CN100426361C - 有源矩阵电致发光显示设备以及其中寻址像素的方法 - Google Patents

有源矩阵电致发光显示设备以及其中寻址像素的方法 Download PDF

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CN100426361C
CN100426361C CNB200580001990XA CN200580001990A CN100426361C CN 100426361 C CN100426361 C CN 100426361C CN B200580001990X A CNB200580001990X A CN B200580001990XA CN 200580001990 A CN200580001990 A CN 200580001990A CN 100426361 C CN100426361 C CN 100426361C
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D·A·费什
J·R·休斯
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Koninklijke Philips NV
TPO Displays Corp
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    • G09G3/30Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
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    • G09G3/22Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
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    • GPHYSICS
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    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
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    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0209Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display
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    • G09G2360/14Detecting light within display terminals, e.g. using a single or a plurality of photosensors
    • G09G2360/145Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light originating from the display screen
    • G09G2360/147Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light originating from the display screen the originated light output being determined for each pixel
    • G09G2360/148Detecting light within display terminals, e.g. using a single or a plurality of photosensors the light originating from the display screen the originated light output being determined for each pixel the light being detected by light detection means within each pixel

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Abstract

一种有源矩阵电致发光显示设备在列方向上具有电源线(26)。提供隔离晶体管(30)来将每个像素的驱动晶体管(22)与该像素的显示元件(2)相隔离。该设备可以两种模式操作。在第一模式中,对于每个像素而言,该隔离晶体管(30)将驱动晶体管(22)与显示元件(2)隔离,并且像素驱动信号被以逐行的顺序提供给该阵列的所有像素。在第二模式中,该隔离晶体管将驱动晶体管耦合至该显示元件,并且电流被驱动通过该显示元件。在这种显示设备中,像素驱动信号在一个阶段中以逐行的方式被加载到该显示阵列中。由于电源线是成列的,因此在像素驱动信号的加载过程中,电流沿电源线一次只被提供给一个像素。此时没有电流被任何显示元件所汲取,因而避免了垂直串扰。这使得能够将像素数据精确地存储在像素上。

Description

有源矩阵电致发光显示设备以及其中寻址像素的方法
技术领域
本发明涉及发光显示设备,例如电致发光显示器,特别是有源矩阵显示设备。
背景技术
采用电致发光的光发射显示元件的矩阵显示设备是公知的。该显示元件可以包括例如使用聚合物材料的有机薄膜电致发光元件,或者使用传统的III-V半导体化合物的发光二极管(LED)。近来在有机电致发光材料、特别是聚合物材料方面的发展已经证明了它们实际上用于视频显示设备的能力。这些聚合物材料通常包括夹在一对电极之间的一层或多层半导体共轭聚合物,其中一个电极是透明的,另一个电极由适合于将空穴或电子注入聚合物层中的材料制成。
可利用CVD工艺或使用可溶共轭聚合物的溶液的旋涂技术来制造聚合物材料。也可以采用喷墨印刷。有机电致发光材料显示出类二极管的I-V特性,因而它们能够提供显示功能和开关功能,因此可用在无源型显示器中。可选地,这些材料可用于有源矩阵显示设备,其中每个像素包括显示元件和用于控制通过显示元件的电流的开关设备。
这种类型的显示设备具有电流驱动的显示元件,因而常规的模拟驱动方案包括给显示元件供应可控电流。已知的是,提供电流源晶体管作为像素结构的一部分,其中供应给电流源晶体管的栅极电压确定通过显示元件的电流。在寻址阶段之后存储电容器保持栅极电压。
图1示出已知的有源矩阵寻址的电致发光显示设备。该显示设备包括面板,该面板具有由块1表示的规则间隔的像素的行和列矩阵阵列,并且包括位于行(选择)地址导线4和列(数据)地址导线6的交叉组之间的交点处的电致发光显示元件2以及相关的开关装置。为简单起见,在该图中仅示出几个像素。实际上可能存在几百行和列的像素。由外围驱动电路通过行和列地址导线组来寻址像素1,该外围驱动电路包括连接到各组导线的端部的行扫描驱动器电路8和列数据驱动器电路9。
电致发光显示元件2包括有机发光二极管,其在此处被表示为二极管元件(LED)并包括一对电极,在该对电极之间夹着由有机电致发光材料制成的一个或多个有源层。该阵列的显示元件与相关的有源矩阵电路一起被装在绝缘支架的一侧上。显示元件的阴极或阳极由透明导电材料形成。该支架由诸如玻璃之类的透明材料制成,并且最接近基板的显示元件2的电极可以由诸如ITO之类的透明导电材料构成,以使由电致发光层产生的光透射通过这些电极和支架,以便对于支架另一侧的观看者而言是可见的。
图2以简化示意图的形式示出一个用于提供电压编程操作的已知像素电路布置。每个像素1包括EL显示元件2和相关的驱动器电路。该驱动器电路具有地址晶体管16,该地址晶体管16通过行导线4上的行地址脉冲来接通。当接通该地址晶体管16时,列导线6上的电压可传递到像素的其余部分。特别是,地址晶体管16将列导线电压提供给电流源20,该电流源20包括驱动晶体管22和存储电容器24。将列电压提供给驱动晶体管22的栅极,并且即使在行地址脉冲结束之后,也由存储电容器24将栅极保持在该电压。驱动晶体管22从电源线26汲取(draw)电流。
在该电路中的驱动晶体管22被实施为p型TFT,以使存储电容器24保持固定的栅-源电压。这导致固定的源-漏电流通过该晶体管,因此这提供期望的像素的电流源操作。
