KR20050049827A - Light emitting display device and driving method thereof - Google Patents

Abstract

The present invention relates to a light emitting display device and a driving method thereof. A light emitting display device according to the present invention includes a plurality of data lines for transmitting a data voltage corresponding to an image signal, a plurality of scan lines for transmitting a selection signal, and a plurality of pixel circuits electrically connected to the scan lines and the data lines. An apparatus, comprising: a pixel circuit comprising a light emitting element that emits light in response to an applied current, a first electrode, a second electrode connected to a power source, and a third electrode electrically connected to the light emitting element, the first electrode and the second electrode A transistor for controlling the current output to the third electrode by a voltage applied between the electrodes, a first switching element for diode-connecting the transistor in response to the first control signal, a capacitor, one electrode connected to the first electrode of the transistor, and a scanning line A second switching element for applying a data voltage to the other electrode of the capacitor in response to a selection signal from the capacitor; It is connected between the electrode and the power source, in response to a second control signal and a third switching element to the second electrode of the capacitor and the power cut off.

Description

LIGHT EMITTING DISPLAY DEVICE AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device and a driving method thereof, and more particularly to an organic electroluminescent display device.

In general, an organic EL display device is a display device for electrically exciting a fluorescent organic compound to emit light, and is capable of representing an image by voltage or current writing N × M organic light emitting cells. The organic light emitting cell has a structure of an anode, an organic thin film, and a cathode layer as shown in FIG. 1. The organic thin film has a multilayer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) to improve the emission efficiency by improving the balance between electrons and holes. It also includes a separate electron injecting layer (EIL) and a hole injecting layer (HIL).

The organic light emitting cell may be driven using a simple matrix method and an active matrix method using a thin film transistor (TFT) or a MOSFET. In the simple matrix method, the anode and the cathode are orthogonal and the line is selected and driven, whereas the active driving method connects the thin film transistor and the capacitor to each indium tin oxide (ITO) pixel electrode to maintain the voltage by the capacitor capacitance. It is a driving method. In this case, the active driving method is divided into a voltage programming method and a current programming method according to the type of signal applied to maintain the voltage on the capacitor.

FIG. 2 shows a pixel circuit of a conventional voltage writing method for driving an organic EL element, and FIG. 3 shows a drive waveform diagram for driving the pixel circuit shown in FIG.

As shown in Fig. 2, a conventional voltage write type pixel circuit includes transistors M1, M2, M3, M4, capacitors C1, C2, and an organic EL element OLED.

The transistor M1 controls the amount of current flowing to the drain according to the voltage applied between the gate and the source, and the transistor M2 writes the data voltage to the capacitor C1 in response to the selection signal from the scan line Sn. . Transistor M3 diode-connects transistor M1 in response to the selection signal from scan line AZn, and transistor M4 draws current from transistor M1 in response to the selection signal from scan line AZBn. Transfer to device OLED.

Capacitor C1 is connected between the gate of transistor M1 and the drain of transistor M2, and capacitor C2 is connected between the gate and source of transistor M1.

Hereinafter, the operation of the conventional pixel circuit will be described with reference to FIG. 3.

First, when the transistor M3 is turned on by the selection signal from the scan line AZn, the transistor M1 is diode-connected to store the threshold voltage of the transistor M1 in the capacitor C2.

After that, when the transistor M3 is turned off and the data voltage is applied, the amount of change of the data voltage applied to the data line Dm and the driving transistor M1 is applied to the capacitor C2 due to the boosting action of the capacitor C1. The voltage corresponding to the sum of the threshold voltages of the voltages is stored, and the transistor M4 is turned on so that a current corresponding to the data voltage flows through the organic EL element OLED.

The conventional pixel circuit includes two capacitors C1 and C2 and transistors M3 and M4 to compensate for variations in the threshold voltage of the transistor M1, but three different scan lines are required. There is a problem that the pixel circuit and the driving circuit are complicated, and the aperture ratio of the light emitting display device is lowered. In addition, since data is written after compensating for the variation of the threshold voltage during one pixel selection time, the application of the high resolution panel is difficult due to data charging problem.

An object of the present invention is to drive a pixel circuit of a light emitting display device with few signal lines.

