Flat Panel Displays: Beyond The Basics

Transcription

1 Flat Panel Displays: Beyond The Basics Robert Dunhouse, Sr. Engineering Manager, Display BU Class ID: 4C03I Renesas Electronics America Inc.

2 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

3 Renesas Technology & Solution Portfolio 3

4 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

5 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 a follow-on to the LCD basics course. It addresses interfacing issues, display design considerations and what are some of the technologies available which target challenging environmental conditions. 5

6 Agenda Common LCD display interfaces General Design Considerations Challenges of Outdoor Viewing LED Drivers and Facts 6

7 Common LCD Interfaces 7

8 18-bit Parallel Digital CMOS R0 R1 R2 R3 R4 R5 G0 G1 G2 G3 G4 G5 B0 B1 B2 B3 B4 B5 6 color bits for each primary color (RGB) Minimum of 22 conductors not including power & grounds. 12 maximum cable length. Resolution up to SVGA (800 x 600). HSYNC VSYNC DE CLK 8

9 18-bit Single Channel LVDS R0 R1 R2 R3 R4 R5 G0 G1 G2 G3 G4 G5 B0 B1 B2 B3 B4 B5 LVDS Transmitter Low Voltage Differential Signal G0 R5 R4 R3 R2 R1 R0 B1 B0 G5 G4 G3 G2 G1 DE VS HS B5 B4 B3 B2 CLK Achieves 64 shades of gray and 262,144 colors. Reduced to 8 conductors not including power & grounds. Lower power differential signaling. Less susceptible to noise. Cable should be 100 Ohm twisted pair. Up to 10 meters. HS VS DE CLK 9

10 24-bit Single Channel LVDS R0 R1 R2 R3 R4 R5 G0 G1 G2 G3 G4 G5 B0 B1 B2 B3 B4 B5 R6 R7 G6 G7 B6 B7 LVDS Transmitter Low Voltage Differential Signal G0 R5 R4 R3 R2 R1 R0 B1 B0 G5 G4 G3 G2 G1 DE VS HS B5 B4 B3 B2 NC B7 B6 G7 G6 R7 R6 CLK Adds two more color bits/color to achieve 256 shades of gray, 16.7M colors. 10 conductors not including power & grounds. LVDS was originally used for XGA and above resolutions but is now found in VGA and above. HS VS DE CLK 10

11 24-bit 2 Channel LVDS Odd Pixels G0 B1 DE NC R5 B0 VS B7 R4 G5 HS B6 R3 G4 B5 G7 CLK R2 G3 B4 G6 R1 G2 B3 R7 R0 G1 B2 R6 Even and odd pixel data is sent through separate channels. Reduces the demands on cable bandwidth. Typically used for SXGA (1280 x 1024) & UXGA (1600 x 1200) resolutions. Even Pixels G0 B1 DE R5 B0 VS R4 G5 HS R3 G4 B5 R2 G3 B4 R1 G2 B3 R0 G1 B2 Four channel LVDS is used for QXGA (3M pixel) and QSXGA (5M pixel). NC B7 B6 G7 G6 R7 R6 CLK 11

12 LVDS Color Bit Mapping Standards G0 R5 R4 R3 R2 R1 R0 VESA B1 B0 G5 G4 G3 G2 G1 Video Electronics Standard Association DE NC VS B7 HS B6 B5 G7 B4 G6 B3 R7 B2 R6 Open LVDS Display Interface (Open LDI) CLK MSB color bits are mapped to the upper differential data pair. G2 R7 R6 R5 R4 R3 R2 JEIDA B3 DE NC B2 VS B1 G7 HS B0 G6 B7 G1 G5 B6 G0 G4 B5 R1 G3 B4 R0 Japan Electronic Industries Development Association CLK LSB color bits are mapped to the upper differential data pair. 12

13 LVDS Cable Construction 13

14 General Design Considerations 14

15 Power Sequencing VCC 3.0V ON OFF ON Display Signals 10us Tr < 30ms Toff > 50ms 0ms < t < 35ms VALID Period 0ms < t < 35ms Min & Max VCC-to-active video times must be met at startup Minimum VCC cycle time Once video is established there can be NO interruption of the control signals or VCC must be power cycled 15

