KR20170122432A - Organic light emitting diode display device and driving method the same - Google Patents

Abstract

The present invention relates to an organic light emitting diode (OLED) display device and a driving method thereof. Each of a plurality of pixels comprises: a light emitting element and a pixel driving circuit for driving the light emitting element. The pixel driving circuit comprises: a driving switching element (DT) having a lower gate electrode and an upper gate electrode and connected in series between a first power supply line (VDDL) and a second power supply line (VSSL) together with an OLED; a first switching device (ST1) connecting a data signal line (DL) with a first node (N1) connected to the lower gate electrode of the drive switching device while corresponding to a first scan signal; a second switching element (ST2) connecting a ground terminal with a second node (N2) connected to the upper gate electrode of the drive switching element while corresponding to a second scan signal; a first capacitor (C1) positioned between the first node and the ground node, and a second capacitor (C2) positioned between the second terminal and a third node (N3) connected to a drain of the drive switching element.

Description

[0001] The present invention relates to an organic light emitting diode (OLED) display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting diode (OLED) display device and a driving method thereof.

2. Description of the Related Art Recently, various flat panel display devices capable of reducing weight and volume, which are disadvantages of cathode ray tubes (CRTs), have been developed. Examples of the flat panel display include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting display OLED).

Among the flat panel display devices, the organic light emitting display device displays an image using an organic light emitting device that generates light by recombination of electrons and holes, and has advantages of fast response speed and low power consumption .

2. Description of the Related Art Conventionally, an organic light emitting display (OLED) is classified into a passive matrix type OLED (PMOLED) and an active matrix type OLED (AMOLED) according to a method of driving an organic light emitting diode.

The AMOLED includes a plurality of gate electrode lines, a plurality of data lines, a plurality of power supply lines, and a plurality of pixels connected to the lines and arranged in a matrix. Each of the pixels includes an organic light emitting element composed of an organic light emitting layer between the anode and the cathode, and a pixel circuit for independently driving the OLED. The pixel circuit mainly comprises a switching transistor for transferring a data signal, a driving transistor for driving the EL element in accordance with the data signal, and a capacitor for holding the data voltage. The switching transistor charges the data voltage to the capacitor in response to the scan pulse. The driving transistor controls the amount of current supplied to the OLED according to the data voltage charged in the capacitor to control the amount of light emitted from the OLED.

Such an AMOLED has advantages such as low power consumption but a characteristic difference such as a threshold voltage (Vth) and mobility of a driving transistor driving an organic light emitting element is generated, and a variation in the threshold voltage (Vth) The intensity of the current flowing through the organic light emitting element changes, resulting in display unevenness. In addition, a voltage drop of the high-potential voltage (VDD) occurs, and the amount of current driving the OLED is varied, thereby causing a luminance deviation between the pixels.

That is, since the characteristics of the transistors included in each pixel change according to manufacturing process parameters, it becomes difficult to manufacture the transistors so that the characteristics of all the transistors of the AMOLED become the same.

In general, a difference in characteristics of the initial driving transistor causes a speck or pattern on the screen, and a characteristic difference due to the deterioration of the driving transistor caused by driving the OLED causes a problem that the lifetime of the OLED display panel is reduced or after- have.

Recently, a compensation circuit including a plurality of transistors and capacitors has been studied in order to overcome such a problem, and this compensation circuit is overcome by forming additional compensation circuits in each pixel. However, in this case, And the capacitor must be mounted.

More specifically, when a compensation circuit is added to each pixel as described above, the aperture ratio of the AMOLED panel is reduced by adding the transistors and the capacitors constituting each pixel and the signal lines controlling the transistors, There is a disadvantage in that the probability of occurrence of defects increases with increasing complexity.

Accordingly, there is a need for a compensation circuit and an AMOLED display device of a new structure capable of reducing the problem caused by the threshold voltage (Vth) difference characteristic between each pixel of the transistor generated in each pixel without decreasing the aperture ratio of the AMOLED panel do.

As described above, the inventors of the present invention have invented a new structure of an OLED display device which can compensate for the characteristic deviation of the threshold voltage (Vth) of the driving transistor DT, thereby reducing luminance deviation between pixels and improving picture quality.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving method of a driving transistor in which a gate electrode of a driving transistor DT and a driving transistor DT constituted of a double gate electrode compensates for a threshold voltage And a method of driving the OLED display device.

According to an embodiment of the present invention, an organic light emitting diode (OLED) display device includes an organic light emitting diode (OLED), a driving transistor, a lower gate electrode, an oxide semiconductor layer, a source / drain electrode, A driving transistor DT having a double-gate electrode structure in which electrodes are sequentially arranged and a compensating transistor TRT connected directly to the upper gate electrode of the driving transistor DT to compensate for a threshold voltage Vth deviation of the driving transistor DT. And a compensation capacitor C2 which is disposed between the source electrode of the driving transistor DT and the drain electrode of the compensation transistor ST2 and stores the threshold voltage Vth.

