CN1316443C

Movatterモバイル変換

Info

Publication number: CN1316443C
Application number: CNB031209432A
Authority: CN
Inventors: 林巧茹
Original assignee: AU Optronics Corp
Current assignee: AUO Corp
Priority date: 2003-03-24
Filing date: 2003-03-24
Publication date: 2007-05-16
Anticipated expiration: 2023-03-24
Also published as: CN1532788A

Abstract

A current driven active matrix organic light emitting diode pixel circuit and a driving method thereof are provided, in the current driven active matrix organic light emitting diode pixel, before the scanning stage of charging and discharging a capacitor by a current source, a driving power supply is applied to pre-charge the capacitor, so as to improve the problem of insufficient low gray display brightness.

Description

Translated fromChinese

电流驱动的有源矩阵有机发光二极管像素电路及驱动方法Current driven active matrix organic light emitting diode pixel circuit and driving method

技术领域technical field

本发明是有关于一种有源矩阵有机发光二极管像素电路，且特别是有关于一种电流驱动的有源矩阵有机发光二极管像素电路及其驱动方法。The present invention relates to an active matrix organic light emitting diode pixel circuit, and in particular to a current-driven active matrix organic light emitting diode pixel circuit and its driving method.

背景技术Background technique

随着信息科技的发达，各式各样如电脑、移动电路、个人数字助理(PDA)及数字相机等信息设备，均不断地推陈出新。在这些信息设备中，显示器始终扮演着举足轻重的地位，而平面显示器(Flat PanelDisplay)由于具有薄型化、轻量化及省电的特性，乃逐渐地受到欢迎。With the development of information technology, various information devices such as computers, mobile circuits, personal digital assistants (PDAs) and digital cameras are constantly being introduced. In these information devices, the display has always played a pivotal role, and the flat panel display (Flat Panel Display) is gradually popular because of its thinness, light weight and power saving characteristics.

在各种平面显示器中，有源矩阵有机发光二极管(Active MatrixOrganic Emitting Diode，简称AMOLED)显示器因具有视角广、色彩对比效果好、响应速度快及成本低等优点，故十分适用于如电子时钟、移动电路、个人数字助理及数字相机等小尺寸显示器之应用。Among various flat-panel displays, Active Matrix Organic Emitting Diode (AMOLED) displays are very suitable for applications such as electronic clocks, Applications for small-sized displays such as mobile circuits, personal digital assistants, and digital cameras.

请参看图1所示，其为一种电压驱动的有源矩阵有机发光二极管像素示意图。图中显示，此有源矩阵有机发光二极管像素包括：切换开关薄膜晶体管110、驱动薄膜晶体管120、电容130及有机发光二极管140。其显示灰度是由数据线上的电压所决定，当扫描线扫描至此像素时，会导通切换开关薄膜晶体管110，以将数据线的电压传送至驱动薄膜晶体管120的栅极，获得栅极电压Vg以驱动所需电流流经有机发光二极管140显示。然而，由于不同像素的驱动薄膜晶体管120的临界电压与迁移率(mobility)会因为工艺的不均而不同，以致在相同灰度电压下，流经有机发光二极管140的电流也会不同，造成画面显示不均匀的情形。Please refer to FIG. 1 , which is a schematic diagram of a voltage-driven active matrix OLED pixel. As shown in the figure, the active matrix organic light emitting diode pixel includes: a switching thin film transistor 110 , a driving thin film transistor 120 , a capacitor 130 and an organic light emitting diode 140 . Its display grayscale is determined by the voltage on the data line. When the scan line scans to this pixel, the switching thin film transistor 110 will be turned on, so as to transmit the voltage of the data line to the gate of the driving thin film transistor 120 to obtain a gate electrode. The voltage Vg is displayed by flowing the OLED 140 with the required current. However, since the threshold voltage and mobility of the driving thin film transistor 120 of different pixels will be different due to the unevenness of the process, so that the current flowing through the organic light emitting diode 140 will also be different under the same gray-scale voltage, resulting in a large picture. Shows unevenness.

