CN102708791B - 像素单元驱动电路和方法、像素单元以及显示装置 - Google Patents
像素单元驱动电路和方法、像素单元以及显示装置 Download PDFInfo
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Abstract
本发明提供了一种像素单元驱动电路和方法、像素单元以及显示装置。所述像素单元驱动电路包括驱动薄膜晶体管、第一开关元件、存储电容和驱动控制单元;驱动薄膜晶体管的源极通过所述第一开关元件与数据线连接;所述驱动薄膜晶体管,漏极通过驱动控制单元分别与所述OLED的阳极和所述驱动电源的低电平输出端连接,源极通过驱动控制单元与驱动电源的高电平输出端连接,栅极通过驱动控制单元与驱动薄膜晶体管的漏极连接;驱动控制单元用于通过控制所述存储电容充放电,以控制驱动薄膜晶体管工作于饱和区而驱动薄膜晶体管的栅源电压补偿驱动薄膜晶体管的阈值电压。本发明能解决OLED面板亮度不均匀和亮度衰减的问题。
Description
技术领域
本发明涉及有机发光显示领域,尤其涉及一种AMOLED(有源矩阵有机发光二极管)的像素单元驱动电路和方法、像素单元以及显示装置。
背景技术
现有的像素单元驱动电路如图1所示,该驱动电路包括两个晶体管和一个电容,其中一个晶体管为开关管T1,由扫描线输出的扫描信号Vscan所控制,目的是为了控制数据线上的数据信号Vdata的输入,另一个晶体管为驱动管T2,控制OLED发光;Cs为存储电容,用于在非扫描期间维持对驱动管T2所施加的电压,上述电路被称为2T1C像素单元驱动电路。
AMOLED(Active Matrix Organic Light Emitting Diode,有源矩阵有机发光二极管)能够发光是由驱动晶体管在饱和状态时产生的电流所驱动,因为输入相同的灰阶电压时,所述驱动晶体管的不同的阈值电压会导致产生不同的驱动电流,造成电流的不一致性。而LTPS(低温多晶硅技术)制程上阈值电压Vth的均匀性非常差,同时Vth也有漂移,因此传统的2T1C像素单元驱动电路的亮度均匀性一直很差。
发明内容
本发明的主要目的在于提供一种像素单元驱动电路和方法、像素单元以及显示装置,以提高OLED面板亮度均匀度。
为了达到上述目的,本发明提供了一种像素单元驱动电路,用于驱动OLED,包括驱动薄膜晶体管、第一开关元件、存储电容和驱动控制单元;
所述存储电容,第一端与所述驱动薄膜晶体管的栅极连接,第二端与驱动电源的高电平输出端连接;
所述驱动薄膜晶体管的源极通过所述第一开关元件与数据线连接;
所述驱动薄膜晶体管,漏极通过所述驱动控制单元分别与所述OLED的阳极和所述驱动电源的低电平输出端连接,源极通过所述驱动控制单元与所述驱动电源的高电平输出端连接,栅极通过所述驱动控制单元与所述驱动薄膜晶体管的漏极连接;
所述驱动控制单元,用于通过控制所述存储电容充放电,以控制所述驱动薄膜晶体管工作于饱和区而所述驱动薄膜晶体管的栅源电压补偿Vth,其中,Vth为所述驱动薄膜晶体管的阈值电压。
实施时,所述驱动薄膜晶体管为p型薄膜晶体管。
实施时,所述第一开关元件是p型薄膜晶体管;
所述第一开关元件,栅极与用于传输控制信号的扫描线连接,源极与数据线连接,漏极与所述驱动薄膜晶体管的源极连接。
实施时,所述驱动控制单元包括第二开关元件、第三开关元件、第四开关元件和第五开关元件;
所述驱动薄膜晶体管的漏极和所述驱动电源的低电平输出端之间连接有所述第二开关元件;
所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极之间连接有所述第三开关元件;
所述驱动薄膜晶体管的漏极和所述OLED的阳极之间连接有第四开关元件;
所述驱动薄膜晶体管的源极和所述驱动电源的高电平输出端之间连接有所述第五开关元件。
实施时,所述第二开关元件、所述第三开关元件、所述第四开关元件和所述第五开关元件为p型TFT;
