AMOLED顯示器之OLED畫素微小電流感測電路設計

Abstract

Active Matrix Organic light emitting diode (AMOLED) 是最近一項各家面板廠商急著爭取的技術。其不可抹滅的優點包括高電源效能、高解析度、廣泛的觀測角度和它的高影像反應時間。AMOLED對於影像處理比一般的傳統電視速度上較快，面板和電路感測架構之間長走線的寄生電容和寄生電阻造成的RC delay將會降低AMOLED的反應速度。針對此點，push pull transient feedforward (PPTCF)被引用來解決這個問題並加快系統到穩態的時間。計畫目標的寄生電容和寄生電阻被設定在2K ohm和20 pF，畫素電流（0.5nA~500nA）在經過PPTCF後到穩態速度提升至7μs。整體PPTCF電路下線面積控制在125 μm × 46 μm。最後PPTCF的輸出電流將會送到current ADC做比較，並產生數位值。

Active Matrix Organic light emitting diode (AMOLED) is a new display technology that is rapidly commercialized for many applications in these few years. It has some undoubted advantages over other technologies such as more energy efficiency, highly saturated colors and wide viewing angle. Since one of the main attractions of AMOLED is the characteristic of fast response, the process of sensing pixel current is required to be fast and accurate. However, the parasitic resistance and capacitance slow down the response time due to RC delay. As a result, push pull transient feedforward (PPTCF) technique is introduced in this particular issue. For the RC delay generated by the data line between pixel circuit and current sensing circuit, PPTCF provides with a reduced settling time. With the parasitic RC of 2k and 20pF, the setting speed is dramatically improved, and the result is minimized under 7μs for sensing pixel current between 0.5nA to 500nA. The readout circuit consumes a static current of 15.35μA and a tape-out area of 125 μm × 46 μm. The result current of PPTCF is then sent to current ADC after for generating digital output.