Another object of the present invention is to improve the aperture ratio of a light emitting display device by simplifying the pixel circuit.

Another object of the present invention is to provide a method of driving a light emitting display device that can be applied to a high resolution panel.

In order to achieve the above object, a light emitting display device according to an aspect of the present invention includes a plurality of data lines for transmitting a data voltage corresponding to an image signal, a plurality of scan lines for transmitting a selection signal, and the scan lines and the data lines. A light emitting display device comprising a plurality of pixel circuits electrically connected to the light emitting display device, wherein the pixel circuits are electrically connected to the light emitting device, a first electrode, a second electrode connected to a power supply, and a light emitting device to emit light corresponding to an applied current. And a third electrode connected to the transistor, the transistor controlling a current output to the third electrode by a voltage applied between the first electrode and the second electrode, and diode-connecting the transistor in response to a first control signal. A first switching element, one capacitor connected to said first electrode of said transistor, from said scanning line A second switching element that applies the data voltage to the other electrode of the capacitor in response to a selection signal, and is connected between the other electrode of the capacitor and the power source, and connects the other electrode of the capacitor to the power source in response to a second control signal. And a third switching element for blocking.

In a light emitting display device according to an aspect of the present invention, the first and second switching elements are formed of transistors having channels of the same type as each other, and the first control signal is substantially equal to the selection signal from the scan line. Is the same signal.

In the light emitting display device according to an aspect of the present invention, the third switching element is formed of a transistor having a channel of a different type from the first switching element, and the second control signal is different from the selection signal from the scanning line. Is substantially the same signal.

A light emitting display device according to an aspect of the present invention, further comprising a fourth switching element for electrically blocking the third electrode and the light emitting element of the transistor in response to a third control signal.

In a light emitting display device according to an aspect of the present invention, the fourth switching element is formed of a transistor having a channel of a different type from the first switching element, and the third control signal is different from the selection signal from the scanning line. Is substantially the same signal.

In the light emitting display device according to an aspect of the present invention, the fourth switching element is formed of a transistor having a channel of the same type as the third switching element, and the third control signal is substantially the same as the second control signal. As is the same signal.

In a light emitting display device according to an aspect of the present invention, after the first and second switching elements are closed at substantially the same timing, the third and fourth switching elements are closed at substantially the same timing.

According to an aspect of the present invention, a display panel of a light emitting display device includes a plurality of data lines for transmitting a data voltage corresponding to an image signal, a plurality of scan lines for transmitting a selection signal, and electrically connected to the scan lines and the data lines. A display panel of a light emitting display device including a plurality of pixel circuits, wherein the pixel circuits are electrically connected to a light emitting device that emits light in response to an applied current, a first electrode, a second electrode connected to a power supply, and the light emitting device. A transistor having a third electrode connected thereto and controlling a current output to the third electrode by a voltage applied between the first electrode and the second electrode, wherein one electrode is connected to the first electrode of the transistor A capacitor and a switch for applying the data voltage to the other electrode of the capacitor in response to a selection signal from the scan line A first period in which the data voltage is applied to the other electrode of the capacitor by a selection signal from the scan line, the transistor is diode-connected, and the other electrode of the capacitor is connected to the power source, The output current of the transistor is operated in the order of the second interval in which the light emitting device is applied.

A method of driving a light emitting display device according to an aspect of the present invention includes a plurality of data lines for transmitting a data voltage corresponding to an image signal, a plurality of scan lines for transmitting a selection signal, and electrically connected to the scan lines and the data lines. A driving method of a light emitting display device including a plurality of pixel circuits, the pixel circuit including a first electrode, a second electrode connected to a power supply, and a third electrode, and between the first electrode and the second electrode. A transistor for outputting a current corresponding to the applied voltage to the third electrode, a capacitor connected to the first electrode of the transistor, and a light emitting device connected to the third electrode of the transistor; In the driving method, the data voltage is applied to the other electrode of the capacitor in response to the selection signal, and is connected to one electrode of the capacitor. And a second step of applying a threshold voltage of the transistor between the second electrodes of the transistor, and a second step of connecting the other electrode of the capacitor to the power source in response to a first control signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the following description, when a part is connected to another part, this includes not only a case where the part is directly connected but also an electric part with another element in the middle. In the drawings, parts irrelevant to the present invention are omitted for clarity, and like reference numerals designate like parts throughout the specification.

