主動式有機發光二極體顯示器之畫素電路採用薄膜電晶體作為開關與驅動元件，但是電晶體元件特性會因製程上的誤差以及長時間操作導致變異。此外，有機發光二極體發光效率會隨長時間操作而衰減，導致整體面板亮度均勻性下降。在一般顯示面板已經有相關畫素補償電路及顯著改善效果，但是對於高頻率的三維顯示器而言，過短的補償時間使儲存電容的充放電不足，導致畫面補償效果不佳而影響顯示品質。
針對上述問題，本論文提出三個新式改良畫素電路。前兩個電路以電流驅動的架構操作於一般顯示模式。第一個電路為6T1C架構，除了不受電晶體臨界電壓變異影響之外，也可以改善傳統電流式補償電路在低灰階充電過慢的問題，以及補償有機發光二極體因材料老化所造成的亮度下降。模擬驗證顯示電晶體臨界電壓變異時，電流誤差率均在5%內，而在操作540小時之後，有機發光二極體發光效率由17.26 (燭光/安培)衰減為14.69 (燭光/安培)，而亮度誤差只有3%。但是此電路元件數及訊號線較為複雜，使開口率較低。第二個電路為3T1C架構，利用較少的元件以及簡單的控制訊號線增加開口率，可以補償電晶體元件特性的變異，同時也改進在低灰階充電過慢的缺點，模擬結果顯示在電晶體臨界電壓變異時，電流誤差率都在10%內。第三個則是三維顯示電路，因為電流驅動特性的限制並不適用於三維顯示，所以此電路採用電壓驅動方式，架構為3T1C。在符合三維顯示規格所需之高操作頻率下，同時補償全面板畫素內電晶體臨界電壓變異以達到面板均勻性的目的。經由模擬驗證，此電路可操作在240赫茲、360赫茲和480赫茲的頻率，而電晶體臨界電壓變異時，電流誤差率分別在4.4%、4.3%和4.4%內。本論文提出的三個電路均能改善因電晶體特性變異所導致亮度不均勻的現象，第一個電路可以補償OLED材料老化所造成的亮度衰減及加快操作速度；第二個電路著重在精簡畫素元件數，雖然不能補償OLED亮度衰減但開口率較高；第三個電路維持較高開口率，可適用於三維顯示電路技術，因此本論文所提之三個畫素補償電路各具有其應用價值。

The pixel circuit of an active matrix organic light-emitting diode (AMOLED) display uses thin-film transistors (TFTs) for the switching and driving components. However, the electrical characteristics of TFTs may vary due to fabrication process variation or long-term operation. Additionally, the efficiency of OLED material will degrade gradually, resulting in brightness nonuniformity and luminance decay. Numerous pixel compensation circuits have been proposed and exhibit effective compensation capability in 2D displays, whereas for three-dimensional (3D) displays, the short programming time causes incomplete compensation of TFT threshold voltage, and thus influences the image quality of 3D AMOLED display.
In order to solve the issues mentioned above, this thesis proposes three novel pixel circuits. The first two pixel circuits adopt current-programming structure to operate in 2D displays. The first 6T1C circuit has immunity against the variation of threshold voltage of TFT and reduces the charging time at low grayscale. The simulation results demonstrate current error rate is under 5% with TFT threshold voltage variation, and the luminance degradation is 3% over 540 hours while the efficiency of OLED drops from 17.26 (cd/A) to 14.69 (cd/A). However, the aperture ratio of this circuit is reduced because of the excessive components and complex control signals. The second 3T1C circuit with few components and control signals increases aperture ratio and improves the defects in charging time as mentioned above. The simulation results show the current error rate is under 10% with TFT threshold voltage variation. Due to characteristics limitation for 3D displays, the third 3T1C circuit uses the voltage-programming approach to maintain brightness uniformity. The design of the driving signal can simultaneously compensate for TFT threshold voltage variation of the entire panel, shortening the operation time to meet the specifications required in 3D displays. Based on the simulation results, while the circuit operates at 240Hz, 360Hz, and 480Hz, the current error rate is 4.4%, 4.3% and 4.4% respectively.
The proposed pixel circuits in this thesis improve the brightness nonuniformity caused by the variation of the transistor characteristics. The first circuit can compensate for luminance decay due to OLED material aging and accelerates the operation speed. The second circuit focuses on simplifying the number of pixel elements, although it can’t compensate for OLED luminance decay, the aperture ratio is higher. The third circuit maintains a higher aperture ratio and can be applied to 3D display technology. The presented circuits improve the display image and will significantly contribute to AMOLED applications in the future.