According to another aspect of the present invention, an OLED display device includes a switching transistor ST1 (not shown) electrically connected to a lower gate electrode of a driving transistor DT and involved in transmission of a data voltage (Vdata) And a storage capacitor C1 that is involved in charging of the data voltage.

According to another aspect of the present invention, an organic light emitting display includes a switching transistor ST1 having a gate electrode, an oxide semiconductor layer, and a source / drain electrode, wherein the source electrode is connected to the lower gate electrode of the driving transistor DT And is directly connected to the first node N1.

According to another aspect of the present invention, in the OLED display device, one electrode of the storage capacitor Cl is connected to the first node N1, and the other electrode is grounded.

According to another aspect of the present invention, in the OLED display device, the drain electrode of the driving transistor DT is electrically connected to the first power supply line VDDL, and the source electrode thereof is connected to the third node N3 .

According to another aspect of the present invention, in an OLED display device, the compensating transistor ST2 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. A drain electrode of the compensating transistor ST2 includes a source electrode And is directly connected to the second node (N2) connected to the upper gate electrode.

According to another aspect of the present invention, in the OLED display device, when the switching transistor ST1 and the compensating transistor ST2 are turned on, the source electrode of the compensating transistor ST2 of the second node N2 is grounded, The driving transistor DT is turned on, the third node N3 is applied with a negative threshold voltage -Vth, and the compensating capacitor C2 is stored with the threshold voltage Vth .

According to another aspect of the present invention, the OLED display is characterized in that when the compensation transistor ST2 is turned off, the second node N2 is in a floating state.

According to another aspect of the present invention, in the OLED display, when the switching transistor ST1 and the compensating transistor ST2 are turned off, the organic light emitting element is turned on and the organic light emitting element is connected to the third node N3. And a voltage (VOLED) applied thereto is applied.

According to another aspect of the present invention, in the organic light emitting diode display, the second node N2 includes an on voltage VOLED of the organic light emitting element to maintain the threshold voltage Vth stored in the compensation capacitor C2, A voltage obtained by adding the threshold voltage Vth of the driving transistor DT is applied.

The voltage across the second node N2 and the third node N3 is maintained at the threshold voltage Vth so that the upper gate electrode of the driving transistor DT, Is characterized by directly varying the threshold voltage (Vth).

In order to achieve the above object, a pixel driving circuit according to an embodiment of the present invention includes a lower gate electrode and an upper gate electrode, and electrically connects the first power supply line (VDDL) and the second power supply line (VSSL) And a first node N1 connected to the data signal line and the lower gate electrode of the drive switching device DT in correspondence with the first scan signal SCAN1, A second switching element ST2 for electrically connecting the second node N2 connected to the top gate electrode of the driving switching element DT and the ground terminal corresponding to the first switching element ST1 and the second scanning signal SCAN2 A first capacitor C1 and a second node N2 electrically connected between the first node N1 and the ground terminal and a third node N3 connected to the source electrode of the drive switching device DT And a second capacitor C2 electrically connected to the second capacitor C2.

In order to achieve the above object, an OLED display according to an embodiment of the present invention includes a plurality of pixels each including a light emitting element and a pixel driving circuit for driving the light emitting element. Also, the pixel driving circuit includes a driving switching element DT having a lower gate electrode and an upper gate electrode and connected in series between the first power supply line VDDL and the second power supply line VSSL together with the organic light emitting element, A first switching element ST1 for connecting the data signal line DL and the first node N1 connected to the lower gate electrode of the driving switching element to each other in correspondence with the first scanning signal, A second switching element ST2 connecting the ground node and the second node N2 connected to the upper gate electrode of the driving switching element, a first capacitor C1 located between the first node and the ground node, And a second capacitor (C2) located between a third node (N3) connected to the drain of the drive switching element.

The pixel driving circuit also includes an initialization period for initializing the first and second nodes N1 and N2 by turning on the first and second switching elements ST1 and ST2, The first switching device ST1 is turned on and the second switching device ST2 is turned off so that the threshold voltage Vth is sensed by charging the second capacitor with the threshold voltage Vth, A programming period in which the voltage of the second node N2 is changed to the organic light emitting element voltage VOLED and the threshold voltage Vth that are applied to the organic light emitting element and the programming period in which the first and second switching elements ST1 and ST2 are turned off And the light emitting period in which the driving switching element DT supplies the driving current to the organic light emitting element correspondingly to the data signal inputted from the first switching element ST1.

The details of other embodiments are included in the detailed description and drawings.