请参看图2所示，其为公知的一种电流驱动的有源矩阵有机发光二极管像素示意图。图中显示，此有源矩阵有机发光二极管像素包括：第一切换开关210、第二切换开关220、第三切换开关230、有机发光二极管240、驱动薄膜晶体管250及电容260。操作时，首先导通第二切换开关220及第三切换开关230，使电流源提供的电流流经驱动薄膜晶体管250，并对电容260充电，此时，会完成记忆栅极电压的动作。然后，切断第二切换开关220及第三切换开关230，并导通第一切换开关210，以控制有源矩阵有机发光二极管像素进入发光显示阶段。Please refer to FIG. 2 , which is a schematic diagram of a known current-driven active matrix OLED pixel. As shown in the figure, the active matrix organic light emitting diode pixel includes: afirst switch 210 , asecond switch 220 , athird switch 230 , an organiclight emitting diode 240 , a drivingthin film transistor 250 and acapacitor 260 . During operation, thesecond switch 220 and thethird switch 230 are first turned on, so that the current provided by the current source flows through the drivingthin film transistor 250 and charges thecapacitor 260 , at this time, the action of memorizing the gate voltage is completed. Then, thesecond switch 220 and thethird switch 230 are turned off, and thefirst switch 210 is turned on, so as to control the active matrix organic light emitting diode pixel to enter the light-emitting display stage.

明显地，此种电流驱动的有源矩阵有机发光二极管像素的灰度是由电流源的电流的大小来决定，其不会受到不同像素间的驱动薄膜晶体管250的临界电压与迁移率的影响，而造成画面显示不均匀的情形。然而，当此种电流驱动的有源矩阵有机发光二极管像素欲显示低灰度时，由于电流源的电流较小，容易受到显示板的寄生电阻、电容所造成的迟滞效应的影响，使得像素无法在扫描时间内完成对栅极电容的充电，因而记忆到错误的栅极电压，以致在后续的发光显示阶段，显示的亮度不足。Obviously, the grayscale of this current-driven active matrix organic light-emitting diode pixel is determined by the magnitude of the current of the current source, which will not be affected by the threshold voltage and mobility of the drivingthin film transistor 250 between different pixels, As a result, the screen display is uneven. However, when such a current-driven active matrix organic light-emitting diode pixel intends to display low grayscale, the current source current is relatively small, which is easily affected by the hysteresis effect caused by the parasitic resistance and capacitance of the display panel, so that the pixel cannot The charging of the gate capacitance is completed within the scan time, so the wrong gate voltage is memorized, so that the display brightness is insufficient in the subsequent light-emitting display stage.

发明内容Contents of the invention

有鉴于此，本发明提供一种电流驱动的有源矩阵有机发光二极管像素电路及其驱动方法，其可于电流源对电容充放电的扫描阶段前，应用一驱动电源来对电容预充电，以改善低灰度显示亮度不足之问题。In view of this, the present invention provides a current-driven active matrix organic light-emitting diode pixel circuit and its driving method, which can apply a driving power supply to pre-charge the capacitor before the scanning phase of the current source charging and discharging the capacitor, so as to Improve the problem of insufficient brightness of low grayscale display.

为达上述及其它目的，本发明提供一种电流驱动的有源矩阵有机发光二极管像素电路，其包括：有源矩阵有机发光二极管像素及预充切换开关。其中，有源矩阵有机发光二极管像素连接一电流源，用以对驱动薄膜晶体管的栅极上的电容充放电，而有源矩阵有机发光二极管像素的灰度，是由电流源的电流的大小来决定。预充切换开关则耦接驱动薄膜晶体管的栅极与一驱动电源，用以在电流源对电容充放电前，控制驱动电源对电容的预充电。To achieve the above and other objectives, the present invention provides a current-driven active matrix organic light emitting diode pixel circuit, which includes: an active matrix organic light emitting diode pixel and a pre-charge switch. Wherein, the active matrix organic light emitting diode pixel is connected with a current source for charging and discharging the capacitance on the gate of the driving thin film transistor, and the gray scale of the active matrix organic light emitting diode pixel is determined by the magnitude of the current of the current source. Decide. The pre-charging switch is coupled to the gate of the driving thin film transistor and a driving power source, and is used for controlling the pre-charging of the capacitor by the driving power source before the current source charges and discharges the capacitor.

