KR102244932B1 - Organic light emitting display device and method for driving thereof - Google Patents

Abstract

In the embodiment according to the present invention, the voltage on the anode electrode of the organic light-emitting device is kept constant regardless of the deviation of the threshold voltage of the driving transistor, so that the boosting loss is uniformly increased as the voltage on the anode electrode of the organic light-emitting device rises to the operating point. Thus, the luminance deviation can be compensated.

Description

An organic light emitting display device and its driving method TECHNICAL FIELD OF THE INVENTION

The present invention relates to a display device, and more particularly, to an organic light emitting display device including a thin film transistor.

In recent years, as the era develops into an information society, the importance of a flat panel display device having excellent characteristics such as reduction in thickness, weight, and low power consumption is increasing. Among flat panel displays, liquid crystal displays including thin film transistors and organic light-emitting displays are excellent in resolution, color display, and image quality, and are widely commercialized as display devices for televisions, notebook computers, tablet computers, or desktop computers. In particular, the organic light emitting display device has a high response speed, low power consumption, and is self-luminous, so it is drawing attention as a next-generation flat panel display device because there is no problem in viewing angle.

1 is a circuit diagram illustrating a pixel structure of a general organic light emitting display device

to be. Referring to FIG. 1, a pixel P of a general organic light emitting display device includes a switching transistor Tsw, a driving transistor Tdr, a capacitor Cst, and an organic light emitting diode OLED.

The switching transistor Tsw is switched according to the scan pulse SP supplied to the scan line SL to supply the data voltage Vdata supplied to the data line DL to the driving transistor Tdr.

The driving transistor Tdr is switched according to the data voltage Vdata supplied from the switching transistor Tsw, so that the data current Ioled flows from the driving power EVdd supplied from the driving power line to the organic light emitting diode OLED. Control.

The capacitor Cst is connected between the gate terminal and the source terminal of the driving transistor Tdr to store a voltage corresponding to the data voltage Vdata supplied to the gate terminal of the driving transistor Tdr, and the stored voltage is used for the driving transistor. Turn on (Tdr).

The organic light emitting diode OLED is electrically connected between the source terminal of the driving transistor Tdr and the cathode line EVss to emit light by the data current Ioled supplied from the driving transistor Tdr.

Each pixel P of such a general organic light-emitting display device controls the amount of data current Ioled flowing through the organic light-emitting device OLED by using switching of the driving transistor Tdr according to the data voltage Vdata. By emitting the device OLED, a predetermined image is displayed. However, in a general organic light-emitting display device, there is a problem in that the threshold voltage Vth of the transistors Tdr and Tsw, particularly the driving transistor Tdr, differs for each pixel according to the non-uniformity of the manufacturing process of the thin film transistor. Accordingly, in a typical organic light emitting diode display, there is a problem in that reliability of the thin film transistor and the display panel is deteriorated due to an initial dispersion of the threshold voltage of the thin film transistor included in each pixel or a shift of the threshold voltage over time. In order to solve this problem, a lot of techniques have been introduced to compensate for the deviation of the threshold voltage of the thin film transistor by applying a data voltage reflecting the threshold voltage of the thin film transistor. However, in the general threshold voltage compensation method, the voltage on the source node of the driving transistor, that is, the organic light-emitting device connected to the source node of the driving transistor, according to the threshold voltage of the driving transistor during the emission period in which the threshold voltage is compensated and an image is displayed based on it. The voltage of the anode electrode is different. As the voltage of the anode electrode of the organic light-emitting device varies, the amount of boosting loss that occurs when the voltage on the anode increases to the operating point of the organic light-emitting device varies depending on the voltage on the anode electrode before rising to the operating point. There is a problem that luminance deviation occurs.

The embodiments of the present invention have been devised to solve the above-described problems, and an object of the present invention is to provide an organic light emitting display device and a driving method thereof capable of compensating for a change in driving characteristics of a driving transistor.

In addition, an embodiment according to the present invention is to provide an organic light emitting display device and a driving method thereof, which is capable of extending the reliability and life of a switching transistor for compensation of the driving transistor while compensating for the threshold voltage of the driving transistor. It should be.

In addition, another object of the present invention is to provide an organic light-emitting display device and a driving method thereof in which image quality can be improved by accurately compensating for a threshold voltage of a driving transistor between pixels.

In addition, in the embodiment according to the present invention, the voltage on the anode electrode of the organic light emitting device is kept constant regardless of the deviation of the threshold voltage of the driving transistor, thereby reducing the boosting loss as the voltage on the anode electrode of the organic light emitting device rises to the operating point. By making it uniform, it is possible to compensate for the luminance deviation.

In addition to the technical problems of the present invention mentioned above, other features and advantages of the present invention will be described below or will be clearly understood by those of ordinary skill in the art from such technology and description.

An embodiment of the present invention includes a data line, a gate line group, and a pixel connected to a reference line, wherein the pixels control an organic light-emitting device, a current flowing through the organic light-emitting device, and have a semiconductor layer interposed therebetween. A driving transistor including overlapping first and second gate electrodes, a first switching transistor selectively supplying a data voltage supplied to the data line to a first node connected to the first gate electrode, and a first or second sensing A second switching transistor selectively supplying a voltage for the second gate electrode to the second gate electrode, a third switching transistor selectively connecting a second node connected to the source electrode of the driving transistor to the first node, and the reference line A fourth switching transistor selectively connected to a second node, a first capacitor connected between the second gate electrode and the second node to store a threshold voltage of the driving transistor, and a first capacitor connected between the first and second nodes to be connected to the second node. And a second capacitor storing a difference voltage between the first and second nodes, wherein the second sensing voltage is a sum voltage of the first sensing voltage and a threshold voltage of the driving transistor, and the second sensing When the driving transistor is operated in the source follower mode according to the voltage, the voltage of the source terminal of the driving transistor, that is, the anode terminal of the organic light emitting device, becomes the first sensing voltage, and the threshold voltage of the driving transistor is shifted. Regardless of the light emission driving, the image quality may be uniform by making the boosting degree equal to the operating point from the first sensing voltage.