Each pixel of the present invention includes a compensating transistor which is connected to one of gate electrodes of a driving transistor DT and a driving transistor DT constituted by a double gate electrode and directly compensates for a threshold voltage Vth deviation of the driving transistor DT, And a compensation capacitor for storing the threshold voltage (Vth) between the source electrode of the driving transistor DT and the drain electrode of the compensating transistor. As a result, in each pixel structure of the present invention, the sum of the threshold voltage (Vth) of the driving transistor (DT) and the ON voltage of the organic light emitting diode OLED is applied to one gate electrode of the driving transistor DT Lt; / RTI >

Accordingly, the present invention solves the problem caused by the threshold voltage (Vth) difference characteristic between each pixel of the driving transistor (DT) generated in each pixel without decreasing the aperture ratio of the AMOLED panel. The present invention efficiently compensates for the threshold voltage (Vth) of the driving transistor (DT), thereby preventing a driving failure due to long driving, improving reliability, and enhancing luminance uniformity, thereby prolonging the life of the product.

1 is a configuration diagram of an OLED display device according to an embodiment of the present invention.
2 is a circuit diagram of the pixel shown in FIG. 1 according to an embodiment of the present invention.
3 is a driving waveform diagram of the pixel shown in FIG. 1 according to the embodiment of the present invention.
FIGS. 4A and 4D are circuit diagrams illustrating a signal flow of each section of the driving waveform diagram of FIG. 3 according to another embodiment of the present invention.
5 is a plan view of a driving transistor of the pixel shown in FIG. 1 according to an embodiment of the present invention.
6 is a cross-sectional view of the driving transistor shown in FIG. 2 according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, and the like disclosed in the drawings for describing the embodiments of the present invention are illustrative, and thus the present invention is not limited thereto.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Where the terms "comprises", "having", "done", and the like are used in this specification, other portions may be added unless "only" is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

In interpreting the constituent elements, it is construed to include the error range even if there is no separate description. In the case of a description of the positional relationship, for example, if the positional relationship between two parts is described as 'on', 'on top', 'under', and 'next to' Or " direct " is not used, one or more other portions may be located between the two portions.

It will be understood that when an element or layer is referred to as being on another element or layer, it encompasses the case where it is directly on or intervening another element or intervening another element or element.

Although the first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, the first component mentioned below may be the second component within the technical spirit of the present invention.

Like reference numerals refer to like elements throughout the specification.

The sizes and thicknesses of the individual components shown in the figures are shown for convenience of explanation and the present invention is not necessarily limited to the size and thickness of the components shown.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other partially or entirely and technically various interlocking and driving is possible as will be appreciated by those skilled in the art, It may be possible to cooperate with each other in association.

In the present invention, the transistor may be of P type or N type. In the following embodiments, the transistors are of N type for convenience of explanation. In describing the pulse-type scan signals SCAN1 and SCAN2 inputted to the gate electrode, the gate electrode high voltage (VGH) state is defined as "high state ", and the gate electrode low voltage (VGL) State ".

Thus, the high voltage VGH is the gate electrode ON voltage that turns on the transistor, and the gate electrode low voltage VGL is the gate electrode OFF voltage that turns off the transistor.

In the present specification, "involving" means directly performing a specific operation of a specific component, or directly or indirectly intervening such that a specific operation of a specific component is performed smoothly. For example, in the present specification, "involved in driving an organic light emitting element" means directly or indirectly intervening in driving such as driving a direct organic light emitting element or transmitting a specific signal so that the organic light emitting element is driven smoothly .

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

1 is a configuration diagram of an organic light emitting diode display according to an embodiment of the present invention.

1 includes a display panel 2 in which a plurality of gate electrode lines GL and a plurality of data lines DL intersect to define respective pixels 1 and a plurality of gate electrode lines A data driver 3 for driving a plurality of data lines DL and a video driver 3 for supplying image data RGB inputted from outside to the data driver 3, And a timing controller 5 for outputting a gate electrode control signal GCS and a data control signal DCS to control the gate driver 4 and the data driver 3.

Each pixel 1 of the present invention includes a pixel driving circuit for independently driving an organic light emitting diode OLED including an organic light emitting diode OLED and a driving transistor for supplying a driving current to the organic light emitting diode OLED do. The pixel driving circuit compensates the electrical characteristic deviations of the driving transistor such as the threshold voltage Vth and the mobility and compensates the luminance deviation between the pixels 1 due to the difference in current supplied to the organic light emitting element OLED Can be reduced. The pixel 1 of the present invention will be described later in detail with reference to Figs. 2 to 6. Fig.

The display panel 2 has a plurality of gate electrode lines GL and a plurality of data lines DL intersecting with each other and a plurality of pixels 1 are provided in an intersection region of these gate lines GL and DL. Each pixel 1 includes an organic light emitting element OLED and a pixel driving circuit. Each pixel 1 is connected to a gate electrode line GL, a data line DL, a high-potential voltage (VDD) supply line, and a low-potential voltage (VSS) supply line line.

