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Smart Driver for Power Reduction in Next Generation Bistable Electrophoretic Display Technology

Smart Driver for Power Reduction in Next Generation Bistable Electrophoretic Display Technology. Michael A. Baker Aviral Shrivastava Karam S. Chatha Arizona State University Tempe, Arizona, USA October 4, 2014. Power: A Critical Constraint in ES.

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Smart Driver for Power Reduction in Next Generation Bistable Electrophoretic Display Technology

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  1. Smart Driver for Power Reduction in Next Generation Bistable Electrophoretic Display Technology Michael A. Baker Aviral Shrivastava Karam S. Chatha Arizona State University Tempe, Arizona, USA October 4, 2014

  2. Power: A Critical Constraint in ES • Impact of energy consumption of embedded systems • Most important factor in usability of electronic devices • Performance/Power requirements of handhelds • Increase by 30X in a decade • Battery capacity • Increase by 3X in a decade • Considering technological breakthroughs, e.g. fuel cells

  3. Displays: Major power consumer • LCDs consume 30-60% of power in handhelds • Up to 90% is due to backlight • HP iPAQ • 320 x 240 QVGA LCD consumes 220 mW

  4. Electrophoretic Displays (EPDs) • 320 x 240 QVGA display • < 15 mW (Compare to 220 mW for LCD) • 14X less power consumption • Much Higher reflectivity • Similar to newspaper • Usable in bright sunlight • Extremely thin ~1.7 mm (Compare to 3mm of LCDs) • Wider viewing angle ~170o (Compare with 120o for LCDs) • Extremely durable and flexible • Wearable computers • Displaying static images with almost zero power

  5. Agenda • Electrophoretic Displays • Contribution • Previous Work • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  6. EPD: A Bistable Display Technology • Information remains for hours or weeks without power • Tremendous energy savings in static image applications • Electronic paper / Books • Slide Show • Signs / Advertising • Future displays to provide color and motion, where bistable memory has advantages Image: Plastic Logic Limited, UK

  7. EPD Technology • Electrically charged particles physically displaced by electric field • Resolution independent of capsule size

  8. Capsule diameter about 50μm ~ 6 capsules/subpixel ~ 17 capsules/pixel + - + - E-Ink Corp. EPD Technology pixel array (greyscale) capsule Negatively charged pigment particle Positively charged pigment particle

  9. Agenda • Electrophoretic Displays • Contributions • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  10. Contributions • Power characterization and modeling of EPDs • Device drivers to use them in video applications • Exploit EPD properties to further optimize performance and save power?

  11. Agenda • Electrophoretic Displays • Contributions • Related Work • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  12. Previous Work • EPD technology studied for over 30 years • Fundamental Properties • [1] EPD Characterization of colloidal suspension (Phillips Laboratories, 1977 ) • [2] Model for driving EPDs (Xerox Research Center of Canada, 1979) • [3] EPD ink and capsule characterization (MIT Media Laboratory, 1998) • Simulation • [4] EPD properties and simulation (Ghent University, 2005) • Applicable LCD driver power reduction efforts • [5] Reducing driver cost in active matrix displays (Texas Instruments, 1982) [1] A. L. Dalisa, “Electrophoretic Display Technology”, IEEE Transactions on Electron Devices, Vol. ED-24, No. 7, July 1977 [2] M. A. Hopper, V. Novotny, “An Electrophoretic Display, Its Properties, Model, and Addressing”, IEEE Transactions on Electron Devices, Vol. ED-26, No. 8, August 1979 (Model for driving EPDs) [3] B. Comiskey, J. D. Albert, H. Yoshizawa, J. Jacobson, “An electrophoretic ink for all-printed reflective electronic displays”, Nature 394, 253-255, 16 July 1998 [4] T. Bert, H. De Smet, F. Beunis, K. Neyts, Complete electrical and optical simulation of electronic paper, Science Direct, 13 October 2005 [5] W. Marks, “Power Reduction in Liquid-Crystal Display Modules”, IEEE Transactions on Electron Devices, Vol. ED-29, No. 12, December 1982

  13. Agenda • Electrophoretic Displays • Contributions • Related Work • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  14. Physically Modeling EPD Capsule • Particle velocity requirement derived from capsule diameter and frame write period • Particle velocity drives mobility requirement determining suspension fluid viscosity capsule diameter Particle mobility: Suspension fluid viscosity:

  15. EPD Capsule Power Model • Particle motion analogous to current in a resistor • Storage capacitor • Large capacitor per RGB sub-pixel (8.6 pF) • Capsule capacitance is small (<1 pF) • Charge capacitor during row scan then discharged after frame period • Required due to relatively slow electrophoretic response

  16. Capacitor Energy Dissipation EPD Capsule Power Model • Model uses storage capacitor energy stored during row-write to calculate power • Sequential row-write power equivalent to instantaneous display power V(s_cap.)

  17. Agenda • Electrophoretic Displays • Contributions • Previous Work • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  18. Smart Bistable Display Driver How can we exploit EPD properties to increase power performance?