在一实施例中，上述的驱动薄膜晶体管为N型薄膜晶体管，而其有源矩阵有机发光二极管像素则更包括：有机发光二极管、第一切换开关、第二切换开关及第三切换开关。其中，有机发光二极管具有阳极端及阴极端，阳极端耦接至正电源。第一切换开关的一端耦接有机发光二极管的阴极端，另一端耦接驱动薄膜晶体管的漏极。第二切换开关的一端耦接电流源，另一端亦耦接驱动薄膜晶体管的漏极。第三切换开关的一端耦接驱动薄膜晶体管的漏极，另一端耦接驱动薄膜晶体管的栅极与电容的一端，而电容的另一端与驱动薄膜晶体管的源极则耦接至负电源。In one embodiment, the above-mentioned driving thin film transistor is an N-type thin film transistor, and the active matrix organic light emitting diode pixel further includes: an organic light emitting diode, a first switching switch, a second switching switch and a third switching switch. Wherein, the OLED has an anode end and a cathode end, and the anode end is coupled to a positive power supply. One end of the first switching switch is coupled to the cathode end of the organic light emitting diode, and the other end is coupled to the drain of the driving thin film transistor. One end of the second switching switch is coupled to the current source, and the other end is also coupled to the drain of the driving thin film transistor. One end of the third switching switch is coupled to the drain of the driving thin film transistor, and the other end is coupled to the gate of the driving thin film transistor and one end of the capacitor, and the other end of the capacitor and the source of the driving thin film transistor are coupled to a negative power supply.

在另一实施例中，上述的驱动薄膜晶体管为P型薄膜晶体管，而其有源矩阵有机发光二极管像素则更包括：有机发光二极管、第一切换开关、第二切换开关及第三切换开关。其中，有机发光二极管具有阳极端及阴极端，阴极端耦接至负电源。第一切换开关的一端耦接有机发光二极管的阳极端，另一端耦接驱动薄膜晶体管的漏极。第二切换开关的一端耦接电流源，另一端亦耦接驱动薄膜晶体管的漏极。第三切换开关的一端耦接驱动薄膜晶体管的漏极，另一端耦接驱动薄膜晶体管的栅极与电容的一端，而电容的另一端与驱动薄膜晶体管的源极则耦接至正电源。In another embodiment, the above-mentioned driving thin film transistor is a P-type thin film transistor, and the active matrix organic light emitting diode pixel further includes: an organic light emitting diode, a first switching switch, a second switching switch, and a third switching switch. Wherein, the OLED has an anode end and a cathode end, and the cathode end is coupled to a negative power supply. One end of the first switching switch is coupled to the anode end of the OLED, and the other end is coupled to the drain of the driving thin film transistor. One end of the second switching switch is coupled to the current source, and the other end is also coupled to the drain of the driving thin film transistor. One end of the third switching switch is coupled to the drain of the driving thin film transistor, the other end is coupled to the gate of the driving thin film transistor and one end of the capacitor, and the other end of the capacitor and the source of the driving thin film transistor are coupled to a positive power supply.

其中，第一切换开关、第二切换开关、第三切换开关及预充切换开关可以为N型薄膜晶体管或P型薄膜晶体管。而驱动电源则亦可使用上述的正电源或负电源，或使用可将电容预充电至电压差接近于驱动薄膜晶体管的临界电压值的驱动电源，以执行电容的预充电。Wherein, the first switching switch, the second switching switch, the third switching switch and the pre-charging switching switch may be N-type thin film transistors or P-type thin film transistors. The driving power can also use the above-mentioned positive power or negative power, or use a driving power that can precharge the capacitor until the voltage difference is close to the critical voltage value of the driving thin film transistor, so as to precharge the capacitor.

此外，为了改善驱动薄膜晶体管的临界电压值，会随着操作时间而漂移的问题，也可以使用具有两个不同电位的驱动电源。也就是当预充电时，使用可将电容预充电至接近于驱动薄膜晶体管的临界电压值的电位，其余时间则使用与预充电极性相反的电位，以排除陷入驱动薄膜晶体管栅极绝缘层中的电荷。In addition, in order to improve the problem that the threshold voltage value of the driving thin film transistor will drift with the operation time, the driving power supply with two different potentials can also be used. That is, when precharging, use a potential that can precharge the capacitor to a value close to the critical voltage value of the driving thin film transistor, and use a potential opposite to the polarity of the precharging for the rest of the time, so as to avoid sinking into the gate insulating layer of the driving thin film transistor charge.

