KR20040078437A - Method and apparatus for driving active matrix type electro-luminescence display device - Google Patents

Abstract

PURPOSE: A method and an apparatus for driving an active matrix type EL(Electro Luminescence) display device are provided to alleviate the deterioration of an organic light-emitting layer by making reverse current flow into organic EL cells. CONSTITUTION: An apparatus for driving an active matrix type EL display device includes the first driving circuit and the second driving circuit(74). The first driving circuit makes organic light-emitting cells emit light by supplying forward current to the organic light-emitting cells. And, the second driving circuit(74) supplies inverse current to the organic light-emitting cells within the non-emission period of the cells.

Description

TECHNICAL FIELD AND APPARATUS FOR DRIVING ACTIVE MATRIX TYPE ELECTRO-LUMINESCENCE DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence display device, and more particularly, to a method and apparatus for driving an active matrix type electroluminescence display device which reduces deterioration of an electroluminescence display device to stabilize driving and extend its life. will be.

Recently, various flat panel displays have been developed to reduce weight and volume, which are disadvantages of cathode ray tubes. Flat display devices include liquid crystal displays (hereinafter referred to as "LCDs"), field emission displays (FEDs), plasma display panels (hereinafter referred to as "PDPs"), and electroluminescence. A sense (Electro-luminescence: "EL") display device and the like.

PDP is most advantageous for large screens because of its relatively simple structure and manufacturing process, but it has the disadvantages of low luminous efficiency, low luminance and high power consumption.

As LCDs are mainly used as display elements in notebook computers, demand is increasing. However, since LCD is manufactured by a semiconductor process, it is difficult to make a large screen and it is not a self-emitting device, so a separate light source is required and power consumption is large due to the light source. In addition, LCD has a disadvantage of high light loss and a narrow viewing angle due to optical elements such as a polarizing filter, a prism sheet, and a diffusion plate.

EL display devices are classified into inorganic ELs and organic ELs, and have advantages of fast response speed and high luminous efficiency, luminance, and viewing angle. The organic EL display element is attracting attention as a next generation display element because it can display an image with a high luminance of tens of thousands [cd / m 2] with a voltage around 10 [V].

The organic EL cell forms an anode 2 made of a transparent conductive material on the glass substrate 1 as shown in FIG. 1, on which the hole injection layer 3, the light emitting layer 4 made of organic material, and a low work function are formed. A cathode 5 made of metal is stacked. When an electric field is applied between the anode 2 and the cathode 5, the holes in the hole injection layer 3 and the electrons in the metal proceed toward the light emitting layer 4, respectively, and are combined in the light emitting layer 4. Then, the fluorescent material in the light emitting layer 4 is excited and transitions to generate visible light. At this time, the luminance becomes proportional to the current between the anode 2 and the cathode 6.

The driving method of the organic EL display element is divided into a passive method and an active method.

2 and 3 show a passive organic EL display element and its driving waveform.

2 and 3, a passive organic EL display device includes a constant current source 21 for supplying current to the data lines DL1 to DLm, and a scan voltage to each of the scan lines SL1 to SLn. Switch elements 22 and 23 for supplying Vhigh and the ground voltage GND.

m × n organic EL cells 20 are formed at intersections of the m data lines DL1 to DLm and the n scan lines SL1 to SLn.

The data lines DL1 to DLm are connected to the anode of the organic EL cell 20 to supply the constant current from the constant current source 21 to the anode of the organic EL cell 20. The scan lines SL1 to SLn are connected to the cathode of the organic EL cell 20 and are connected to the scan voltage source Vhigh and the base voltage source GND via the switch elements 22 and 23 to switch element ( The scan bias voltage Vhigh and the ground voltage GND from 22 and 23 are supplied to the cathode of the organic EL cell 20.

The constant current source 21 is generally implemented as a current mirror including two or more switch elements and a current source.

The switch elements 22 and 23 are implemented with transistor elements such as MOS-FETs. The switch elements 22 connected to the ground voltage source GND sequentially supply scan pulses of the ground voltage GND to the scan lines SL1 to SLn in response to the control signal T1 to display the data. Select lines SL1 through SLn. The switch elements 23 connected to the scan high voltage source Vhigh supply the scan bias voltage Vhigh to the scan lines SL1 to SLn in response to the control signal T2. do.

