低溫多晶矽薄膜電晶體具有優越的電流驅動能力以及其能達到小的電路佈局面積，因此常被應用在製作智慧手機及智慧手錶之主動式矩陣有機發光二極體顯示器背板。然而，低溫多晶矽薄膜電晶體製程因為雷射退火製程之雷射能量不一致造成臨界電壓變異，導致驅動有機發光二極體的電流失真。因此許多畫素補償電路被提出來以補償低溫多晶矽薄膜電晶體之臨界電壓變異，然而其中部分畫素電路並未同時考慮到閃爍現象及電壓源因電線線阻造成之電壓下降，這些缺陷會降低顯示器之對比度、增加額外的功率消耗及造成顯示畫面之亮度不均勻。為應用在穿戴式裝置上例如智慧手錶，這些行動裝置需要一個低功率消耗之顯示器以達到消費者的長時間使用需求，因此透過降低顯示器之操作頻率，達到減少IC資料電壓供應及畫素電路內電容充放電所造成的功率消耗。然而低溫多晶矽薄膜電晶體的高漏電流會導致儲存電容無法維持所需發光電流之資料電壓，進而導致畫面失真。
為了應用在智慧手錶之低畫面更新頻率顯示器，本論文提出四個應用於主動式矩陣有機發光二極體顯示器的畫素電路。四個設計的畫素電路皆改善漏電流之影響以應用在穿戴式裝置上。第一個7T1C畫素電路有效補償臨界電壓變異來達到高均勻度之顯示畫面，且此電路也避免閃爍現象，提供高對比之顯示畫面，模擬結果證明其有效改善畫面之均勻度及減緩漏電流影響。然而，此電路尚未考慮到電壓源的變異的影響，因此第二個8T2C畫素電路，以源極隨耦器之架構來補償臨界電壓與電壓源之變異並避免閃爍現象，此電路也同樣能達到緩和漏電流影響之效果。然而為在小尺寸顯示器上提高解析度，需要更精簡的畫素電路架構。因此，提出第三個7T2C畫素電路，其架構不僅能達到臨界電壓及電壓源變異之補償，且漏電流補償能不受有機發光二極體元件特性影響，達到一致的漏電補償效果，然而此畫素電路之7T2C架構仍較為複雜，增加應用在高解析度之小尺寸面板的困難度，且兩次的電容耦合效應會影響臨界電壓變異之補償效果，因此提出第四個7T1C達到補償臨界電壓變異、電壓源變異、畫素電路內的驅動電晶體閘極端漏電現象及抑制閃爍現象，且進一步縮減電容與訊號線數目，達到更小的電路佈局面積以利應用於更高解析度之小尺寸面板。

Active-matrix organic light-emitting diode (AMOLED) displays based on low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) backplanes are widely adopted in mobile devices, such as smartphones and smartwatches, owing to the great current driving capability of LTPS TFTs and the small layout area. However, the non-uniform energy of excimer laser annealing (ELA) during the LTPS TFTs fabrication results in inevitable TFT VTH variation and the subsequent difference in OLED emission current. Numerous pixel circuits have been proposed to compensate for the VTH variation of LTPS TFTs. Nevertheless, the image flicker and the voltage current-resistance (I-R) drop in power lines are not considered in some pixel circuits. The defect leads to the reduction of contrast ratio, the increase of additional power consumption, and the non-uniform luminance of display images. For the display applications of wearable devices such as smartwatches, a power-saving display is required to meet consumers’ demand of long-term use. Thus, displays adopt low-frame-rate operation to reduce the frequency of data voltage supply from integrated circuits (ICs) and capacitors charging or discharging, thereby cutting down the power consumption. Nevertheless, the high leakage current of LTPS TFTs leads to the failure of storing the accurate data voltage in capacitors, resulting in image distortion.
This thesis proposes four pixel circuits for low-frame-rate AMOLED displays. The four pixel circuits are designed to ameliorate the leakage current issue and achieve low power consumption for wearable devices. The first 7T1C pixel circuit compensates for VTH variation to achieve highly uniform images. Also, the circuit prevents flicker to provide the high quality of black images. Simulation results verify that the circuit effectively improves the uniformity of image and alleviates the leakage current. However, VDD I-R drop compensation is required in pixel circuits. Therefore, the second 8T2C pixel circuit is designed with a source-follower type structure to compensate for VTH variation and VDD I-R drops without image flicker. Also, the leakage current is also mitigated. Nevertheless, implementing higher resolution in small-size display requires the simpler structure of pixel circuits. Thus, the third 7T2C pixel circuit utilizing a source-follower connection structure is proposed for compensating the both variations of VTH and voltage drops in power lines. Furthermore, the image flicker is suppressed to enhance contrast ratio, and the leakage during the long-term emission period is also improved. However, the capacitive coupling effect after compensating period influences the accuracy of VTH compensation. Thus, the fourth 7T1C pixel circuit is proposed with an effective compensation of TFT VTH variation, VDD I-R drops, the leakage at the gate node of the driving TFT in pixel circuits, and the suppression of flicker phenomenon. Scan signals and capacitors are also reduced to achieve smaller layout area for pursuing high-resolution AMOLED displays in small-sized panels.

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