本发明另提供一种电流驱动的有源矩阵有机发光二极管像素驱动方法，此有源矩阵有机发光二极管像素连接一电流源及一驱动电源，用以分别对驱动薄膜晶体管的栅极上的电容充放电。此方法包括下列步骤：首先以驱动电源来对电容执行预充电；然后以电流源来调整电容的灰度充电电压值；以及切断电流源对电容的充放电，以控制有源矩阵有机发光二极管像素进入发光显示阶段。The present invention also provides a current-driven active matrix organic light emitting diode pixel driving method. The active matrix organic light emitting diode pixel is connected to a current source and a driving power supply for charging the capacitance on the gate of the driving thin film transistor respectively. discharge. The method includes the following steps: firstly, a driving power supply is used to precharge the capacitor; then, a current source is used to adjust the grayscale charging voltage value of the capacitor; and the current source is cut off to charge and discharge the capacitor, so as to control the active matrix organic light emitting diode pixel Enter the luminous display stage.

其中，使用可将电容预充电至电压差接近于驱动薄膜晶体管的临界电压值的驱动电源，或如上述地使用具有两个不同电位的驱动电源。Wherein, use a driving power supply that can precharge the capacitor until the voltage difference is close to the critical voltage value of the driving thin film transistor, or use a driving power supply with two different potentials as described above.

由上述说明中可知，应用本发明所提供的一种电流驱动的有源矩阵有机发光二极管像素电路及其驱动方法，因在电流源对电容充放电的扫描阶段前，已应用一驱动电源来对电容预充电，故可解决低灰度显示时，因寄生电阻、电容所造成的迟滞效应导致的亮度不足的问题。From the above description, it can be known that the application of a current-driven active matrix organic light emitting diode pixel circuit and its driving method provided by the present invention has applied a driving power supply to the current source before the scanning phase of charging and discharging the capacitor. The capacitor is pre-charged, so it can solve the problem of insufficient brightness caused by the hysteresis effect caused by parasitic resistance and capacitance during low grayscale display.

附图说明Description of drawings

图1显示一种电压驱动的有源矩阵有机发光二极管像素接线图；Figure 1 shows a wiring diagram of a voltage-driven active matrix OLED pixel;

图2显示公知的一种电流驱动的有源矩阵有机发光二极管像素接线图；FIG. 2 shows a known current-driven active matrix organic light emitting diode pixel wiring diagram;

图3显示根据本发明第一实施例的一种电流驱动的有源矩阵有机发光二极管像素电路接线图；3 shows a wiring diagram of a current-driven active matrix organic light emitting diode pixel circuit according to the first embodiment of the present invention;

图4显示图3中使用N型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路接线图；FIG. 4 shows a wiring diagram of an active matrix organic light-emitting diode pixel circuit using an N-type thin film transistor to make a switch in FIG. 3;

图5显示图4中切换开关的控制信号的操作时序图；Fig. 5 shows the operation timing diagram of the control signal of the switch in Fig. 4;

图6显示根据本发明第二实施例的一种电流驱动的有源矩阵有机发光二极管像素电路接线图；6 shows a wiring diagram of a current-driven active matrix organic light emitting diode pixel circuit according to a second embodiment of the present invention;

图7显示图6中使用P型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路接线图；以及FIG. 7 shows a wiring diagram of an active matrix organic light emitting diode pixel circuit using a P-type thin film transistor to make a switch in FIG. 6; and

图8显示图3中的驱动电源Vt的应用波形图。FIG. 8 shows an application waveform diagram of the driving power Vt in FIG. 3 .

110切换开关薄膜晶体管110 switch thin film transistor

120、250、650驱动薄膜晶体管120, 250, 650 drive thin film transistors

130、260、660电容130, 260, 660 capacitance

140、240、640有机发光二极管140, 240, 640 OLED

210、610第一切换开关210, 610 first switch

220、620第二切换开关220, 620 second switch

230、630第三切换开关230, 630 third switch

270、670预充切换开关270, 670 pre-charge switch

具体实施方式Detailed ways

请参考图3所示，其为根据本发明第一实施例的一种电流驱动的有源矩阵有机发光二极管像素电路。图中显示，此电流驱动的有源矩阵有机发光二极管像素电路除了包含图2的有源矩阵有机发光二极管像素外，更包括连接至驱动电源Vt的一预充切换开关270。Please refer to FIG. 3 , which is a current-driven active matrix OLED pixel circuit according to a first embodiment of the present invention. As shown in the figure, the current-driven AMOLED pixel circuit not only includes the AMOLED pixel shown in FIG. 2 , but also includes apre-charge switch 270 connected to the driving power Vt.

