KR20080113998A - Active matrix organic light emitting display device and driving method thereof - Google Patents

Abstract

In the active matrix organic light emitting diode display, in order to solve the problem that each transistor is not uniform in its characteristics across the entire display panel due to process variation, and the image quality is degraded due to residual DC charge,

A light emitting device that emits light correspondingly by a current to which the pixel cell is applied, a first transistor controlled by a scan signal supplied from a first gate line, and connected between a first node and a second node, and the first A second transistor controlled by a scan signal supplied from the gate line and connected between the third node and the second voltage supply line, and controlled by an emission control signal supplied from the emission control line, the first voltage supply line and the first node A third transistor connected therebetween, a gate electrode connected to a second node, a fourth transistor connected between the first node and the light emitting element, and controlled by a scan signal supplied from a second gate line; A fifth transistor connected between a line and the third node, and connected between the second node and a third node Provided is an active matrix organic light emitting display device including a first capacitor.

Description

Active Matrix Organic Light Emitting Diode Display Device and Driving Method Thereof}

1 is a configuration diagram showing the configuration of a conventional active matrix organic light emitting display device.

2 is a circuit diagram showing the configuration of a pixel cell in a conventional active matrix organic light emitting display device.

3 is a circuit diagram showing the configuration of an active matrix organic light emitting display device according to a first embodiment of the present invention;

4 is a timing chart of an active matrix organic light emitting display device according to a first embodiment of the present invention;

5 is a circuit diagram illustrating a configuration of an active matrix organic light emitting display device according to a second embodiment of the present invention;

6 is a graph illustrating output currents of light emitting devices according to input voltages of a conventional active matrix organic light emitting display device and an active matrix organic light emitting display device according to an embodiment of the present invention;

 <Description of Symbols for Main Parts of Drawings>

GL1 to GLn: gate lines DL1 to DLm: data lines

PXL: pixel cell OLED: light emitting element

12: pixel region 20: gate driver

30: data driver VDD: driving voltage

VSS: Base voltage VDL: Drive voltage supply line

VSL: ground voltage supply line T _DR : drive transistor

T _SW : Switching Transistor Cst: Capacitor

GLa: first gate line GLb: second gate line

DL: data line V1L: first voltage supply line

V2L: second voltage supply line EML: light emission control line

T1 to T5: first to fifth transistors

N1 to N3: first to third nodes

Vth_T4: Threshold voltage of the fourth transistor

I_OLED: Current flowing through the light emitting device EM: Light emission control signal

142: first electrode of the first capacitor 144: second electrode of the first capacitor

146: first electrode of the second capacitor 148: second electrode of the second capacitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix organic light emitting diode display device (AMOLED), and more particularly, to an active matrix organic light emitting display device which prevents deterioration of image quality due to a threshold voltage of a transistor and its It relates to a driving method.

With the development of the information society, it is required to develop a new image display device that improves disadvantages such as heavy weight and large volume of the conventional CRT (Cathode Ray Tube).

Accordingly, liquid crystal display devices (LCDs), organic light emitting diode display devices (OLEDs), plasma panel display devices (PDPs), surface-conduction electron-emitter display devices (SEDs), and the like. The same various flat panel display devices are attracting attention.

Among them, the organic light emitting diode display uses an organic light emitting diode, which is a self-luminous device that emits phosphors by recombination of electrons and holes, and has excellent display characteristics such as contrast ratio and response time. In addition, since it is easy to implement a flexible display, it is attracting attention as an ideal next generation display.

According to a driving method, an organic light emitting diode display includes a passive matrix method for controlling pixels by a matrix unit of electrodes composed of rows and columns, and an active matrix for controlling pixels using switching elements provided for each cell. Matrix),

In particular, in order to achieve high resolution, an active matrix organic light emitting display device has an advantage over a passive matrix organic light emitting display device.

1 is a block diagram illustrating a configuration of a conventional active matrix organic light emitting display device.