[1] R. M. A. Dawson, Z. Shen, D. A. Furst, S. Connor, J. Hsu, M. G. Kane, R. G. Stewart, A. Ipri, C. N. King, P. J. Green, R. T. Flegal, S. Pearson,W. A. Barrow, E. Dickley, K. Ping, C. W. Tang, S. Van Slyke, F. Chen, J. Shi, J. C. Sturm, and M. H. Lu, “Design of an improved pixel for apolysilicon active-matrix organic LED display,” in SID Tech. Dig., pp. 11-14 , 1998.
[2] R. M. A. Dawson, Z. Shen, D. A. Furst, S. Connor, J. Hsu, M. G. Kane, R. G. Stewart, A. Ipri, C. N. King, P. J. Green, R. T. Flegal, S. Pearson,W. A. Barrow, E. Dickey, K. Ping, S. Robinson, C. W. Tang, S. VanSlyke, F. Chen, J. Shi, M.H. Lu, and J. C. Sturm, “The impact of the transient response of organic light emitting diodes on the design of active matrix OLED displays,” in IEEE IEDM 98, pp. 875-878, 1998.
[3] P. E. Burrow, S. R. Forrest, T. X. Zhou, and L. Michalski, “Operating lifetime of phosphorescent organic light emitting devices,” Appl. Phys. Lett., vol. 76, no. 18, pp. 2493-2495, May. 2000.
[4] Y. He, R. Hattori, and J. Kanicki, “Current-source a-Si:H thin-film transistor circuit for active-matrix organic light-emitting displays,” IEEE Electron Device Lett., vol. 21, no. 18, pp. 590-592, Dec. 2000.
[5] Y. He, R. Hattori, and J. Kanicki, “Improved a-Si:H TFT pixel electrode circuits for active-matrix organic light emitting displays,” IEEE Trans. Electron Devices, vol. 48, no. 7, pp. 1322-1325, Jul. 2001.
[6] Y. Hong, J. Kaniki, and R. Hattori, “Novel poly-Si TFT pixel electrode circuits and current programmed active-matrix driving methods for AMOLEDs,” in SID Tech. Dig., pp .618-621, 2002.
[7] Y. C. Lin, D. Shieh, and F. Yang, “Current driving pixel circuities for active matrix organic light emitting diode display,” in SID Tech. Dig., pp. 610-613. 2002
[8] M. Ohta, H. Tsutsu, H. Takahara, I. Kobayashi, T. Uemura, and Y. Takubo, “A novel current programmed pixel for active Martix OLED displays,” in SID, International Symp. Proc., pp. 108-111, 2003.
[9] S. J. Ashtiani, P. Servati, D. Striakhilev, and A. Nathan, “A 3-TFT current-programmed pixel circuit for AMOLEDs,” IEEE Trans. Electron Devices, vol. 52, no. 7, pp. 1514-1518, Jul. 2005.
[10] X. Guo and S. R. P. Silva, “A simple and effective approach to improve the output linearity of switched-current AMOLED pixel circuitry,” IEEE Electron Device Lett., vol. 28, no. 10, pp. 1514-1518, Oct. 2007.
[11] J. Lee, W. Nam, S. Jung, and M. Han, “A new current scaling pixel circuit for AMOLED,” IEEE Electron Device Lett., vol. 25, no. 5, pp. 280-282, May 2004.
[12] J. Yamashita, K. Uchino, T. Yamamoto, T. Sasaoka , and T. Urabe, “New driving method with current subtraction pixel circuit for AMOLED displays,” in SID Tech. Dig., pp. 1452-1455, 2005.
[13] G. R. Chaji, S. J. Ashtiani, N. Safavian, and A. Nathan, “A novel driving scheme and pixel circuit for AMOLED displays,” in SID Tech. Dig., pp.216-219. 2006.
[14] Y. W. Kim, O. K. Kwon, K. Kim, D. Y Shin, B. H. Kim, and H. K. Chung, “A new current programmable pixel structure for large-size and high-resolution AMOLEDs,” in IDW, International Symp. Proc., pp. 367-370, 2002.
[15] Y.C. Lin, D. Shieh, and J. Kanicki, “A novel current-scaling a-Si:H TFTs pixel electrode circuit for AMOLEDs,” IEEE Trans. Electron Devices, 214 vol. 52, no. 6, pp. 1123-1231, Jun. 2005.
[16] H. Lee, Y. C. Lin, D. Shieh, and J. Kanicki, “Current-scaling a-Si:H TFT pixel-electrode circuit for AMOLEDs: electrical properties and stability,” IEEE Trans. Electron Devices, vol. 54, no. 9, pp. 2403-2409, Sep. 2007.
[17] C. L. Lin, C. C. Hung, S. K. Hsu, and K. W. Chou, “A new current programming pixel circuit for compensating luminance degradation of AMOLED,” in SID Tech. Dig., SID Tech. Dig., pp. 1292-1295, 2011.