其操作方式为：首先导通预充切换开关270，以使驱动电源Vt可以在电流源对电容260充放电前，先行对电容260预充电至一电压差。此电压差较佳地为接近于驱动薄膜晶体管250的临界电压值的准位，以使电流源对电容260充放电时，因驱动薄膜晶体管250已导通，而可以使电容260的电压差快速地稳定于对应电流源的灰度电流的驱动电压准位。当然，如欲简化像素电路的拉线及电源组数，则亦可以像素的正电源Vdd来作为驱动电源Vt，以对电容260预充电至一电压准位。The operation method is as follows: first turn on theprecharge switch 270 so that the driving power Vt can precharge thecapacitor 260 to a voltage difference before the current source charges and discharges thecapacitor 260 . This voltage difference is preferably at a level close to the threshold voltage value of the drivingthin film transistor 250, so that when the current source charges and discharges thecapacitor 260, the voltage difference of thecapacitor 260 can be rapidly increased because the drivingthin film transistor 250 is turned on. The ground is stable at the driving voltage level of the grayscale current corresponding to the current source. Of course, if it is desired to simplify the number of pull lines and power groups of the pixel circuit, the positive power Vdd of the pixel can also be used as the driving power Vt to precharge thecapacitor 260 to a voltage level.

在预充电后则进入驱动电压调整阶段，此时，切断预充切换开关270并导通第二切换开关220及第三切换开关230，则电容260的电压差将可快速地调整至对应电流源的灰度电流的驱动电压准位。也就是说，若电容260的电压差高于对应电流源的灰度电流的驱动电压准位时，电容260会放电至对应的驱动电压准位，而当电容260的电压差低于对应电流源的灰度电流的驱动电压准位时，电容260会充电至所需的驱动电压准位。After pre-charging, it enters the driving voltage adjustment stage. At this time, thepre-charging switch 270 is turned off and thesecond switch 220 and thethird switch 230 are turned on, so that the voltage difference of thecapacitor 260 can be quickly adjusted to the corresponding current source. The driving voltage level of the gray scale current. That is to say, if the voltage difference of thecapacitor 260 is higher than the driving voltage level of the grayscale current corresponding to the current source, thecapacitor 260 will discharge to the corresponding driving voltage level, and when the voltage difference of thecapacitor 260 is lower than the corresponding current source When the driving voltage level of the grayscale current is reached, thecapacitor 260 will be charged to the required driving voltage level.

之后，像素电路进入发光显示阶段，此时，切断第二切换开关220及第三切换开关230，并导通第一切换开关210。于是流经有机发光二极管240、驱动薄膜晶体管250的漏极与源极的电流，将因电容260之电压差的驱动而等于设定的电流源的灰度电流。Afterwards, the pixel circuit enters into a light-emitting display stage, at this time, thesecond switch 220 and thethird switch 230 are turned off, and thefirst switch 210 is turned on. Therefore, the current flowing through the organiclight emitting diode 240 and the drain and source of the drivingthin film transistor 250 is driven by the voltage difference of thecapacitor 260 to be equal to the grayscale current of the set current source.

其中，第一切换开关210、第二切换开关220、第三切换开关230及预充切换开关270可以为N型薄膜晶体管或P型薄膜晶体管。使用N型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路如图4所示，其切换开关的控制信号的操作时序则如图5所示。而使用P型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路虽未绘示，然熟习此艺者经由参考图4与图5，将可容易地明暸其结构与操作程序。Wherein, thefirst switch 210 , thesecond switch 220 , thethird switch 230 and thepre-charge switch 270 may be N-type thin film transistors or P-type thin film transistors. An active matrix organic light emitting diode pixel circuit using N-type thin film transistors to make switches is shown in FIG. 4 , and an operation sequence of control signals of the switches is shown in FIG. 5 . Although the AMOLED pixel circuit using P-type thin film transistors to make switches is not shown, those skilled in the art can easily understand its structure and operation procedures by referring to FIG. 4 and FIG. 5 .