As shown in FIG. 1, a conventional active matrix organic light emitting diode display includes a plurality of gate lines GL1 through GLn and a plurality of data lines DL1 through DLm defining a pixel region 12 by crossing the gate lines, and the pixels. A display panel 10 having a plurality of pixel cells PXL provided in an area 12, a gate driver 20 supplying a scan signal for driving the gate lines GL1 to GLn, and the data line And a data driver 30 for supplying a data signal to the DL1 to DLm.

Each of the pixel cells PXL is connected to the gate line and the data line, receives a data signal from the data line according to a scan signal supplied from the gate line, and drives the pixel cell PXL to implement an image. .

As illustrated in FIG. 2, the pixel cell PXL is connected between a driving voltage supply line VDL for supplying a driving voltage VDD and a ground voltage supply line VSL connected to a ground voltage VSS. The light emitting device OLED and the pixel circuit 40 for driving the light emitting device OLED are provided.

In the light emitting device OLED, an anode electrode is electrically connected to the pixel circuit 40 and a cathode electrode is electrically connected to a ground voltage supply line VSL. The light is emitted in accordance with the current corresponding to the supplied data signal.

The pixel circuit 40 includes a driving transistor T _DR that supplies a current corresponding to the data signal to the light emitting device OLED according to a voltage between its gate electrode and the source electrode, and a scan pulse supplied to the gate line GL. a switching transistor (T _SW), and a gate of the driving transistor (T _DR) for supplying a data signal on the data line (DL) to the gate electrode of the driving transistor (T _DR) in accordance with-connected between a source switching transistor (T _SW) And a capacitor Cst for storing a voltage corresponding to the data signal supplied from the data signal.

Here, the driving transistor T _DR and the switching transistor T _SW are P-type metal oxide semiconductor field effect transistors (MOSFETs).

The source electrode of the switching transistor T _SW is electrically connected to the data line DL, and the drain electrode of the switching transistor T _SW is electrically connected to the gate electrode of the driving transistor T _DR . In addition, the gate electrode of the switching transistor T _SW is electrically connected to the gate line GL.

The source electrode of the driving transistor T _DR is electrically connected to the driving voltage supply line VDL, and the drain electrode is electrically connected to the anode electrode of the light emitting device OLED. In addition, the gate electrode of the driving transistor T _DR is electrically connected to the drain electrode of the switching transistor T _SW . The driving transistor T _DR controls the amount of light emitted from the light emitting element OLED by controlling the amount of current I_OLED supplied from the driving voltage supply line VDL to the light emitting element OLED in response to a data signal supplied to the gate electrode. Adjust

The capacitor Cst is electrically connected between the first node N1 and the driving voltage supply line VDL connected to the gate electrode of the driving transistor T _DR and the drain electrode of the switching transistor T _SW . The capacitor Cst stores a voltage corresponding to the data signal supplied to the first node N1 via the switching transistor T _SW in a section in which a scan pulse is supplied to the gate line GL. When the switching transistor T _SW is turned off, the turned-on state of the driving transistor T _DR is maintained for one frame by using the stored voltage.

The driving method of the pixel cell PXL is as follows.

First, the switching transistor T _SW is turned on by a scan pulse in a low state supplied to the gate line GL, so that a data signal on the data line DL passes through the switching transistor T _SW . Supplied to N1).

Next, the driving transistor T _DR is turned on by the data signal supplied to the first node N1, and a current corresponding to the data signal from the driving voltage supply line VDL is driven by the driving transistor T _DR . It is supplied to the light emitting device (OLED) via the.

Accordingly, the light emitting device OLED emits light with brightness corresponding to the current supplied from the driving transistor T _DR . At the same time, the capacitor Cst stores a voltage corresponding to the data signal supplied on the first node N1.

Next, the switching transistor T _SW is turned off because the scan pulse in the low state supplied to the gate line GL transitions to the high state. When the switching transistor T _SW is turned off, the capacitor Cst maintains the turn-on state of the driving transistor T _DR for one frame by using a voltage corresponding to the stored data signal. Accordingly, the light emitting device OLED emits light for one frame by the current supplied from the driving voltage supply line VDL through the driving transistor T _DR , which is turned on by the capacitor Cst.