The scan pulse SCAN of the base voltage GN is applied to the cathode of the organic EL cell 20 as a forward voltage of the organic EL cell 20 to the scan lines SL1 to SLn as shown in FIG. 3. The data pulse DATA is applied to the data lines DL1 to DLm with a positive constant current in synchronization with the scan pulse SCAN.

Of the organic EL cells 20, only the cells 21 to which the scan pulse SCAN of the base voltage GND and the constant current are applied are emitted. On the other hand, the organic EL cells 20 to which the positive scan bias voltage Vhigh is applied or to which the constant current is not applied do not emit light because the reverse voltage is applied.

In the pass type organic EL device, since reverse voltage is always applied to the organic EL cells 20 that are not selected, crosstalk and degradation of the organic light emitting layer are relatively small.

4 to 6 show an active organic EL display element and its driving waveform.

4 to 6, an active organic EL display device includes m × arranged in a matrix type in a pixel region between m column lines CL1 to CLm and n row lines RL1 to RLn. n pixels, thin film transistors SW-TFT and DRV-TFT for driving the pixels, and a capacitor Cst connected between the gate terminal and the source terminal of the driving TFT DRV-TFT. Equipped.

The thin film transistors SW-TFT and DRV-TFT are formed at the intersection of the row lines RL1 to RLn and the column lines CL1 to CLm to respond to scan voltages on the row lines RL1 to RLn. A switch TFT (SW-TFT) which is turned on / off and a driving TFT (DRV-TFT) for adjusting a current i supplied to the organic EL cells 20 in response to the drain voltage of the switch TFT (SW-TFT). It includes.

The switch TFT SW-TFT is turned on in response to the negative scan voltages from the low lines RL1 to RLn to conduct a current path between its source and drain terminals, as well as the low lines RL1 to RLn. ) Is maintained when the voltage on the circuit is below its threshold voltage (Vth). During the on-time period of the switch TFT (SW-TFT), the data voltage Vcl on the column lines CL1 to CLm is supplied to the gate terminal of the driving TFT DRV_TFT via the switch TFT SW-TFT. In the off time period of the switch TFT (SW-TFT), the current path between the source terminal and the drain terminal of the switch TFT (SW_TFT) is opened.

The source terminal of the driving TFT (DRV-TFT) is connected to one terminal of the driving voltage source VDD and the capacitor Cst, and the gate terminal is connected to the other terminal of the capacitor Cst and the drain terminal of the switch TFT (SW-TFT). do. The drain terminal of the driving TFT (DRV-TFT) is connected to the anode of the organic EL cell 20. The driving TFT (DRV-TFT) controls the amount of electric charge flowing between the source and drain terminals in response to the data voltage Vcl supplied to its gate terminal, thereby controlling the current i between the source terminal and the drain terminal, thereby controlling organic EL. The cells 20 emit light.

The capacitor Cst stores the difference voltage between the data voltage Vcl and the cell driving voltage VDD to maintain a constant voltage applied to the gate terminal of the driving TFT DRV_TFT for one frame period, and the organic EL cells ( The current i applied to 20) is kept constant for one frame period.

However, in the organic EL display device of the active type, a forward current, that is, a current flowing from the anode to the cathode is always applied to the organic EL cells 20, thereby increasing the fatigue phenomenon of the organic light emitting layer 4 in FIG. 1. As a result, the active type organic EL display device has a disadvantage in that the lifetime of the organic light emitting layer 4 is short due to deterioration of the organic light emitting layer 4.

Accordingly, it is an object of the present invention to provide a method and apparatus for driving an active matrix type EL display element which reduce deterioration of the organic EL display element to stabilize driving and extend its life.

1 is a cross-sectional view schematically showing a conventional organic electroluminescent cell.

Fig. 2 is a plan view showing an organic electroluminescent display element of a pass method and a driving device thereof.

3 is a waveform diagram illustrating a driving signal of the organic electroluminescent display device illustrated in FIG. 2.

Fig. 4 is a plan view showing an organic electroluminescent display element of an active type and a driving device thereof.

FIG. 5 is an equivalent circuit diagram of the pixel illustrated in FIG. 4.

6 is a waveform diagram illustrating driving signals of the organic electroluminescent display device illustrated in FIGS. 4 and 5.

7 is a block diagram illustrating an active matrix type electro luminescence display device and a driving device thereof according to an embodiment of the present invention.

FIG. 8 is an equivalent circuit diagram of the pixel illustrated in FIG. 7.

9 is a waveform diagram illustrating a method of driving an active matrix type electroluminescence display device according to a first embodiment of the present invention.