16 Defining Timing Signals Four control signals CLK - Clock Also called Dot clock DE Data Enable When video data is actively written to the display HSYNC Horizontal Sync Resets the line scan VSYNC Vertical Sync Resets the frame scan Data signals 24-bit color RED0 RED7 GRN0 GRN7 BLU0 BLU7 16

17 Defining Timing Signals Hsync Data Enable Hsync cycle Hsync pulse width Hsync back porch Hsync front porch Horizontal display period Vsync Data Enable Vsync cycle Vsync pulse width Vsync back porch Vsync front porch N Vertical display period 17

18 Timing Worksheets 18

19 Image Retention 19

20 Image Retention Cross Section of LCD Glass Both positive and negative charged ionic contaminants exist in liquid crystal material. A DC voltage applied across the LC cell causes ionic alignment. AC drive disperses ionic concentrations. Over time a static image will create a DC component. Removal of the drive voltage leaves a weak residual field. 20

21 AC Drive V V source + VREF VCOM V source - FRAME 1 FRAME 2 FRAME 3 FRAME 4 FRAME N FRAME N+1 t V source + V source - V gate V gate VCOM C storage VCOM C storage 21

22 TFT Cell Model V drain C gd V gate C gs V source Re Co Cst Rlc Clc Vcom Re Electrode resistance Co Surface plate capacitance Rlc Liquid crystal resistance Clc Liquid crystal capacitance Cst Storage capacitance 22

23 Image Retention & Countermeasures Image retention exists in all Liquid Crystal Displays but to varying degrees. Newer panels use purified LC material, better alignment layer materials and have improved the wiping process during manufacturing. Ways to counteract image retention Use screensavers. Move image several pixels at a pre-determined period. Drive with full white or black image. Extreme image retention conditions drive the display as above and at high temperature (50C). High temperature improves mobility of the ionic contaminants. 23

24 Viewing Angle Technologies 24

25 Viewing Angle Technologies Twisted Nematic Fast response, limited viewing angles, most common, less expensive In Plane Switching Widest viewing angles, highest color stability, w/ overdrive comparable to TN response, black not as good as VA, most used in color critical applications. Vertical Alignment / Patterned VA Black better than TN, response slower, viewing angles inferior to IPS, contrast/color shift off angle viewing, vibration error. Multi-Domain Vertical Alignment Multiple LC alignment, better color stability than VA, viewing angles inferior to IPS, less transmissive. Optically Compensated Bend Fast 2ms response 25

26 The Challenges of Outdoor Viewing 26

27 Counteracting the Effects of Bright Light Preserving contrast not peak luminance is key. Most shop peak luminance what they buy is contrast. Methods to create outdoor viewing: Transmissive panels 2 methods Active Brute force adds many backlight elements to overpower the effects of sunlight. Passive Film or glass based enhancements. Transflective panels: Renesas offers 2 technologies SR-NLT - A reflective layer is added to the TFT layer. Using a patterned surface wide viewing angles are achieved. ST-NLT - A standard transmissive panel that adds a proprietary AR film and backlight recycling to create transflective properties. 27

28 SR-NLT Super Reflective NLT Backlight ON or OFF Highly reflective surface, great for direct sunlight applications where backlight is normally off for maximum power savings 28

29 ST-NLT Super Transmissive NLT Backlight ON High efficient backlight + proprietary AR 29

30 Contrast Ratio in Sunlight Direct Bonding ST-NLT Normal LCD 3:1 is minimum contrast ratio that can be seen in sunlight 30

31 SR-NLT Cross Section AR Polarizer Glass Substrate Reflective Layer Frequency shift due to longer light path Glass Substrate Polarizer 1. Texture is added to the reflective layer to increase viewing angle. 2. When light is reflected from different depths and angles the frequency of light changes. This spectral change is viewed as a multitude of colors. 3. The rainbow effect can be reduced at the expense of viewing angle. 31

32 SR-NLT Reflective Layer Backlight ON 32

33 SR-NLT Reflective Layer Backlight OFF 33

34 Advantages of ST-NLT & SR-NLT ST-NLT & SR-NLT products carry full manufacturer s warranty. NEC uses passive enhancements and avoids the reliability issues of brute force method. Most shop luminance what they buy is contrast. By increasing the peak (white) luminance, black level also rises making the panel no better in contrast. It may actually cause wash out. 34