The gate driver 4 supplies a plurality of gate electrode signals to the plurality of gate electrode lines GL in accordance with a plurality of gate electrode control signals GCS provided from the timing controller 5. [ The plurality of gate electrode signals includes first and second scan signals SCAN1 and SCAN2, and these signals are supplied to each pixel 1 through a plurality of gate electrode lines GL. The high-potential voltage VDD has a voltage relatively higher than the low-potential voltage VSS. The low potential voltage VSS may be a ground voltage.

The data driver 3 outputs the digital image data RGB input from the timing controller 5 to the data voltage Vdata using the reference gamma voltage in accordance with a plurality of data control signals DCS provided from the timing controller 5 Conversion. And supplies the converted data voltage Vdata to the plurality of data lines DL. On the other hand, the data driver 3 outputs the data voltage Vdata in the programming period t3 (see Fig. 3) of each pixel 1.

The timing controller 5 arranges image data RGB input from the outside in accordance with the size and resolution of the display panel 2 and supplies the image data RGB to the data driver 3. The timing controller 5 generates a plurality of signals by using the synchronizing signals SYNC input from the outside, for example, a dot clock DCLK, a data enable signal DE, a horizontal synchronizing signal Hsync, and a vertical synchronizing signal Vsync And a data control signal (GCS, DCS). The gate driver 4 and the data driver 3 are controlled by supplying the generated gate electrodes and the data control signals GCS and DCS to the gate driver 4 and the data driver 3, respectively.

Hereinafter, the pixel of the present invention will be described in detail. 2 is a circuit diagram of the pixel shown in Fig.

Referring to FIG. 2, a pixel includes a pixel driving circuit that includes an organic light emitting diode (OLED), three transistors, and two capacitors to drive the organic light emitting diode OLED. Specifically, the pixel driving circuit includes a driving transistor DT, first and second switching transistors ST1 and ST2, and first and second capacitors C1 and C2.

The first switching transistor ST1 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. The source electrode is connected to a first node N1 connected to a bottom gate (BG) of the driving transistor DT. Lt; / RTI >

The first switching transistor ST1 is turned on or off according to the first scan signal SCAN1 and connects the data line DL and the first node N1 to each other. That is, the data voltage Vdata provided from the data line DL is supplied to the first node N1

Next, the second switching transistor ST2 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. The source electrode of the second switching transistor ST2 is grounded and the drain electrode is directly connected to the second node N2 connected to the upper gate electrode TG of the driving transistor DT.

The second switching transistor ST2 is turned on or off according to the second scan signal SCAN2. When the second switching transistor ST2 is turned on, the second node N2 may be connected to the ground and the voltage of the second node N2 may be 0V. When the second switching transistor ST2 is turned off, the second node N2 becomes a floating state in which there is no element for determining the voltage.

The second switching transistor ST2 is a compensating transistor which is electrically connected to an upper gate electrode (TG) of the driving transistor DT to compensate for the deviation of the threshold voltage Vth of the driving transistor DT.

Next, the driving transistor DT is connected in series between the first power supply line VDDL and the second power supply line VSSL together with the organic light emitting element OLED, and a driving current . The first power supply line VDDL transfers a high level voltage (VDD_10V) or a low level voltage (VDD_-10V) to the drain electrode of the driving transistor DT. The second power supply line VSSL transmits a high level voltage VSS_10V or a low level voltage VSS_-10V to the organic light emitting diode OLED. The voltage transmitted from the first power supply line VDDL may be referred to as a high potential power supply VDD. In addition, the voltage transmitted from the second power supply line VDDL may be referred to as a low potential power supply (VSS).

The driving transistor DT has a double gate electrode structure in which a bottom gate electrode (BG), an oxide semiconductor layer, a source / drain electrode, and a top gate electrode (TG) are sequentially arranged. The lower gate electrode TG is connected to the first node N1 to which the data voltage Vdata is supplied and the upper gate electrode TG is connected to the second node N2.

The first capacitor C1 is connected to the first node N1 and holds the data voltage Vdata for one frame so that the amount of the current flowing through the organic light emitting diode OLED is constant, And may be a storage capacitor Cst that keeps the gradation displayed by the light emitting device OLED constant. One electrode of the first capacitor C1 may be connected to the second node N2 and the other electrode may be grounded.

The second capacitor C2 is connected between the second node N2 and the third node N3 and is formed between the source electrode of the driving transistor DT and the drain electrode of the second switching transistor ST2 do. The second capacitor C2 stores the threshold voltage Vth of the driving transistor DT. As a result, the second capacitor C2 is connected between the second node N2 and the third node N3, and stores the threshold voltage Vth of the driving transistor DT so that the sensing capacitor Sensing capacitor.

Referring to FIG. 2, the organic light emitting diode display of the present invention includes a lower gate electrode BG, an oxide semiconductor layer, a source / drain electrode, The gate electrode TG is sequentially formed so that the driving transistor DT having the double gate electrode structure and the upper gate electrode TG of the driving transistor DT are directly connected to each other to form the threshold voltage Vth of the driving transistor DT, A plurality of pixels including a compensating transistor ST2 for compensating a deviation and a compensating capacitor C2 formed between a source electrode of the driving transistor DT and a drain electrode of the compensating transistor ST2 and storing a threshold voltage Vth, Respectively.