10 is a waveform diagram illustrating a method of driving an active matrix type electroluminescence display device according to a second embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

1 glass substrate 2 anode

3: hole injection layer 4: light emitting layer

5: cathode 20: organic EL cell

71: timing controller 72: data drive circuit

73: scan driving circuit 74: reverse voltage driving circuit

In order to achieve the above object, a method of driving an active matrix type EL display element according to an embodiment of the present invention comprises the steps of: emitting a light emitting the organic light emitting cell by supplying a forward current to the organic light emitting cell; And supplying a reverse current to the organic light emitting cell within the non-light emitting period of the organic light emitting cell.

The emitting of the organic light emitting cell may include supplying a scan signal to the organic light emitting cell; Supplying data synchronized with a scan signal to the organic light emitting cell; And controlling a current flowing in the organic light emitting cell by using a switch element responsive to at least one of the scan signal and the data.

In the reverse current supplying to the organic light emitting cell, a voltage higher than the anode voltage of the organic light emitting cell is supplied to the cathode of the organic light emitting cell.

A driving device of an active matrix type EL display element according to an embodiment of the present invention comprises: a first driving circuit for supplying a forward current to an organic light emitting cell to emit light of the organic light emitting cell; And a second driving circuit for supplying reverse current to the organic light emitting cell within the non-light emitting period of the organic light emitting cell.

The first driving circuit includes a scan driving circuit for supplying a scan signal to the organic light emitting cell; A data driver circuit for supplying data synchronized with a scan signal to the organic light emitting cell; And a switch element configured to control a current flowing in the organic light emitting cell in response to at least one of the scan signal and the data.

The second driving circuit includes an electrode line connected to the cathode of the organic light emitting cell; A switch element is provided for supplying any one of a voltage and a base voltage set higher than the anode voltage of the organic light emitting cell to the electrode line.

The driving apparatus of the active matrix type EL display element according to the embodiment of the present invention further includes a timing controller for controlling the first and second driving circuits.

The second driving circuit is configured to supply a reverse current to the organic light emitting cells included in the lines bisscanned under the control of the timing controller.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 7 to 10.

7 and 8, an EL display device of an active matrix type according to an embodiment of the present invention is disposed in a pixel region between m column lines CL1 to CLm and n row lines RL1 to RLn. M × n pixels arranged in a matrix type, thin film transistors SW-TFT and DRV-TFT for driving the pixels, auxiliary lines AL1 to ALn connected to the pixels, and a driving TFT. A capacitor Cst connected between the gate terminal and the source terminal of the DRV-TFT is provided.

The switch TFT (SW-TFT) is turned on in response to the scan voltages from the low lines RL1 to RLn to conduct a current path between its source terminal and the drain terminal, and on the low lines RL1 to RLn. When the voltage is below its threshold voltage, it is kept off.

The driving TFT (DRV-TFT) emits the organic EL cells 20 by controlling the current between the source and the drain terminals flowing by the driving voltage source VDD in response to the data voltage supplied to its gate terminal.

The capacitor Cst stores the difference voltage between the data voltage Vcl and the cell driving voltage VDD to maintain a constant voltage applied to the gate terminal of the driving TFT DRV_TFT for one frame period, and the organic EL cells ( The current i applied to 20) is kept constant for one frame period.

The auxiliary lines AL1 to ALn are connected to the cathode of the organic EL cell 20.

The driving device of this EL display element includes a data driving circuit 72 for supplying data to the column lines CL1 to CLm, and a scan driving circuit 73 for supplying scan signals to the row lines RL1 to RLn. ), A reverse voltage driving circuit 74 for supplying the reverse bias voltage Vr to the auxiliary lines AL1 to ALn, and a timing controller 71 for controlling the respective driving circuits 72, 73, and 74. It is provided.

The timing controller 71 supplies digital video data RGB from the main driving circuit (not shown) to the data driving circuit 72, and the vertical / horizontal synchronization signals V and H from the main driving circuit board and the main clock. By using MCLK, timing control signals TC1, TC2, and TC3 necessary for the respective driving circuits 72, 73, and 74 are generated.

The data driving circuit 72 performs pulse width modulation on the data RGB under the control of the timing controller 71 and supplies the modulated data to the column lines CL1 to CLm by one line in synchronization with the scan pulse. .

The scan driving circuit 73 sequentially supplies scan pulses to the row lines RL1 to RLn under the control of the timing controller 71.