所述第二开关元件,栅极与第一控制线连接,源极与所述驱动薄膜晶体管的漏极连接,漏极与所述驱动电源的低电平输出端连接;
所述第三开关元件,栅极与所述扫描线连接,源极与所述驱动薄膜晶体管的栅极连接,漏极与所述驱动薄膜晶体管的漏极连接;
所述第四开关元件,栅极与第二控制线连接,源极与所述驱动薄膜晶体管的漏极连接,漏极与所述OLED的阳极连接;
所述第五开关元件,栅极与所述第二控制线连接,源极与所述驱动电源的高电平输出端连接,漏极与所述驱动薄膜晶体管的源极连接。
本发明还提供了一种像素单元驱动方法,其应用于上述的像素单元驱动电路,所述像素单元驱动方法包括:
像素充电步骤:驱动控制单元控制存储电容被充电;
像素放电步骤:驱动控制单元控制所述存储电容通过驱动薄膜晶体管放电,直至所述驱动薄膜晶体管的栅源电压为所述驱动薄膜晶体管的阈值电压Vth;
驱动OLED发光显示步骤:所述驱动控制单元控制所述驱动薄膜晶体管工作于饱和区,并控制所述存储电容两端的电压差值不变,以使得所述驱动薄膜晶体管的栅源电压补偿所述驱动薄膜晶体管的阈值电压Vth,通过所述驱动薄膜晶体管驱动OLED发光。
实施时,所述像素充电步骤包括:第一开关元件断开驱动薄膜晶体管的源极和数据线的连接;所述驱动控制单元导通所述驱动薄膜晶体管的漏极和所述OLED的阴极的连接,导通所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极的连接,导通所述驱动薄膜晶体管的源极和所述数据线的连接,断开所述驱动薄膜晶体管的源极和所述电源线的连接,并控制所述存储电容被充电;
所述像素放电步骤包括:所述驱动控制单元断开所述驱动薄膜晶体管的漏极和所述OLED的阴极的连接,所述驱动控制单元控制所述存储电容通过所述驱动薄膜晶体管放电,直至所述驱动薄膜晶体管的栅源电压为所述驱动薄膜晶体管的阈值电压Vth;
所述驱动OLED发光显示步骤包括:所述第一开关元件导通所述驱动薄膜晶体管的源极和数据线的连接;所述驱动控制单元断开所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极的连接,断开所述驱动薄膜晶体管的源极和所述数据线的连接,导通所述驱动薄膜晶体管的源极和所述电源线的连接,控制所述驱动薄膜晶体管工作于饱和区,并控制所述存储电容两端的电压差值不变,以使得所述驱动薄膜晶体管的栅源电压补偿所述驱动薄膜晶体管的阈值电压Vth,通过所述驱动薄膜晶体管驱动OLED发光。
本发明还提供了一种像素单元,包括OLED和上述的像素单元驱动电路,该像素单元驱动电路与OLED的阳极连接,所述OLED的阴极与驱动电源的低电平输出端连接。
本发明还提供了一种显示装置,其特征在于,包括多个上述的像素单元。
与现有技术相比,本发明所述的像素单元驱动电路和方法、像素单元以及显示装置,通过所述驱动控制单元控制存储电容Cs放电以使得驱动薄膜晶体管的栅源电压补偿驱动OLED的驱动薄膜晶体管的阈值电压,从而解决OLED面板亮度不均匀和亮度衰减的问题。
附图说明
图1是现有的2T1C像素单元驱动电路的电路图;
图2是本发明第一实施例所述的像素单元驱动电路的电路图;
图3是本发明第二实施例所述的像素单元驱动电路的电路图;
图4是本发明第三实施例所述的像素单元驱动电路的电路图;
图4A是本发明第三实施例所述的像素单元驱动电路处于第一时间段时的等效电路的电路图;
图4B是本发明第三实施例所述的像素单元驱动电路处于第二时间段时的等效电路的电路图;
图4C是本发明第三实施例所述的像素单元驱动电路处于第三时间段时的等效电路的电路图;
图4D是本发明第三实施例所述的像素单元驱动电路处于第四时间段时的等效电路的电路图;
图5是该实施例所述的像素单元驱动电路中的各信号的时序图。
具体实施方式