35 LED Drivers and Facts 35

36 General LED Notes LED lifetime = 50% of the original luminance Lifetime figures are provided by the LED manufacturers and are for only the LED device itself. Actual panel lifetimes will be lower. High temperature is the enemy of LEDs. Some manufacturers use common anode and cathode LED strings. In this configuration an open or shorted LED series string will result in higher current flow through the remaining LED strings. With individual string connections select LED driver with independent branch regulation. Better maintaining luminance uniformity. 36

37 General LED Notes - continued Additional LED controller features: Open & short circuit protection Programmable configuration Dimming and current settings An automatic efficiency optimizer Reduces the LED forward voltage to minimize power Fault condition notification Dedicated output that sets a flag when an open or short condition is sensed 37

38 LED Driver Block Diagram VOUT Power Supply FB R TOP R BOTTOM COUT STR0 STR1 STR2 STRn 1N4148 FBO1 38

39 Relative luminance (%) LED vs. CCFL Temperature Performance *100% at 25C 6.5XGA (LED) 12.1XGA (LED) 12.1XGA (CCFL) Ambient temperature (C) LED luminance is better over temperature 39

40 Relative Luminance (%) LED Temperature (Hrs) Hours of Operation 40

41 Defect Specifications 41

42 Defect Specifications All manufacturers have defect specifications that define the maximum allowable pixel, mechanical and cosmetic defects. Many manufacturers do not include defect specs in their data sheets so ask. Include defect specs when comparing LCD displays from different manufacturers. Actual defect yields will be less. 42

43 Defect Specification - Example 5 or less bright red dots are allowed. 43

44 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 a follow-on to the LCD basics course. It addresses interfacing issues, display design considerations and what are some of the technologies available which target challenging environmental conditions. Feel smarter? There s more. Please attend the follow-on Advanced Technology Trends presentation. 44

45 Questions? 45

46 Please Provide Your Feedback Please utilize the Guidebook application to leave feedback or Ask me for the paper feedback form for you to use 46

47 Renesas Electronics America Inc.

48 Appendix Summary Timing Worksheets LCD Defect Specification LCD Handling Procedures 48

49 Appendix - Timing Worksheets 49

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60 Appendix LCD Defect Specification 60

61 LCD panel inspection should be before any panel is assembled into the final product or its associated sub-assemblies 61

62 What s found in a Defect Specification? Bright Dot Category Dark Dot Category Bright and Dark Dot Combination Category Line Defect Category Inspection Condition This presentation will show an example of a 6.5 NL6448BC20-08E defect specification. All other Defect Specifications from other sizes can be followed similarly. 62

63 Bright Dot Category Highlighted is a Bright Dot Category from a 6.5 NL6448BC20-08E defect specification Note: One Dot refers to one Subpixel of a pixel. A pixel contains 3 sub-pixels of Red, Green and Blue. Dot and Sub-pixel are used interchangeably. 63

64 Dark Dot Category Highlighted is a Dark Dot Category from a 6.5 NL6448BC20-08E defect specification 64

65 Bright and Dark Dot Combinations Highlighted is a Bright Dot and Dark Dot Combination Category from a 6.5 NL6448BC20-08E defect specification 65

66 Line Defect Category Highlighted is a Line Defect Category from a 6.5 NL6448BC20-08E defect specification 66

67 Inspection Conditions Highlighted is the Inspection conditions where certain requirements should be met before evaluation. 67

68 Inspection Conditions Panel inspection should be at a room temperature of about 25 degrees Celsius. The panel should be at a distance of about 8 in or 20cm from your eyes and is viewed from its front center perpendicular surface. Inspection angles can vary from 20 degrees left/right and/or 20 degrees up when measured from front center perpendicular. The ambient room illumination measured on the front panel surface should be about 60 lx, which is about equivalent to 6 burning candles one foot away from the panel. Basically this is a low light condition. 68

