CN101040313A - 有机el驱动电路和有机el显示装置 - Google Patents
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Abstract
提供能防止D/A变换电路的较高耐压的晶体管的输出电流下降引起的有机EL面板的显示画面的烧伤的有机EL显示装置。本发明在电流反射镜电路结构的D/A(1)的输出一侧1和D/A的输出端子(10a)之间串联设置多个较高耐压的晶体管(Q1、Q2),构成电流反射镜电路的D/A的输出一侧晶体管(TNb~TNn)用耐压较低的晶体管构成,在D/A的给定输出端子驱动模拟变换电流。据此,D/A的输出一侧晶体管能是与输入一侧晶体管同样耐压低的晶体管,能降低D/A的专有面积。
Description
技术领域
本发明涉及有机EL驱动电路和有机EL显示装置,具体而言,涉及防止串联插入到设置在无源矩阵型有机EL显示面板的电流驱动电路的内部的D/A变换电路(D/A)的输出一侧晶体管的较高耐压的晶体管的热载流子引起的耗尽层的烧伤现象,从而能防止输出电流的下降引起的有机EL面板的烧伤的有机EL驱动电路。
背景技术
在无源矩阵型或有源矩阵型的有机EL显示面板中,为了降低耗电,在以3V~5V左右的电源电压工作的基准电流发生电路中生成基准电流,把该基准电流用基准电流分配电路对应地分配给有机EL面板的各端子。分配的各端子对应的基准电流输送给对应设置在各端子的D/A等,作为端子对应的基准驱动电流。在端子上对应设置的D/A中,根据基准驱动电流,对显示数据进行D/A变换,生成与显示数据对应的驱动电流,驱动与各端子对应设置的用电源电压15V~20V工作的输出电流源。输出电流源的输出电流作为驱动电流输送给有机EL面板的端子,分别发光驱动与端子对应设置的有机EL元件,发光(专利文献1)。
因此,在电流驱动电路中分别设置以3V~5V左右的低的电源电压工作的驱动电路和以15V~20V左右的高电源电压工作的电路。因此,在它们之间,跨2个电源电压工作的电路成为必要。在专利文献1中,由电流反射镜电路构成的D/A的输出一侧晶体管担当该电路。因此,D/A的电流反射镜电路的输入一侧晶体管以电源电压3V~5V工作,电流反射镜电路的输出一侧晶体管以高的电源电压15V~20V左右工作的电路。
专利文献1:特开2003-308043号公报
构成专利文献1中表示的D/A的电流反射镜电路的输出一侧晶体管使用高耐压的MOS晶体管。输出一侧晶体管为了D/A变换,具有位权重,设置多个,所以高耐压晶体管的数量变得非常多。因此,存在D/A的专有面积增加的问题。
为了解决这样的问题,申请人把在电流反射镜电路的输入一侧晶体管和输出一侧晶体管串联插入较高耐压的MOS晶体管的发明作为特愿2004-95006号提出。
据此,存在能使电流反射镜电路的输出一侧晶体管为低耐压的晶体管,并且能减小输出一侧晶体管的专有面积的优点。
可是,对端子输送的有机EL元件的驱动电流为了对成为电容性负载的有机EL元件进行初始充电、驱动,在驱动初期为峰值电流。驱动电流的峰值电流的生成存在由比D/A更前级的电路进行的情形和由比D/A更后级的电路进行的情形。在所述的特开2003-234655号公报中,在D/A和输出级电流源之间放置峰值电流生成电路(专利文献2)。在特开2003-308043号中,在D/A的电流反射镜电路的输入一侧设置峰值电流生成电路(专利文献3)。
专利文献2:特开2003-234655号公报
专利文献3:特开2003-308043号公报
发明内容