本发明提供了一种像素单元驱动电路和方法、像素单元以及显示装置,利用二极管接法(Diode Connection)并通过控制存储电容放电以使得驱动薄膜晶体管的栅源电压补偿驱动OLED的驱动薄膜晶体管的阈值电压,从而解决OLED面板亮度不均匀和亮度衰减的问题。
如图2所示,本发明第一实施例所述的像素单元驱动电路的电路图,该实施例所述的像素单元驱动电路,用于驱动OLED,包括驱动薄膜晶体管DTFT、第一开关元件21、存储电容Cs和驱动控制单元22;
所述存储电容Cs,第一端与所述驱动薄膜晶体管DTFT的栅极连接,第二端与输出电压VDD的驱动电源的高电平输出端连接;
所述驱动薄膜晶体管DTFT的源极通过所述第一开关元件21与数据线Data连接;
所述驱动薄膜晶体管DTFT,漏极通过所述驱动控制单元22分别与所述OLED的阳极和输出电压VSS的所述驱动电源的低电平输出端连接,源极通过所述驱动控制单元22与所述驱动电源的高电平输出端连接,栅极通过所述驱动控制单元22与所述驱动薄膜晶体管DTFT的漏极连接;
所述驱动控制单元22,用于通过控制所述存储电容Cs充放电,以控制所述驱动薄膜晶体管DTFT工作于饱和区而所述驱动薄膜晶体管DTFT的栅源电压补偿Vth,其中,Vth为所述驱动薄膜晶体管DTFT的阈值电压;
所述驱动控制单元22还分别与用于传输控制信号的扫描线SCAN和控制线CR连接。
如图3所示,本发明第二实施例所述的像素单元驱动电路的电路图。本发明第二实施例所述的像素单元驱动电路是基于本发明第一实施例所述的像素单元驱动电路。
在本发明第二实施例所述的像素单元驱动电路中,所述第一开关元件21是标号为T1的第一开关TFT,T1是p型薄膜晶体管;
所述第一开关元件21,栅极与用于传输控制信号的扫描线SCAN连接,源极与数据线Data连接,漏极与所述驱动薄膜晶体管DTFT的源极连接。
如图4所示,本发明第三实施例所述的像素单元驱动电路的电路图,该实施例所述的像素单元驱动电路采用6T1C电路,通过补偿Vth,以使得所述驱动TFT的驱动电流与所述驱动TFT的阈值电压Vth无关,达到电流一致,改善均匀性和可靠性。
在该实施例中,所述第一开关元件为标号为T1的第一开关TFT,所述第二开关元件为标号为T2的第二开关TFT,所述第三开关元件为标号为T3的第三开关TFT,所述第四开关元件为标号为T4的第四开关TFT,所述第五开关元件为标号为T5的第五开关TFT,所述驱动TFT的标号为DTFT,其中,
所述第一开关TFT、所述第二开关TFT、所述第三开关TFT、所述第四开关TFT和所述驱动TFT是p型TFT,p型TFT的阈值电压Vth<0;
T4的漏极与所述OLED的阳极连接,T4的源极与DTFT的漏极、T2的源极和所述第三开关的漏极连接,T4的栅极与T5的栅极连接;
T2的漏极与所述OLED的阴极连接并接地;
T3的源极与所述驱动TFT的栅极和所述存储电容Cs的第一端连接,所述T3的栅极与T1的栅极连接;
T1的漏极与T5的漏极连接,T4的源极与数据线Data连接;
T5的源极与所述电源线连接,T5的漏极与DTFT的源极连接;
T3的栅极和T1的栅极与用于传输控制信号的扫描线SCAN连接;
T2的栅极与控制线CR1连接;
T4的栅极和T5的栅极与控制线CR2连接;
如图4A所示,本发明第三实施例所述的像素单元驱动电路工作时,在第一时间段,即预充电阶段,所述扫描线SCAN和所述控制线CR1输出低电平,以控制T2、T3和T1导通,所述控制线CR2关闭,以控制T4和T5关闭,此时,所述存储电容Cs的第一端接地,所述存储电容Cs的第二端与输出电压为VDD的所述驱动电源的高电平输出端连接,所述存储电容Cs被充电;A点(即所述驱动TFT的漏极)电压和B点(即所述驱动TFT的栅极)电压为0,C点(即所述驱动TFT的源极)电压为所述数据线Data输出的电压Vdata;
