KR101380525B1 - 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, first and second scan wirings, and data wirings are positioned in a matrix. The first transistor connected to the first scan wiring and the gate connected to the first scan wiring, the first capacitor connected to the second electrode of the first transistor, and the first electrode connected to the second electrode of the first capacitor. A second transistor having a gate connected to the first scan wiring, a third transistor having a gate connected to the second electrode of the first capacitor and a first electrode connected to the second electrode of the second transistor, and a gate of the third transistor A second capacitor having a first electrode connected to the second electrode of the third transistor and a second electrode connected to the second power supply wiring in common; a gate connected to the second scan wiring; and a second electrode of the second transistor connected to the second electrode. 2nd transistor An organic light emitting display device includes a fourth transistor having a first electrode connected to an electrode in common, and an organic light emitting diode connected to a first electrode connected to a first power line and connected to a second electrode of a fourth transistor. to provide.

Organic light emitting display device, sub pixel, compensation structure

Description

Organic Light Emitting Display and Driving Method of the same

1 is a diagram illustrating a gate voltage of a driving transistor included in a conventional subpixel structure.

2 is a diagram illustrating a driving current of an organic light emitting diode included in a conventional subpixel structure.

3 is a diagram illustrating a subpixel structure of an organic light emitting display device according to an embodiment of the present invention.

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

5 is a diagram illustrating a gate voltage of a driving transistor included in a subpixel structure according to the present invention.

6 is a view showing a driving current of an organic light emitting diode included in a subpixel structure according to the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

VDD: First Power Wiring GND: Second Power Wiring

TFT1, TFT2, TFT3, TFT4: first, second, third and fourth transistors

SCAN1 [n]: first scan wiring SCAN2 [n]: second scan wiring

SCAN1 [n-1]: first scan wiring located at the front end

DATA [n]: data line D: organic light emitting diode

C1, C2: first and second capacitors

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 general, a subpixel of an organic light emitting display device uses two or more transistors and one or more capacitors.

1 is a diagram illustrating a gate voltage of a driving transistor included in a conventional sub pixel structure, and FIG. 2 is a diagram showing a driving current of an organic light emitting diode included in a conventional sub pixel structure.

As shown in Figs. 1 and 2, the conventional sub pixel structure has a current non-uniformity of the driving transistor due to the characteristic nonuniformity of the driving transistor, or a change in the time-dependent characteristic, for example, the threshold voltage (Vth). The device, that is, the current supplied to the organic light emitting diode is reduced. In particular, such a problem causes a decrease in external quantum efficiency (EQF) and a decrease in luminance, and thus, the display quality of the organic light emitting display device is deteriorated, and as a result, many limitations are required to secure the lifetime.

An object of the present invention for solving the above-described problems is to provide a sub-pixel capable of compensating the threshold voltage fluctuation characteristics of the driving transistor to improve the display quality of the organic light emitting display device as well as to secure a lifetime.

According to an aspect of the present invention, a display panel includes a plurality of first and second power supply wirings, first and second scan wirings, and a subpixel connected to a data wiring in a matrix form. A first transistor having a first electrode connected to the data line and a gate connected to the first scan line; a first capacitor having a first electrode connected to a second electrode of the first transistor; and a second electrode of the first capacitor. A second transistor having a first electrode connected thereto and a gate connected to a first scan line positioned at a front end thereof, a third gate connected to a second electrode of the first capacitor and a first electrode connected to a second electrode of the second transistor A second capacitor having a transistor, a first electrode connected to the gate of the third transistor, and a second electrode connected to the second electrode and the second power supply wiring of the third transistor in common; and a gate connected to the second scan wiring; 2 transistor An organic light emitting diode having a first transistor connected to the second electrode and a second electrode of the third transistor in common; a first electrode connected to the first power line; and a second electrode connected to the second electrode of the fourth transistor An organic light emitting display device including a diode is provided.

