KR101365808B1 - Organic Light Emitting Display and Driving Method of the same - Google Patents

Abstract

The present invention includes a display panel in which subpixels connected to a plurality of first and second power supply wirings, scan wirings, and data wirings are positioned in a matrix form, wherein the subpixels are connected to gates of the scan wirings and provided to the data wirings. A first transistor connected to one electrode, a second transistor connected to a gate of the scan line, a first electrode connected to the first node, and a second electrode connected to the second node, and a gate connected to the first node A third transistor having a first electrode connected to the second electrode of the transistor and a second electrode connected to the second node; a gate connected to the first node; a first electrode connected to the second node; A fourth transistor having two electrodes connected thereto, a capacitor having a first electrode connected to the first node and a second electrode connected to the second power line, a first electrode connected to the first power line, and a first electrode of the third transistor Organic light emitting diode having a second electrode connected thereto An organic light emitting display device including a diode is provided.

Organic light emitting display device, voltage compensation, deterioration

Description

Organic Light Emitting Display and Driving Method of the same

1 is a block diagram illustrating a subpixel circuit of an organic light emitting display device according to an exemplary embodiment of the present invention.

2 is an exemplary view of a drive waveform according to an embodiment of the present invention.

3 is a graph showing a voltage change of a capacitor according to a threshold voltage change.

4 is a graph showing a current change of an organic light emitting diode according to a threshold voltage variation.

5 is an exemplary drive waveform diagram for explaining negative annealing.

6 is a graph showing a current decrease of an organic light emitting diode according to a threshold voltage variation.

DESCRIPTION OF THE REFERENCE NUMERALS

VDD: First Power Wiring GND: Second Power Wiring

T1, T2, T3, T4: first, second, third and fourth transistors

SCAN [n]: scan wiring DATA [n]: data wiring

D: organic light emitting diode C: capacitor

The present invention relates to an organic light emitting display and a driving method thereof.

2. Description of the Related Art In recent years, the importance of flat panel displays (FPDs) has been increasing with the development of multimedia. In response to this, various kinds of devices such as a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), an organic light emitting display A planar display of a branch has been put into practical use.

The organic light emitting display device may be driven by a passive matrix method and an active matrix method using a thin film transistor (hereinafter, referred to as a transistor). In this case, the passive matrix method is formed so that the anode and the cathode are orthogonal and the line is selected and driven, whereas the active matrix method connects a thin film transistor to each indium tin oxide (ITO) pixel electrode and a capacitor connected to the gate electrode of the thin film transistor. Drive according to the maintained voltage.

In order to structurally compensate the subpixels of the organic light emitting display device, a 4T1C structure including four transistors and one capacitor is used. In the conventional subpixel structure, a power supply is cut off during writing in which the organic light emitting diode does not emit light and power is supplied to a light emitting step in which the organic light emitting diode emits light.

This method has a problem in that the amount of current flowing through the organic electroluminescent device changes according to the threshold voltage Vth variation in the subpixel. Thus, in order to solve this problem, the sub-pixel structure uses the 4T1C structure as described above, but has a complicated structure with four signal wires, and a separate power supply for performing negative anneal on the sub-pixels. Had to be authorized. Thus, the increase in power wiring located in the panel not only complicates the layout, but also inevitably adopts a complex driving method, which is difficult to realize high resolution and is not applicable to the actual panel.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to improve the sub-pixel structure of the organic light emitting display device to solve the problem of current reduction and luminance reduction of the organic light emitting diode due to the threshold voltage change of the driving transistor. In addition, the present invention provides an organic light emitting display device suitable for high resolution as well as improving display quality.

The present invention for solving the above problems includes a display panel in which subpixels connected to a plurality of first and second power supply wirings, scan wirings, and data wirings are positioned in a matrix, wherein the subpixels are gated to the scan wiring. A first transistor connected to a first electrode connected to the data line, a second transistor connected to a gate of the scan line, a first electrode connected to the first node, and a second electrode connected to the second node, and a first node A third transistor having a gate connected to the first electrode connected to the second electrode of the first transistor, a second electrode connected to the second node, a gate connected to the first node, and a first electrode connected to the second node A fourth transistor having a second electrode connected to the second power line, a capacitor connected with the first electrode to the first node, and a second electrode connected to the second power line, and a first electrode connected to the first power line, First electrode of the third transistor An organic light emitting display device including an organic light emitting diode connected to a second electrode is provided.

The first, second, third and fourth transistors may be N-Mos type.

The first, second, third and fourth transistors may be a-Si transistors.

Meanwhile, in another aspect, the present invention provides a method of driving an organic light emitting display device including a display panel in which subpixels including first, second, third, and fourth transistors, a capacitor, and an organic light emitting diode are positioned in a matrix form. A method comprising: turning on first and second transistors and storing a data signal supplied to the capacitor as a data voltage; and turning on the third and fourth transistors using the data voltage stored in the capacitor to turn on the organic light emitting diode. A method of driving an organic light emitting display device comprising a light emitting step of emitting light is provided.

