Flat Panel Displays: LCD Technologies and Trends Robert Dunhouse, Sr. Engineering Manager, Display BU Class ID: 4C01B Renesas Electronics America Inc.
Robert F. Dunhouse, Jr. Sr. Engineering Manager, Display BU North American Apps Engineering manager 15+ years engineering experience with NEC LCD Displays. Design demonstration computers and display housings for field demo program. Circuit design & board layout of display interfaces. Mechanical design of equipment housings. Work directly with NLT Technologies Japan to solve technical issues and help define future products. De-bug customer applications and provide design guidance. Over 25 years experience in the electronics industry Research & development at Cincinnati Microwave (founders of ESCORT radar detectors) Opened a branch office in Sydney Australia Founded US design and manufacturing company Creative Circuits 2
Renesas Technology & Solution Portfolio 3
Display Module Solutions Sophisticated solutions Sustainable support LED Backlight LCDs Low power consumption Long life LEDs Thin profile and light weight design Replaceable LED light source unit Enhanced View TFT (EVT) Suited for a variety of ambient-light environments Proprietary transflective LCD technologies Reflective-Enhanced View TFT (R-EVT) Transmissive-Enhanced View TFT (T-EVT) Wide Format LCDs Super-Fine TFT (SFT) More data on a single screen 16:9 aspect ratio High luminance and wide color gamut Superior image quality Ultra-wide viewing angles Industrial Mobile Displays Emerging Technologies Robust feature sets Long-term product support Amorphous silicon (A-Si) displays Low-temperature polysilicon (LTPS) displays 2D/3D displays On-cell touch PCAP touch 4
Enabling The Smart Society Challenge: As the technology driving today s smart society evolves the manto-machine interface remains one of the most critical components. Understanding and selecting the right display with the right capabilities for your product is key. Solution: This course is an introduction into Liquid Crystal Displays. The discussion will include how they work, how they are made, common industry terms and definitions and follows with a common sense step-by-step selection method. 5
Agenda Overview of an LCD display module Liquid Crystal Displays work as light valves Terms, Definitions & Measurements LCD Selection Checklist 6
Building a TFT LCD Display 7
Backlight Light guide Back reflective sheet CCFL or LED Diffusion sheet Backlight assembly frame 8
TFT Glass Assembly TFT glass assembly TFT column driver TAB Timing controller board TFT row driver TAB Row board 9
Marriage of Assemblies 10
A Closer Look at the TFT Glass Assembly Alignment layer Color filter ITO common electrode Outer polarizer Outer Glass Substrate Epoxy sealer Short Bonding pad Alignment layer a-si TFT layer & pixel electrode (ITO) Inner glass substrate Inner polarizer Ball spacer LC material 11
How LCD Displays Work as Light Valves 12
The Liquid Crystal Cell 13
Light Passing Through 14
Primary Color TFT Cells 15
Common Terms and Definitions 16
Size Size = Diagonal measurement of the active video area. 17
Resolution Pixels Lines Resolution = Horizontal pixels x Vertical lines Ie. 640 x 480 is 640 pixels by 480 lines or one video frame. Total Thin Film Transistor (sub-pixel) count would be: 640 x 3 x 480 = 921,600 18
Contrast Ratio Contrast ratio = White luminance/black luminance Black is not absolute. When measuring, white must be driven. 19
Color Filter LCD display color filters are arranged in Red, Green & Blue vertical stripes. 20
Pixels & Lines One pixel is made of three sub-pixels. Red, green & blue are the primary colors. Pixel pitch is the distance between any two like color sub-pixels Rows of pixels make up one line. 21
Viewing Angle θl θu θd θr Viewing angle is measured from center perpendicular to where contrast ratio decreases to 10:1. Specmanship happens when comparing viewing angles of 5:1 contrast ratio. 12 O clock viewing is θu and 6 O clock is θd from the panel s perspective. 22
TN Viewing Angle Characteristics Standard TN (Twisted Nematic) panels have optimized vertical viewing angles Wash out loss of contrast Color inversion colors darken and invert. Appears like a film negative effect. 23
Gray Scale Gray scale is the transition from white to black. Color is superimposed over gray scale to determine all the various shades of that color. LCD displays are typically either 18-bit or 24-bit color. This is defined as the number of color bits for each primary color times three. 24- bit color = 8 bits of Red + 8 of Green + 8 of Blue Total different colors displayed: 2²⁴ = 16.7 million 24