如图4B所示,本发明第三实施例所述的像素单元驱动电路工作时,在第二时间段,即数据写入和放电补偿阶段,所述扫描线SCAN输出低电平,以控制T3和T1导通,所述控制线CR1和所述控制线CR2输出高电平,以控制T4、T2、T5截止,所述驱动TFT的栅极和漏极短接,因此所述驱动TFT等效为二极管工作;所述存储电容Cs的第一端与DTFT的栅极连接,所述存储电容Cs的第二端与输出电压为VDD的驱动电源的高电平输出端连接同时所述驱动TFT的源极(即C点)连接到输出电压为Vdata的所述数据线Data;
DTFT的栅源极电压Vgs(即VB-VC)为-Vdata,其小于Vth,因此DTFT导通,所述存储电容Cs通过DTFT放电到所述数据线Data,直到DTFT的Vgs增大到DTFT的阈值电压Vth,此时DTFT进入亚阈导通,C点电压维持在Vdata,B点和C点之间的电压差值(即Vgs)为DTFT的阈值电压Vth,因此DTFT的栅极(即B点)电压为VC+Vth=Vdata+Vth,所述存储电容Cs的第二端与第一端之间的电压差值为VDD-VB即VDD-Vdata-Vth;
如图4C所示,本发明第三实施例所述的像素单元驱动电路工作时,在第三时间段,即切换缓冲阶段,所述扫描线SCAN、所述控制线CR1和所述控制线CR2输出高电平,以控制T1、T2、T3、T4、T5关闭,DTFT的栅极(即B点)电压由所述存储电容Cs稳定为Vdata+Vth;
如图4D所示,本发明第三实施例所述的像素单元驱动电路工作时,在第四时间段,即OLED驱动阶段,所述控制线CR2输出低电平,以控制T4、T5导通,所述控制线CR1和所述扫描线SCAN输出高电平,以控制T2、T3、T1关闭,此时,DTFT工作于饱和区,驱动电流流过所述OLED,使其发光;
DTFT的栅极(即B点)电压为Vdata+Vth,DTFT的源极通过T5连接输出电压为VDD的所述电源线,即DTFT的栅源极电压Vgs为Vdata+Vth-VDD,此时流过所述OLED的电流I的计算公式为由公式(1)所示:
I=K×(Vgs-Vth)2
=K×(Vdata+Vth-VDD-Vth}2
=K×(Vdata-VDD)2; 公式(1)
其中,K为DTFT的电流系数;
μ、COX、X、W、L分别为DTFT的场效应迁移率,栅绝缘层单位面积电容、沟道宽度、长度;
该第四时间段为OLED发光阶段,所述OLED将持续发光到所述数据线Data上下一帧数据的写入;
如此,便使得所述驱动TFT的驱动电流即流过所述OLED的电流只由Vdata-VDD决定,不受所述驱动TFT的阈值电压Vth以及所述OLED的阳极电压Vth_oled的影响,避免了该驱动电流随所述驱动TFT的阈值电压以及所述OLED的阳极电压漂移而产生变化,以改善流过所述的电流的均匀性,达到OLED面板的亮度的均匀。
图5是该实施例所述的像素单元驱动电路中的扫描线SCAN输出的扫描信号VSCAN、数据线Data输出的数据信号Vdata、第一控制线CR1输出的控制信号VCR1和第二控制线CR2输出的控制信号VCR2的时序图;在图5中,D、E、F、G分别标示的是第一时间段、第二时间段、第三时间段、第四时间段。
以上说明对本发明而言只是说明性的,而非限制性的,本领域普通技术人员理解,在不脱离所附权利要求所限定的精神和范围的情况下,可做出许多修改、变化或等效,但都将落入本发明的保护范围内。
Claims (6)
1.一种像素单元驱动电路,用于驱动OLED,其特征在于,包括驱动薄膜晶体管、第一开关元件、存储电容和驱动控制单元;
所述存储电容,第一端与所述驱动薄膜晶体管的栅极连接,第二端与驱动电源的高电平输出端连接;
所述驱动薄膜晶体管的源极通过所述第一开关元件与数据线连接;
所述驱动薄膜晶体管,漏极通过所述驱动控制单元分别与所述OLED的阳极和所述驱动电源的低电平输出端连接,源极通过所述驱动控制单元与所述驱动电源的高电平输出端连接,栅极通过所述驱动控制单元与所述驱动薄膜晶体管的漏极连接;