Each pixel is electrically connected to the lower gate electrode BG of the driving transistor DT and is connected to the switching transistor ST1 which is involved in the transfer of the data voltage Vdata necessary for controlling the driving transistor DT, And further includes an associated storage capacitor C1.

Referring to FIG. 2, the drain electrode of the driving transistor DT is electrically connected to the first power supply line VDDL, and the source electrode thereof is connected to the third node N3.

When the switching transistor ST1 and the compensating transistor ST2 are turned on, the source electrode of the compensating transistor ST2 is grounded and 0V is applied to the second node N2. When the driving transistor DT is turned on, The third node N3 is applied with a negative threshold voltage (-Vth), and the compensation capacitor C2 stores the threshold voltage (Vth).

When the compensating transistor ST2 is turned off, the second node N2 is in a floating state.

When the switching transistor ST1 and the compensating transistor ST2 are turned off, the organic light emitting diode OLED is turned on and the voltage VOLED applied to the organic light emitting diode OLED is applied to the third node N3 .

The second node N2 is turned on when the ON voltage VOLED of the organic light emitting element and the threshold voltage Vth of the driving transistor DT are added to maintain the threshold voltage Vth stored in the compensation capacitor C2 .

The voltage across the second node N2 and the third node N3 is maintained at the threshold voltage Vth so that the upper gate electrode of the driving transistor DT can directly change the threshold voltage Vth.

Referring to FIG. 2, the pixel driver circuit according to the embodiment of the present invention includes a lower gate electrode BG and an upper gate electrode TG, and includes a first power supply line VDDL and a second power supply line VSSL A first node N1 connected to the lower gate electrode BG of the data signal line DL and the driving switching element DT in correspondence with the first scan signal, And a second node N2 connected to the upper gate electrode TG of the driving transistor DT and the ground terminal corresponding to the second scan signal are electrically connected to each other The first node N1 and the first capacitor C1 electrically connected between the ground terminal and the second node N2 and the source electrode of the drive switching element DT, And a second capacitor C2 electrically connected between the third node N3.

As a result, the pixel driving circuit according to an embodiment of the present invention can adjust the threshold voltage Vth stored in the second capacitor C2 by applying an arbitrary voltage to the upper gate electrode TG. That is, the pixel driver circuit of the present invention can compensate for the threshold voltage (Vth) deviation of the driving transistor DT.

3 is a driving waveform diagram of the pixel shown in FIG. 1 according to an embodiment of the present invention.

3, the pixel of the present invention includes an initialization period t1, a sampling period t2, a programming period t3, and a light emission period t4 in accordance with pulse timings of a plurality of gate electrode signals to be supplied. .

In the initialization period t1, the first and second scan signals SCAN1 and SCAN2 are output at a high level (for example, 13V), and the high level power supply VDD is at a high level (for example, 10V) -10 V). The low potential power supply VSS is changed from a low level (for example, -10V) to a high level (for example, 10V), and a low level (for example, -20V) is applied to the organic light emitting element OLED. The data driver 6 does not supply the data voltage Vdata from the plurality of data lines DL during the initialization period t1 of each pixel P. [ That is, in this period, the data voltage (Vdata) becomes 0V.

During the sampling period t2, the first and second scan signals SCAN1 and SCAN2 are maintained at a high level (for example, 13 V) and the low potential power supply VSS is maintained at a high level (for example, 10 V). The data voltage Vdata supplied through the plurality of data lines DL in the data driver 6 is not continuously supplied. The high-potential power supply VDD is changed from a low level (for example, -10V) to a high level (for example, 10V) and output.

During the programming period t3, the first scan signal SCAN1 is maintained at a high level (for example, 13V), and the second scan signal SCAN2 is changed to a low level (for example, -5V). The low potential power supply VSS is changed from a high level (for example, 10V) to a low level (for example, -10V) and output. Also, during this period, the data driver 6 supplies the data voltage Vdata to the first node N1 through a plurality of data lines DL.

In the light emission period t4, the organic light emitting diode OLED is output in a high level state and the first and second scan signals SCAN1 and SCAN2 are output in a low level (for example, -5V).

FIGS. 4A and 4D are circuit diagrams illustrating a signal flow of each section of the driving waveform diagram of FIG. 3 according to another embodiment of the present invention. Hereinafter, a pixel driving circuit of an OLED display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 to 4D.

First, in the initialization period t1, the first and second switching transistors ST1 and ST2 are turned on. The data voltage Vdata supplied from the plurality of data lines DL is supplied to the first node N1 through the first switching transistor ST1 and the ground voltage Vdata electrically connected to the second switching transistor ST2, Is supplied to the second node N2.