69 What Are You Looking For? You Are Looking For: Bright Dots (sub-pixels) explained under the Bright Dots Category Dark Dots (sub-pixels) explained under "Dark Dot Category Bright and Dark Dots combinations (sub-pixels) explained under the "Bright and Dark Dots combination Category Line Defects under "Line Defect Category" 69

70 Best Image for Bright Dots The best image to look for a bright dot is on an all black image. 70

71 Best Image for Dark Dots The best image to look for a dark dot is on an all white image. 71

72 Best Image for Bright and Dark Dot Combination If you feel you've seen both (Dark and Bright Dots) and you're questioning the Allowable combination of both Dark and Bright dots, then the best image to view these are on a gray image where the dark and bright dots can be seen together. 72

73 Dot Defect Examples in Close Up View Black Image Shows Bright Dot defects Close Up View White Image Shows Dark Dot Defects Close Up View 73

74 Bright Dot Category and Other Categories The Bright Dot defect category will be reviewed here. The other categories will not be reviewed as they are similar to the Bright Dot defect category. The Line Defect category is self-explanatory. If either a bright or dark line defect is observed the panel is considered defective and should be returned. 74

75 Appendix Bright Dot Category Reviewed 75

76 Red Dot Condition 5 or less bright red dots are allowed. 76

77 Green Dot Condition 3 or less bright green dots are allowed. 77

78 Blue Dot Condition 5 or less bright blue dots are allowed. 78

79 Red + Green + Blue Dot Condition Total combined bright dots (of all colors) must be 5 or less 79

80 Linked Defects of 2 dots of same color When 2 bright dots of the same color are linked, the panel is defective. Further details are explained on following slides. 80

81 Definition of Linked Dots Linked dots are dots that are adjacent horizontally, vertically or diagonally 81

82 Two Linked Bright Dots of Same Color 1 set of bright dots single color (red) are shown as an example. There are 3 possible color combinations. Patterns of this type are NOT allowed 82

83 Two Linked Bright Dots of Different Colors When 2 bright defect dots of different colors are linked, the panel is not considered defective. Further details are explained in the next slide. 83

84 Two Linked Bright Dots of Different colors 3 sets of bright dot defects each with two colors of red and green are shown as examples. There are 9 sets of any two color patterns possible. Patterns of this type are allowed until Red, Green or Blue conditions are exceeded. 84

85 Linked Bright Dot Defects of 3 or More When 3 or more bright defect dots of different or same colors are linked, the panel is considered defective. Further details are explained in the next few slides. 85

86 Three Bright Dots or More (Single Color) 1 set of bright defect dots in a single color of red are shown as an example. There are three possible combinations (3 red or 3 blue or 3 green). Patterns of this type are NOT allowed. 86

87 Three Bright Dots or More (Dual Color) 10 sets of 3 linked bright dot defects each with 2 colors of red and green are shown as examples. There are 30 possible combinations. Patterns of this type are NOT allowed. 87

88 Three Bright Dots or More (Triple Color) 9 sets of 3 linked different color bright dot defects are shown as examples. There are 27 possible combinations. Patterns of this type are NOT allowed. 88

89 Close Defect Dots of Same Color D 6.5mm D denotes the distance between two defective dots. Panels with same color bright dots which are 6.5 mm or less apart are considered defective. 89

90 Close Defect Dots of Same Color D 6.5mm Using the as an example, if Da is less than or equal to 6.5 mm the panel is defective. An easy way to measure 6.5 mm is in pixels. The panel s pixel width is 0.20 mm. Dividing 6.5mm by the pixel width of 0.20mm yields 32.5 pixels. If two defects dots are 33 pixels or less distance then the panel is defective. 90

91 Close Defect Dots of Different Colors D 6.5mm Panels with different color bright dot defects which are 6.5 mm or less but greater than zero are allowed. Panels with bright dot defects greater than 6.5 mm apart are allowed. 91

92 Close Defect Dots of Different Colors D 6.5mm Da 6.5mm, Db 6.5mm If two or three defective pixels of same color are greater than 6.5mm apart then the panel is still considered good and allowable. If defective pixels are either greater or lesser than 6.5mm apart and different colors from either other, the panel is still considered good and allowable. 92