The writing step may include an initialization step of cutting off the power supplied to the organic light emitting diode and performing negative annealing on the fourth transistor while the first and second transistors are turned on.

In the writing step, when the data signal is supplied to the capacitor to store the data voltage, the precharging may be performed first and the data signal may be supplied in a lower state than the power supplied to the organic light emitting diode in the light emitting step.

The third transistor can drive in the saturation region and the fourth transistor can drive in the linear region.

The first, second, third and fourth transistors may be N-Mos type formed of a-Si.

<Example 1>

1 is a block diagram illustrating a subpixel circuit of an organic light emitting display device according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an organic light emitting display device according to an exemplary embodiment of the present invention includes a plurality of first and second power supply lines VDD and GND, a scan line SCAN1 [n], and a data line DATA [n. ) Includes a display panel in which subpixels (1 pixel) connected in the form of a matrix are disposed in a matrix form.

Here, one subpixel includes a first transistor T1 having a gate connected to the scan line SCAN1 [n] and a first electrode connected to the data line DATA [n].

In addition, the transistor includes a second transistor T2 having a gate connected to the scan line SCAN1 [n], a first electrode connected to the first node A, and a second electrode connected to the second node B.

Also, a third transistor T3 having a gate connected to the first node A, a first electrode connected to the second electrode of the first transistor T1, and a second electrode connected to the second node B may be included. do.

Also, a fourth transistor T4 includes a gate connected to the first node A, a first electrode connected to the second node B, and a second electrode connected to the second power line GND.

In addition, a first electrode is connected to the first node (A) and a second electrode is connected to the second power line (GND) (C), and the first electrode is connected to the first power line (VDD) The organic light emitting diode D may include an organic light emitting diode D connected to a first electrode of the third transistor T3.

The first and second electrodes of the first, second, third and fourth transistors T1, T2, T3, and T4 described above may be selected as a source and a drain or a drain and a source electrode, respectively. It may be an N-Mos type transistor formed of Si (Amorphous Silicon). In addition, the first electrode and the second electrode of the organic light emitting diode D may also be selected as an anode and a cathode or a cathode and an anode, respectively, according to the subpixel circuit configuration.

The organic light emitting diode (D) includes an organic light emitting layer (EML) interposed between a common film such as a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and an electron injection layer (EIL). .

In such a circuit configuration, the first power line VDD may be commonly connected to the subpixels positioned in a matrix form or may be divided and connected to each of R, G, and B subpixels. That is, all of the sub pixels can be supplied with the same power through the first power line VDD, or different power can be supplied for each of the R, G, and B sub pixels.

On the other hand, in the sub-pixel circuit composed of 4T1C (4 Transistor 1 Capacitor) as in the present invention, the third transistor T3 and the fourth transistor T4, which are some transistors, saturate due to current scaling. ) And the fourth transistor T4 can be driven in the linear region. The supplementary description thereof will be described in more detail in the following driving method.

For reference, the organic light emitting display device as described above supplies power to the plurality of first and second power lines VDD and GND positioned on the display panel, and supplies a scan signal to the scan line SCAN1 [n]. When the data signal is supplied to the data line DATA [n], the sub-pixel selected by the scan line SCAN1 [n] emits light to implement an image on the display panel.

Here, the first and second power supply wirings VDD and GND are referred to as "VDD" and "GND" in the description of the description, but the power supplied to the first and second power supply wirings VDD and GND has a mutual voltage difference. Of course, it can be based on the positive or negative power level supplied.

The apparatus for supplying power and signals for driving to the first and second power wirings VDD and GND, the scan wiring SCAN1 [n], and the data wiring DATA [n] described above may be a display panel or an external display panel. It may be selectively positioned on the back.

Such devices may generally include a power supply unit supplying power, a scan driver supplying a scan signal, a data driver supplying a data signal, and the like. These devices are driven in cooperation with a memory unit and a timing controller for storing an image signal supplied from the outside.

Hereinafter, a driving method of an organic light emitting display device according to an embodiment of the present invention will be described with reference to FIG. 2.

2 is an exemplary view of a driving waveform according to an embodiment of the present invention.

As described with reference to FIG. 1, the display panel of the organic light emitting display device according to an exemplary embodiment of the present invention includes a first and second transistors T1, T2, T3, and T4. Sub pixels including C1 and the organic light emitting diode D are positioned in a matrix form.

2, a driving method according to an embodiment of the present invention includes a writing step and a light emission step.

First, writing is a step of turning on the first and second transistors T1 and T2 and storing data in the capacitor C. FIG.