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

In another aspect, the present invention provides an organic electric field including a display panel in which subpixels including first, second, third, and fourth transistors, first and second capacitors, and an organic light emitting diode are positioned in a matrix. A method of driving a light emitting display device, the method comprising: turning on a second transistor, turning on a first transistor, and turning off a fourth transistor; and turning on and turning on a second transistor after turning the second transistor off. A sensing step of turning off and then turning off the fourth transistor and a writing step of turning off the second transistor, turning on the first transistor, turning off the fourth transistor, and storing data in the first and second capacitors And turn off the second transistor, turn off the first transistor, turn on the fourth transistor, and turn on the third transistor with the data voltages stored in the first and second capacitors. The present invention provides a method of driving an organic light emitting display device, the method comprising a light emitting step of emitting an organic light emitting diode.

The first transistor is selectively driven by the scan signal supplied through the first scan wire, the second transistor is selectively driven by the scan signal supplied by the first scan wire located at the front end, and the fourth transistor is the second scan wire. It can be selectively driven by the scan signal supplied through.

In the sensing step, the scan signal may be supplied so that the fourth transistor is turned on first and the second transistor is overlapped and turned on in a portion of the interval before the fourth transistor is turned off.

In the sensing step and the writing step, the scan signal supplied to the first scan wiring positioned at the front end and the scan signal supplied to the first scan wiring may be supplied so as not to overlap each other.

The first, second, third and fourth transistors are N-Mos type and may be turned on when the scan signal is logic high.

<Example 1>

3 is a subpixel structure diagram of an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 3, an organic light emitting display device according to an exemplary embodiment of the present invention includes a plurality of first and second power supply wirings VDD and GND, and first and second scan wirings SCAN1 [n] and SCAN2 [. n]) and a sub-pixel (1pixel) connected to the data line DATA [n] in a matrix form.

Here, one subpixel 1pixel includes a first transistor TFT1 having a first electrode connected to the data line DATA [n] and a gate connected to the first scan line SCAN1 [n].

In addition, the first transistor C1 includes a first capacitor C1 connected to the second electrode of the first transistor TFT1. In addition, the first transistor is connected to the second electrode of the first capacitor C1 and includes a second transistor TFT2 having a gate connected to the first scan line SCAN1 [n-1] positioned at the front end.

In addition, a gate transistor is connected to the second electrode of the first capacitor C1 and a third transistor TFT3 is connected to the second electrode of the second transistor TFT2. Also, a second capacitor C2 having a first electrode connected to the gate of the third transistor TFT3 and having a second electrode connected to the second electrode and the second power line GND of the third transistor TFT3 in common. Include.

In addition, a fourth transistor having a gate connected to the second scan line SCAN2 [n] and having a first electrode connected to the second electrode of the second transistor TFT2 and the second electrode of the third transistor TFT3 in common. TFT4). In addition, the organic light emitting diode D may include an organic light emitting diode D having a first electrode connected to the first power line VDD and a second electrode connected to the second electrode of the fourth transistor TFT4.

The first and second electrodes of the first, second, third, and fourth transistors TFT1, TFT2, TFT3, and TFT4 described above may be selected as a source and a drain, or a drain and a source electrode, respectively. 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 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 the first and second scan lines SCAN1 [n] and SCAN2 [n]. After supplying the scan signal to the data signal and supplying the data signal to the data line DATA [n], the subpixels selected by the first and second scan lines SCAN1 [n] and SCAN2 [n] emit light. By doing so, it is possible to implement an image on the display panel.

On the other hand, the power and signals required for driving the first and second power wirings VDD and GND, the first and second scan wirings SCAN1 [n], SCAN2 [n], and the data wiring DATA [n] are provided. The supplying device may be selectively positioned on a display panel or an exterior of the display panel. 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. 4.

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

As described with reference to FIG. 3, a display panel of an organic light emitting display device according to an exemplary embodiment of the present invention includes first, second, third, and fourth transistors TFT1, TFT2, TFT3, and TFT4. The subpixel 1pixel including the second capacitors C1 and C2 and the organic light emitting diode D is positioned in a matrix form.

3 and 4 together for better understanding of the description, the driving method according to an embodiment of the present invention is largely the initial step (Reset), the sensing step (Vth Sensing), the writing step (Writing) and the light emitting step ( Emission).