Color Gamut The CIE 1931 diagram represents the total colors the human eye can perceive. CIE 1931 Chromaticity Diagram NTSC Standard Red 0.67, 0.33 Green 0.21, 0.71 Blue 0.14, 0.08 White 0.3101, 0.3162 The color gamut of an LCD display is stated as a percentage of the National Television Standards Committee (NTSC) standard. In this example the LCD reproduces 40% of the NTSC standard. 25
Panel Response White Luminance 100% 90% Black 10% 0% Ton Toff 26
Panel Response Notes The lower the number the better Be sure the measurement represents black-to-white-to-black times. Specmanship happens when only showing one way time. Traditional measurement method is white-to-black. In reality rarely is an image switched this way so newer comparisons will specify gray-to-gray switching times. Surprisingly gray-to-gray times can be larger than white-to-black. Response Time Compensation momentarily applies an overvoltage to the TFT cell to quicken crystal alignment. 27
Peak Luminance 50cm Photometer 1 degree focal angle Peak luminance is measured with an optical photometer placed 50cm from the center perpendicular front surface of the display. Measurements are taken in dark room conditions. Same test setup is used to measure contrast ratio. 28
Luminance Uniformity 1 2 3 4 5 Luminance uniformity defines how well an LCD maintains even luminance over the total surface of the display. Maximum and minimum luminance measurements are made in 5 locations. Luminance uniformity = Max Luminance (1 to 5) / Min Luminance (1 to 5) 29
LCD Selection Checklist 30
LCD Selection Checklist Panel size Select a general size based on your preliminary design. Remember to include margin for frame components. Resolution What clarity of image is needed? The higher the resolution the clearer the image appears. Does the manufacturer have an upgrade path? How much information needs to be displayed and once its translated to the video image will it be useable? Do you need normal aspect or wide format? 4:3 is typical, 16:9 is the newer wide format. Color or monochrome? 31
LCD Selection Checklist What format is your video source? Analog RGB Parallel digital CMOS LVDS single, dual or four channel Composite or S-Video DVI Digital Visual Interface HDMI High Definition Multimedia Interface Does the video format match the display? Yes video source and panel are compatible No A video interface will needed to convert the video source format to one compatible with the panel. 32
LCD Selection Checklist What type of backlight? LED or CCFL? Most new products have transitioned to LED LEDs may still have a slight initial cost disadvantage Reduction of Hazardous Substances (RoHS) has driven the change to LED LEDs are now more energy efficient, have longer lifetimes and are more mechanically robust. 33
LCD Selection Checklist Does the LCD module include a backlight driver? CCFLs use high voltage AC inverters. Safety concerns for medical applications Switching noise considerations LEDs uses constant current drivers. Typical LED string forward voltage is below 40VDC EMI low Both are approximately the same in cost. LED driver board footprints can be small. 34
LCD Selection Checklist Power Newer generation LED backlit panels are generally lower power. For maximum power savings consider a reflective technology LCD. These panels enable the user to turn off the backlight in higher ambient lighting. The new e-paper displays only consume power when writing a new image. Once the image is written ALL power can be removed. Certain premium viewing angle technologies consume more logic power. 35
LCD Selection Checklist What environment will the panel be used in? Indoor or outdoor Temperature Moisture Direct sunlight exposure Solar thermal loading Preservation of contrast Vandal proof Shock & vibration requirements? Industrial rated panels have higher shock, vibration & temperature parameters. Industrial panels tend to be mechanically larger than commercial panels. Frames are more robust and backlights brighter. 36
LCD Selection Checklist Bottom line is the best test is your eyes. Schedule a side-by-side comparison of several panels that look good on paper. The Renesas Display Business Unit has an easy to use demo system. 37
Enabling The Smart Society Challenge: As the technology driving today s smart society evolves the manto-machine interface remains one of the most critical components. Understanding and selecting the right display with the right capabilities for your product is key. Solution: This course is an introduction into Liquid Crystal Displays. The discussion will include how they work, how they are made, common industry terms and definitions and follows with a common sense step-by-step selection method. Feeling smarter? There s more. Please attend the follow-on Beyond the Basics presentation. 38
Questions? 39
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