请参考图6所示，其为根据本发明第二实施例的一种电流驱动的有源矩阵有机发光二极管像素电路。图中显示，此电流驱动的有源矩阵有机发光二极管像素电路除了包含以P型薄膜晶体管来制作驱动薄膜晶体管650的有源矩阵有机发光二极管像素690外，更包括连接至驱动电源Vt的一预充切换开关670。其中，有源矩阵有机发光二极管像素690更包括：电容660、有机发光二极管640、第一切换开关610、第二切换开关620及第三切换开关630。而有机发光二极管640具有阳极端及阴极端，阴极端耦接至负电源Vss。第一切换开关610的一端耦接有机发光二极管640的阳极端，另一端耦接驱动薄膜晶体管650的漏极。第二切换开关620的一端耦接电流源，另一端亦耦接驱动薄膜晶体管650的漏极。第三切换开关630的一端耦接驱动薄膜晶体管650的漏极，另一端耦接驱动薄膜晶体管650的栅极与电容660的一端，而电容660的另一端与驱动薄膜晶体管650的源极则耦接至正电源Vdd。Please refer to FIG. 6 , which is a current-driven active matrix OLED pixel circuit according to a second embodiment of the present invention. As shown in the figure, the current-driven active matrix organic light emitting diode pixel circuit not only includes the active matrix organic light emitting diode pixel 690 made of a P-type thin film transistor to make the drivingthin film transistor 650, but also includes a preset circuit connected to the driving power supply Vt.Charge toggle switch 670. Wherein, the AMOLED pixel 690 further includes: acapacitor 660 , anOLED 640 , afirst switch 610 , asecond switch 620 and athird switch 630 . TheOLED 640 has an anode terminal and a cathode terminal, and the cathode terminal is coupled to the negative power supply Vss. One end of thefirst switch 610 is coupled to the anode end of theOLED 640 , and the other end is coupled to the drain of the drivingthin film transistor 650 . One end of thesecond switch 620 is coupled to the current source, and the other end is also coupled to the drain of the drivingthin film transistor 650 . One end of thethird switch 630 is coupled to the drain of the drivingthin film transistor 650, the other end is coupled to the gate of the drivingthin film transistor 650 and one end of thecapacitor 660, and the other end of thecapacitor 660 is coupled to the source of the drivingthin film transistor 650. Connect to the positive power supply Vdd.

其操作方式为：首先导通预充切换开关670，以使驱动电源Vt可以在电流源对电容660充放电前，先行对电容660预充电至一电压差。此电压差较佳地为接近于驱动薄膜晶体管650的临界电压值的准位，以使电流源对电容660充放电时，因驱动薄膜晶体管650已导通，而可以使电容660的电压差快速地稳定于对应电流源的灰度电流的驱动电压准位。当然，如欲简化像素电路的拉线及电源组数，则亦可以像素的负电源Vss来作为驱动电源Vt，以对电容660预充电至一电压准位。The operation method is as follows: first turn on theprecharge switch 670 so that the driving power Vt can precharge thecapacitor 660 to a voltage difference before the current source charges and discharges thecapacitor 660 . This voltage difference is preferably at a level close to the threshold voltage value of the drivingthin film transistor 650, so that when the current source charges and discharges thecapacitor 660, the voltage difference of thecapacitor 660 can be rapidly increased because the drivingthin film transistor 650 is turned on. The ground is stable at the driving voltage level of the grayscale current corresponding to the current source. Of course, if it is desired to simplify the number of pull lines and power supply groups of the pixel circuit, the negative power supply Vss of the pixel can also be used as the driving power supply Vt to precharge thecapacitor 660 to a voltage level.

在预充电后则进入驱动电压调整阶段，此时，切断预充切换开关670并导通第二切换开关620及第三切换开关630，则电容660的电压差将可快速地调整至对应电流源的灰度电流的驱动电压准位。也就是说，若电容660的电压差高于对应电流源的灰度电流的驱动电压准位时，电容660会放电至对应的驱动电压准位，而当电容660的电压差低于对应电流源的灰度电流的驱动电压准位时，电容660会充电至所需的驱动电压准位。After pre-charging, it enters the driving voltage adjustment stage. At this time, thepre-charging switch 670 is turned off and thesecond switch 620 and thethird switch 630 are turned on, so that the voltage difference of thecapacitor 660 can be quickly adjusted to the corresponding current source. The driving voltage level of the gray scale current. That is to say, if the voltage difference of thecapacitor 660 is higher than the driving voltage level of the grayscale current corresponding to the current source, thecapacitor 660 will discharge to the corresponding driving voltage level, and when the voltage difference of thecapacitor 660 is lower than the corresponding current source When the driving voltage level of the grayscale current is reached, thecapacitor 660 will be charged to the required driving voltage level.