However, such a conventional active matrix organic light emitting display device has a threshold voltage (Vth: Threshold Voltage), a charge carrier mobility, and a leakage current of each of the driving transistor and the switching transistor due to the variation occurring between processes. Characteristics such as leakage current and device stability are not uniform across the display panel, resulting in uneven image quality.

In addition, there is a problem in that the driving transistor is degraded and image sticking occurs due to the residual DC charge.

In addition, there is a problem in that it is difficult to precisely control the driving transistor because the residual DC charge does not have linearity with respect to the voltage supplied with the current flowing through the driving transistor.

The present invention has been made to solve such a problem, and an active matrix that compensates the threshold voltage of a driving transistor for driving the light emitting device of each pixel cell and can remove residual DC charge present in each pixel cell. An object of the present invention is to provide an organic light emitting diode and a driving method thereof.

In order to achieve the above technical problem, an active matrix organic light emitting display device according to a first embodiment of the present invention,

A plurality of first gate lines and second gate lines, a plurality of data lines crossing the first gate line and the second gate line to define a pixel region, and a plurality of first voltage supply lines supplying a first voltage And a plurality of second voltage supply lines for supplying a second voltage, a plurality of pixel cells provided for each pixel region, and a plurality of light emission control lines connected to each pixel cell,

The pixel cell may include a light emitting device that emits light corresponding to an applied current, a first transistor controlled by a scan signal supplied from the first gate line, and connected between a first node and a second node; A second transistor controlled by a scan signal supplied from a first gate line and connected between a third node and a second voltage supply line, and controlled by an emission control signal supplied from the emission control line, the first voltage supply line A third transistor connected between the first node and the first node, a fourth transistor connected between the first node and the light emitting element, the gate electrode being connected to the second node, and a scan supplied from the second gate line A fifth transistor controlled by a signal and connected between the data line and the third node; And a first capacitor connected to the second node and a second electrode connected to the third node.

In addition, in the active matrix organic light emitting diode display according to the second embodiment of the present invention, a first electrode is connected to the second voltage supply line and a second electrode is connected to the third node in parallel with the second transistor. It further comprises a second capacitor connected.

That is, the active matrix organic light emitting diode display according to the second embodiment of the present invention further includes a second capacitor connected in parallel with the second transistor so that the current can be stably supplied to the light emitting device for one frame. Has

Next, an active matrix organic light emitting display device according to a first embodiment of the present invention will be described with reference to the accompanying drawings.

3 is a circuit diagram illustrating a pixel cell PXL in an active matrix organic light emitting display device according to a first embodiment of the present invention.

4 is a timing chart of an active matrix organic light emitting display device according to a first embodiment of the present invention.

As shown in FIG. 3, the active matrix organic light emitting diode display according to the first exemplary embodiment of the present invention,

A plurality of data lines DL crossing the first gate line GLa and the second gate line GLb and the first gate line GLa and the second gate line GLb to define pixel regions. And a plurality of first voltage supply lines V1L for supplying the first voltage V1 and a plurality of second voltage supply lines V2L for supplying the second voltage V2, and a plurality of pixels provided for each pixel region. Pixel cells PXL and a plurality of emission control lines EML connected to each pixel cell PXL,

The pixel cell PXL is controlled by a light emitting device OLED that emits light corresponding to an applied current, and is controlled by a scan signal supplied from the first gate line GLa. The first transistor T1 connected between the two nodes N2 and the scan signal supplied from the first gate line Gla are controlled between the third node N3 and the second voltage supply line V2L. A second transistor T2 connected to the second transistor T2 and a light emission control signal EM supplied from the light emission control line EML, and connected between the first voltage supply line V1L and the first node N1. A third transistor T3 and a gate electrode connected to a second node N2 and a fourth transistor T4 connected between the first node N1 and the light emitting element OLED, and the second gate It is controlled by the scan signal supplied from the line GLb and the data line DL. The fifth transistor T5 connected between the third node N3, the first electrode 142 is connected to the second node N2, and the second electrode 144 is connected to the third node N3. It comprises a first capacitor (C1) connected to.

