The paper of our laboratory was published in the July issue of IEEE JDT
The IEEE Journal of Display Technology, an important journal in the field of international flat-panel display, published our lab paper named by “An Accurate and Fast Current-Biased Voltage-Programmed AMOLED Pixel Circuit With OLED Biased in AC Mode” (the article link is http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7088540) in the 7th issue of this year.
The thin film transistor (TFT)-based active-matrix organic light-emitting diode (AMOLED) displays have attracted increasing attention due to their superior characteristics such as fast response, low power consumption, high contrast ratio and so forth. One of the major issues is the threshold voltage variations and shifts of the driving TFTs and the OLED itself, which would cause non-uniform image quality of AMOLEDs. Therefore, pixel circuits of the AMOLEDs usually need to compensate for the threshold voltage variation and deterioration of both the TFTs and OLEDs. Nowadays, the compensation can be categorized into two main modes: 1) current programming (CP) mode and 2) voltage programming (VP) mode. Although the CP mode allows potentially an accurate compensation, it suffers from a long settling time, especially at low driving current. On the other hand, the VP mode can provide a fast programming speed, but it usually cannot ensure a precise compensation and needs a complicated circuit configuration.
Recently, we proposed a simple 2T2C current-biased voltage programmed (CBVP) pixel circuit which can fast and accurately compensate for the driving TFT’s threshold voltage shift and OLED degradation. However, an instantaneous current would pass through the OLED in the selection period lowering the contrast ratio of the AMOLED displays. Moreover, the driving scheme for light-emission is not the conventional progressive one, possibly limiting the application range.
On the other hand, it has been revealed that the degradation of OLED could be suppressed effectively when it is biased under AC driving mode with a proper negative bias voltage. A number of the AC driving schemes have been thus proposed to minimize the OLED degradation. However, among those schemes, neither can the VTH variation of driving TFT be compensated; nor can the reverse-biased time of OLED be long enough for suppressing the OLED deterioration effectively. Moreover, an additional TFT is used for generating the reverse-bias voltage.
In this paper, we propose a new modified CBVP pixel circuit with OLED biased in AC driving mode, which allows accurate and fast compensation for the performance variation and degradation of both the driving TFT and OLED. The negative bias in the AC mode prevents the OLED from a possible light emitting during the programming period and potentially suppresses the degradation of the OLED.
The first author of this paper is the PhD candidate Cuicui Wang. This work was conducted in Shenzhen TFT and Advanced Display Key Lab and supported by NSFC under project 61274084 and in part by Shenzhen Municipal Scientific Program under Grant (JCYJ 20120829170028552). The co -authors of this paper include Leng Chuanli, Wang Longyan, Lu Wengao and Zhang Shengdong. Congratulations to them.