可是,为了使电流反射镜电路的输出一侧晶体管为低耐压的晶体管,必须增大对它串联插入的较高耐压的MOS晶体管的漏极-源极间电压VDS。结果,由于高的电源电压一侧的电压变动,漏极电压VD超过饱和电压VDsat,如果栅极-源极间电压为VGS,栅极阈值为Vth,就发生VGS-Vth<<VDS的情形。据此,在电流反射镜电路的输出一侧晶体管串联插入的较高耐压的MOS晶体管的漏极一侧产生热载流子。在暂时的时间中,热载流子消除,沟道-漏极之间的耗尽层的宽度回到原来,但是如果跨长时间在所述较高耐压的MOS晶体管上作用高的漏极电压VD,在它的漏极一侧夹断固定下来,出现所谓的沟道-漏极之间的耗尽层残留的耗尽层的烧伤现象。这时,栅氧化膜充电,栅极阈值Vth上升,输出电流下降。因此,由来自与它对应的端子的驱动电流驱动的有机EL元件的亮度下降,发生显示画面的烧伤现象。
如专利文献3那样,如果在D/A的电流反射镜电路的输入一侧设置峰值电流生成电路,与峰值电流对应的D/A变换的模拟变换的电流值增大,所以容易产生热载流子。
本发明的目的在于,解决所述以往技术的问题,提供防止在D/A的输出一侧晶体管串联插入的较高耐压的晶体管的热载流子引起的耗尽层的烧伤现象,从而能防止输出电流的下降引起的有机EL面板的显示画面的烧伤的有机EL驱动电路。
本发明的其他目的在于,提供能防止D/A变换电路的较高耐压的晶体管的输出电流下降引起的有机EL面板的显示画面的烧伤的有机EL显示装置。
用于实现这样的目的的本发明的有机EL驱动电路和有机EL显示装置的结构是一种有机EL驱动电路,由电流反射镜电路构成的D/A变换电路在电流反射镜电路的输入一侧晶体管接受给定的电流,把显示数据进行D/A变换,把对有机EL的端子输出的驱动电流或成为其基础的电流对D/A变换电路的输出端子输出,其中:在电流反射镜电路的输出一侧晶体管和输出端子之间具有第一和第二晶体管的串联电路,输入一侧晶体管和输出一侧晶体管是比第一和第二晶体管的耐压低的晶体管,输入一侧晶体管通过电路元件或者电路与第一电源线连接,串联电路通过其他电路元件或者其他电路与比第一电源线的电压还高的第二电源线连接。
本发明在电流反射镜电路结构的D/A的输出一侧和D/A的输出端子之间串联多个较高耐压的晶体管,构成电流反射镜电路的D/A的输出一侧晶体管由耐压较低的晶体管构成,在D/A的给定输出端子驱动模拟变换电流。据此,能使D/A的输出一侧晶体管为与输入一侧晶体管同样耐压低的元件,能降低D/A的专有面积。输出一侧晶体管成为耐压低的晶体管,从而在电流反射镜电路结构的D/A中,能减少较高耐压的元件的数量。此外,在D/A的输出一侧和D/A的给定输出端子之间串联多个较高耐压的晶体管,所以电源电压由这些晶体管分压,各晶体管的漏极电压接受分压的电压。因此,构成D/A的各较高耐压的晶体管的漏极电压能抑制在热载流子感应电压VDshc或其以下。
据此,在电流反射镜电路结构的D/A的输出一侧晶体管和D/A的输出端子之间插入的较高耐压的晶体管中难以发生热载流子,能防止有机EL面板的显示画面的烧伤。而且,能用耐压较低的晶体管构成D/A的输出一侧晶体管,所以能抑制电流驱动电路的电路规模的增加。
附图说明
图1是应用本发明的有机EL驱动电路的一个实施例的无源型有机EL驱动面板的有机EL驱动电路的框图。
图2是构成D/A的单元电路的电路结构的说明图。
图3是在输出级电流源和D/A的输出端子之间设置高耐压源极跟随器2级的串联电路时的D/A的输出电流的经年变化特性的说明图。
符号的说明。
1-晶体管单元电路;9-有机EL元件(OEL元件);10-列驱动器;10a-输出端子;11-D/A;12-恒流源;13-输出级电流反射镜电路;14~16-恒压偏置电路;17-控制电路;18-晶体管;19-MPU;Q1~Q3-MOS晶体管;Tr1~Tr3-MOS晶体管;TNa~TNn-1-MOS晶体管;SW-复位开关电路。
具体实施方式
图1是应用本发明的有机EL驱动电路的一个实施例的无源型有机EL驱动面板的有机EL驱动电路的框图,图2是构成D/A的单元电路的电路结构的说明图,图3是在输出级电流源和D/A的输出端子之间设置高耐压源极跟随器(follower)2级的串联电路时的D/A的输出电流的经年变化特性的说明图。在图1中,10是有机EL驱动电路的列驱动器IC,11是它的D/A,12是产生基准驱动电流Ir的恒流源,14~16是恒压偏置电路,17是控制电路,18是存储显示数据的寄存器,19是MPU。