According to an exemplary embodiment of the present invention, the threshold voltage of the driving transistor can be externally sensed and the threshold voltage of the driving transistor can be compensated by an external compensation method through data correction, thereby accurately correcting the threshold voltage deviation of the driving transistor between pixels. There is an effect that the image quality can be improved by compensating.

In addition, in the embodiment according to the present invention, the voltage on the anode electrode of the organic light emitting device is kept constant regardless of the deviation of the threshold voltage of the driving transistor, thereby reducing the boosting loss as the voltage on the anode electrode of the organic light emitting device increases to the operating point. By making it uniform, there is an effect of compensating for luminance deviation.

1 is a circuit diagram illustrating a pixel structure of a general organic light emitting diode display.
2 is a diagram illustrating a structure of a pixel according to an embodiment of the present invention in an organic light emitting diode display according to an embodiment of the present invention.
3 is a view for explaining the structure of the driving transistor shown in FIG. 2.
4 is a signal waveform diagram on a scan control line, a sensing control line, and a reset control line of a gate line group according to an embodiment of the present invention.
5 is a voltage waveform diagram on two gate electrodes and a second node according to the waveform diagram of FIG. 4.
6 to 11 are views illustrating an operation of an organic light emitting diode display according to an exemplary embodiment of the present invention.
12 is a diagram illustrating a structure of a pixel according to another exemplary embodiment of the present invention.
13 is a diagram illustrating a structure of a pixel according to another exemplary embodiment of the present invention.
14 is a diagram illustrating an organic light emitting display device according to an exemplary embodiment of the present invention.
15 is a diagram conceptually illustrating driving of an organic light emitting diode display according to an exemplary embodiment of the present invention.
16 is a view for explaining the column driver shown in FIG. 14;

Hereinafter, an organic light emitting diode display according to an exemplary embodiment of the present invention and a driving method thereof will be described in detail with reference to the drawings. The following embodiments are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In addition, in the drawings, the size and thickness of the device may be exaggerated for convenience. The same reference numerals represent the same elements throughout the specification.

The meaning of the terms described in this specification should be understood as follows. Singular expressions should be understood as including plural expressions unless clearly defined differently in context, and terms such as “first” and “second” are used to distinguish one element from other elements, The scope of rights should not be limited by these terms. It is to be understood that terms such as "comprises" or "have" do not preclude the presence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. The term “at least one” is to be understood as including all possible combinations from one or more related items. For example, the meaning of “at least one of the first item, the second item, and the third item” means that each of the first item, the second item, or the third item, as well as the first item, the second item, and the third item, It means a combination of all items that can be presented from more than one. The term "on" means not only when a certain component is formed directly on the top of another component, but also when a third component is interposed between these components. Means to include.

Hereinafter, exemplary embodiments of an organic light emitting diode display and a driving method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a diagram illustrating a structure of a pixel according to a first exemplary embodiment of the present invention in an organic light emitting display device according to an exemplary embodiment of the present invention, and FIG. 3 is a diagram illustrating the structure of the organic light emitting element illustrated in FIG. 2. to be. And FIG. 4 is a diagram for explaining the structure of the driving transistor shown in FIG. 2.

Referring to FIG. 2, the pixel P according to the first embodiment of the present invention includes a data line DL, a gate line group GLG, a reference line RL, a first driving power line PL1, and a second power supply line. It is connected to the driving power supply line PL2.

The data line DL is formed along a first direction, for example, a vertical direction of a display panel (not shown). A data voltage Vdata is supplied to the data line DL from a data driver (not shown).

The gate line group GLG is formed along a second direction of the display panel, for example, a horizontal direction to cross the data line DL. The gate line group GLG includes a scan control line Lscan, a sensing control line License, and a reset control line Lreset.

The reference line RL is formed to be parallel to the data line DL. The reference line RL may be selectively connected to a reference power line to which a reference voltage Vref of a constant DC level is supplied, may be connected to a sensing unit to be described later, or may be in a floating state.

The first driving power line PL1 is formed to be parallel to the data line DL, and a high potential voltage EVdd is supplied from the outside.

The second driving power line PL2 is formed in a cylindrical shape or a line shape to be connected to the organic light emitting device, and a low potential voltage EVss is supplied from the outside.

The pixel P may be a red pixel, a green pixel, a blue pixel, or a white pixel. The pixel P includes an organic light emitting diode (OLED), a driving transistor (Tdr), first to fourth switching transistors (Tsw1, Tsw2, Tsw3, Tsw4), and first and second capacitors (C1, C2). It is composed of. Here, each of the transistors (Tsw1, Tsw2, Tsw3, Tsw4, Tdr) is an N-type thin film transistor (TFT), and may be an a-Si TFT, a poly-Si TFT, an oxide TFT, or an organic TFT. have.