之后，像素电路进入发光显示阶段，此时，切断第二切换开关620及第三切换开关630并导通第一切换开关610。于是流经驱动薄膜晶体管650的源极、漏极与有机发光二极管640的电流，将因电容660的电压差的驱动而等于设定的电流源的灰度电流。Afterwards, the pixel circuit enters into a light-emitting display stage. At this time, thesecond switch 620 and thethird switch 630 are turned off and thefirst switch 610 is turned on. Therefore, the current flowing through the source and drain of the drivingTFT 650 and theOLED 640 is driven by the voltage difference of thecapacitor 660 to be equal to the grayscale current of the set current source.

同样地，第一切换开关610、第二切换开关620、第三切换开关630及预充切换开关670可以为P型薄膜晶体管或N型薄膜晶体管。使用P型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路如图7所示，其切换开关是控制信号的操作时序亦如图5所示。而使用N型薄膜晶体管来制作切换开关的有源矩阵有机发光二极管像素电路虽未绘示，然熟习此艺者经由参考图7与图5，将可容易地明暸其结构与操作程序。Likewise, thefirst switch 610 , thesecond switch 620 , thethird switch 630 and thepre-charge switch 670 can be P-type thin film transistors or N-type thin film transistors. The active matrix organic light emitting diode pixel circuit using P-type thin film transistors to make switches is shown in FIG. 7 , and the operation sequence of the switching switches as control signals is also shown in FIG. 5 . Although the AMOLED pixel circuit using N-type thin film transistors to make switches is not shown, those skilled in the art can easily understand its structure and operation procedures by referring to FIG. 7 and FIG. 5 .

此外，为了改善驱动薄膜晶体管的临界电压值，会随着操作时间而漂移的问题，也可以使用具有两个不同电位的驱动电源。请参考图8所示，其为图3的驱动电源Vt的应用波形图，图中当预充电时，是使用可将电容预充电至接近于驱动薄膜晶体管250的临界电压值的正电位，而其余时间则使用与预充电极性相反的负电位，以排除陷入驱动薄膜晶体管250栅极绝缘层中的电荷。In addition, in order to improve the problem that the threshold voltage value of the driving thin film transistor will drift with the operation time, the driving power supply with two different potentials can also be used. Please refer to FIG. 8, which is an application waveform diagram of the driving power Vt in FIG. For the rest of the time, a negative potential opposite to that of the pre-charging polarity is used to eliminate charges trapped in the gate insulating layer of the drivingthin film transistor 250 .

综上所述，可归纳一种电流驱动的有源矩阵有机发光二极管像素驱动方法。此有源矩阵有机发光二极管像素连接一电流源及一驱动电源，用以分别对驱动薄膜晶体管的栅极上的电容充放电。此方法包括下列步骤：首先以驱动电源来对电容执行预充电；然后以电流源来调整电容的灰度充电电压值；以及切断电流源对电容的充放电，以控制有源矩阵有机发光二极管像素进入发光显示阶段。In summary, a current-driven active matrix organic light-emitting diode pixel driving method can be summarized. The active matrix organic light emitting diode pixel is connected with a current source and a driving power supply for charging and discharging the capacitance on the gate of the driving thin film transistor respectively. The method includes the following steps: firstly, a driving power supply is used to precharge the capacitor; then, a current source is used to adjust the grayscale charging voltage value of the capacitor; and the current source is cut off to charge and discharge the capacitor, so as to control the active matrix organic light emitting diode pixel Enter the luminous display stage.

其中，系使用可将电容预充电至电压差接近于驱动薄膜晶体管的临界电压值的驱动电源，或使用具有两个不同电位的驱动电源。Wherein, a driving power source that can precharge the capacitor until the voltage difference is close to the critical voltage value of the driving thin film transistor is used, or a driving power source with two different potentials is used.