近年來主動式有機發光二極體顯示器蓬勃發展，低溫多晶矽薄膜電晶體由於極佳的電流驅動能力被廣泛應用於主動式有機發光二極體顯示器之背板。然而低溫多晶矽薄膜電晶體因受到準分子雷射退火技術雷射能量不一影響，造成電晶體臨界電壓產生變異導致有機發光二極體發光電流的不均勻性。因此，許多研究相繼提出補償技術以改善臨界電壓的不一致性，然而隨著顯示器的解析度逐漸上升，顯示器每列掃描時間隨之縮減，傳統漸進式驅動法的補償時間因為受限於掃描時間，使畫素電路的補償效果不佳進而影響顯像品質。另一方面，針對需考量功率消耗的智慧手錶顯示器而言，畫素電路操作過程中應避免產生大電流增加額外的功率消耗，並利用降低顯示器的畫面更新頻率以減少資料線之充放電頻率來進一步減少功率消耗，然而在延長的發光時間下，電晶體之漏電流會導致驅動電壓失真，使有機發光二極體發光電流產生嚴重變化且造成顯示器畫面的不均勻性。
本論文針對不同應用之主動式有機發光二極體顯示器提出三個畫素電路以改善顯示器畫面之均勻性，第一個4T1C畫素電路適用於高解析度主動式有機發光二極體顯示器，其利用電流偏壓的方式加快補償速度，並搭配平行補償驅動法調整補償時間以精準補償電晶體臨界電壓變異，藉由模擬結果驗證，此電路在電晶體臨界電壓變異±0.5 V以及電源變異±0.5 V時，其相對電流誤差率分別小於4.44%與1.40%，第二個9T2C畫素電路適用於低畫面更新頻率之智慧手錶顯示器，透過電容耦合的方式提供ㄧ高電位對驅動電晶體閘極端充電，減緩長發光週期下驅動電晶體閘極端電壓之變化，電路模擬結果顯示在電晶體臨界電壓變異±0.5 V的情況下，其相對電流誤差率皆小於4.73%，且在延長的發光週期下，高、中、低灰階的電流變化量皆小於10.51 nA，為了降低電路複雜度以及減少電路所需佈局面積，因此本論文提出第三個7T1C畫素電路，此電路採用一參考電壓提供高電位來防止驅動電晶體閘極端之漏電，模擬結果顯示透過適當的調整參考電壓，此電路在電晶體臨界電壓變異±0.5 V時，其相對電流誤差率皆低於4.12%，並且在延長的發光週期下驅動電壓的變化率僅3.79%，驗證所提出之電路高度適用於低畫面更新頻率之智慧手錶顯示器。

Active-matrix organic light-emitting diode (AMOLED) displays have been widely developed in recent years. Low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) are adopted as the backplane of AMOLED displays because of their excellent current driving capabilities. However, the threshold voltage (VTH) of LTPS TFTs varies owing to the fluctuations of the laser beaming in the excimer laser annealing (ELA) process, inducing the non-uniformity of the OLED driving current. To compensate for the VTH variations of LTPS TFTs, many studies have presented the corresponding driving methods. As the resolution of displays increases, the scan time for each row in displays decreases and further restricts the compensation period of conventional progressive emission methods. Hence, the capability of compensation for the pixel circuit is degraded severely, affecting the quality of the displayed images. Moreover, for use in smartwatch displays, the power consumption of displays has to be taken into account. The pixel circuits should prevent a huge current being generated to avoid increasing the additional power consumption during the circuit operation. To further reduce the power consumption, the frame rate of displays is decreased, reducing the charging and discharging frequency of data lines. Nonetheless, the leakage currents of TFTs induce the distortion of the driving voltage, thereby causing the severe variation of OLED currents and leading to the non-uniform brightness of the image.
This thesis proposes three pixel circuits for two different applications to ameliorate the image uniformity of the AMOLED displays. The first 4T1C pixel circuit utilizes the current-biased voltage-programmed method and the parallel addressing driving scheme for use in high-resolution AMOLED displays. The proposed pixel circuit can achieve high-speed operation and compensate for the VTH variations accurately. Simulated results demonstrate that the relative current error rates are below 4.44% and 1.40% when VTH and VDD vary by ±0.5 V, respectively. The second 9T2C pixel circuit utilizes capacitive coupling effect to generate a high voltage for providing the compensating leakage current for use in low-frame-rate AMOLED smartwatch displays. Simulated results reveal that the relative current error rates are lower than 4.73% with the TFT VTH variations of ±0.5 V. During the extended emission time of 66.7 ms, the variations of OLED currents are within 10.51 nA at high, medium, and low gray levels. The third 7T1C pixel circuit has been proposed for reducing the circuit complexity and the required layout area. Herein, the third circuit adopts a reference voltage to provide a high voltage level to prevent the leakage current at the gate node of the driving TFT. By adjusting the reference voltage properly, the simulated results demonstrate that the relative current error rates are all less than 4.12% when the VTH of the driving TFT varies by ±0.5 V. Additionally, the variations of driving voltages are only 3.79% even though the emission time is prolonged to 66.7 ms, confirming that the proposed pixel circuit is suitable for use in AMOLED smartwatch displays with a low frame rate.

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