本发明尤其涉及电源线26平行于列导线6的像素结构,其例如由同一金属层形成。该金属层通常是制造工艺的顶部金属层,该顶部金属层可以比通常用于形成行导线的底部金属层厚,并因此比底部金属层的电阻少。对于横向显示器,电源线的长度于是更短,因此沿该线的电压降将更低,从而使得能够制造更大的显示器。
如果图2的像素电路被修改为采用垂直电源线,那么它将遭受严重的串扰。特别是,当数据被存储在像素中时,该像素通过切断显示元件的电流供应来操作,并且所存储的数据电压是与电源线电压相关的电压。该切断由图2的电路中的附加晶体管28来执行,尽管可以采用其它措施。例如,已经提出使阴极电压或电源线电压成为可切换的。作为垂直电源线的结果,数据电压将被电源线电压降破坏,该电源线电压降是由在该列中仍然沿阻性电源线汲取电流的其它像素引起的。这直观上被看作垂直串扰。
电流镜电路并不遭受这种缺陷,因为供应给像素的电源可以是连续的,并且不必被中断。出于这个原因,电流镜电路通常用于实施具有垂直电源线的像素结构。这些是电流寻址的像素电路而不是电压寻址的像素电路。
然而,驱动器电路和驱动方案对电压寻址的像素比对电流寻址的像素更简单,并且对采用垂直电源线的电压寻址的像素而言仍然需要以简单的方式解决垂直串扰的问题。
发明内容
根据本发明,提供一种有源矩阵电致发光显示设备,该设备包括以行和列的方式布置的显示像素的阵列,每个像素包括:
电致发光(EL)显示元件;
驱动晶体管,用于驱动来自相关的电源线的电流通过该显示元件,每条电源线将电源提供给相应列的显示像素;
地址晶体管,用于将来自数据线的像素驱动信号提供给该驱动晶体管的栅极;以及
隔离晶体管,用于将该驱动晶体管与该显示元件隔离,
其中该设备可以两种模式操作,在第一模式中,对于每个像素而言,该隔离晶体管将驱动晶体管与显示元件隔离,并且像素驱动信号被以逐行的顺序提供给该阵列的所有像素,以及在第二模式中,该隔离晶体管将驱动晶体管耦合至该显示元件,并且电流被驱动通过该显示元件。
在该显示设备中,像素驱动信号在一个阶段(phase)中被以逐行的方式加载到显示阵列中。由于电源线是成列的,所以在像素驱动信号的加载过程中,沿电源线一次只给一个像素提供电流。此时没有电流被任何显示元件所汲取,从而避免了垂直串扰。这使得像素数据能够被精确地存储在像素上。
该EL显示元件和驱动晶体管优选被串联连接在第一和第二电源线之间。
该隔离晶体管优选被连接在该显示元件和该驱动晶体管之间。
每个像素还可包括在该驱动晶体管的栅极和源极之间的存储电容器。在这种情况下,每个像素还可包括用于根据该显示元件的光输出对存储电容器进行放电的依赖于光的设备。
该光反馈布置提供用于显示元件特性的老化的补偿。然而,这还需要更高的峰值(初始)电流被显示元件所汲取。
为了克服较高的初始峰值电流,在第二模式中,可以接通不同行的像素的隔离晶体管,以对于这些行的像素而言依次将驱动晶体管耦合至显示元件。这使得像素的初始驱动能够被交错,以使任何列的像素(共用电源线)只有一个像素汲取峰值初始电流,并且从电源汲取的总电流总是接近平均值。
本发明还提供一种寻址有源矩阵电致发光显示设备的像素的方法,该有源矩阵电致发光显示设备包括显示像素的行和列的阵列,每个像素包括电致发光(EL)显示元件和用于驱动电流通过该显示元件的驱动晶体管,该方法包括:
在第一模式中,在每个像素中将驱动晶体管与显示元件相隔离,并以逐行的顺序将像素驱动信号提供给该阵列的所有像素;以及
在第二模式中,在每个像素中将驱动晶体管耦合至显示元件,并通过汲取来自列电源线的电流通过该驱动晶体管和该显示元件来驱动电流通过该显示元件。
该方法提供消除了垂直串扰的具有列电源线的像素电路的操作。
在第二模式中,对于这些行的像素,可以将驱动晶体管依次耦合至显示元件。这特别适合于光反馈像素,在该光反馈像素中来自显示元件的部分光输出被用于控制驱动晶体管的操作。该驱动方案需要较高的初始像素驱动电流,并且通过对于这些行的像素将驱动晶体管依次耦合至显示元件,这些初始峰值电流被交错。
附图说明
现在将参考附图详细描述本发明的例子,其中:
图1示出常规的有源矩阵LED显示器;
图2示出图1的显示器的第一已知像素布局;
图3示出本发明的第一像素布局;
图4示出图3的像素布局的操作的时序图;
图5示出已知光反馈像素布局;
图6示出根据本发明如何修改图5的像素布局;