D/A11由基于输入一侧晶体管单元TNa和输出一侧晶体管单元TNb~TNn的电流反射镜电路构成。
各晶体管单元TNa~TNn由把具有漏极端子D和栅极端子G1、G2、输入端子Din、源极端子S的图2所示的N沟道晶体管Tr1~Tr3在电源线和地线之间纵向串联的单元电路1构成。
各单元电路1的源极端子S连接在地线GND上。晶体管单元TNa的单元电路1的输入端子Din连接在偏压线Va上,维持在ON状态。各晶体管单元TNb~TNn的各单元电路1的输入端子Din从显示寄存器18分别接受显示数据D0~Dn-1,各晶体管单元TNb~TNn的开关电路SW(各单元电路1的晶体管Tr3)按照显示数据D0~Dn-1而导通/断开。显示数据D0~Dn-1按照控制电路17的闩锁脉冲,从MPU19设置到显示寄存器18。
各晶体管单元TNa~TNn的各单元电路1的栅极端子G1、G2分别公共连接,晶体管单元TNa的单元电路1的栅极端子G2连接在D/A11的输入端子11a上。此外,晶体管单元TNa的单元电路1的漏极端子D也连接在D/A11的输入端子11a上。据此,晶体管单元TNa的单元电路1的晶体管Tr2进行二极管连接,该晶体管Tr2成为电流反射镜电路的输入一侧晶体管,从恒流源12接受驱动电流Ir。
须指出的是,如所述特开2003-308043号那样,在D/A的电流反射镜电路的输入一侧设置峰值电流生成电路时,如图1中用虚线表示的单元电路1那样,并联设置2个输入一侧晶体管单元TNa,并联设置的第二个输入一侧晶体管单元TNa的单元电路1的输入端子Din不与偏压线Va连接,接受产生峰值电流的控制脉冲(未图示)的反相信号,在不产生峰值电流的期间导通。据此,把电流源12的驱动电流Ir分流到2个输入一侧晶体管单元TNa,能降低恒流驱动时的输入一侧晶体管的驱动电流。须指出的是,第二个输入一侧晶体管单元TNa的栅极宽度比对于第一个输入一侧晶体管单元TNa,成为1∶n(n是2以上的整数)。
恒流源12连接在5V左右的电源线+VDD上,它与基准电流分配电路的输出电流源对应。基准电流分配电路是由电流反射镜电路构成的输入一侧晶体管接受基准电流,在与端子对应并联设置的多个输出一侧晶体管,作为反射镜电流,复制基准电流,与列端子对应分配的电路。输出一侧晶体管是恒流源12。
各晶体管单元TNb~TNn的各单元电路1的漏极端子D通过分别对应设置的较高耐压的N沟道的各晶体管Q1的源极-漏极,公共连接在N沟道的晶体管Q2的源极上。晶体管Q2的漏极连接在D/A11的输出端子11b上。
这里,晶体管Q1、Q2对于电流反射镜电流输出电路13的输入一侧晶体管TPu、TPx,形成2级源极跟随器的串联电路。
据此,各晶体管单元TNb~TNn的各漏极端子D通过耐压较高的晶体管Q1、Q2的串联电路连接在输出端子11b上。输出端子11b连接在电流反射镜电流输出电路13的输入端子13b上。
这里,晶体管Q1、Q2的栅极电压VGM、VGH设定在5V、10V左右,各晶体管单元TNb~TNn的各漏极端子D与输入一侧晶体管单元TNa同样限制在5V以下。因此,即使电源电压+Vcc稍微变动,各晶体管Q1、Q2的漏极电压也成为把高的电源电压分压的形式,所以能把各漏极电压抑制在热载流子感应电压VDshc或它以下的电压。
这里,如果D/A11的模拟变换电流的输出电流值为Ia,就对输出级电流反射镜电路13的输入端子13b输入驱动电流Ia。
输出级电流反射镜电路13具有构成基电流修正驱动用的电流反射镜电路的P沟道MOSFET晶体管TPu、TPw、构成输出级电流反射镜电路的P沟道MOSFET晶体管TPx、TPy。