所述驱动控制单元,用于通过控制所述存储电容充放电,以控制所述驱动薄膜晶体管工作于饱和区而所述驱动薄膜晶体管的栅源电压补偿Vth,其中,Vth为所述驱动薄膜晶体管的阈值电压;
所述第一开关元件是p型薄膜晶体管;
所述第一开关元件,栅极与用于传输控制信号的扫描线连接,源极与数据线连接,漏极与所述驱动薄膜晶体管的源极连接;
所述驱动控制单元包括第二开关元件、第三开关元件、第四开关元件和第五开关元件;所述驱动薄膜晶体管的漏极和所述驱动电源的低电平输出端之间连接有所述第二开关元件;所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极之间连接有所述第三开关元件;所述驱动薄膜晶体管的漏极和所述OLED的阳极之间连接有第四开关元件;所述驱动薄膜晶体管的源极和所述驱动电源的高电平输出端之间连接有所述第五开关元件;
所述第二开关元件、所述第三开关元件、所述第四开关元件和所述第五开关元件为p型TFT;
所述第二开关元件,栅极与第一控制线连接,源极与所述驱动薄膜晶体管的漏极连接,漏极与所述驱动电源的低电平输出端连接;
所述第三开关元件,栅极与所述扫描线连接,源极与所述驱动薄膜晶体管的栅极连接,漏极与所述驱动薄膜晶体管的漏极连接;
所述第四开关元件,栅极与第二控制线连接,源极与所述驱动薄膜晶体管的漏极连接,漏极与所述OLED的阳极连接;
所述第五开关元件,栅极与所述第二控制线连接,源极与所述驱动电源的高电平输出端连接,漏极与所述驱动薄膜晶体管的源极连接。
2.如权利要求1所述的像素单元驱动电路,其特征在于,所述驱动薄膜晶体管是p型薄膜晶体管。
3.一种像素单元驱动方法,其应用于如权利要求1所述的像素单元驱动电路,其特征在于,所述像素单元驱动方法包括:
像素充电步骤:驱动控制单元控制存储电容被充电;
像素放电步骤:驱动控制单元控制所述存储电容通过驱动薄膜晶体管放电,直至所述驱动薄膜晶体管的栅源电压为所述驱动薄膜晶体管的阈值电压Vth;
驱动OLED发光显示步骤:所述驱动控制单元控制所述驱动薄膜晶体管工作于饱和区,并控制所述存储电容两端的电压差值不变,以使得所述驱动薄膜晶体管的栅源电压补偿所述驱动薄膜晶体管的阈值电压Vth,通过所述驱动薄膜晶体管驱动OLED发光。
4.如权利要求3所述的像素单元驱动方法,其特征在于,
所述像素充电步骤包括:第一开关元件断开驱动薄膜晶体管的源极和数据线的连接;所述驱动控制单元导通所述驱动薄膜晶体管的漏极和所述OLED的阴极的连接,导通所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极的连接,导通所述驱动薄膜晶体管的源极和所述数据线的连接,断开所述驱动薄膜晶体管的源极和所述电源线的连接,并控制所述存储电容被充电;
所述像素放电步骤包括:所述驱动控制单元断开所述驱动薄膜晶体管的漏极和所述OLED的阴极的连接,所述驱动控制单元控制所述存储电容通过所述驱动薄膜晶体管放电,直至所述驱动薄膜晶体管的栅源电压为所述驱动薄膜晶体管的阈值电压Vth;
所述驱动OLED发光显示步骤包括:所述第一开关元件导通所述驱动薄膜晶体管的源极和数据线的连接;所述驱动控制单元断开所述驱动薄膜晶体管的栅极和所述驱动薄膜晶体管的漏极的连接,断开所述驱动薄膜晶体管的源极和所述数据线的连接,导通所述驱动薄膜晶体管的源极和所述电源线的连接,控制所述驱动薄膜晶体管工作于饱和区,并控制所述存储电容两端的电压差值不变,以使得所述驱动薄膜晶体管的栅源电压补偿所述驱动薄膜晶体管的阈值电压Vth,通过所述驱动薄膜晶体管驱动OLED发光。
5.一种像素单元,其特征在于,其包括OLED和如权利要求1或2所述的像素单元驱动电路,该像素单元驱动电路与OLED的阳极连接,所述OLED的阴极与驱动电源的低电平输出端连接。
6.一种显示装置,其特征在于,包括多个如权利要求5所述的像素单元。
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