4 schematically illustrates an active matrix display device according to an embodiment of the present invention.

As shown in FIG. 4, the display device according to the exemplary embodiment includes an organic EL display panel 100, a scan driver 200, and a data driver 300.

The organic EL display panel 100 includes a plurality of data lines D1-Dm extending in the column direction, a plurality of scanning lines S1-Sn extending in the row direction, and a plurality of pixel circuits 10. The data lines D1 -Dm transfer the data signals representing the image signals to the pixel circuit 10, and the scan lines S1 -Sn transfer the selection signals to the pixel circuit 10. The pixel circuit 10 is formed in a pixel area defined by two neighboring data lines D1 -Dm and two neighboring scan lines S1 -Sn.

The scan driver 200 sequentially applies a selection signal to the scan lines S1 -Sn, and the data driver 300 applies a data voltage corresponding to the image signal to the data lines D1 -Dm.

The scan driver 200 and / or the data driver 300 may be electrically connected to the display panel 100 or may be attached to a tape carrier package (TCP) that is electrically attached to the display panel 100. It may be mounted in the form of a chip. Alternatively, the display panel 100 may be mounted in a flexible printed circuit (FPC) or a film that is adhered to and electrically connected to the display panel 100 in the form of a chip. Alternatively, the scan driver 200 and / or the data driver 300 may be directly mounted on the glass substrate of the display panel, or may be replaced with a driving circuit formed of the same layers as the scan line, the data line, and the thin film transistor on the glass substrate. It may be mounted directly.

Hereinafter, the pixel circuit 10 of the organic EL display device according to the first embodiment of the present invention will be described in detail with reference to FIGS. 5 to 7.

FIG. 5 is an equivalent circuit diagram of a pixel circuit according to a first embodiment of the present invention, and FIG. 6 illustrates the pixel circuit shown in FIG. 5 in more detail. 7 illustrates a driving waveform for driving the pixel circuit shown in FIG. 6. 5 and 6 illustrate only the pixel circuits connected to the m-th data line Dm and the n-th scan line Sn for convenience of description.

As shown in FIG. 5, the pixel circuit 10 according to the first embodiment of the present invention includes a transistor M1, a switching element SW1-SW4, a capacitor Cst, and an organic EL element OLED. do. In FIG. 5, the transistor M1 is illustrated as a transistor having a P type channel, but the transistor M1 may be implemented as a transistor having an N type channel.

The transistor M1 is connected between the power supply VDD and the organic EL element OLED to control the current flowing through the organic EL element OLED. Specifically, the source of the transistor M1 is connected to the power supply VDD, and the drain is connected to the anode of the organic EL element OLED via the switching element SW4. The cathode of the organic EL element OLED may be grounded and may be connected to a voltage source lower than the power source VDD. In addition, one electrode A of the capacitor Cst is connected to the gate of the transistor M1, and the switching element SW2 is connected to the other electrode B of the capacitor Cst.

The switching element SW2 transfers the voltage of the data line Dm to the other electrode B of the capacitor Cst in response to the selection signal from the scan line Sn. The switching element SW1 diode-connects the transistor M1 in response to the selection signal from the scan line Sn. The switching element SW3 is connected between the power supply VDD and the other electrode B of the capacitor Cst, and supplies the other electrode B of the capacitor Cst to the power supply VDD in response to a selection signal from the scanning line Sn. ). The switching element SW4 is connected between the transistor M1 and the organic EL element OLED, and blocks the transistor M1 and the organic EL element OLED in response to a selection signal from the scanning line Sn.

According to an embodiment of the present invention, a separate control signal may be applied to the switching elements SW1-SW4, but channels of different types are provided for the switching elements SW1 and SW2 and the switching elements SW3 and SW4. When implemented with a transistor having a transistor, all of the switching elements SW1-SW4 can be controlled by one selection signal.

Specifically, when the data signal is to be written when the selection signal is at the low level, as shown in FIG. 6, the switching elements SW1 and SW2 are transferred to the transistors M2 and M3 having a P-type channel. The switching elements SW3 and SW4 are preferably implemented by transistors M4 and M5 having N-type channels.