The organic light emitting diode OLED is connected between a first driving power line PL1 supplied with a high potential voltage EVdd and a second driving power line PL2 supplied with a low potential voltage EVss. Referring to FIG. 3, the organic light emitting diode OLED includes an anode electrode connected to a second node n2, which is a source electrode of the driving transistor Tdr, an organic layer (not shown) formed on the anode, and an organic layer. It includes a cathode electrode. In this case, the organic layer may be formed to have a structure of a hole transport layer/organic emission layer/electron transport layer or a structure of a hole injection layer/hole transport layer/organic emission layer/electron transport layer/electron injection layer. Furthermore, the organic layer may further include a functional layer for improving the luminous efficiency and/or lifespan of the organic emission layer. In addition, the cathode electrode is formed for each pixel row or column along the length direction of the gate line group GLG or the data line DL, or a second driving power line PL2 formed to be commonly connected to all pixels P. Is connected to As such, the organic light-emitting device OLED emits light by a current flowing from the first driving power line PL1 to the second driving power line PL2 according to the driving of the driving transistor Tdr.

The driving transistor Tdr is connected between the first driving power line PL1 and the anode electrode of the organic light-emitting device OLED to measure the amount of current flowing to the organic light-emitting device OLED according to a gate-source voltage. Control. To this end, the driving transistor Tdr is, as shown in FIG. 4, a first gate electrode g1_Tdr, a gate insulating layer 12, a semiconductor layer 14, a source electrode s_Tdr, and a drain electrode d_Tdr. ), a protective layer 16 and a second gate electrode g2_Tdr.

The first gate electrode g1_Tdr is formed on the transistor array substrate 10 of the display panel.

The gate insulating layer 12 is formed on the transistor array substrate 10 to cover the first gate electrode g1_Tdr. The semiconductor layer 14 is formed on the gate insulating layer 12 to overlap the first gate electrode g1_Tdr. The semiconductor layer 14 may be made of amorphous silicon (a-Si), polycrystalline silicon (poly-Si), oxide, or organic material. Here, the oxide semiconductor layer is made of an oxide such as Zinc Oxide, Tin Oxide, Ga-In-Zn Oxide, In-Zn Oxide, or In-Sn Oxide, or Al, Ni, Cu, Ta, Mo, Zr , V, Hf, or Ti may be formed of an oxide doped with ions.

The source electrode s_Tdr is formed in a region of one side of the semiconductor layer 14 overlapping the second gate electrode g1_Tdr. The drain electrode d_Tdr is formed in a region on the other side of the semiconductor layer 12 overlapping the first gate electrode g1_Tdr while being spaced apart from the source electrode s_Tdr.

The protective layer 16 is formed on the transistor array substrate 110 to cover the semiconductor layer 14 and the source and drain electrodes s_Tdr and d_Tdr.

The second gate electrode g2_Tdr is formed on the protective layer 16 so as to partially or entirely overlap the second gate electrode g1_Tdr with the semiconductor layer 14 interposed therebetween.

As described above, the threshold voltage of the driving transistor Tdr is changed according to the voltage applied to the first gate electrode g1_Tdr and the second gate electrode g2_Tdr overlapping each other with the semiconductor layer 14 interposed therebetween. It will be. Specifically, the driving transistor Tdr including the second gate electrode g2_Tdr has a characteristic that the gate-source voltage Vgs decreases as a high voltage is applied to the second gate electrode g2_Tdr, and the driving transistor The threshold voltage Vth of (Tdr) has a characteristic that decreases as the second gate voltage has a higher voltage level. Accordingly, the threshold voltage Vth of the driving transistor Tdr is changed to have a negative correlation with the voltage supplied to the second gate electrode g2_Tdr.

Referring back to FIGS. 2 and 4, the first switching transistor Tsw1 is turned on by the scan control signal CS1 supplied to the scan control line Lscan, and the data supplied to the data line DL. The voltage Vdata is supplied to the first node n1 connected to the first gate electrode g1_Tdr of the driving transistor Tdr. To this end, the first switching transistor Tsw1 includes a gate electrode connected to the scan control line Lscan, a first electrode connected to the data line DL, and a second electrode connected to the first node n1. Here, the first and second electrodes of the first switching transistor Tsw1 may be a source electrode or a drain electrode according to a current direction.

The second switching transistor Tsw1 is turned on by a sensing control signal CS2 supplied to the sensing control line Lsense to apply a sensing voltage Vdata_sen supplied to the data line DL to the driving transistor. It is supplied to the second gate electrode g2_Tdr of (Tdr). To this end, the second switching transistor Tsw2 includes a gate electrode connected to the sensing control line Lsense, a first electrode connected to the data line DL, and a second gate electrode g2_Tdr of the driving transistor Tdr. And a second electrode connected to. Here, the first and second electrodes of the second switching transistor Tsw2 may be a source electrode or a drain electrode according to a current direction.

The third switching transistor Tsw3 is turned on by a sensing control signal CS2 supplied to the sensing control line Lsense and is connected to the source electrode s_Tdr of the driving transistor Tdr. (n2) is connected to the first node n1. That is, the third switching transistor Tsw3 selectively shorts the first gate electrode g1_Tdr and the source electrode s_Tdr of the driving transistor Tdr. To this end, the third switching transistor Tsw3 includes a gate electrode connected to the sensing control line Lsense, a first electrode connected to the first node n1, and a second electrode connected to the second node n2. Includes. Here, the first and second electrodes of the third switching transistor Tsw3 may be a source electrode or a drain electrode according to a current direction. The fourth switching transistor Tsw4 is turned on by a reset control signal CS3 supplied to the reset control line Lreset to connect the reference line RL to the second node n2. To this end, the fourth switching transistor Tsw4 includes a gate electrode connected to the reset control line Lreset, a first electrode connected to the reference line RL, and a second electrode connected to the second node n2. do. Here, the first and second electrodes of the fourth switching transistor Tsw4 may be a source electrode or a drain electrode according to a current direction.