In the initialization period t1, however, the data voltage Vdata is not input, and the voltage of the first capacitor C1 is discharged so that 0V is applied to the first node N1. In addition, the voltage of the second capacitor C2 is discharged to the second node N2 by 0 V by the ground power source electrically connected to the second switching transistor ST2. As a result, the first capacitor C1 and the second capacitor C2 are initialized in this period.

The high-potential power supply VDD connected to the driving transistor DT is changed from a high level (for example, 10V) to a low level (for example, -10V). Then, a low level (for example, -10 V) voltage is applied to the third node N3 connected to the driving transistor DT. The low potential power supply VSS connected to the organic light emitting element OLED is changed from a low level (for example, -10 V) to a high level (for example, 10 V). As a result, during the initialization period t1, the organic light emitting diode OLED becomes a turn-off state in which no current flows and no light is emitted.

Subsequently, in the sampling period t2, the high-potential power supply VDD connected to the driving transistor DT is changed from a low level (for example, -10 V) to a high level (for example, 10 V). Since the gate electrode-source voltage Vgs of the driving transistor DT is larger than the threshold voltage Vth, the driving transistor DT is turned on. Then, during the sampling period t2, the third node N3 changes from the low level (for example, -10V) to the negative threshold voltage Vth (-Vth). Then, when the third node N3 reaches the negative threshold voltage Vth (-Vth), the driving transistor DT is turned off.

The second node N2 is maintained at 0V and the third node N3 is applied with a negative threshold voltage Vth (-Vth), so that the threshold voltage Vth is stored in the second capacitor C2. Further, the organic light emitting diode OLED is still in a turn-off state.

 Subsequently, in the programming period t3, the first switching transistor ST1 maintains the turn-on state. The data voltage Vdata supplied to the data driver 6 through the plurality of data lines DL is supplied to the first node N1 through the first switching transistor ST1, The data voltage (Vdata) supplied to the driving transistor DT turns on the driving transistor DT. Further, the low potential power supply VSS connected to the organic light emitting element OLED is changed from a high level (for example, 10V) to a low level (for example, -10V).

As a result, a current path is formed between the driving transistor DT and the organic light emitting diode OLED, so that the voltage of the third node N3 is the voltage VOLED applied to the organic light emitting diode OLED at the negative threshold voltage- .

During the programming period t3, the second switching transistor ST2 is turned off. When the second switching transistor ST2 is turned off, the second node N2 in which the OV is applied does not have a voltage determining element, and thus becomes a floating state.

Since one electrode of the second capacitor C2 is connected to the second node N2 so that the second capacitor C2 can maintain the voltage of the stored threshold voltage Vth in the floating state, The second node N2 connected to one electrode of the capacitor C2 is boosted at a voltage of 0 V plus a threshold voltage Vth and a voltage VOLED applied to the organic light emitting diode OLED.

As a result, the threshold voltage Vth of the driving transistor DT stored in the second capacitor C2 can be sensed and the threshold voltage Vth sensed in proportion to the initial threshold voltage Vth can be adjusted .

 For example, since the second capacitor C2 maintains the threshold voltage Vth constant, the second node N2 is supplied with the threshold voltage Vth plus the voltage VOLED applied to the organic light emitting diode OLED And a voltage VOLED applied to the organic light emitting diode OLED is applied to the third node N3. Accordingly, when a voltage of 1V is applied to the upper gate electrode TG, the threshold voltage Vth of the driving transistor DT is lowered by 1V in order to maintain the threshold voltage Vth in the second capacitor C2.

Then, in the light emission period t4, the first switching transistor ST1 is turned off. Then, the high potential voltage VDD is applied to the drain of the driving transistor DT, and the driving transistor DT supplies the driving current to the organic light emitting element OLED. Therefore, the pixel P of the present invention compensates for the characteristic deviation of the driving transistor DT, thereby reducing the luminance deviation between the pixels P. [

Meanwhile, the organic light emitting diode display according to the embodiment of the present invention employs a source follower method in which a load is connected to a source electrode of a driving transistor DT without supplying a fixed voltage thereto. Therefore, the organic light emitting display according to the embodiment of the present invention can sense the threshold voltage Vth even when the polarity of the threshold voltage Vth of the driving transistor DT is negative, so that the threshold voltage Vth The deviation of the threshold voltage Vth can be compensated for irrespective of the polarity of the threshold voltage Vth.

When the threshold voltage Vth of the driving transistor DT included in the pixel of the organic light emitting display device is sensed by the element connection method connecting the gate electrode and the drain electrode of the driving transistor DT, The threshold voltage Vth can not be sensed when the threshold voltage Vth is negative. However, when the source-follower scheme is used as in the embodiment of the present invention, even when the threshold voltage Vth is negative, (Vth) can be sensed.

In other words, the organic light emitting diode display according to the embodiment of the present invention compensates for the variation of the current flowing through the organic light emitting diode OLED according to the deviation of the positive or negative threshold voltage Vth, The current according to the data voltage Vdata can be kept constant regardless of the polarity.