[18] T. Sasaoka, M. Sekiya, A. Yumoto, J. Yamada, T. Hirano, Y. Iwase, T. Yamada, T. Ishibashi, T. Mori, M. Asano, S. Tamura, and T. Urabe, “A 13.0-inch AMOLED display with top emitting structure and adaptive current mode programmed pixel circuit (TAC),” in SID Tech. Dig., pp. 384-387, 2001.
[19] C. Chen, J. Kanicki, K. Abe, and H. Kumomi, “AMOLED pixel circuits based on a-InGaZnO thin film transistors,” in SID Tech. Dig., pp. 1128-1131, 2009.
[20] K. Sakariya, P. Servati, and A. Nathan, “Stability analysis of current programmed a-Si:H AMOLED pixel circuits,” IEEE Trans. Electron Devices, vol. 51, no. 12, pp. 2019-2025, Dec. 2004.
[21] Y. Lin and H. P. D. Shieh, “A novel current memory circuit for AMOLEDs,” IEEE Trans. Electron Devices, vol. 51, no. 6, pp.1037-1040, Jun. 2004.
[22] S. H. Jung, W. J. Nam, and M. K. Han, “A new voltage-modulated AMOLED pixel design compensating for threshold voltage variation in poly-Si TFTs,” IEEE Electron Device Lett., vol. 25, no. 10, pp. 690-692, Oct. 2004.
[23] C. L. Lin and T. T. Tsai, “A novel voltage driving method using 3-TFT pixel circuit for AMOLED,” IEEE Electron Device Lett., vol. 28, no. 6, pp. 489-491, Jun. 2007.
[24] C. L. Lin and Y. C. Chen, “A novel LTPS-TFT pixel circuit compensating for TFT threshold-voltage shift and OLED degradation for AMOLED,” IEEE Electron Device Lett., vol. 28, no. 2, pp. 129-131, Feb. 2007.
[25] C. L. Lin, T. T. Tsai, and Y. C. Chen, “A novel voltage-feedback pixel circuit for AMOLED displays,” IEEE Journal of Display Technology, vol. 4, no.1, pp. 54-60, Mar. 2008.
[26] G. R. Chaji, C. Ng, A. Nathan, A. Werner, J. Birnstock, O. Schneider, and J. B. Nimoth, “Electrical compensation of OLED luminance degradation,” IEEE Electron Device Lett., vol. 28, no. 12, pp. 1108-1110, Dec. 2007.
[27] H. J. In and O. K. Kwon, “External compensation of nonuniform electrical characteristics of thin-film transistors and degradation of OLED devices in AMOLED displays,” IEEE Electron Device Lett., vol. 30, no. 4, pp. 377-379, Apr. 2009.
[28] O. K. Kwon and H. J. In, “External compensation of non-uniform image quality and image sticking in active matrix organic light emitting diode displays,” in IDMC, S01-01, 2009.
[29] A. Nathan, A. Kumar, K. Sakariya, P. Servati, S. Sambandan, K. S. Karim, and D. Striakhilev, “Amorphous silicon thin film transistor circuit integration for organic LED displays on glass and plastic,” IEEE Journal of Solid State Circuits, vol. 39, pp. 1477-1486, Sep. 2004.
[30] S. Ono and Y. Kobayashi, “An accelerative current-programming method for AM-OLED,” IEICE Trans. Electron, vol.e88-c, no.2, Feb. 2005.
[31] A. Nathan, G. R. Chaji, and S. J. Ashtiani, “Driving schemes for a-Si and LTPS AMOLED displays,” IEEE/OSA Journal of Display Technology, vol. 1, no.2, pp. 267-277, Dec. 2005.
[32] 劉楷哲, 吳其霖, 黃偉豪, 陳信榮, 李錕, 和羅豐祥, “基於3D顯示器格式之即時3D內容合成技術”, 影像與識別2010, vol. 16, no. 2.
[33] http://www.mobile01.com/topicdetail.php?f=350&t=1804449
[34] D. W. Park, C. K. Kang, Y. Park, B. Chung, K. H. Chung, B. H. Kim, and S. S. Kim, “High-speed AMOLED pixel circuit and driving scheme,” in SID Tech. Dig., pp. 806-809, 2010.
[35] B. W. Lee, B. H. Kim, S. M. Han, S. D. Sung, L. S. Shin, J. D. Lee, B. H. Kim, B. H. Berkeley, and S. S. Kim, “Novel simultaneous emission driving scheme,” in SID Tech. Dig., pp. 758-761, 2010.
[36] C. L. Lin, C. C. Hung, and F. C. Chang, “A new AMOLED pixel circuit with compensation of luminance decay for 3D display,” in IDMC, PS-044, 2009.