The reverse voltage driving circuit 74 controls the reverse bias voltage Vr set higher than the anode voltage of the organic EL cell 20 under the control of the timing controller 71 for the non-display period or the time allocated within the display period. Supply to the cathode of 20). The reverse current ir flows through the organic EL cell 20 by the reverse bias voltage Vr from the reverse voltage driving circuit 74.

The reverse voltage driving circuit 74 includes switch elements S1 for selectively supplying the base voltage GND and the reverse bias voltage Vr as shown in FIG. 8. The switch elements S1 supply the ground voltage GND to the organic EL cells 20 of the lines (or display lines) that are scanned under the control of the timing controller 71, while the non-scanned lines ( Alternatively, the reverse bias voltage VR is supplied to the organic EL cells 20 of the non-display lines.

As a result, the reverse voltage driving circuit 74 causes the forward current or the reverse current to flow in the organic EL cells 20 under the control of the timing controller 71.

Fig. 9 shows driving waveforms of an active matrix type EL display element according to an embodiment of the present invention.

Referring to FIG. 9, the scan pulses SCAN falling to the base voltage or the negative voltage are sequentially supplied to the low lines RL1 to RLm during the high period of the vertical synchronization signal Vsync corresponding to the display period. The data DATA synchronized with the scan pulse SCAN is supplied to the column lines CL1 to CLm.

During the low period of the vertical synchronization signal Vsync corresponding to the period after the full screen is displayed or before the full screen is displayed, voltages set higher than the anode voltages of the organic EL cells 20 are simultaneously supplied to the auxiliary lines ALn. do. At this time, the reverse current ir, that is, the current flowing from the cathode to the anode flows through the organic EL cells 20.

In contrast, the reverse voltage driving circuit 74 supplies the reverse voltage Vr to the organic EL cells 20 included in the lines after some lines are scanned within the display period under the control of the timing controller 71. After the remaining lines are scanned, the reverse voltage Vr may be supplied to the organic EL cells 20 included in the remaining lines.

For example, as shown in FIG. 10, when the EL display device is dividedly driven into the upper half and the lower half, the reverse voltage driving circuit 74 has a reverse bias voltage (or reverse bias voltage) on the auxiliary lines AL1 to ALn / 2 of the upper half after the upper half is scanned. Supply Vr). After all of the lower half is scanned, the reverse bias voltage Vr is supplied to the auxiliary lines ALn / 2 + 1 to ALn in the lower half.

As described above, the method and apparatus for driving an active matrix type EL display element according to the present invention supply a reverse bias voltage to the organic EL cells for a predetermined period so that a reverse current flows in the organic EL cells so that a forward current flows through the organic EL cells. It is to alleviate the deterioration of the organic light emitting layer when the flow continuously. As a result, the active matrix type organic EL display device according to the present invention can minimize the deterioration of the organic light emitting layer, thereby extending its lifespan.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (8)

Emitting a light through the organic light emitting cell by supplying a forward current to the organic light emitting cell; And supplying a reverse current to the organic light emitting cell within the non-light emitting period of the organic light emitting cell. The method of claim 1, Emitting the organic light emitting cell, Supplying a scan signal to the organic light emitting cell; Supplying data in synchronization with the scan signal to the organic light emitting cell; And controlling a current flowing in the organic light emitting cell by using a switch element corresponding to at least one of the scan signal and the data. The method of claim 1, Supplying a reverse current to the organic light emitting cell, And supplying a voltage higher than the anode voltage of the organic light emitting cell to the cathode of the organic light emitting cell. A first driving circuit for supplying a forward current to the organic light emitting cell to emit light of the organic light emitting cell; And a second driving circuit for supplying a reverse current to the organic light emitting cells within a non-light emitting period of the organic light emitting cells. The method of claim 4, wherein The first driving circuit, A scan driving circuit which supplies a scan signal to the organic light emitting cell; A data driver circuit for supplying data synchronized with the scan signal to the organic light emitting cell; And a switch element for controlling a current flowing in the organic light emitting cell in response to at least one of the scan signal and the data. The method of claim 4, wherein The second driving circuit, An electrode line connected to a cathode of the organic light emitting cell; And a switch element for supplying any one of a voltage and a base voltage set higher than the anode voltage of the organic light emitting cell to the electrode line. The method of claim 4, wherein And a timing controller for controlling the first and second driving circuits. The method of claim 7, wherein And the second driving circuit supplies the reverse current to the organic light emitting cells included in the lines which are bisscanned under the control of the timing controller.