无源矩阵驱动高分子发光显示屏的典型串扰分析

Analysis of Typical Crosstalk in Passive Matrix Polymer Light Emitting Diodes

无源驱动对高分子发光显示屏质量要求较高,每个像素都应具有完好的二极管特性。为了在选通像素时,消除D.Braun串扰 [1],无源驱动必须断绝选通像素与非选通像素之间的关联,所以需空闲行列上加以反向偏压。但研究表明,对于整流特性比较低的像素,在行扫描的空闲时间内,使驱动IC的VDD与VEE短路,产生相当大的漏电流并在显示屏的电阻网络上形成异常的压降,从而改变空闲行列上的原有电位。这样也就改变了非选通像素的偏置状态,使之正偏导通发光,形成了新的串扰。其表现为两种亮线:一是列串扰,亮度分布与阳极ITO及金属引线电阻有关;二是行串扰。从实验上讨论此两种串扰的产生原因,并提出减缓串扰的可能性。

PM (Passive Matrix) driver demands high quality PLEDs (Polymer Light Emitting Diodes). Each pixel should have perfect diode characteristic, with rectification ratio over 10~4, or else the application of such new type of display will be hampered by crosstalk. For diminishing D.Braun's crosstalk^([1]), PM driver must break off the relation between selected pixels and idle pixels when driving selected pixels, so reverse voltage (V_(DD)-V_(EE)) is necessary to apply to idle rows and (columns) when row was scaned, thus AC-PM driver is formed. However, it was found that the leakage of a pixel can cause PLED screen to produce two sorts of crosstalks, and the leaking pixel has no diode characteristic, but has low reverse resistance. During idle time of row scan, the leaking pixel shorts V_(DD) and V_(EE) in IC, produces considerable leaking current which forms abnormal voltage drop on resistance net distributing in display screen and driver IC, thus previous voltage on idle rows and columns is changed, and bias status of idle pixels on them is changed to forward bias, leading to (emission) and forming new type of crosstalk. Such typical crosstalk is expressed two lighting lines: one is column crosstalk, caused by high voltage on ITO anode instead of low V_(EE), which represents brightness distributing relevant to ITO resistance and metal line resistance; another is row crosstalk, caused by low voltage on metal cathode instead of high V_(DD), accompanying with selected pixels in eyes. Based on experiment test and phenomenon inspection, discusses that the coincidence reason of row crosstalk and column crosstalk from the low rectification ratio pixel, depicts its influenced rules in the form of miniature. Finally obtains vital consequence resulting in circuit which can be probed, and submits the possibility of lessen the crosstalk, especially the idea from IC re-designing aspects which can relieve crosstalk occurred in products.