输出级电流反射镜电路13的晶体管TPx和晶体管TPy的沟道宽度(栅极宽度)比是1∶N(可是,N>1),这些晶体管的源极不是电源线+VDD(5V),连接在比它高的电压例如+15V~20V左右的电源线+Vcc上。输出一侧晶体管TPy的输出连接在列一侧的输出端子10a上,在驱动时,N×Ia的驱动电流流到输出端子10a,以电流驱动有机EL面板。在输出端子10a和地线GND之间连接有机EL元件9。须指出的是,输出端子10a是有机EL元件9的列端子的同时,也是输出级电流反射镜电路13的输出端子。图中的13a是把N沟道晶体管进行3级从属连接的输出级电流反射镜电路13的偏置电路,Vb是偏压线。
在输出端子10a和地线GND之间设置复位开关电路SW。复位开关电路SW从控制电路17接受复位信号RS。各晶体管单元TNa~TNn的公共连接的各单元电路1的栅极端子G1连接在恒压偏置电路14上。用由恒压偏置电路14设定的栅极电压VGL,各单元电路1的上游一侧的晶体管T1以给定的电阻值设定为导通状态。栅极电压VGL是3V左右的电压。
各晶体管Q1的栅极公共连接,连接在恒压偏置电路15上,用据此设定的栅极电压VGM,例如5V,以给定的电阻值设定为导通状态。晶体管Q2的栅极连接在恒压偏置电路16上,用据此设定的栅极电压VGH,例如10V,以给定的电阻值设定为导通状态。通过这些栅极电压VGM、VGH,各晶体管单元TNb~TNn的漏极端子D把各单元电路1的各晶体管Tr1的漏极电压限制在5V或它以下,用耐压低的晶体管就可以。
在输出一侧晶体管串联插入晶体管Q1、Q2,通过这些晶体管,产生比较大的电压下降,能降低晶体管TPa和各晶体管单元TNa~TNn的工作电压。
各晶体管Q1的栅极连接在恒压偏置电路14上,能把各晶体管单元TNb~TNn的漏极端子D的电压设定为实质上相等的值。对D/A11的输出一侧的各晶体管单元TNb~TNn使用耐压低的晶体管。而且,在输出端子11b和各晶体管单元TNb~TNn之间插入的较高耐压的晶体管Q1、Q2中,因为漏极电压由这些晶体管分割,所以难以产生热载流子,能防止热载流子引起的输出电流下降导致的烧伤现象。
输出一侧晶体管成为耐压低的晶体管,在电流反射镜电路结构的D/A中,较高耐压的元件的数量减少。
结果,D/A的占有面积减少,并且能提高D/A变换精度,也能防止D/A的晶体管Q1、Q2热载流子引起的输出电流下降导致的显示画面的烧伤现象。
D/A的变换特性的偏移减少,列端子相互的输出电流的偏移减少,据此,能抑制显示画面的亮度不均匀、亮度偏移。可是,与各晶体管单元对应表示的×1、×2、×4…的数字表示并联的单元电路1的数量。×1时,没有并联。按照单元电路数,输出一侧晶体管单元TNb~TNn对各输出付与位权重。
那么,构成D/A11的各晶体管单元TNa~TNn的单元电路1如图2所示,由在源极-漏极和电源线和地线GND之间纵向堆积串联的3个N沟道晶体管Tr1~Tr3构成。晶体管Tr3构成开关电路SW,源极连接在源极端子S上。晶体管Tr1的漏极连接在漏极端子D上。
晶体管Tr2的栅极连接在栅极端子G1上,晶体管Tr3的栅极连接在栅极端子G2上。
须指出的是,晶体管Tr1~Tr3的后栅极公共连接在源极端子S上。
图3是在输出端子11b和各晶体管单元TNb~TNn之间设置由晶体管Q1、Q2构成的高耐压的2级源极跟随器的串联电路的图1所示的D/A11的输出电流的经年变化特性的说明图。
纵轴是输出电流Ia[μA],横轴是时间t[h],曲线A不是晶体管Q2,是在D/A的输出端子11b和输出一侧晶体管之间连接晶体管Q1的情形。曲线B是在输出端子11b串联晶体管Q1、Q2的所述实施例的情形。电源电压+Vcc以22V设定为110%左右高的值。
在曲线A中,随着超过100小时,输出电流渐渐下降,但是在曲线B中,即使超过1000小时,也能维持特定。
产业上的可利用性
虽然以上已经说明,但是在实施例中,较高耐压的多个晶体管Q1与D/A的电流反射镜电路的各输出一侧晶体管单元TNb~TNn的输出(漏极D)分别对应设置,这些晶体管Q1与一个晶体管Q2串联连接。可是,本发明虽然D/A变换精度下降,但是晶体管Q1为一个,对于晶体管Q1、Q2的一个串联电路,当然公共连接电流反射镜电路的各输出一侧晶体管单元TNb~TNn的输出(漏极D)。