93 Appendix Appearance Specification 93

94 Appearance Specification Dust, Stain Category Bubble, Wrinkle, Dent Category Scratch Category Inspection Condition 94

95 Dust, Stain Category Highlighted is the Dust, Stain Category 95

96 Bubble, Wrinkle, Dent Category Highlighted is the Bubble, Wrinkle, Dent Category 96

97 Scratch Category Highlighted is the Scratch Category 97

98 Inspection Condition Highlighted is Inspection Condition 98

99 Inspection Condition Panel inspection should be at a room temperature of about 25 degrees Celsius. The panel should be at a distance of about 8 in or 20cm from your eyes and is viewed from its front center perpendicular surface. Inspection angles can vary from 45 degrees left/right and/or 45 degrees up/down when measured from front center perpendicular. The ambient room illumination measured at the inspection table should be about 700 lx, which is about equivalent to 70 burning candles one foot away from the panel. Basically this is a bright office lighting condition. 99

100 Dust, Stain Category If dust or stains in either dot or line shapes are over the size as defined above the panel is defective. 100

101 Bubble, Wrinkle, Dent Category If a bubble, wrinkle or dent is greater than the size Defined above the panel is defective. 101

102 Scratch Category 102

103 Appendix LCD Handling Procedures 103

104 General Handling Procedures 1. The LCD module should be removed from the shipping box by holding the panel frame at the sides. Be careful to not grasp the circuit boards or cable connections. 2. Do not use any connector or cable to aid in removing the panel from the packaging. Also, be careful not to allow these to snag during removal. 3. To move the panel temporarily, the panel should always be placed on a flat, clean surface with the display side down and with the clear protective film in place. 4. Do not press or rub the display surface as damage may result. If it is necessary to clean the surface always use a clean, soft & lint free cloth with a ethanol based LCD screen cleaner. 5. Take all necessary pre-cautions to prevent Electro Static Discharge (ESD) as damage may result. 6. When handling, it is advisable to use the clear protective film provided with each display to protect against scratches to the outer surface polarizer. Use of adhesive type protection films is not recommended. 7. Remember, the panel is made of glass. Do not attempt to handle if broken. 104

105 General Operating Precautions Caution symbols found in the LCD specification 1. Incorrect operation of this component may result in personal physical injury. Review & understand the following precautionary symbols: Incorrect operation will result in damage to the LCD or personal injury. Incorrect operation will result in electrical shock. Examples: Incorrect operation will result in personal physical injury. Do not remove or disturb any connection during operation as this would result in incorrect power sequencing and damage may result. Do not bend the lamp cables as breakage may occur resulting in failure of the lamps and possible exposure to high voltage electrical shock. Do not touch a working backlight as burn injuries may result. Do not subject the panel to shock exceeding 539m/s² for 11ms or pressure exceeding 19.6N as glass breakage may result. 105

106 Environmental Precautions 1. Do not store or operate in high temperature, high humidity environments or where condensation is likely to occur. 2. When preparing to use a LCD panel stored in low temperatures, it is recommended to allow the LCD to warm in it s original packing box for a period of time that insures slow warming. This is necessary to avoid condensation from occurring. NEC recommends 6 hours or more in the original packaging. 3. Do no store or operate in corrosive environments. 4. For long term storage use the provided anti-static bag and avoid exposure to sunlight & dust. Store at room temperature. 5. Do not operate in high magnetic fields as circuits may fail. 6. This product is not designed to be free from Radio Frequency Interference (RFI) 106

107 General Mechanical Considerations 1. Install the LCD module using the provided mounting holes. Care should be taken to insure the mounting locations are in a true flat plane and that the hole centers are correctly located. Any undue stress to the LCD frame will cause problems with video uniformity and in worst cases may break the glass. 2. The torque for the mounting locations should never exceed 0.249N m as distortion of the frame bezel may result. 3. Do not disassemble or adjust variable resistors as this will alter operation and void warranty. 107

108 Handling Precautions LCD modules should be vertical and separate! 108

109 Handling Precautions Do not stack LCD modules! 109

110 Handling Precautions Only remove protective film at final assembly! 110

111 Handling Precautions Keep in clean area. There are many entry points for dirt! 111