Next, an operation of the pixel cell PXL in the active matrix organic light emitting diode display according to the first exemplary embodiment of the present invention will be described with reference to FIGS. 3 and 4.

First, the scan signal of the first logic state is supplied to the first gate line GLa to turn on the first transistor T1 and the second transistor T2 and supplied through the emission control line EML. The third transistor T3 is turned on in response to the light emission control signal EM in the first logic state.

At this time, the first voltage V1 is supplied to the first node N1 through the third transistor T3, and the voltage supplied to the first node N1 is second through the first transistor T1. It is supplied to the node N2.

At the same time, the second voltage V2 having the same value as the first voltage is supplied to the third node N3 through the second transistor T2 through the second voltage supply line V2L.

That is, the first electrode 142 of the first capacitor C1 is connected to the second node N2 to apply a first voltage, and the second electrode 144 of the first capacitor C1 is connected to the third node ( Since a second voltage connected to N3) and having the same value as that of the first voltage is applied, the voltage applied to both electrodes is the same and thus is in a reset state.

In this manner, after the first capacitor C1 is reset, a second voltage transitioned to the base voltage VSS is supplied through the second voltage supply line V2L.

In this case, since the fourth transistor T4 is in a diode-connected state, the second electrode of the first capacitor C1 is connected to the third node N3 supplied with the base voltage, so that the fourth transistor T4 A threshold voltage Vth_T4 is stored in the first capacitor C1.

Next, when the scan signal supplied to the first gate line is in the second logic state, the first transistor T1 and the second transistor T2 are turned off, and the second logic state is supplied through the emission control line. The third transistor is also turned off in response to the emission control signal of.

Next, when the scan signal of the first logic state is input to the second gate line, the fifth transistor T5 is turned on in response to the input signal, and the data signal supplied from the data line DL is supplied to the fifth transistor T5. Is supplied to the third node N3.

In this case, a data voltage Vdata corresponding to the data signal is additionally stored in the first capacitor C1, and the stored voltage is expressed as follows.

Next, when the scan signal of the second logic state is input through the second gate line, the fifth transistor T5 is turned off and again by the light emission control signal of the first logic state supplied through the light emission control line. The third transistor is turned on again.

As such, the first voltage supplied through the turned-on third transistor supplies current to the light emitting device OLED through the fourth transistor T4 driven for one frame by the voltage stored in the first capacitor. To emit light for one frame.

As described above, the active matrix organic light emitting diode display according to the first exemplary embodiment of the present invention drives the pixel cell PXL after resetting the first capacitor, thereby removing the residual DC charge remaining in the pixel cell in the previous driving step. By driving

It provides an effect that can solve the problem of remaining afterimage due to the residual DC charge.

Next, an active matrix organic light emitting display device according to a second embodiment of the present invention will be described with reference to FIG. 5.

5 is a circuit diagram illustrating a configuration of an active matrix organic light emitting display device according to a second embodiment of the present invention.

As shown in FIG. 5, an active matrix organic light emitting display device according to a second embodiment of the present invention

A plurality of data lines DL crossing the first gate line GLa and the second gate line GLb and the first gate line GLa and the second gate line GLb to define pixel regions. And a plurality of first voltage supply lines V1L for supplying the first voltage V1 and a plurality of second voltage supply lines V2L for supplying the second voltage V2, and a plurality of pixels provided for each pixel region. Pixel cells PXL and a plurality of emission control lines EML connected to each pixel cell PXL,