In addition, the transistors M1-M5 include a first electrode, a second electrode, and a third electrode, and the current flowing from the second electrode to the third electrode by a voltage applied between the first electrode and the second electrode. It can be implemented as an active device for controlling.

Hereinafter, an operation of the pixel circuit according to the first embodiment of the present invention will be described with reference to FIG. 7.

As shown in FIG. 7, the select signal becomes low in the period t1, and the transistor M2 is turned on, and the transistor M1 is diode-connected by the transistor M2. Therefore, the threshold voltage of the transistor M1 is applied between the gate and the source of the transistor M1. Since the source of the transistor M1 is connected to the power supply voltage VDD, the threshold of the power supply voltage VDD and the transistor M1 is applied to the gate of the transistor M1, that is, one electrode A of the capacitor Cst. The voltage corresponding to the sum of the voltages is applied. In addition, the transistor M3 is turned on to apply the data voltage from the data line Dm to the other electrode B of the capacitor Cst.

Thereafter, in the section t2, the transistors M2 and M3 are turned off by the high level selection signal. In addition, the transistor M4 is turned on to apply the power supply voltage VDD to the other electrode B of the capacitor Cst. At this time, the voltage of the other electrode B of the capacitor Cst is changed from the data voltage to the power supply voltage VDD, and since no current path is formed in the pixel circuit, the voltage of the one electrode A of the capacitor Cst. The voltage of the other electrode B is increased by the amount of change. That is, the voltage V _A applied to the one electrode A of the capacitor Cst is represented by Equation 1 below.

Here, V _TH1 represents the threshold voltage of the transistor M1, and ΔV B represents the amount of change of the voltage applied to the other electrode _B of the capacitor Cst, as shown in Equation 2 below.

In the period t2, the transistor M5 is turned on and a current flowing through the transistor M1 is applied to the organic EL element OLED to emit light. In this case, the current I _OLED applied to the organic EL element OLED may be represented by Equation 3 below.

Here, β is a constant, and V _GS1 represents the gate-to-source voltage of the transistor M1.

As can be seen from Equation 3, since the current flowing through the organic EL element OLED is not affected by the threshold voltage V _{TH1 of} the driving transistor M1, the threshold of the driving transistor M1 existing between the pixel circuits. The deviation of the voltage can be compensated for.

Therefore, according to the first embodiment of the present invention, since the deviation of the threshold voltage V _TH1 of the driving transistor M1 can be compensated for by one scan line Sn, the aperture ratio of the pixel can be increased, and the driving circuit can be increased. It can be configured more simply.

According to the first embodiment of the present invention, the switching transistors M2, M3, M4, and M5 are controlled by one selection signal. According to the second embodiment of the present invention, as shown in FIG. The selection signals from the scanning lines Sn are applied to the M2 and M3, and the selection signals from the scanning lines En can be applied to the transistors M4 and M5. In this case, all of the transistors M2-M5 may be implemented as transistors having channels of the same type, in which case, the selection signal applied to the transistors M2 and M3 and the selection applied to the transistors M4 and M5. The polarities of the signals must be different.

In addition, according to the third embodiment of the present invention, as shown in FIG. 9, the driving transistor M1 may be implemented as a transistor having an N-type channel.

At this time, the drain of the transistor M1 is connected to the cathode of the organic EL element OLED via the transistor M5, and the anode of the organic EL element OLED is connected to the power supply VDD. In addition, the source of the transistor M1 and the source of the transistor M4 are connected to the power supply VSS.

10 illustrates a pixel circuit according to a fourth embodiment of the present invention.

In the pixel circuit according to the fourth exemplary embodiment, the drain of the transistor M4 is connected to the compensation voltage Vsus, thereby compensating not only the variation of the threshold voltage of the driving transistor between the pixel circuits but also the variation of the power supply voltage VDD. It has the advantage that it can.

Specifically, when the selection signal from the scan line Sn is at a low level, the transistors M2 and M3 are turned on to apply a data voltage to the other electrode A of the capacitor Cst, and to supply the power to one electrode A. A voltage corresponding to the sum of the voltage VDD and the threshold voltage of the driving transistor M1 is applied.