The first capacitor C1 is connected between the second gate electrode g2_Tdr of the driving transistor Tdr and the second node n2, and the driving transistor Tdr is switched according to the switching of the second switching transistor Tsw2. It stores the gate-source voltage, that is, the threshold voltage (Vth). To this end, the first electrode of the first capacitor C1 is connected to the second gate electrode g2_Tdr of the driving transistor Tdr, and the second electrode of the first capacitor C1 is the second node ( connected to n2).

The second capacitor C2 is connected between the first node n1 and the second node n2, and is connected to the data line DL according to the switching of the first to third switching transistors Tsw1, Tsw2, and Tsw3. The data voltage Vdata supplied to) is stored, and the driving transistor Tdr is driven with the stored voltage. To this end, the first electrode of the second capacitor C2 is connected to the first node n1, and the second electrode of the second capacitor C2 is connected to the second node n2.

Meanwhile, by using the data line DL without providing a separate sensing voltage line for providing the sensing voltage Vsen, there is an effect of improving the aperture ratio.

The above-described first to fourth switching transistors Tsw2, Tsw2, Tsw3, and Tsw4 are current determined by a difference voltage Vdata-Vsen1 between the display data voltage Vdata and the first sensing voltage Vsen1. The organic light-emitting device (OLED) is configured to emit light. That is, the switching unit is switched according to the control signals CS1, CS2, CS3 supplied to the gate line group GLG, stores the threshold voltage of the driving transistor Tdr in the first capacitor C1, and is used for display. After storing the difference voltage (Vdata-Vsen1) between the data voltage Vdata and the first sensing voltage Vsen1, the display data voltage using the voltages stored in each of the first and second capacitors C1 and C2 The organic light emitting diode OLED emits light with a current determined by a difference voltage Vdata-Vsen1 between (Vdata) and the first sensing voltage Vsen1. Accordingly, the pixel P according to the exemplary embodiment of the present invention may automatically compensate for a change in the threshold voltage of the driving transistor Tdr.

Meanwhile, the threshold voltage sensing driving may be performed on at least one horizontal line for each vertical blank period, but is not limited thereto. Here, the vertical blank period may be set to overlap the blank period of the vertical synchronization signal in a blank period of the vertical synchronization signal or a period between the last data enable signal of the previous frame and the first data enable signal of the current frame. In addition, it is performed for a plurality of frames by sensing at least one horizontal line in each vertical blank period, at a user setting, a set period (or time), or a power-on period of the organic light-emitting display device, or a power-off of the organic light-emitting display device. It may be sequentially performed for all horizontal lines within at least one frame for each period, a power-on period after a set driving time, or a power-off period after a set driving time.

FIG. 4 is a signal waveform diagram on a scan control line, a sensing control line, and a reset control line of a gate line group according to an embodiment of the present invention, and FIG. 5 is a voltage on two gate electrodes and a second node according to the waveform diagram of FIG. 4. It is a waveform diagram. 6 to 11 are diagrams illustrating an operation of an organic light emitting diode display according to an exemplary embodiment of the present invention.

<First initialization and threshold voltage sensing period: t1~t2>

6 and 7 are diagrams illustrating a threshold voltage sensing driving of a pixel in a driving mode of an organic light emitting diode display according to an exemplary embodiment of the present invention.

<First initialization period (t1)>

First, as shown in FIGS. 4, 5, and 6, in the first initialization period t1, the first switching transistor Tsw1 is turned by the scan control signal CS1 of the gate-off voltage Voff. -Is turned off, the second and third switching transistors Tsw2 and Tsw3 are turned on by the sensing control signal CS2 of the gate-on voltage Von, and the fourth switching transistor Tsw4 is turned on at the gate-on voltage Von. ) Is turned on by the reset control signal CS3. In this case, a first sensing voltage Vsen1 is supplied to the data line DL, and a reference voltage Vref is supplied to the reference line RL. Here, the first sensing voltage Vsen1 may have a bias voltage level for driving the driving transistor Tdr in a source follower mode, and the reference voltage Vref may have a voltage level in the range of 0V to 1V. In addition, since the first sensing voltage Vsen1 is supplied to the second gate electrode g2_Tdr of the driving transistor Tdr, the first capacitor C1 has the first sensing voltage Vsen1 and the reference voltage ( It is initialized to the difference voltage (Vsen1-Vref) of Vref). In this case, the organic light-emitting device OLED does not emit light due to the reference voltage Vref supplied to the second node n2 through the fourth switching transistor Tsw4. As described above, by initializing the voltages of the first and second nodes n1 and n2 and the second gate electrode g2_Tdr, the accuracy of detection of a threshold voltage, which will be described later, may be improved.

<Threshold voltage sensing period (t2)>

4, 5, and 7, in the threshold voltage sensing period t2, each of the first to fourth switching transistors Tsw1 to Tsw4 maintains the switching state of the initialization period T1. , While the first sensing voltage Vsen1 is continuously supplied to the second gate electrode g2_Tdr of the driving transistor Tdr, the reference line RL is connected to the external sensing unit 236. Here, the reference line RL may be connected to the sensing unit 236 after maintaining the floating state for a predetermined time. Accordingly, in the threshold voltage sensing period t2, as the driving transistor Tdr operates in a source follower mode by the first sensing voltage Vsen1 supplied to the second gate electrode g2_Tdr, the driving transistor A voltage corresponding to the current flowing through Tdr is charged in the reference line RL. Further, the current flowing through the driving transistor Tdr flows until the difference between the voltage between the first sensing voltage Vsen1 and the second node N2 becomes the threshold voltage Vth of the driving transistor Tdr. Thereafter, the sensing unit 236 senses (or samples) the voltage of the reference line RL, and compares the voltage with the first sensing voltage Vsen1 to detect the threshold voltage of the driving transistor Tdr. -The second sensing data voltage Vsen2 is generated through digital conversion. As described above, by using an external compensation method when detecting the threshold voltage, the threshold voltage information can be processed externally, and information for generating the second sensing voltage Vsen2 necessary for compensation of a boosting loss, which will be described later. Treatment can take place.