First, the initial stage Reset is a step of turning on the second transistor TFT2, turning on the first transistor TFT1, and turning off the fourth transistor TFT4. In the initial step (Reset), it is a step of initializing unnecessary data, signals, etc. located on the wiring connected to the corresponding sub-pixel.

Thereafter, the sensing step Vth Sensing is a step of turning off after turning off the second transistor TFT2, turning off the first transistor TFT1, and turning off the fourth transistor TFT4. In the sensing step Vth sensing, the gates of the second and fourth transistors TFT2 and TFT4 positioned in the corresponding subpixel are turned on to detect the threshold voltage Vth of the third transistor TFT3.

Afterwards, the writing step turns off the second transistor TFT2, turns on the first transistor TFT1, turns off the fourth transistor TFT4, and applies the first and second capacitors C1 and C2 to the first and second capacitors C1 and C2. This step is to save the data.

In the writing step, a current is supplied to the first and second capacitors C1 and C2 positioned in the corresponding subpixel, so that the amount supplied to the capacities of the first and second capacitors C1 and C2 is equal to the voltage. This step stores the data voltage.

Afterwards, the emission step is to turn off the second transistor TFT2, turn off the first transistor TFT1, turn on the fourth transistor TFT4, and turn on the first and second capacitors C1 and C2. The third transistor TFT3 is turned on with the data voltage stored in the C1 to emit light of the organic light emitting diode D.

In the emission step, the fourth transistor TFT4 is turned on, so that power is supplied to the organic light emitting diode D through the first power line VDD. In this case, the data voltages stored in the first and second capacitors C1 and C2 supply the gates with values greater than or equal to the threshold voltage Vth of the third transistor TFT3. As a result, the third transistor TFT3 is turned on and current flows through the path formed from the first power line VDD to the second power line GND by driving the organic light emitting diode D. Is the step of emitting light.

In the above-described step, the first transistor TFT1 is selectively driven by the scan signal supplied through the first scan wire SCAN1 [n], and the second transistor TFT2 is the first scan wire SCAN1 positioned at the front end. The fourth transistor TFT4 may be selectively driven by the scan signal supplied through the second scan line SCAN2 [n].

Here, the scan signal supplied in the sensing step Vth Sensing may be turned on by first turning on the fourth transistor TFT4 and overlapping the second transistor TFT2 in a portion of the interval before the fourth transistor TFT4 is turned off. Turn on This is an example for effectively detecting the threshold voltage Vth of the third transistor TFT3 which is the driving transistor in the sensing step Vth Sensing, but is not limited thereto.

The scan signal supplied to the first scan line SCAN1 [n-1] positioned at the front end and the first scan line SCAN1 [n] in the sensing step Vth Sensing and the writing step Writng. The scan signals are supplied so as not to overlap each other. This is for the purpose of supplying a data signal by selecting only one subpixel instead of selecting two subpixels in a subsequent writing step.

Meanwhile, since the first, second, third and fourth transistors TFT1, TFT2, TFT3, and TFT4 included in the sub pixel structure of the organic light emitting display device according to the embodiment of the present invention are N-Mos type, The first, second, third and fourth transistors TFT1, TFT2, TFT3, and TFT4 are turned on when the scan signal is logic high.

When the display panel is formed using the same sub-pixel structure as in the above-described embodiment, it is possible to compensate for a problem caused by the threshold voltage Vth of the third transistor, which is a driving transistor for driving the organic light emitting diode. .

5 and 6 of the present invention, as well as the prior art of Figs. 1 and 2, the conventional subpixel structure and the subpixel structure according to the present invention will be described.

5 illustrates a gate voltage of a driving transistor included in a subpixel structure according to the present invention, and FIG. 6 illustrates a driving current of an organic light emitting diode included in the subpixel structure according to the present invention.

When the gate voltage of the driving transistor included in the conventional subpixel structure is changed due to the shift of the threshold voltage Vth as shown in FIG. 1, the driving current reduction rate of the organic light emitting diode is large as shown in FIG. 2.

