1. ID C10C: Flat Panel Display Basics
Robert Dunhouse, Display BU
Engineering Manager
12 October 2010
Revision 1.1
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2. Robert F. Dunhouse, Jr. Displays Applications Engineering Manager
Application Engineering support for North America
Electrical & mechanical consultation. Customer equipment debugging.
Direct communication with NEC LCD Technologies in Japan to resolve technical issues and advise direction for future designs.
Design demonstration computers and display housings for field demo program. Includes circuit design & circuit board layout of LCD video interfaces and mechanical design of equipment housings.
14 years engineering experience with NEC LCD Displays.
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
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3. Display Module Solutions
Robust feature sets
Long-term product support
Amorphous silicon (A-Si) displays
Low-temperature polysilicon (LTPS) displays
Industrial Mobile Displays
Low power consumption
Long life LEDs
Thin profile and light weight design
Replaceable LED light source unit
LED Backlight LCDs
Suited for a variety of ambient-light environments
Proprietary transflective LCD technologies
Super Reflective NLT (SR-NLT)
Super Transmissive NLT (ST-NLT)
Natural Light TFT (NLT)
Sophisticated solutions Sustainable support
2D/3D displays
Color enhancement
E-paper
On-cell touch
Emerging Technologies
Here are the Display Module Solutions. I am not going to cover any specific information on these solutions, but rather I want to show you where this session is focused
High luminance and wide color gamut
Superior image quality
Ultra-wide viewing angles
Super-Fine TFT (SFT)
More data on a single screen
16:9 aspect ratio
Wide Format LCDs 3
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4. Display Module Solutions
Emerging Technologies
Robust feature sets
Long-term product support
Amorphous silicon (A-Si) displays
Low-temperature polysilicon (LTPS) displays
Industrial Mobile Displays
New 2/3 dimensional displays
Color enhancement
e-Paper
On-cell Touch
Long Term Support/Production
Low power consumption
Long life LEDs
Thin profile and light weight design
Replaceable LED light source unit
LED Backlight LCDs
Suited for a variety of ambient-light environments
Proprietary transflective LCD technologies
Super Reflective NLT (SR-NLT)
Super Transmissive NLT (ST-NLT)
Natural Light TFT (NLT)
Sophisticated solutions Sustainable support
2D/3D displays
Color enhancement
E-paper
On-cell touch
Emerging Technologies
These are the Devices and Solutions where this presentation applies
High luminance and wide color gamut
Superior image quality
Ultra-wide viewing angles
Super-Fine TFT (SFT)
More data on a single screen
16:9 aspect ratio
Wide Format LCDs 4
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5. Innovation
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6. Innovation
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7. Our High Performance Liquid Crystal Displays
Renesas has an extensive lineup of “Industrial” grade Liquid Crystal Displays.
Our products are designed with extended shock, vibration & temperature standards, enhanced front of screen performance and long product cycles.
We demonstrate industry leading technologies in transflective, high resolution, high color, 3D, e-Paper and low power portable displays all to help solve many of today’s design challenges.
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8. Agenda Overview of an LCD display module
Liquid Crystal Displays work as light valves
Terms, Definitions & Measurements
LCD Selection Checklist
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9. Key Take aways
You will be able to speak intelligently about LCD displays
You will be able to make informed decisions when selecting a new panel for your project.
You will have enough background to attend the follow up session “Beyond the Basics” to learn about more advanced design considerations.
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10. Remember these?
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11. And now this!
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12. Selecting the Best Display
How things have changed!
Selecting the right Liquid Crystal Display determines the “face” of your product and ultimately its success. It is likely the most expensive and influential component so getting it right the first time is a must.
This presentation is an entry level exposure to Liquid Crystal Displays (LCDs). It is intended to provide enough information to understand how they work, the common terms used in the industry and demonstrate a method in which to select from the many displays available in today’s market.