<2nd initialization and boosting loss compensation period: t3~t4>

8 to 11 are diagrams illustrating boosting loss compensation driving in a driving mode of an organic light emitting diode display according to an exemplary embodiment of the present invention.

<2nd initialization period (t2)>

4, 5, and 8, in the second initialization period t2, the first switching transistor Tsw1 is turned off by the scan control signal CS1 of the gate-off voltage Voff. , The second and third switching transistors Tsw2 and Tsw3 are turned on by the sensing control signal CS2 of the gate-on voltage Von, and the fourth switching transistor Tsw4 is reset of the gate-on voltage Von. It is turned on by the control signal CS3. In this case, a second sensing voltage Vsen2 is supplied to the data line DL, and a reference voltage Vref is supplied to the reference line RL. Here, the second sensing voltage Vsen2 may be defined as a sum voltage of the first sensing voltage Vsen1 and the detected threshold voltage Vth of the driving transistor Tdr. That is, it can be defined as Vsen2=Vsen1+Vth. Since the second sensing voltage Vsen2 is supplied to the second gate electrode g2_Tdr of the driving transistor Tdr, the first capacitor C1 is equal to the second sensing voltage Vsen2 and the reference voltage Vref. It is initialized to the difference voltage (Vsen2-Vref). In this case, the organic light-emitting device OLED does not emit light due to the reference voltage Vref supplied to the second node n2 through the fourth switching transistor Tsw4.

As described above, the voltages of the first and second nodes n1 and n2 and the second gate electrode g2_Tdr are re-initialized, so that the voltage on the anode electrode of the organic light-emitting device OLED is first adjusted in the boosting loss compensation period to be described later. It can be accurately matched with the sensing voltage (Vsen1).

<Boosting loss compensation period (t4)>

4, 5, and 9, the first switching transistor Tsw1 maintains a turn-off state, and the second and third switching transistors Tsw2 and Tsw3 maintain a turn-on state. , The fourth switching transistor Tsw4 is turned off by the reset control signal CS3 of the gate-off voltage Voff. At this time, the second sensing voltage Vsen2 is continuously supplied to the data line DL. Accordingly, in the boosting loss compensation period t4, as the fourth switching transistor Tsw4 is turned off, the driving transistor Tdr is, as shown in FIG. 5, the second gate electrode g2_Tdr A voltage corresponding to the threshold voltage Vth of the driving transistor Tdr is stored in the first capacitor C1 by being driven in the source follower mode by the second sensing voltage Vsen2 supplied to ). That is, when the fourth switching transistor Tsw4 is turned off, a current flows through the driving transistor Tdr, and by this current, the second node n2, which is the source voltage Vs_Tdr, of the driving transistor Tdr. The voltage increases toward the voltage level of the second sensing voltage Vsen2 supplied to the second gate electrode g2_Tdr of the driving transistor Tdr, and the voltage of the second node n2 is the driving transistor Tdr The charge equal to the threshold voltage Vth of) rises until the first capacitor C1 is charged. The threshold voltage Vth of the driving transistor Tdr stored in the first capacitor C1 is maintained during the next light emission period t5.

<Data writing period and light emission period (t5, t6)>

4, 5, and 10, in the data writing period t5, the second and third switching transistors Tsw2 and Tsw3 are applied to the sensing control signal CS2 of the gate-off voltage Voff. And the fourth switching transistor Tsw4 is turned off by the reset control signal CS3 of the gate-off voltage Voff, and the first switching transistor Tsw1 is turned off at the gate-on voltage Von. It is turned on by the scan control signal CS1 of. In addition, a display data voltage Vdata is supplied to the data line DL. In this case, the first node n1 is charged with the display data voltage Vdata, and a current flows through the driving transistor Tdr according to a potential difference between the first and second nodes n1 and n2, and the second node ( The voltage at n2) rises. In addition, the voltage of the second gate electrode g2 increases as much as the voltage of the second node n2 increases according to the coupling phenomenon of the first capacitor C1, so that the charging voltage of the first capacitor C1 is the threshold voltage ( Vth). And, as shown in FIGS. 4, 5, and 11, the first switching transistor Tsw1 is turned off in the light emission period t6, and the second node n2 is turned off by the current of the driving transistor Tdr. The voltage increases and the voltage on the floating first node n1 also increases according to the coupling phenomenon of the second capacitor C2. And when the voltage on the second node n2 is the operating point of the organic light-emitting device OLED, the organic light-emitting device OLED is turned on and a current from the first driving power line PL1 to the second driving power line PL2 is turned on. Flows, and the organic light-emitting device (OLED) emits light in proportion to this current. Further, the voltage of the first capacitor C1 is continuously maintained so that the organic light-emitting device OLED continuously emits light until the next frame. In this way, in the light-emitting period t6, the driving transistor Tdr is driven by the voltages Vdata-Vsen1 and Vth stored in the first and second capacitors C1 and C2, so that the organic light-emitting device OLED is , As shown in Equation 1 below, light is emitted by the current Ids_Tdr of the driving transistor Tdr determined by the difference voltage Vdata-Vsen1 between the data voltage Vdata and the first sensing voltage Vsen1. .