However, in the driving transistor included in the subpixel structure according to the present invention, even if the gate voltage is changed by the threshold voltage Vth shift as shown in FIG. 5, the driving current reduction rate of the organic light emitting diode is small as shown in FIG. 6. .

Herein, the prior art of FIG. 2 and the present invention of FIG. 6 are described in more detail. In the conventional structure of FIG. 2, the driving current of the organic light emitting diode is approximately 85% due to the variation of the threshold voltage Vth of the driving transistor. It can be seen that the current decrease rate is shown. However, in the structure according to the exemplary embodiment of FIG. 6, it can be seen that the driving current of the organic light emitting diode exhibits a current reduction rate of approximately 25% due to the variation of the threshold voltage Vth of the driving transistor.

As can be seen from the above description, the application of the sub-pixel structure of the present invention can compensate for the threshold voltage fluctuation characteristics of the driving transistor, thereby improving display quality of the organic light emitting display device and securing lifetime. Will be obtained. In addition, problems such as reduced external quantum efficiency (EQF) and reduced luminance can be solved.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, As will be understood by those skilled in the art. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. 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 provides an sub-pixel capable of compensating the threshold voltage fluctuation characteristics of the driving transistor, thereby improving display quality of the organic light emitting display device and securing lifetime.

Claims (8)

And a display panel in which sub-pixels connected to the plurality of first and second power lines, the first and second scan lines, and the data lines are positioned in a matrix form. The sub- A first transistor having a first electrode connected to the data line and a gate connected to the first scan line, a first capacitor having a first electrode connected to a second electrode of the first transistor, and a second of the first capacitor A second transistor having a first electrode connected to the electrode and a gate connected to a first scan line positioned at a front end, a gate connected to the second electrode of the first capacitor, and a first electrode connected to the second electrode of the second transistor A second capacitor connected to the connected third transistor, a first electrode connected to a gate of the third transistor, and a second electrode connected to the second electrode of the third transistor and the second power line in common; A fourth transistor having a gate connected to the scan line and having a first electrode connected to the second electrode of the second transistor and the second electrode of the third transistor in common; and a first electrode connected to the first power line, The organic light emitting display includes an organic light emitting diode a second electrode connected to a second electrode of the fourth transistor. The method according to claim 1, The first, second, third and fourth transistors, N-Mos type organic light emitting display device. A driving method of an organic light emitting display device comprising a display panel in which subpixels including first, second, third and fourth transistors, first and second capacitors, and an organic light emitting diode are positioned in a matrix form. An initial step of turning on the second transistor, turning on the first transistor, and turning off the fourth transistor; A sensing step of turning on and then turning off the second transistor and turning off the first transistor and turning off the fourth transistor; A write step of turning off the second transistor, turning on the first transistor, turning off the fourth transistor, and storing data in the first and second capacitors; The second transistor is turned off, the first transistor is turned off, the fourth transistor is turned on, and the third transistor is turned on using data voltages stored in the first and second capacitors to emit the organic light emitting diode. A method of driving an organic light emitting display device comprising the step of emitting light. The method of claim 3, The first transistor is selectively driven by a scan signal supplied through a first scan wire, the second transistor is selectively driven by a scan signal supplied through a first scan wire located at a front end, and the fourth transistor is driven by a first signal. 2. A driving method of an organic light emitting display device which is selectively driven by a scan signal supplied through a scan wiring. 5. The method of claim 4, In the sensing step, the scan signal, And turning on the fourth transistor first and supplying the second transistor so that the second transistor overlaps and turns on a part of the interval before the fourth transistor is turned off. 5. The method of claim 4, In the sensing step and the writing step, And a scan signal supplied to the first scan wiring located at the front end and a scan signal supplied to the first scan wiring so as not to overlap each other. 5. The method of claim 4, And the first, second, third and fourth transistors are N-mos type and are turned on when the scan signal is logic high. The method according to claim 1, The first to fourth transistors are turned on at least once through an initial stage, a sensing stage, a writing stage, and a light emitting stage, In the sensing step and the writing step, And a time point at which the first transistor and the second transistor are turned on does not overlap each other.

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