The pixel cell PXL is controlled by a light emitting device OLED that emits light corresponding to an applied current, and is controlled by a scan signal supplied from the first gate line GLa. The first transistor T1 connected between the two nodes N2 and the scan signal supplied from the first gate line Gla are controlled between the third node N3 and the second voltage supply line V2L. A second transistor T2 connected to the second transistor T2 and a light emission control signal EM supplied from the light emission control line EML, and connected between the first voltage supply line V1L and the first node N1. A third transistor T3 and a gate electrode connected to a second node N2 and a fourth transistor T4 connected between the first node N1 and the light emitting element OLED, and the second gate The data line DL is controlled by a scan signal supplied from the line GLb. The fifth transistor T5 connected between the third node N3, the first electrode 142 is connected to the second node N2, and the second electrode 144 is connected to the third node N3. A first capacitor C1 connected to the first electrode 146 and a first electrode 146 connected to the second voltage supply line V2L, and a second electrode 148 connected to the third node N3. And a second capacitor C2 connected in parallel with the transistor T2.

Next, an operation of the pixel cell PXL in the active matrix light emitting display device according to the second embodiment of the present invention will be described.

First, the first transistor T1 and the second transistor T2 are turned on by supplying a scan signal having a first logic state to the first gate line GLa, and simultaneously supplied to the emission control line EML. The third transistor T3 is turned on in response to the light emission control signal EM in one logic state.

At this time, the first voltage V1 is supplied to the first node N1 through the third transistor T3, and the voltage supplied to the first node N1 is second through the first transistor T1. It is supplied to the node N2.

At the same time, the second voltage V2 having the same value as the first voltage is supplied to the third node N3 through the second transistor T2 through the second voltage supply line V2L.

That is, the first electrode 142 of the first capacitor C1 is connected to the second node N2 to apply a first voltage, and the second electrode 144 of the first capacitor C1 is connected to the third node ( Since a second voltage connected to N3) and having the same value as that of the first voltage is applied, the voltage applied to both electrodes is the same and thus is in a reset state.

In addition, a second voltage is applied to the first electrode 146 connected to the second voltage supply line V2L and the second capacitor C2 connected in parallel with the second transistor T2 is connected to the third node. Since the second voltage is also applied to the second electrode 148 connected to N3), the voltage applied to both electrodes is also the same, and is in a reset state.

As described above, after the first capacitor C1 and the second capacitor C2 are reset, the second voltage is transferred to the base voltage VSS through the second voltage supply line V2L.

In this case, since the fourth transistor T4 is in a diode-connected state, the second electrode of the first capacitor C1 is connected to the third node N3 supplied with the base voltage, so that the fourth transistor T4 Threshold voltage Vth_T4 is stored in the first capacitor C1.

Next, when the scan signal supplied to the first gate line is in the second logic state, the first transistor T1 and the second transistor T2 are turned off, and the second logic state is supplied through the emission control line. The third transistor is also turned off in response to the emission control signal of.

Next, when the scan signal of the first logic state is input to the second gate line, the fifth transistor T5 is turned on in response to the input signal, and the data signal supplied from the data line DL is supplied to the fifth transistor T5. Is supplied to the third node N3.

In this case, the data voltage Vdata corresponding to the data signal is additionally stored in the first capacitor C1, and the data voltage Vdata is stored in the second capacitor C2.

Next, when the scan signal of the second logic state is input through the second gate line, the fifth transistor T5 is turned off and again by the light emission control signal of the first logic state supplied through the light emission control line. The third transistor is turned on again.

As such, the first voltage supplied through the turned-on third transistor is driven through the fourth transistor T4 driven for one frame by the voltage stored in the first capacitor and the second capacitor. It supplies current to emit light for one frame.

As described above, the active matrix organic light emitting diode display according to the second exemplary embodiment of the present invention further includes a second capacitor connected in parallel with the second transistor, so that the fourth transistor is more stable for one frame than when the fifth transistor is turned off. Provides the effect of driving a transistor.

6 is a graph comparing output currents of light emitting devices according to input voltages in an active matrix organic light emitting display device according to a second exemplary embodiment of the present invention and a conventional active matrix organic light emitting display device.