Equation 1

In Equation 1, "K" is the mobility of holes or electrons.

Meanwhile, referring to FIG. 5, in an exemplary embodiment of the present invention, in the boosting loss compensation period t4, the voltage on the anode electrode of the organic light emitting diode OLED reaches the first sensing voltage Vsen1. This is irrelevant to the change in the threshold voltage Vth of the driving transistor Tdr. Thus, the voltage change amount delta V up to the operating point of the organic light-emitting device OLED is constant regardless of the change in the threshold voltage Vth of the driving transistor Tdr. In this way, since the voltage change amount (delata V) is constant, the boosting loss generated when the voltage on the anode electrode rises until it reaches the operating point becomes constant regardless of the change in the threshold voltage (Vth), so that the overall boosting loss becomes constant. It has the effect of increasing the uniformity of image quality.

12 is a diagram illustrating a structure of a pixel according to another exemplary embodiment of the present invention.

12 is a diagram illustrating a structure of a pixel according to another exemplary embodiment of the present invention, which further includes a sensing voltage line for supplying a sensing voltage to a second switching transistor.

First, in the pixel P of the exemplary embodiment described above, the first electrode of the second switching transistor Tsw2 is connected to the data line DL, and the data line DL is connected to the data line DL according to the sensing control signal CS2. The sensing voltage Vsen supplied to is supplied to the second gate electrode g2 of the driving transistor Tdr. On the other hand, as can be seen from FIG. 12, in the pixel P according to another embodiment of the present invention, a sensing voltage line SVL connected to the first electrode of the second switching transistor Tsw2 is additionally formed. Has been. The sensing voltage Vsen is independently supplied from the outside to the sensing voltage line SVL. Accordingly, the pixel P according to another exemplary embodiment of the present invention may provide the same effect as the pixel P according to the exemplary embodiment of the present invention. However, compared to the pixel P according to the exemplary embodiment of the present invention, in the case of the pixel P according to another exemplary embodiment of the present invention, the aperture ratio decreases as much as the area occupied by the sensing voltage line SVL, but the data line ( By reducing a voltage transition of a column driver (not shown) that supplies the data voltage Vdata and the sensing voltage Vsen to the DL), power consumption may be reduced.

13 is a diagram illustrating a structure of a pixel according to another exemplary embodiment of the present invention, which is configured by changing a connection structure between first and second gate electrodes of a driving transistor Tdr. Hereinafter, only different configurations will be described. First, in the pixel P according to the exemplary embodiment described above, the first gate electrode g1 of the driving transistor Tdr is the first and third switching transistors Tsw1 and Tsw3 through the first node n1. And a second capacitor C2, and a second gate electrode g2 of the driving transistor Tdr is connected to a second switching transistor Tsw2 and a first capacitor C1. On the other hand, as can be seen from FIG. 13, in the structure of the pixel P according to another embodiment of the present invention, the positions of the first and second gate electrodes g1 and g2 of the driving transistor Tdr are It is formed by changing. That is, the first gate electrode g1 of the driving transistor Tdr is connected to the second switching transistor Tsw2 and the first capacitor C1, and the second gate electrode g2 of the driving transistor Tdr is It is connected to the first and third switching transistors Tsw1 and Tsw3 and the second capacitor C2 through the first node n1. That is, the first gate electrode g1 is formed on the semiconductor layer, and the second gate electrode g2 is formed under the semiconductor layer so as to overlap with the first gate electrode g1. Since the first and second gate electrodes g1 and g2 of the driving transistor Tdr are formed to overlap each other with a semiconductor layer therebetween, as shown in FIG. 3, the first and second gate electrodes g1 and g2 of the driving transistor Tdr are formed so as to overlap each other. And even if the connection structures of the second gate electrodes g1 and g2 are changed, the pixel P according to the third exemplary embodiment of the present invention is driven in the same manner as the pixel P according to the exemplary embodiment of the present invention. Additionally, as shown in FIG. 12, the pixel P according to another embodiment of the present invention may further include the sensing voltage line SVL. Accordingly, the pixel P according to another embodiment of the present invention may provide the same effect as the pixel P of the above-described embodiment of the present invention. 14 is a diagram for explaining an organic light-emitting display device according to an embodiment of the present invention, FIG. 15 is a diagram for conceptually explaining driving of an organic light-emitting display device according to an embodiment of the present invention, and FIG. 16 is A diagram for explaining the column driver shown in FIG. 14.

14 to 16, the organic light emitting display device according to the exemplary embodiment of the present invention may include a display panel 100 and a panel driver 200. The display panel 100 may include a plurality of data lines DL1 to DLn, a plurality of reference lines RL1 to RLn, a plurality of gate line groups GLG1 to GLGm, and a plurality of pixels P. Each of the plurality of data lines DL1 to DLn may be formed in parallel to have a predetermined interval along a first direction, that is, a vertical direction of the display panel 100. Each of the plurality of reference lines RL1 to RLn is formed at regular intervals so as to be parallel to each of the plurality of data lines DL1 to DLn, and a reference voltage Vref having a constant DC level may be supplied from the outside. Each of the plurality of gate line groups GLG1 to GLGm may be formed along a second direction of the display panel, for example, a horizontal direction to cross the data line DL. Each of the plurality of data lines DL1 to DLn may include a scan control line Lscan, a sensing control line License, and a reset control line Lreset. Additionally, the display panel 100 may further include a first driving power line PL1 and a second driving power line PL2 connected to each pixel P, and in some cases, the above-described sensing It may be configured to further include a voltage line SVL.