图7示出图6的像素布局的操作的时序图;以及
图8示出对本发明的像素布局的修改。
具体实施方式
本发明提供一种有源矩阵电致发光显示设备,该设备具有列电源线,并且其中在像素编程的过程中每个像素的驱动晶体管都与显示元件相隔离。在驱动任何显示像素之前,对所有像素逐行地进行像素编程。由于电源线是成列的并且像素编程是逐行的,因此在像素编程期间,电流沿电源线一次只被提供给一个像素。此时任何显示元件都没有汲取电流,从而避免了垂直串扰。
图3示出本发明的像素布置。与图2中出现的相同部件被给予相同的附图标记。如所示,每条电源线26将电源提供给相应列的显示像素。在驱动晶体管22和显示元件2之间提供隔离晶体管30,以用于将驱动晶体管与显示元件相隔离。
像素可以两种模式操作,并且参考图4来说明这些模式,该图4是图3的像素电路的操作的时序图。
曲线40示出场脉冲,其分离图像数据的顺序帧的寻址。曲线42示出行地址脉冲,其用于对整行的像素接通地址晶体管16。脉冲表示地址晶体管的导通状态。图4示出三行的行地址脉冲,但是在场周期中,当然所有的行都被依次寻址。曲线44示出隔离晶体管30的操作的时序。
第一模式50是像素编程模式。对于每个像素而言,隔离晶体管30将驱动晶体管22与显示元件2隔离,并且像素驱动信号被以逐行的顺序提供给该阵列的所有像素。由于电源线26是成列的,因此在像素驱动信号的加载过程中,电流沿电源线一次只被提供给一个像素。作为隔离晶体管的结果,此时任何显示元件都没有汲取电流,从而避免了垂直串扰。这使得能够将像素数据精确地存储在像素上。
第二模式52是像素驱动模式。隔离晶体管30将驱动晶体管22耦合至显示元件2,并且电流被驱动通过显示元件2。
在图4的驱动方案中,同时驱动所有的像素。
对于补偿LED材料的老化的电压寻址的像素电路已经有一些建议。例如,已经提出了其中像素包括光敏元件的各种像素电路。该元件对显示元件的光输出作出响应,并且起到响应于光输出而泄漏在存储电容器上存储电荷的作用,以便在地址周期期间控制显示器的整体的光输出。图5示出出于这个目的的已知像素布局的一个例子。在WO01/20591和EP 1 096 466中详细描述了这种类型的像素结构的例子。
在图5的像素电路中,光电二极管27对在电容器24上存储的栅极电压进行放电。当驱动晶体管22上的栅极电压达到阈值电压时,EL显示元件2将不再发光,于是存储电容器24将停止放电。从光电二极管27中泄漏电荷的速率是显示元件输出的函数,因此光电二极管27用作光敏反馈设备。可以表明,考虑到光电二极管27的影响,整体的光输出由下式给出:
L T = C S η PD ( V ( 0 ) - V T ) . . . [ 1 ]
在该等式中,ηPD是光电二极管的效率,其在显示器上是非常均匀的,CS是存储电容,V(0)是驱动晶体管的初始栅-源电压,以及VT是驱动晶体管的阈值电压。因此,光输出与EL显示元件效率无关,并且从而提供了老化补偿。VT在显示器上的确是变化的,并且已经提出了各种其它技术来补偿这些阈值电压的变化。
由于光输出在该电路中衰减,因此需要高的初始电流来获得高的初始亮度,该高的初始亮度于是被光反馈系统降低以提供期望的平均光输出。这意味着在图5的电路中像素驱动阶段开始时非常大的电流将沿电源行流动,这恶化了电源线电压降的上述问题。
特别是,这些行的像素通常被同时寻址,并且在图5的常规电路中,这些像素全部从同一行电源线同时汲取高的大初始电流。
出于这个原因,垂直电源线的使用对于参考图5所解释的类型的光反馈电路是特别理想的。当使用垂直电源线并逐行寻址像素时,不同行中的像素处于像素驱动周期的不同阶段,因此沿着列的像素未被同时汲取高的初始电流。
本发明可被应用在这种光反馈电路中,以便再次克服与列电源线相关的垂直串扰问题。根据本发明,图5的电路被修改为图6所示的那样。
如图6所示,在驱动晶体管22和显示元件2之间再次提供隔离晶体管30。
图4的驱动方案需要修改以用于光反馈像素的实施。在图4中,像素的逐行驱动被取消,并且所有像素被同时驱动。因此,在光发射阶段52开始时,所有像素初始将汲取大的电流。为了克服这个问题,对不同行交错光发射脉冲44。
图7示出具有该交错的光发射阶段52的图6的电路的操作的时序图。