5 shows the electrical characteristics of the driving transistor DT according to an embodiment of the present invention.

Referring to FIG. 5, as the bias voltage applied to the upper gate electrode TG in the driving transistor DT increases, the electrical characteristics of the driving transistor DT change. When the bias voltage applied to the upper gate electrode TG is applied at -10 V, -5 V, 0 V, and 5 V, respectively, the threshold voltage of the driving TFT DT is set to a negative shift shift occurs and the threshold voltage Vth can be directly compensated.

6 is a cross-sectional view of the driving transistor DT shown in FIG. 2 according to an embodiment of the present invention.

The driving transistor DT of the present invention includes a substrate 110, a lower gate electrode 120, a gate insulating layer 130, an activation layer 140, source and drain electrodes 150A and 150B, (160) and an upper gate electrode (170).

Referring to FIG. 6, the driving transistor DT includes a lower layer formed under the activation layer 140 in a Coplanar type in which the source and drain electrodes 150A and 150B are all located on the activation layer 140, And a gate electrode (120). A lower gate electrode 120 is formed on the substrate 110 and a gate insulating layer 130 is formed between the lower gate electrode 120 and the activation layer 140. [ Is formed. Source and drain electrodes 150A and 150B, a passivation layer 160 and an upper gate electrode 170 are sequentially formed on the activation layer 140. [

As described above, the present invention efficiently compensates the threshold voltage (Vth) of the driving transistor (DT), thereby preventing a driving failure due to long-time driving and reducing luminance deviation between pixels, thereby improving image quality.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. Will be clear to those who have knowledge of.

1: pixel 2: display panel
3: Data driver 4: Gate driver
5: timing controller 110: substrate
120: lower gate electrode 130: gate insulating layer
140: activation layer 150A, 150B: source and drain electrodes
160: protection layer 170: upper gate electrode

Claims (28)