After that, when the selection signal from the scan line Sn becomes high, the transistor M4 is turned on, and the compensation voltage Vsus is applied to the other electrode B of the capacitor Cst. At this time, the increased voltage of the first electrode (A) of the capacitor (Cst) is the other by a voltage variation of the electrode (B), the voltage variation of the second electrode (B) of the capacitor (Cst) (△ V _B) is formula Same as 4.

In addition, the transistor M5 is turned on and a current flowing through the driving transistor M1 is applied to the organic EL element OLED, thereby emitting light. The current I _OLED applied to the organic EL element OLED is represented by Equation 5 below.

As can be seen from Equation 5, the current I _OLED flowing in the organic EL element OLED is not affected by the threshold voltage V _TH1 and the power supply voltage VDD of the transistor M1.

In the fourth embodiment of the present invention, the current flowing through the organic EL element OLED is affected by the compensation voltage Vsus, but since the current path is not formed through the compensation voltage Vsus in the pixel circuit, the compensation voltage There is no voltage drop in the line supplying (Vsus). Therefore, substantially the same compensation voltage Vsus can be applied to all the pixels, and by controlling the data voltage, a desired current can flow in the organic EL element OLED.

In FIG. 10, although the selection signals from the scanning lines Sn are applied to all the switching transistors M2-M5, different control signals may be applied to each transistor. In addition, the same first control signal may be applied to the transistors M2 and M3, and the same second control signal may be applied to the transistors M4 and M5. Furthermore, of course, the driving transistor M1 can be formed as a transistor having an N-type channel.

In the first to fourth embodiments, the switching transistors M2-M5 are all implemented as MOS transistors. However, the switching transistors M2-M5 may be implemented using other switching elements capable of switching both electrodes in response to an applied selection signal. In addition, it will be apparent to those skilled in the art that the channel types of the switching transistors M2, M3, M4, and M5 may be changed according to embodiments.

Although the light emitting display device according to the embodiment of the present invention has been described above, the above-described embodiment is merely an embodiment to which the concept of the present invention is applied, and the scope of the present invention is not limited to the above embodiment. Many variations can be made using the inventive concepts as they are.

According to the present invention, it is possible to provide a light emitting display device in which the variation in the threshold voltage of the driving transistor is compensated with a small signal line.

In addition, the driving circuit and the pixel circuit can be simplified to improve the aperture ratio of the light emitting display device.

Furthermore, a method of driving a light emitting display device applicable to a high resolution panel can be provided.

1 is a conceptual diagram of an organic electroluminescent display device.

2 illustrates a pixel circuit of a conventional voltage writing method.

FIG. 3 illustrates driving waveforms for driving the pixel circuit shown in FIG. 2.

4 schematically illustrates an active matrix display device according to an embodiment of the present invention.

5 illustrates a pixel circuit according to a first embodiment of the present invention.

FIG. 6 illustrates the pixel circuit shown in FIG. 5 in more detail.

7 is a driving waveform diagram for driving a pixel circuit according to a first embodiment of the present invention.

8 illustrates a pixel circuit according to a second embodiment of the present invention.

9 illustrates a pixel circuit according to a third embodiment of the present invention.

10 illustrates a pixel circuit according to a fourth embodiment of the present invention.

Claims (22)