通过交错各行的发射脉冲44的起动时间,由一行中的像素所汲取的高初始电流与由另一行中的像素所汲取的高初始电流不一致。结果,由列电源汲取的总电流接近像素驱动电流的平均值。
这种修改可应用于所有的像素设计,并且不仅仅在光反馈实施方面具有好处。
本发明的驱动方案包括将数据编程到像素中,随后在像素驱动阶段之前有一个短延迟。该延迟对于不同的行是不同的,尽管对于图7的操作而言更少。重要是要防止漏电流对存储电容器进行放电,并且为了这个目的可采用一个附加晶体管60,如图8中所示。如所示,该附加晶体管能够与隔离晶体管共用同一个控制线。
该晶体管阻止光电二极管中的漏电流或暗电流对存储电容器进行放电。
如上所述,一些补偿方案也已经被提出以补偿在基板上的阈值电压变化。这些方案能够用于修改上述的像素电路和驱动方案。对于非晶硅驱动晶体管和多晶硅驱动晶体管已经提出了不同的阈值电压补偿方案。非晶硅晶体管尤其受到阈值电压中电压应力诱发的变化的影响,因此需要随着时间的补偿。多晶硅晶体管尤其受到在基板上的阈值电压的变化的影响,但随着时间的流逝这些变化仍然相当恒定,因此需要初始补偿。
本发明可应用于采用n型或p型驱动晶体管、采用任何晶体管技术、以及对阈值电压或对其它补偿因素采用任何适当的附加补偿方案的像素电路。
对于本领域熟练技术人员而言,各种其它修改将是显而易见的。

Claims (12)

1、 一种有源矩阵电致发光显示设备,包括以行和列的方式布置的显示像素(1)的阵列,每个像素包括:
电致发光(EL)显示元件(2);
驱动晶体管(22),用于驱动来自相关的电源线(26)的电流通过该显示元件(2),每条电源线(26)将电源提供给相应列的显示像素(1);
地址晶体管(16),用于将来自数据线的像素驱动信号提供给该驱动晶体管(22)的栅极;以及
隔离晶体管(30),用于将该驱动晶体管与该显示元件隔离,
其中该设备可以两种模式操作,在第一模式(50)中,对于每个像素而言,该隔离晶体管(30)将该驱动晶体管(22)与该显示元件隔离,并且像素驱动信号被以逐行的顺序提供给该阵列的所有像素,以及在第二模式(52)中,该隔离晶体管将驱动晶体管(22)耦合至该显示元件(2),并且电流被驱动通过该显示元件。
2、 如权利要求1所述的设备,其中该EL显示元件和该驱动晶体管被串联连接在第一电源线(26)和第二电源线之间。
3、 如权利要求2所述的设备,其中该隔离晶体管(30)被连接在该显示元件(2)和该驱动晶体管(22)之间。
4、 如任一前述权利要求所述的设备,其中该驱动晶体管(22)是多晶硅TFT。
5、 如权利要求1-3中任意一项所述的设备,其中每个像素还包括在该驱动晶体管(22)的栅极和源极之间的存储电容器(24)。
6、 如权利要求5所述的设备,其中每个像素还包括用于根据该显示元件(2)的光输出对该存储电容器(24)进行放电的依赖于光的设备(27)。
7、 如权利要求6所述的设备,其中该依赖于光的设备(27)包括放电光电二极管。
8、 如权利要求1-3中任意一项所述的设备,其中在第二模式中,接通不同行的像素的隔离晶体管(30),以对于这些行的像素依次将驱动晶体管(22)耦合至显示元件(2)。
9、 一种寻址有源矩阵电致发光显示设备的像素的方法,该有源矩阵电致发光显示设备包括显示像素的行和列的阵列,每个像素包括电致发光(EL)显示元件和用于驱动电流通过该显示元件的驱动晶体管,该方法包括:
在第一模式(50)中,在每个像素中将驱动晶体管(22)与显示元件(2)相隔离,并以逐行的顺序将像素驱动信号提供给该阵列的所有像素;以及
在第二模式(52)中,在每个像素中将驱动晶体管(22)耦合至显示元件(2),并通过汲取来自列电源线(26)的电流通过驱动晶体管和显示元件来驱动电流通过显示元件。
10、 如权利要求9所述的方法,其中在第二模式中,对于这些行的像素,驱动晶体管(22)被依次耦合至显示元件。
11、 如权利要求10所述的方法,其中在第二模式中,来自该显示元件(2)的部分光输出被用于控制该驱动晶体管(22)的操作,从而实现光反馈控制回路。
12、 如权利要求9、10或11所述的方法,其中对于一个像素而言将驱动晶体管(22)与显示元件(2)隔离包括断开在该像素的显示元件(2)和驱动晶体管(22)之间的隔离晶体管(30)。
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