An organic light emitting element;
A driving transistor DT having a double gate electrode structure in which a bottom gate electrode, an oxide semiconductor layer, a source / drain electrode, and an upper gate electrode are sequentially arranged in association with driving the organic light emitting diode;
A compensating transistor (ST2) directly connected to the upper gate electrode of the driving transistor (DT) to compensate for a threshold voltage (Vth) deviation of the driving transistor (DT); And
And a compensating capacitor (C2) arranged between a source electrode of the driving transistor (DT) and a drain electrode of the compensating transistor (ST2) and storing a threshold voltage (Vth). . The method according to claim 1,
A switching transistor ST1 electrically connected to a lower gate electrode of the driving transistor DT and involved in transmission of a data voltage Vdata necessary for controlling the driving transistor DT; And
And a storage capacitor (C1) that is involved in charging the data voltage. 3. The method of claim 2,
The switching transistor ST1 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. The source electrode is directly connected to a first node N1 connected to a lower gate electrode of the driving transistor DT Wherein the organic light emitting display device comprises: 3. The method of claim 2,
Wherein one electrode of the storage capacitor (C1) is connected to the first node (N1), and the other electrode is grounded. 3. The method of claim 2,
The drain electrode of the driving transistor DT is electrically connected to the first power supply line VDDL,
And the source electrode is connected to a third node (N3). 5. The method of claim 4,
The compensation transistor ST2 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode, and the drain electrode is directly connected to the second node N2 connected to the upper gate electrode of the driving transistor DT The organic light emitting display device comprising: The method according to any one of claims 3 to 6,
When the switching transistor ST1 and the compensating transistor ST2 are turned on, the source electrode of the compensating transistor ST2 is grounded and 0V is applied to the second node N2,
The driving transistor DT is turned on so that the third node N3 is applied with a negative threshold voltage -Vth,
And the compensation capacitor (C2) stores the threshold voltage (Vth). The method according to claim 6,
And the second node (N2) is in a floating state when the compensating transistor (ST2) is turned off. 8. The method of claim 7,
When the switching transistor ST1 and the compensating transistor ST2 are turned off, the organic light emitting diode is turned on and the voltage VOLED applied to the organic light emitting diode is applied to the third node N3 Wherein the organic light emitting display device comprises: 10. The method of claim 9,
The second node N2 is turned on and off in order to maintain the threshold voltage Vth stored in the compensation capacitor C2 and the threshold voltage Vth of the driving transistor DT ) Is applied to the organic light emitting diode. 11. The method of claim 10,
Since the both-end voltage between the second node N2 and the third node N3 is maintained at the threshold voltage Vth,
And the upper gate electrode of the driving transistor DT directly changes the threshold voltage Vth. A driving switch element DT having a lower gate electrode and an upper gate electrode and electrically connected to the first power supply line VDDL and the second power supply line VSSL;
A first switching element ST1 for electrically connecting the first node N1 connected to the data signal line DL and the lower gate electrode of the drive switching element DT in correspondence with the first scan signal SCAN1, );
A second switching device ST2 corresponding to the second scan signal SCAN2 and electrically connecting the ground node and the second node N2 connected to the upper gate electrode of the drive switching device DT to each other;
A first capacitor (C1) electrically connected between the first node (N1) and the ground terminal; And
And a second capacitor electrically connected between the second node and the third node connected to the source electrode of the drive switching element. 13. The method of claim 12,
The first switching device ST1 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. The gate electrode is connected to a first scan signal line SCL1 for supplying the first scan signal SCAN1 A pixel driving circuit characterized by: 14. The method of claim 13,
Wherein the drain electrode of the first switching device (ST1) is coupled to the data signal line (DL) to receive a data voltage (Vdata). 13. The method of claim 12,
The second switching device ST2 includes a gate electrode, an oxide semiconductor layer, and a source / drain electrode. The gate electrode is connected to a second scan signal line SCL2 for supplying the second scan signal SCAN2. A pixel driving circuit characterized by: 16. The method of claim 15,
And the drain electrode of the second switching device (ST2) is connected to the ground terminal. 13. The method of claim 12,
Wherein when the second switching element ST2 is turned off, the second node N2 enters a floating state without a potential difference due to the ground terminal. 13. The method of claim 12,
Wherein the second capacitor (C2) stores the threshold voltage (Vth) so that the threshold voltage (Vth) of the driving switching device (DT) is sensed. 13. The method of claim 12,
Since the both-end voltage between the second node N2 and the third node N3 is maintained at the threshold voltage Vth,
Wherein the upper gate electrode of the driving switching element (DT) directly varies the threshold voltage (Vth). Each of the plurality of pixels includes a light emitting element and a pixel drive circuit for driving the light emitting element,
The pixel driving circuit
A driving switching element DT having a lower gate electrode and an upper gate electrode and connected in series between a first power supply line VDDL and a second power supply line VSSL together with the organic light emitting element;
A first switching device ST1 for connecting the data signal line DL and the first node N1 connected to the lower gate electrode of the drive switching device in correspondence with the first scan signal;
A second switching device (ST2) for connecting the ground node and the second node (N2) connected to the upper gate electrode of the drive switching device in response to the second scan signal;
A first capacitor (C1) located between the first node and a ground terminal; And
And a second capacitor (C2) located between the second node and a third node (N3) connected to the drain of the drive switching element,
The pixel driving circuit
An initialization period for initializing the first and second nodes N1 and N2 by turning on the first and second switching elements ST1 and ST2;
A sampling period for turning on the drive switching element to sense the threshold voltage Vth by charging the second capacitor with a threshold voltage Vth;
The first switching device ST1 is turned on and the second switching device ST2 is turned off so that the voltage of the second node N2 is lower than the voltage of the organic light emitting device VOLED ) And a threshold voltage (Vth); And
The driving switching element DT applies a driving current to the organic light emitting element in response to a data signal inputted from the first switching element ST1 by turning off the first and second switching elements ST1 and ST2, And a light emitting period for supplying the OLED display. 21. The method of claim 20,
In the initialization period, the first switching device ST1 is turned on and a zero-valued data voltage Vdata 0V is supplied to the first node N1 from the data signal line DL, 1 < / RTI > capacitor < RTI ID = 0.0 > C1. ≪ / RTI > 21. The method of claim 20,
In the initialization period, the second switching device ST2 is turned on, and a zero voltage (0V) is supplied to the second node N2 from the ground terminal, and the second capacitor C2 is turned on And discharging the OLED display device. 21. The method of claim 20,
In the sampling period,
A high level voltage (VDD_10V) is input from the first power supply line VDDL to turn on the drive switching element DT,
A negative threshold voltage (-Vth) is generated at the third node N3,
Wherein the gate-source voltage (Vgs) of the driving switching device (DT) is the threshold voltage (Vth) to turn off the driving switching device (DT). 21. The method of claim 20,
In the sampling period, the second capacitor C2 is charged with the threshold voltage Vth, and a high level voltage VSS_10V is applied to the organic light emitting element from the second power supply line VSSL, And the device does not emit light. 21. The method of claim 20,
In the programming period, a low level voltage (VSS_-10V) is input to the second power supply line (VSSL), the organic light emitting element is turned on, and the organic light emitting element voltage (VOLED) is applied to the OLED display. 21. The method of claim 20,
In the programming period,
The second node is brought into a floating state by the turn-off of the second switching element ST2,
(OLED) display device according to claim 1, characterized in that the voltage of the second node is shifted from 0V to a voltage obtained by adding the organic light emitting element voltage (VOLED) and the threshold voltage (Vth) in order to maintain the threshold voltage (Vth) . 21. The method of claim 20,
And adjusts the threshold voltage (Vth) generated at the second node by a voltage input to the upper gate electrode. 21. The method of claim 20,
Wherein sensing is performed even when the threshold voltage (Vth) of the driving transistor (DT) is negative in the sampling period.

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