此外,在实施例中,用D/A的输出电流驱动输出级电流源,但是本发明在不存在输出级电流源,D/A的输出一侧直接或通过其他电路与高的电源电压线连接,直接把D/A的输出电流输送给有机EL面板的端子的情形,也能应用本发明。
在实施例中,虽然把无源型有机EL显示面板的驱动电路作为例子,但是本发明当然也能应用在有源型有机EL显示面板的驱动电路中。
在实施例中,表示以N沟道MOS晶体管为主体的D/A,但是D/A当然也可以是组合P沟道MOS晶体管和N沟道MOS晶体管的电路。
此外,在实施例中,使用MOS晶体管,但是本发明当然也可以置换MOS晶体管,使用双极性晶体管。
Claims (11)
1.一种有机EL驱动电路,由电流反射镜电路构成的D/A变换电路在所述电流反射镜电路的输入一侧晶体管接受给定的电流,对显示数据进行D/A变换,将对有机EL面板的端子输出的驱动电流或成为其基础的电流输出到所述D/A变换电路的规定的输出端子,其中:
在所述电流反射镜电路的输出一侧晶体管和所述规定的输出端子之间具有第一和第二晶体管的串联电路;
所述输入一侧晶体管和所述输出一侧晶体管是比所述第一和第二晶体管的耐压还低的晶体管,所述输入一侧晶体管通过电路元件或者某一电路与第一电源线连接,所述串联电路通过其他电路元件或者其他某一电路与比所述第一电源线的电压还高的第二电源线连接。
2.根据权利要求1所述的有机EL驱动电路,其中:
所述串联电路经过所述给定的输出端子通过所述其他电路元件或者所述其他某一电路与所述第二电源线连接。
3.根据权利要求1所述的有机EL驱动电路,其中:
在所述第二电源线和基准电位线之间串联所述第一和第二晶体管各自的输出一侧的2端子,而形成所述串联电路,未连接于所述第二晶体管的所述第一晶体管的所述输出一侧的1端子与各所述输出一侧晶体管的输出连接,未连接于所述第一晶体管的所述第二晶体管的所述输出一侧的1端子与所述给定的输出端子连接。
4.根据权利要求3所述的有机EL驱动电路,其中:
所述第一晶体管有多个,所述输出一侧晶体管也有多个,各所述第一晶体管与一个或多个所述输出一侧晶体管的输出公共连接,各所述第一晶体管的另一端子与所述第二晶体管的所述输出一侧的另一端子公共连接。
5.根据权利要求4所述的有机EL驱动电路,其中:
所述第一晶体管和所述第二晶体管是MOS晶体管,所述输出一侧的2端子是源极和漏极,所述第一晶体管与各所述输出一侧晶体管分别对应设置。
6.根据权利要求4所述的有机EL驱动电路,其中:
多个各所述输出一侧晶体管由晶体管单元构成,所述晶体管单元成为多个晶体管串联的单元电路,与D/A变换的位权重对应,所述晶体管单元并联,而构成多个各所述输出一侧晶体管中的几个。
7.根据权利要求6所述的有机EL驱动电路,其中:
作为所述其他某一电路,具有输出级电流源,所述输入一侧晶体管也由所述晶体管单元构成,所述给定的输出端子与所述输出级电流源的输入端子连接,所述输出级电流源以所述第二电源线的电压工作,产生所述驱动电流。
8.根据权利要求7所述的有机EL驱动电路,其中:
所述基准电位的线处于接地电位,所述第一晶体管和所述第二晶体管是MOS晶体管,并且各栅极电位分别设定为所述第二电源线和所述基准电位线之间存在的给定的电位。
9.根据权利要求8所述的有机EL驱动电路,其中:
所述晶体管单元是3个MOS晶体管的源极-漏极在所述第一电源线和所述第二电源线中的任意一个和所述基准电位线之间串联的与所述不同的串联电路。
10.根据权利要求7所述的有机EL驱动电路,其中:
所述输出级电流源的输出通过无源矩阵型有机EL面板的端子对有机EL元件输送。
11.一种有机EL显示装置,具有权利要求1~10中的任意一项所述的有机EL驱动电路。
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