be classified into two broad categories Light Generation (Emissive Displays) Light Modulation (Light Valve Displays) Emissive Displays generate photons from electrical excitation of the picture element (pixels) Cathode Ray Tubes (CRTs), Organic Light Emitting Displays (OLEDs), Plasma Displays (PDs) Light Valve Displays spatially and temporally modulate the intensity pattern of the picture elements (pixels) Liquid Crystal Displays (LCDs), Digital Light Processors (DLPs), Electrophoretic Displays (EPDs) Cathode Ray Tube CRT Display Cathode Electrons beam "boiled off a metal" by heat (thermionic emission) is sequentially scanned across a phosphor screen by magnetic deflection. The electrons are accelerated to the screen acquiring energy and generate light on reaching the screen (cathodoluminescence) Phosphor Screen Courtesy of PixTech Anode Plasma Displays Weber, SID 00 Digest, p. 402. Electrons are accelerated by voltage and collide with gasses resulting in ionization and energy transfer Excited ions or radicals relax to give UV photons UV photons cause hole-electron generation in phosphor and visible light emission (photoluminescence) Organic Light Emitting Diode 17-inch Active Matrix OLED Rajeswaran et al., SID 00 Digest, p. 974 H.-K. Chung et al., SID 05 Digest, p. 956 electroluminescence Digital Mirror Device Courtesy of Texas Instruments Applied voltage deflects Mirror and hence direct light Reflective Light Valves Liquid Crystal Displays Liquid Crystals rotate the plane of polarization of light when a voltage is applied across the cell Polarization Rotator Courtesy of Silicon Graphics TFT AMLCD Fluorescent Lamp (Backlight) Diffuser Rear Polarizer G R B G G R B G G R B G G G G G G R R R R R R R R B B B B B B B B Rear Glass w/TFT Array and Row/Column Drivers Liquid Crystal Layer 82" TFT AMLCD Front Glass w/Common ITO Electrode and Color Filters Front Polarizer K. Sarma SID 05 Figure 1 Standard Display Addressing Modes Sequential Addressing (pixel at a time) CRT, Laser Projection Display Matrix Addressing (line at a time) Row scanning, PM LCD, AMLCD, FED, PDPs, OLEDs Direct Addressing 7-segment LCD Random Addressing Stroke-mode CRT Sequential Addressing (Raster Scan) Time is multiplexed Signal exists in a time cell A pixel is displayed at a time Single data line Rigid time sequence and relative spatial location of signal Raster scan Data rate scales with number of pixels Duty cycle scales with number of pixels Horizontal sync coordinates lines Vertical sync coordinates frames Blanking signals (vertical & horizontal) so that retraces are invisible Scan Lines Retrace Lines Tannas, SID 00 Applications Seminar Composite Frames The `frame' is a single picture (snapshot). It is made up of many lines. Each frame has a synchronizing pulse (vertical sync). Each line has a synchronizing pulse (horizontal sync). Brightness is represented by a positive voltage. Horizontal and Vertical intervals both have blanking so that retraces are not seen (invisible). Analog Video Signal Composite Frame Vertical Sync and Retrace Blanking Horizontal Line Blanking Sync 1/60 sec Horiz. Sync Pulses Active video: 51.8 u sec 63.6 u sec Slide by Professor Don Troxel Display Timing Generator Parameters HTOT = Horizontal Total HBS = Horizontal Blanking Start HSS = Horizontal Sync Start HSE = Horizontal Sync End VTOT = Vertical Total VBS = Vertical Blanking Start VSS = Vertical Sync Start VSE = Vertical Sync End Direct vs. Matrix Addressing Kim, SID 2001 Matrix Addressing Time multiplexed Row at a time scanning A column displayed during the time assigned to a row For a N rows by M columns display M + N electrodes are required Row scanning rate scales with number of rows Data rate scales with number of pixels Duty cycle scales with number of rows Tannas, SID 00 Applications Seminar Active Matrix Addressing Introduce non linear device that improves the selection. Storage of data values on capacitor so that pixel duty cycle is 100% Improve brightness of display by a factor of N (# of rows) over passive matrix drive Display element could be LC, EL, OLED, FED etc Yeh & Gu Grey Shades Generation Techniques Spatial Modulation Frame Modulation Amplitude Modulation Individually selectable Areas per pixel area per dwell time Reduced intensity by skipping frames per pixel area Analog intensity at full dwell time per pixel Grey Scale Generation (Spatial Modulation / Frame Rate Control) Kim, SID 2001 Grey Scale Generation (Amplitude Modulation) Kim, SID 2001 Color Generation Techniques Spatial Color Red Green Blue Sequential Color One broadband emitter per pixel area addressed three times per dwell time at three times the intensity. Coincident Color Red Green Blue Emitter Filter Three selectable color areas per pixel area per dwell time at three times intensity Electronic filter changed three times per dwell time. Three selectable transparent color areas per pixel area per dwell time at one times intensity Dwell time is allotted for each pixel operation Pixel area is total area allotted for spatial infomation Driver Circuits Row Driver Circuits Display Pixel Array Column Driver Circuits Row Driver Circuits Shift Registers N stage shift registers Static vs Dynamic Level shifters Match outside signal to signal on display N-stage shift register Output buffers Typically bi-level Level Shifters Buffers Column Driver Circuits Shift Registers N stage shift registers Static vs Dynamic Level shifters Match outside signal to signal on display N-stage shift register Sample and Holds or Comparators Analog or Digital Buffers Output buffers Typically bi-level Analog Data Driver Point at a time Shift Registers Line at a time Shift Registers Morozumi, SID 00 Seminar Notes Digital Data Drivers Shift Registers DACs Morozumi, SID 00 Seminar Notes Summary of Today's Lecture Overview Flat Panel Display Devices How do Displays Work? Emissive Displays (CRTs, FEDs, OLEDs, PDs) Light Valve Displays (AMLCDs, DMDs, EPDs) Display Drivers Addressing Schemes (Sequential, Direct, Matrix, Random) Display Timing Generator Gray Scale (Spatial, Frame, Amplitude) Color Schemes (Spatial, Sequential, Coincident) Emissive Displays Displays that generate photons when an electrical signal is applied between the terminals Energy causes excitation followed by relaxation Hole + Electron recombination Exciton formation and annihilation Relaxation of excited radicals in a plasma The different types of Luminescence differ mostly in the way the holes and electrons are generated holes and electrons are generated by UV in a phosphor which then recombine and generate red, green or blue light --Photoluminescence or Phosphorescence holes and electrons injected by pn junction or generated by impact ionization or excitation which then recombine and generate red, green or blue light -- Electroluminescence holes and electrons generated by electron beam which then recombine and generate red, green or blue light -- Cathodoluminescence Examples of Emissive Flat Panel Displays Electroluminescence (Light Emitting Diode, Organic-Light Emitting Devices & Inorganic ELectroluminescent Displays) Cathodoluminescence (Cathode Ray Tube, Vacuum Florescent Display, Field Emission Display) Photoluminescence (PLasma Displays) Light Valve Displays Displays that "spatially and temporally" modulate ambient lighting or broad source of light and redirect to the eye. Display element spatially changes the intensity of plane wave of light using Refraction Reflection Polarization change These displays are part of a broader class of devices called Spatial Light Modulators which in general operate though local Amplitude change Polarization change Phase change Intensity change Examples of Light Valve Displays Liquid Crystal Displays (active & passive matrix) Deformable Mirror Displays Membrane Mirror Displays Electrophoretic Displays (E-Ink) ...
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