用以延緩並補償有機發光二極體顯示器劣化的畫素電路以及外部演算法設計

Abstract

本論文針對因長時間電流驅動所導致之主動式有機發光二極體(AMOLED)顯示器的OLED元件劣化，進行延緩以及補償。首先提出以五個電晶體以及一個電容(5T1C)的組成的畫素電路，此電路可於顯示器框架時間(Frame time)的電流驅動停止時間裡，施加負偏壓(Reverse bias)來延緩劣化，並經成功實作於2.4吋AMOLED顯示器後，證實其有預期的延緩劣化效果。為達到提升面板解析度的效用，本論文設計另一4T0.5C畫素電路，此電路設計於兩個畫素電路裡共用一個電容來最小化畫素面積，並亦施加負偏壓於一半的顯示Frame time裡來達到延緩劣化的能力；此外，本論文亦設計外部演算法搭配感測電路來補償因長時間使用下OLED元件劣化所導致的亮度降低問題，此設計藉感測OLED元件的陽極電壓來判斷OLED元件劣化程度，由內建好的OLED模型來輸出修正過的資料訊號(Data-line signal)補償OLED亮度的衰減，此OLED特性模型以獨特的預先量測建模方式取代傳統複雜的數學方程式建模，並可考慮當實際補償衰減亮度時，加大電流導致劣化更劇烈的效應，達到更精確的補償；因此，上述設計之4T0.5C畫素電路搭配外部演算法得以兼具延緩以及補償AMOLED顯示器元件劣化對亮度的影響。最後，本論文亦針對AMOLED顯示器使用之薄膜電晶體(TFT)引起之TFT臨界電壓的變異所導致的面板均勻度問題，在5T1C以及4T0.5C畫素電路分別以電流鏡架構以及外部演算法方式進行補償，使得本論文可以完整改善AMOLED顯示器的問題，達到取代液晶顯示器的目標。

This study aims at alleviating and compensating degradation of OLED components on AMOLED displays during long-time operations. First, to alleviate OLED degradation, a new 5T1C pixel circuit is designed to impose the reverse bias on OLED component at the current-off period of each frame time. The pixel circuit is successfully fabricated on a 2.4-inch AMOLED panel to validate the expected performance of alleviating OLED degradation. To increase the panel resolution, another pixel circuit consisting of 4T0.5C is proposed to minimize the layout area according to the design of sharing a capacitor in two adjacent pixels. This 4T0.5C pixel circuit is also capable of alleviating OLED degradation by imposing reverse bias on OLED component in each half frame time. Furthermore, to compensate the emission decay causing by OLED degradation during the long-time operation, an external algorithm with sensing circuit is proposed. By sensing the anode voltage of OLED component, this algorithm can make discrimination for obtaining the degree of OLED degradation, and then output the corrected data-line signal to compensate the decay according to the established models of OLED characteristics. These models are pre-established by the designed measurement method to replace the complicated mathematical equations. To achieve accurate degradation compensation, these models also consider the effect of degradation aggravation as increasing driving current to compensate OLED emission decay. Therefore, compensating and alleviating OLED degradation realized on a high-resolution panel are made possible in designed new 4T0.5C pixel circuit with external algorithm. Last, to achieve completely the target of replacing LC display, the non-uniformity on AMOLED panel causing by Vth variation of driving TFTs is also compensated in designed 5T1C and 4T0.5C pixel circuits by the compensation methods of current mirror structure and external algorithm, respectively.