The first driving power line PL1 is formed parallel to the data line DL, is connected to the pixel P formed in the pixel column, and a high potential voltage EVdd may be supplied from the outside. The second driving power line PL2 may be formed in a cylindrical shape or a line shape to be connected to the organic light emitting device, and a low potential voltage EVss may be supplied from the outside.

Each of the plurality of pixels P may be any one of a red pixel, a green pixel, a blue pixel, and a white pixel. One unit pixel displaying one image may include adjacent red pixels, green pixels, blue pixels, and white pixels, or may include red pixels, green pixels, and blue pixels. Since each of the plurality of pixels P has a pixel structure according to the above-described embodiment, a redundant description thereof will be omitted.

As described above, the panel driver 200 operates each pixel P formed on the display panel 100 in a compensation mode. The compensation mode may be sequentially performed for each horizontal line in the display section DP of each frame. The threshold voltage sensing driving in the compensation mode may be performed on at least one horizontal line of pixels P for each vertical blank period BP between frames. For example, when 1080 horizontal lines exist in the display panel 100, compensation driving may be sequentially performed by one horizontal line for each vertical blank section BP, and may be performed through a total of 1080 frames. In this case, by performing at least one horizontal line for each vertical blank period, the switching duty of the switching transistors Tsw1 to Tsw4 per frame for the compensation mode is very small, thereby improving the reliability of the switching transistors Tsw1 to Tsw4. In addition, in the power-on period of the organic light-emitting display device, the power-off period of the organic light-emitting display device, the power-on period after the set driving time, or the power-off period after the set driving time, the display period DP or the display period ( DP) and the vertical blank section (BP) may be sequentially performed for all horizontal lines. When detecting the threshold voltage, the panel driver 200 senses the threshold voltage of the driving transistor Tdr for each pixel through each of the plurality of reference lines RL1 to RLn to generate a second sensing voltage Vsen2. can do. The panel driving unit 200 may include a timing control unit 210, a gate driving circuit unit 220, and a column driving unit 230. The timing controller 210 includes a gate control signal GCS for controlling the gate driving circuit unit 220 and the column driving unit 230 in a compensation mode based on a timing synchronization signal TSS input from the outside. Each data control signal (DCS) is generated. In the threshold voltage sensing driving or boosting loss compensation driving in the compensation mode, the timing controller 210 may generate a sensing voltage Vsen and provide it to the column driver 230.

The gate driving circuit unit 220 generates control signals CS1, CS2, CS3 in response to the gate control signal GCS supplied from the timing controller 210 according to the mode, and controls the display panel 100. It supplies to the lines (Lscan, Lsense, Lreset). The gate driving circuit unit 220 according to an example may include a scan line driver 221, a sensing line driver 223, and a reset line driver 225. The scan line driver 221 is connected to the scan control line Lscan of each gate line group GLG1 to GLGm. The scan line driver 221 generates a scan control signal CS1 in response to the gate control signal GCS and sequentially supplies it to the scan control line Lscan of each gate line group GLG1 to GLGm. . The sensing line driver 223 is connected to the first sensing control line Licenses of each of the gate line groups GLG1 to GLGm. The first sensing line driver 223 generates a sensing control signal CS2 in response to the gate control signal GCS and sequentially connects to the sensing control line Lsense of each gate line group GLG1 to GLGm. Supply. The reset line driver 225 is connected to a reset control line Lreset of each gate line group GLG1 to GLGm. The reset line driver 225 generates a reset control signal CS3 in response to the gate control signal GCS and sequentially supplies it to the reset control line Lreset of each gate line group GLG1 to GLGm. . As described above, the gate driving circuit unit 220 is directly formed on the display panel 100 together with the thin film transistor forming process of each pixel P or formed in the form of an integrated circuit (IC), so that the control lines Lscan, Lsense, Lreset) can be connected to one side.

The column driver 230 is connected to each of the plurality of data lines DL1 to DLn and the plurality of reference lines RL1 to RLn, and a required data voltage Vdata (or a sensing voltage Vsen) The column driver 230 may include a data driver 232, a switching unit 234, and a sensing unit 236. The column driver 230 may include a data driver 232, a switching unit 234, and a sensing unit 236. In response to the data control signal DCS supplied from the timing controller 210, the data driver 232 converts the display pixel data (or sensing data) DATA supplied from the timing controller 210 into a data voltage. Converted into (Vdata) and supplied to the corresponding data lines DL1 to DLn The data driver 232 includes a shift register unit, a latch unit, a gradation voltage generator, and a first to nth digital-to-analog converter. It can be configured to include.

The switching unit 234 supplies a reference voltage Vref to the reference line RL or supplies the reference line RL in response to a switching control signal (not shown) supplied from the timing controller 210. It may be connected to the sensing unit 236 or may be connected to the sensing unit 236 after floating the reference line RL for a predetermined time. That is, the switching unit 234 supplies the reference voltage Vref to the reference line RL in the first and second initialization periods T1. In addition, the switching unit 234 connects the reference line RL to the sensing unit 236 during a threshold voltage detection period t2, or floats the reference line RL for a predetermined time, and then the sensing unit You can connect to (236). To this end, the switching unit 234 according to an example may be configured to include a plurality of selectors 234a to 234n connected to each of the plurality of reference lines RL1 to RLn and the sensing unit 236, the The selectors 234a to 234n may be formed of a multiplexer. The sensing unit 236 is connected to the plurality of reference lines RL1 to RLn through the switching unit 234 to sense voltages of each of the plurality of reference lines RL1 to RLn, and a second The sensing voltage Vsen2 is generated and provided to the timing controller 210. To this end, the sensing unit 236 is connected to a plurality of reference lines RL1 to RLn through the switching unit 234 to analog-digital convert a sensing voltage to generate the second sensing voltage Vsen2. It may be configured to include a plurality of analog-to-digital converters (236a to 236n).