In the writing step, the scan signal Scan output from the scan driver is supplied to the corresponding subpixel through the scan line SCAN [n], and the data signal Data output from the data driver is supplied to the data line DATA [. n]) to the corresponding subpixel.

Then, the first and second transistors T1 and T2 connected to the scan line SCAN [n] of the corresponding subpixel are turned on, and at this time, the first and second transistors T1 and T2 are turned on. The data signal Data is induced to the capacitor C as a data voltage.

Subsequently, the emission is a step of turning on the third and fourth transistors with the data voltage stored in the capacitor to emit the organic light emitting diodes.

In the emission step, the data voltage stored in the capacitor C is applied to the gates of the third and fourth transistors T3 and T4 so that the third and fourth transistors T3 and T4 are turned on.

Then, the power supplied to the organic light emitting diode D connected to the first power line VDD flows to the second power line GND through the third and fourth transistors T3 and T4 and thus the organic light emitting diode D ) Will emit light.

However, in the writing step, when supplying the data signal Data to store the data voltage in the capacitor C, the power supply is lower than the power supplied to the organic light emitting diode D in the emission step. Precharging may be performed first and the data signal Data may be supplied.

Refer to FIG. 3 to help understand the description.

3 is a graph of voltage variation of a capacitor according to a threshold voltage change.

Referring to FIG. 3, it can be seen that precharging is first performed through the data line DATA [n] before performing the writing step.

Here, "Vg1" of FIG. 3 represents a voltage applied to the first node A, and "Vd2" represents a voltage applied to the second node B. As shown in FIG.

When precharging is performed as described above, a voltage difference occurs between the first electrode and the second electrode of the turned-on second transistor T2 and a low voltage is applied to the gate and the first electrode of the fourth transistor T4. That is, the voltages of the gate and the first electrode of the fourth transistor T4 are reduced. In this case, the applied low voltage may apply a negative anneal to the fourth transistor T4, which will be described later.

Meanwhile, in this process, the threshold voltage of the third transistor T3 is determined. That is, the current flowing through the organic light emitting diode D to the second power line GND can be determined.

Thus, as a result, the third transistor T3 is driven in the saturation region to directly drive the organic light emitting diode D, and the fourth transistor T4 is linear in order to perform the switching operation. Each is positioned to drive at.

For reference, in the drawing, it can be seen that the voltage is shifted between 3.1 [V], 2.1 [V], and 1.1 [V] according to the variation of the threshold voltage Vth of the third transistor T3 in the emission step. Note that the voltage fluctuation range and the data voltage Vdata shown here are only disclosed for description according to the variation of the threshold voltage Vth.

A current change of the organic light emitting diode D according to the fluctuation of the threshold voltage Vth thus changed is described with reference to FIG. 4.

4 is a graph showing a current change of an organic light emitting diode according to a threshold voltage variation.

Referring to FIG. 4, after the data signal is induced to the capacitor C as the data voltage, the organic light emitting diode may emit light after the third and fourth transistors T3 and T4 are turned on. When the threshold voltage (Vth) fluctuating current change graph is shown.

According to the structure of the present invention, when data voltage Vdata = 7.75 [V] is induced after the data signal is induced to a data voltage in a state in which data voltage Vdata = 0 [V] at the time of precharging, It can be seen that the current supplied to the organic light emitting diode D has a current reduction range of approximately 30% in the period of about 400 [nA] low point and 550 [nA].

Accordingly, it can be seen that the structure according to the present invention is improved to maintain a current reduction range of about 30% even when the threshold voltage Vth changes due to a structural problem of the third transistor T3 which is a driving transistor. .

On the other hand, before the writing step (Writing), as shown in FIG. 2, the fourth transistor (Turn off the power supplied to the organic light emitting diode D and turn on the first and second transistors T1 and T2) It has been described that the initialization step of negative annealing in T4) may be included.

See FIG. 5 and FIG. 6 for a description thereof.

5 is an exemplary driving waveform diagram for explaining a negative anneal.

Referring to FIG. 5, the negative annealing performed on the fourth transistor T4 may be performed in a precharging period before the data signal is supplied, as described above with reference to FIG. 3.

Here, the negative annealing applied to the fourth transistor T4 cuts off the power supplied to the organic light emitting diode D through the first power line VDD, and the second transistor T2 is turned on. This is possible by the node B being lower than the voltage of the first node A. FIG. At this time, the data voltage Vdata drops to a negative voltage and then rises to a positive voltage. For example, with reference to FIG. 5, the data voltage Vdata drops to −5 [V] and then writes data. ) Up to 7.75 [V]. Then, the emission step is performed.

Therefore, the negative anneal applied to the fourth transistor T4 can be performed by the negative voltage applied to the precharging interval, and more precisely, the negative data anneal that anneals to the negative data voltage. It can be seen that.