  19. Smart Bistable Display Driver • Naive Driver • 100% of image redrawn during refresh or update • Even if portions of the image remain unchanged in the new image • Wastes energy since display retains unchanged portions anyway

  20. 1 pixel: RGB sub-pixels Smart Bistable Display Driver • Smart Driver • Unchanged pixels not addressed when new image is drawn--no image degradation • If the 8 bit data value of any subpixel changes, the pixel is updated Pixel data values: R:11111111 B:11111111 G:11111111 (R:255) (B:255) (G:255)

  21. 0 1 2 3 4 5 6 7 Bits ignored: 8 bit value (x3 subpixels): Binary Value: 255 11111111 254 11111110 252 11111100 248 11111000 240 11110000 224 11100000 192 11000000 128 10000000 Smart Bistable Display Driver • Lazy Drivers (Modified Smart Driver) • Similar pixels not addressed when new image is drawn--image degradation • Some number (1-6 / 8) of LSB from Pixel component values ignored during decision comparison • Max pixel color impact due to ignoring bits during comparison:

  22. R G B 011 111 001 01100011 11101110 00100011 011 110 001 01101100 11111010 00110100 011 111 001 011 111 001 Lazy Driver Example • Lazy driver configured to ignore specific number of LSBs. • Example: Lazy Driver ignoring 5 bits: 01100011 11101110 00100011 Current value: 01111010 11001100 00111111 Next value: Change, pixel is updated No change, pixel is not updated

  23. Agenda • Electrophoretic Displays • Contributions • Previous Work • EPD Power Model • Display Driver • Naive Driver • Smart/Lazy Driver • Results • Conclusion

  24. Driver Simulation • Simulator takes series of bitmaps extracted from video stream as input • Outputs series of bitmaps altered in accordance with each driver scheme • Power is calculated based on the number of pixels written in each row • Capacitor energy stored in the drive capacitors energy expended per row write

  25. Video 1: Display Power

  26. Video 1: Display Power

  27. Baroness frame 29 Elecard Ltd. Video 1: Image Degradation no degradation 4 bits 5 bits 6 bits

  28. Video 1: Image Degradation 4 bits Original 5 bits 6 bits Baroness frame 29 5 bits 6 bits

  29. Energy Savings vs. QOS

  30. QOS and Power Savings Results

  31. Ongoing work in EPD • Generating Greyscale • Complex driving waveforms used to generate grayscale • Area Ratio Grayscale also used to achieve gray levels • Producing Color EPDs • Different color pigment particles • Frontplane filters • Improving Response time • Particle mobility Sony E-Book with E-Ink 4 bit waveform driven grayscale 9 gray level ARG element E-Ink Color EPD Prototype

  32. Conclusion • Bistability of electrophoretic displays enables power savings via smart drivers • Smart driver might take advantage of context or user preferences to expand power reduction in exchange for picture quality E-Ink Bendable Clock

  33. + - Questions?

  34. References 1. W. Cheng, Y. Hou, M. Pedram, Power Minimization in a Backlit TFT-LCD Display by Concurrent Brightness and Contrast Scaling, Design, Automation and Test in Europe Conference and Exhibition, Vol.: 1, pp. 252 - 257, 2004 2. I. Choi, H. Shim, N. Chang, Low-Power Color TFT LCD Display for Hand-Held Embedded Systems, International Symposium on Low Power Electronics and Design, August 12-14, 2002 3. NEC NL2432HC17-01B QVGA LCD for mobile applications with touch panel specification 4. F. Gatti, A. Acquaviva, L. Benini, B. Ricco’, Low Power Control Techniques For TFT LCD Displays, CASES, October 2002 5. A. L. Dalisa, Electrophoretic Display Technology, IEEE Transactions on Electron Devices, Vol. ED-24, No. 7, July 1977 6. S. Inoue, H. Kawai, S. Kanbe, T. Saeki, T. Shimoda, High-Resolution Microencapsulated Electrophoretic Display (EPD) Driven by Poly-Si TFTs With Four-Level Grayscale, IEEE Transactions on Electron Devices, Vol. 49, No. 8, August 2002 7. LTSpice manual 8. L. Blackwell, LCD Specs: Not So Swift, PC World, Friday, July 22, 2005 9. Ghent University Liquid Crystals & Photonics Group, http://www.elis.ugent.be/elisgroups/lcd/research/elektink.php 10. B. Comiskey, J. D. Albert, H. Yoshizawa, J. Jacobson, An electrophoretic ink for all-printed reflective electronic displays, Nature 394, 253-255 (16 July 1998) 11. S. Vermael, K. Neyts, G. Stojmenovik, F. Beunis, L. Schlangen, A 1-Dimensional Simulation Tool for Electophoretic Displays, Fourth FTW PhD Symposium, Ghent University, 2003 12. T. Bert, H. De Smet, F. Beunis, K. Neyts, Complete electrical and optical simulation of electronic paper, Science Direct, 13 October 2005 13. M. A. Hopper, V. Novotny, An Electrophoretic Display, Its Properties, Model, and Addressing, IEEE Transactions on Electron Devices, Vol. ED-26, No. 8, August 1979 14. H. Takao, M. Miyasaka, H. Kawai, H. Hara, A. Miyazaki, T. Kodaira, S. W. B. Tam, S. Inoue, T. Shimoda, Flexible Semiconductor Devices: Fingerprint Sensor and Electrophoretic Display on Plastic, ESSDERC Proceeding of the 34th European, pp. 309-312, September 2004 15. B. W. Marks, Power Consumption in Multiplexed Liquid-Crystal Displays, IEEE Transactions on Electron Devices, Vol. ED-29, No. 8, August 1982 16. B. W. Marks, Power Reduction in Liquid-Crystal Display Modules, IEEE Transactions on Electron Devices, Vol. ED-29, No. 12, December 1982 17. Elecard Ltd., http://www.elecard.com/download/clips.php, videos used with permission 18. Semiconductor Gobal LCD Driver IC S6B0723A Specification 19. F. Strubbe, (K. Neyts), Determination of the valency of pigment particles in electrophoretic ink, Ghent Univ., November 2005

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