A light emitting display device comprising: a plurality of data lines for transmitting a data voltage corresponding to an image signal, a plurality of scan lines for transmitting a selection signal, and a plurality of pixel circuits electrically connected to the scan lines and the data lines. The pixel circuit, A light emitting device that emits light in response to an applied current; A first electrode, a second electrode connected to a power supply, and a third electrode electrically connected to the light emitting device, and output to the third electrode by a voltage applied between the first electrode and the second electrode. Transistors for controlling current, A first switching element for diode-connecting the transistor in response to a first control signal, A capacitor connected to the first electrode of the transistor, A second switching element applying the data voltage to the other electrode of the capacitor in response to the selection signal from the scan line; A third switching element connected between the other electrode of the capacitor and the power source, the third switching element disconnecting the other electrode of the capacitor from the power source in response to a second control signal; A light emitting display device comprising a. The method of claim 1, And the first and second switching elements are formed of transistors having channels of the same type as each other, and the first control signal is a signal substantially the same as a selection signal from the scan line. The method of claim 1, And the third switching element is formed of a transistor having a channel of a different type from the first switching element, and the second control signal is a signal substantially the same as the selection signal from the scanning line. The method of claim 1, And a fourth switching element for electrically blocking the third electrode and the light emitting element of the transistor in response to a third control signal. The method of claim 4, wherein And said fourth switching element is formed of a transistor having a channel of a different type from said first switching element, and said third control signal is a signal substantially the same as a selection signal from said scanning line. The method of claim 4, wherein And the fourth switching element is formed of a transistor having a channel of the same type as the third switching element, and the third control signal is substantially the same as the second control signal. The method according to claim 1 or 4, And the third and fourth switching elements are closed at substantially the same timing after the first and second switching elements are closed at substantially the same timing. The method of claim 1, Wherein the transistor is a transistor having a P-type channel, the first electrode is a gate electrode, the second electrode is a source electrode, and the third electrode is a drain electrode. The method of claim 1, Wherein the transistor is a transistor having an N-type channel, the first electrode is a gate electrode, the second electrode is a drain electrode, and the third electrode is a source electrode. The method of claim 1, And an anode of the light emitting element is connected to the third electrode of the transistor, and a cathode of the light emitting element is connected to a second power source. The method of claim 10, The light emitting display device of which the voltage of the second power supply is smaller than the data voltage. A display panel of a light emitting display device comprising: a plurality of data lines transferring a data voltage corresponding to an image signal, a plurality of scanning lines transferring a selection signal, and a plurality of pixel circuits electrically connected to the scanning lines and the data lines. , The pixel circuit, A light emitting device that emits light in response to an applied current; A first electrode, a second electrode connected to a power supply, and a third electrode electrically connected to the light emitting device, and output to the third electrode by a voltage applied between the first electrode and the second electrode. Transistors for controlling current, A capacitor connected to the first electrode of the transistor, and A switching element for applying the data voltage to the other electrode of the capacitor in response to a selection signal from the scan line Including, A first period in which the data voltage is applied to the other electrode of the capacitor by the selection signal from the scan line and the transistor is diode-connected; and A second section in which the other electrode of the capacitor is connected to the power source, and an output current of the transistor is applied to the light emitting device A display panel of a light emitting display device that operates in order. The method of claim 12, The display panel of the light emitting display device, wherein the light emitting element and the third electrode of the transistor are blocked during the first period. The method of claim 12, And an anode of the light emitting element is connected to the third electrode of the transistor, and a cathode of the light emitting element is connected to a second power source. The method of claim 14, The display panel of the light emitting display device, wherein the voltage of the second power supply is smaller than the data voltage. A driving method of a light emitting display device comprising: a plurality of data lines transferring a data voltage corresponding to an image signal, a plurality of scanning lines transferring a selection signal, and a plurality of pixel circuits electrically connected to the scanning lines and the data lines. , The pixel circuit, A transistor having a first electrode, a second electrode connected to a power supply, and a third electrode, and outputting a current corresponding to a voltage applied between the first electrode and the second electrode to the third electrode; A capacitor connected to the first electrode of the transistor, and a light emitting element connected to the third electrode of the transistor, The driving method, A first step of applying the data voltage to the other electrode of the capacitor in response to the selection signal, and applying a threshold voltage of the transistor between one electrode of the capacitor and the second electrode of the transistor; and Connecting the other electrode of the capacitor to the power source in response to a first control signal; Method of driving a light emitting display device comprising a. The method of claim 16, And electrically blocking the third electrode and the light emitting element of the transistor during the first step. The method of claim 16, And the first control signal is a control signal substantially the same as the selection signal from the scan line. The method of claim 16, And the transistor is a transistor having a P-type channel, the first electrode is a gate electrode, the second electrode is a source electrode, and the third electrode is a drain electrode. The method of claim 16, And the transistor is a transistor having an N-type channel, the first electrode is a gate electrode, the second electrode is a drain electrode, and the third electrode is a source electrode. The method of claim 16, And an anode of the light emitting element is connected to the third electrode of the transistor, and a cathode of the light emitting element is connected to a second power source. The method of claim 21, And a voltage of the second power supply is smaller than the data voltage.