Accordingly, the third transistor T3 of the present invention compensates for the variation in the threshold voltage Vth in a circuit, and the fourth transistor T4 can apply negative annealing, so that the threshold voltage Vth due to the negative annealing is applied. Recovery of fluctuations can of course have additional compensation effects.

As described above, the present invention can minimize the effect of the current of the organic light emitting diode D decreasing at a specific time point due to the variation of the threshold voltage Vth, which will be described with reference to FIG. 6.

6 is a graph showing current decrease of an organic light emitting diode according to a threshold voltage variation.

Referring to FIG. 6, "P1" represents a current reduction curve of the organic light emitting diode according to the threshold voltage variation of the conventional 2T1C structure. And "P2" to "P6" represents the current reduction curve of the organic light emitting diode (D) according to the threshold voltage variation of the 4T1C structure of the present invention. Here, the graph is a graph showing the current flow state of the organic light emitting diode (D) by applying different data voltages applied at the time of negative annealing in order to minimize the effect of the threshold voltage (Vth) fluctuation range of about 5 See.

Here, as shown in the graph of FIG. 6, it can be seen that as the negative annealing value "P6" is decreased, the current reduction rate of the organic light emitting diode D decreases as the negative voltage value is increased. That is, as the negative voltage value increases, the recovery rate of the fourth transistor T4 increases.

As described above, the present invention improves the subpixel structure of the organic light emitting display device, thereby solving the problems of current reduction and luminance reduction of the organic light emitting diode due to the threshold voltage change of the driving transistor. In addition, there is an effect of improving the display quality and of providing an organic light emitting display device suitable for high resolution.

However, in the above-described structure, if the transistor included in the sub-pixel is formed in the P-Mos type and the circuit configuration is implemented to be suitable for the P-Mos type, the same effect as the present invention may be obtained.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is indicated by the following claims rather than the detailed description. Also, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

As described above, the present invention improves the sub-pixel structure of the organic light emitting display device, and has the effect of solving the current reduction caused by the threshold voltage change of the driving transistor and the luminance reduction of the organic light emitting diode. In addition, there is an effect of improving the display quality and of providing an organic light emitting display device suitable for high resolution.

Claims (8)

And a display panel in which subpixels connected to the plurality of first and second power lines, scan lines, and data lines are positioned in a matrix form. The sub- A first transistor having a gate connected to the scan line and a first electrode connected to the data line, a gate connected to the scan line, a first electrode connected to a first node, and a second electrode connected to a second node A second transistor; a third transistor having a gate connected to the first node; a first electrode connected to the second electrode of the first transistor; and a second transistor connected to the second node; and a gate connected to the first node; A fourth transistor connected to the second node, a first electrode connected to the second power line, and a second electrode connected to the second power line, a first electrode connected to the first node, and a second electrode connected to the second power line. And an organic light emitting diode connected to a first capacitor connected to the first power line and a second electrode connected to the first electrode of the third transistor. The method of claim 1, The first, second, third and fourth transistors, N-Mos type organic light emitting display device. The method of claim 1, The first, second, third and fourth transistors, An organic light emitting display device which is an a-Si transistor. A first transistor having a gate connected to the scan line and a first electrode connected to the data line, a second transistor connected to a gate of the scan line, a first electrode connected to the first node, and a second electrode connected to the second node A third transistor having a gate connected to the first node, a first electrode connected to the second electrode of the first transistor, a second electrode connected to the second node, and a gate connected to the first node; A fourth transistor having a first electrode connected to the second node and a second electrode connected to a second power line, a capacitor connected to the first node and a second electrode connected to a second power line, An organic light emitting display device comprising a display panel in which a subpixel including an organic light emitting diode having a first electrode connected to a first power line and a second electrode connected to a first electrode of the third transistor is positioned in a matrix form.In the same way, A write step of turning on the first and second transistors and storing a data signal supplied to the capacitor as a data voltage; and turning on the third and fourth transistors with the data voltage stored in the capacitor to turn on the organic light emitting diode A method of driving an organic light emitting display device comprising a light emitting step of emitting light. 5. The method of claim 4, Before the write step, And an initial step of performing negative annealing on the fourth transistor while the power supplied to the organic light emitting diode is cut off and the first and second transistors are turned on. 5. The method of claim 4, In the writing step, When supplying a data signal to store the data voltage to the capacitor, A method of driving an organic light emitting display device which performs precharging first and supplies the data signal in a lower state than a power supplied to the organic light emitting diode in the light emitting step. 5. The method of claim 4, And the third transistor is driven in a saturation region and the fourth transistor is driven in a linear region. 5. The method of claim 4, The first, second, third and fourth transistors, A method of driving an N-Mos type organic light emitting display device formed of a-Si.

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