As shown in FIG. 6, the active matrix organic light emitting diode display according to the second exemplary embodiment of the present invention has a more linear output current according to the input voltage than the conventional active matrix organic light emitting diode display. It can be seen that there is a relationship.

As described above, the active matrix organic light emitting diode display according to the second exemplary embodiment of the present invention has a linear relationship in which the output current of the light emitting device according to the input voltage is approximated, so that the device can be driven more stably. This provides the effect of extending the life of the device and improving the reliability.

In the active matrix organic light emitting diode display according to the present invention, the first to fifth transistors may be implemented as either an N-type transistor or a P-type transistor.

In addition, the first to fifth transistors are amorphous silicon or polysilicon, but a semiconductor layer may be formed of an organic semiconductor material.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those skilled in the art.

As described above, the active matrix organic light emitting diode display according to the present invention provides an effect of resolving the problem that an afterimage remains due to residual DC charge by driving the pixel cell PXL after resetting the first capacitor.

In addition, the active matrix organic light emitting diode display according to the present invention has a linear relationship in which the output current of the light emitting device according to the input voltage is approximated, so that the device can be driven more stably and thus the life of the device is improved. Provide the effect of prolonging and improving reliability.

Claims (8)

A plurality of first gate lines and second gate lines, a plurality of data lines crossing the first gate line and the second gate line to define a pixel region, and a plurality of first voltage supply lines supplying a first voltage And a plurality of second voltage supply lines for supplying a second voltage, a plurality of pixel cells provided for each pixel region, and a plurality of light emission control lines connected to each pixel cell, The pixel cell emits light correspondingly by the applied current; A first transistor controlled by a scan signal supplied from the first gate line and connected between a first node and a second node; A second transistor controlled by a scan signal supplied from the first gate line and connected between a third node and a second voltage supply line; A third transistor controlled by a light emission control signal supplied from the light emission control line and connected between a first voltage supply line and a first node; A fourth transistor having a gate electrode connected to the second node and connected between the first node and the light emitting element; A fifth transistor controlled by a scan signal supplied from the second gate line and connected between the data line and the third node; And a first capacitor having a first electrode connected to the second node and a second electrode connected to the third node. The method of claim 1, The first capacitor is reset by receiving a first voltage supplied through a turned-on first transistor and a second voltage having the same magnitude as that of the first voltage through a second voltage supply line. Light emitting display device. The method of claim 2, And after the first capacitor is reset, a ground potential is supplied to the second voltage supply line, and a threshold voltage of the fourth transistor is stored in the first capacitor. The method of claim 1, And a second capacitor connected between the second voltage supply line and a third node, the second capacitor being connected in parallel with the second transistor. The method of claim 4, wherein The first capacitor and the second capacitor are reset by being supplied with a first voltage supplied through a turned-on first transistor and a second voltage having the same magnitude as the first voltage through a second voltage supply line. An active matrix organic light emitting display device. A plurality of data lines, first and second voltage supply lines, and light emitting devices crossing the emission control lines, the plurality of first gate lines and the second gate lines, and the first and second gate lines to define a pixel area. A driving method of an active matrix organic light emitting display device comprising: a plurality of pixel cells provided in the pixel area and a pixel circuit for driving the pixel cells. Resetting a capacitor provided in the pixel circuit using a first voltage supplied through the first voltage supply line and a second voltage supplied through the second voltage supply line and having a same magnitude as that of the first voltage. ; Translating the second voltage to a base voltage and storing a threshold voltage of a transistor for driving the light emitting element in a capacitor provided in the pixel circuit; Further storing a data voltage in the capacitor; And emitting the light emitting device for one frame by using the voltage stored in the capacitor. The method of claim 6, And the first voltage is controlled according to an emission control signal supplied through the emission control line and supplied to the pixel circuit. The method of claim 7, wherein After storing the threshold voltage in the capacitor, the logic state of the light emission control signal is converted from the first logic state to the second logic state, And after the data voltage is further stored in the capacitor, converting the logic state of the emission control signal back to the first logic state.

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