As described above, the organic light emitting diode display according to the present invention may be driven by compensating for the threshold voltage of the driving transistor Tdr through switching changes of the four switching transistors Tsw1 to Tsw4. That is, the present invention senses the threshold voltage of the driving transistor Tdr through external compensation according to the switching of the four switching transistors Tsw1 to Tsw4, and generates a second sensing voltage Vsen2 based on this, and the driving transistor By storing the threshold voltage of Tdr in the first capacitor C1, the threshold voltage of the driving transistor Tdr can be compensated by an internal compensation method. In this case, the driving transistor Tdr stored in the first capacitor C1 By continuously maintaining the threshold voltage of, the organic light emitting diode OLED emits light, thereby reducing deterioration of the switching transistors Tsw1 to Tsw4 for compensation of the driving transistor Tdr, thereby extending reliability and lifespan. In addition, according to the present invention, the difference in threshold voltage of the driving transistor Tdr is accurately compensated according to the switching of the four switching transistors Tsw1 to Tsw4, thereby improving image quality. In addition, in the organic light emitting diode display according to the present invention, the voltage on the anode electrode of the organic light emitting element is always the same voltage as the first sensing voltage Vsen1 despite the change in the threshold voltage before the light emission period, so that the operation of the organic light emitting element It is possible to increase the uniformity of image quality by making the boosting loss that occurs when rising to the point uniform.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is common in the technical field to which the present invention pertains that various substitutions, modifications and changes are possible within the scope of the technical matters of the present invention. It will be obvious to those who have the knowledge of. Therefore, the scope of the present invention is indicated by the claims to be described later, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

100: display panel
200: panel driving unit
210: timing control unit
220: gate driving circuit unit
221: scan line driver
223: sensing line driver
225: reset line driver
230: column driver
232: data driver
234: switching unit
236: sensing unit

Claims (10)

A data line, a gate line group, and a pixel connected to a reference line, wherein the pixel,
Organic light emitting device;
A driving transistor that controls a current flowing through the organic light-emitting device and includes first and second gate electrodes overlapping each other with a semiconductor layer therebetween;
A first switching transistor selectively supplying a data voltage supplied to the data line to a first node connected to the first gate electrode;
A second switching transistor selectively supplying a first or second sensing voltage to the second gate electrode;
A third switching transistor selectively connecting a second node connected to the source electrode of the driving transistor to the first node;
A fourth switching transistor selectively connecting the reference line to the second node;
A first capacitor connected between the second gate electrode and the second node to store a threshold voltage of the driving transistor; And
A second capacitor connected between the first and second nodes to store a difference voltage between the first and second nodes,
The second sensing voltage is a sum voltage of the first sensing voltage and a threshold voltage of the driving transistor. The method of claim 1,
The pixel is in the first initialization period
An organic light emitting diode display device configured to apply the first sensing voltage to the second gate electrode and a reference voltage to the second node by turning on the second and fourth switching transistors. The method of claim 2,
The pixel is in the threshold voltage detection period
The second node voltage is increased by driving in a source follower mode of the driving transistor according to the first sensing voltage, and a threshold voltage of the driving transistor is stored in the first capacitor,
An organic light emitting diode display device configured to detect a voltage on the second node to detect a threshold voltage of the driving transistor. The method of claim 2,
The pixel is in the second initialization period
An organic light emitting diode display device configured to supply the second sensing voltage to the second gate electrode by turning on the second and fourth switching transistors and to apply a reference voltage to the second node. The method of claim 4,
The pixel is in the boosting loss compensation period.
Turning off the fourth switching transistor to drive the driving transistor in a source follower mode according to the second sensing voltage to increase the voltage on the second node to the first sensing voltage to drive the first capacitor An organic light emitting diode display that stores a threshold voltage of a transistor. The method of claim 5,
Turning off the second to fourth switching transistors,
An organic light emitting diode display device configured to emit light by turning on the first switching transistor to write a data voltage to the first node to emit light. The method of claim 1,
The first and second sensing voltages are supplied to the second gate electrode through the data line. The method of claim 1,
The pixel further includes a sensing voltage line,
The first and second sensing voltages are supplied to the second gate electrode through the sensing voltage line. An organic light-emitting device, controlling a current flowing through the organic light-emitting device, and forming a semiconductor layer
A driving transistor including first and second gate electrodes overlapping with each other, a first capacitor connected between the second gate electrode and the source electrode of the driving transistor, and a first capacitor connected between the first gate electrode and the source electrode. 2. A method of driving an organic light emitting display device having a pixel including a capacitor,
A first initialization step of supplying a first sensing voltage to the second gate electrode and a reference voltage to the source electrode;
Driving the driving transistor in a source follower mode to store a threshold voltage of the driving transistor in the first capacitor;
Detecting the threshold voltage;
A second initialization step of supplying a second sensing voltage to the second gate electrode and supplying the reference voltage to the source electrode;
Including; driving the driving transistor in a source follower mode to increase the voltage of the source electrode to the first sensing voltage; and
The second sensing voltage is a sum voltage of the first sensing voltage and a threshold voltage of the driving transistor. The method of claim 9,
Applying a data voltage to the first gate electrode;
Storing a voltage difference between the voltage of the first gate electrode and the voltage of the source electrode in the second capacitor; And
Driving the driving transistor with voltages of the first and second capacitors to emit light of the organic light-emitting device.

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