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13. Building a TFT LCD Display
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14. Backlight Light guide Back reflective sheet CCFL or LED
Diffusion sheet
Backlight assembly frame
Light guide – Clear acrylic with polished ends for maximum light coupling. Used to channel light from the CCFL or LED light rails through the TFT glass assembly
1. Slab – Used for double edge lit panels. Disadvantage is heavy and thick.
2. Wedge – Used for single edge lit panels. Advantage is lighter & smaller. Disadvantage may not be as bright.
Reflection Sheet
1. Film based. Used to reflect and direct light through TFT glass assembly
CCFL or LED Light Rails – light sources driven normally by external circuit boards
1. Majority of all new products will be LED
2. Conversion from CCFL to LED is driven by the Reduction of Hazardous Substances started in Europe.
3. We use field
Diffusion Sheet
1. Used to “diffuse” the light being channeled through the TFT display. It creates and even light plane.
Backlight Assembly Frame
2. Provides the mechanical structure needed to complete the backlight assembly
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15. TFT Glass Assembly TFT glass assembly TFT column driver TAB
Timing controller board
TFT row driver TAB
Row board
TFT Glass Assembly
1. Complex glass assembly
TFT Column Driver TABs
1. Flexible polyimide circuit populated with bonded column (source) driver IC (TAB). Heat bonded to the TFT glass table on one end and the Timing Controller (TCON) board on the other.
2. Responsible for controlling each sub-pixel.
3. This TAB circuit along with the TCON board is wrapped around the back side of the light guide.
Timing Controller Board
1. Main control board. Contains an ASIC video signal timing controller, DC-DC voltage conversion & gray scale generator.
TFT Row Driver TABs
1. Flexible polyimide circuit populated with bonded row (gate) driver IC (TAB).
2. Responsible for controlling the line writes.
Row Driver Board
1. Row driver TABs mount and pass control information.
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16. Marriage of Assemblies
TFT glass assembly and backlight assemblies are “married” together. Front bezel frame is added to finalize the product.
Three different mounting methods
Corner
Edge
Capture
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17. A Closer Look at the TFT Glass Assembly
Color filter
Outer polarizer
ITO common electrode
Alignment layer
Outer Glass Substrate
Epoxy sealer
Short
Ball spacer
Bonding pad
LC material
Alignment layer
Outer glass substrate. Glass thickness varies between 0.7, 0.5 and 0.3mm. Common is 0.5mm for 5.0” and above.
Color filter – RGB vertical stripe
Inner alignment layer – Polyimide film layer “wiped” with a roller in production to create alignment “grooves”.
Outer polarizer
Inner glass substrate
Thin Film Transistor (TFT) layer
Protection layer – used to protect the TFT layer during production
Inner alignment layer
Epoxy sealer – UV cured sealer
a-Si TFT layer & pixel electrode (ITO)
Inner glass substrate
Inner polarizer
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18. How LCD Displays Work as Light Valves
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19. The Liquid Crystal “Cell”
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20. Light Passing Through
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21. Primary Color TFT Cells
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22. Common Terms and Definitions
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23. Size Size = Diagonal measurement of the active video area.
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24. Resolution Resolution = Horizontal pixels x Vertical lines Pixels
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
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25. Contrast Ratio Contrast ratio = White luminance/Black luminance
Black is not absolute.
When measuring, white must be driven.
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26. Color Filter
LCD display color filters are arranged in Red, Green & Blue vertical stripes.
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27. 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.
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28. Viewing Angle θU θR θL θD
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.
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29. 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.
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30. 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: 2 = 16.7 million
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31. Color Gamut
CIE 1931 Chromaticity Diagram
The CIE 1931 diagram represents the total colors the human eye can perceive.
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.
NTSC Standard Red – 0.67, 0.33
Green – 0.21, 0.71
Blue – 0.14, 0.08
White – ,
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32. Panel Response White Luminance Black Ton Toff 100% 90% 10% 0%
Panel response is the time in which it takes the Liquid Crystal molecular chain to re-align and change states from white to black (Ton) and black to white (Toff). This is defined as the total response time.
Response is measured with a a photo detector. Ton is measured from 90% of full luminance to 10% of full luminance.
Luminance
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33. The lower the number the better
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.
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34. 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.
Peak luminance is measured in dark room conditions.
An optical photometer is placed 50cm from center perpendicular front surface of display with an optical focal angle of 1 degree.
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35. 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)
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36. LCD Selection Checklist
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37. 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?
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38. 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.
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39. 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.
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40. 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.
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41. 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.
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42. 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.
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43. 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.
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44. Action Obtain several LCD datasheets for comparison purposes.
Attend the follow up session ID C22C: Flat Panel Displays “Beyond the Basics” to learn more advanced design and integration considerations. The session is in room Royal E&F at 5:15-6:15PM.
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45. Innovation
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46. Questions?
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47. Thank You
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