KR100515307B1 - Image display apparatus, and driving method thereof - Google Patents

Abstract

The present invention relates to an image display device and a driving method thereof. An image display device according to an embodiment of the present invention includes an image display device including a plurality of data lines for transmitting an image signal, a plurality of scan lines for transmitting a selection signal, a data line, and a plurality of pixel circuits electrically connected to the scan lines. A data driver for supplying a data voltage corresponding to an image signal, a deviation compensator for dropping the data voltage by a first voltage and applying it to the plurality of data lines, and a scan driver for supplying a selection signal to the scan line. do.

Description

Image display device and driving method thereof {IMAGE DISPLAY APPARATUS, AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image 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 driving voltage or current of n × m organic light emitting cells. As shown in FIG. 1, the organic light emitting cell has an anode, an organic thin film, and a cathode layer. 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).

As such a method of driving the organic light emitting cell, there are a simple matrix method and an active matrix method using a thin film transistor (TFT). 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.

In this case, the voltage writing method is a method of displaying an image by supplying a data voltage indicating a gray level to a pixel circuit, and a problem of non-uniformity occurs due to variations in threshold voltage and electron mobility of the driving transistor. The current writing method is a method of displaying an image by supplying a data current indicating a gradation degree to a pixel circuit, thereby ensuring uniformity. However, the current writing method has a problem that it is difficult to secure a charging time for charging the load of the data line because the organic EL element must be controlled as a fine current.

FIG. 2 is a pixel circuit of a voltage write method for compensating a threshold voltage of a driving transistor, and illustrates a pixel circuit disclosed in US Pat. No. 6,362,798.

As shown in Fig. 2, the pixel circuit of US Pat. No. 6,362,798 is composed of four transistors M1-M4 and an organic EL element OLED.

The driving transistor M1 transfers a current corresponding to the voltage between the gate and the source to the organic EL element OLED, and a capacitor Cst is formed between the gate and the source. Transistor M2 is diode connected and its gate is connected to the gate of transistor M1. The gate of the switching transistor M3 is connected to the scan line Sn, and the gate of the transistor M4 is connected to the scan line Sn-1.

At this time, if the threshold voltages of the transistors M1 and M2 are the same, the threshold voltage of the transistor M1 is compensated by the transistor M2. However, when the gate voltage of the driving transistor M1 is higher than the data voltage applied through the transistor M3, the transistor M2 is diode-connected in the reverse direction so that the data voltage is not transferred to the gate of the driving transistor M1. A problem arises.

In order to prevent this, in the related art, the precharge voltage Vp is applied to the gate of the driving transistor M1 while the selection signal is applied from the scan line Sn-1, and the precharge voltage Vp is lower than the lowest data voltage. It was made into a small value. In this case, since the gate voltage of the driving transistor M1 becomes the precharge voltage Vp when the data voltage is applied, the transistor M2 is always connected in the forward direction.

The conventional pixel circuit shown in FIG. 2 further includes a transistor M2 and a transistor M4 to compensate for the threshold voltage of the driving transistor M1 and prevent the transistor M2 from being diode-connected in the reverse direction. However, as the number of transistors is increased, there is a problem that the aperture ratio of the pixel is lowered and the pixel circuit is complicated.

An object of the present invention is to provide a pixel circuit in which the number of transistors included in the pixel circuit is reduced while compensating the threshold voltage of the driving transistor.

In addition, the present invention is to provide a pixel circuit that can simplify the circuit configuration, ensure a high aperture ratio, and increase the resolution of the display device.

In order to achieve the above object, an image display device according to an aspect of the present invention includes a plurality of data lines for transmitting an image signal, a plurality of scanning lines for transmitting a selection signal, a plurality of electrically connected to the data lines and the scanning lines. An image display device comprising a pixel circuit of a data source, comprising: a data driver for supplying a data voltage corresponding to the image signal; A deviation compensator for dropping the data voltage by a first voltage to apply the data voltage to the plurality of data lines; And a scan driver for supplying the selection signal to the scan line.

In the image display device according to an aspect of the present invention, the deviation compensator includes a plurality of compensation transistors respectively connected between the plurality of data lines and the data driver.

In the image display device according to an aspect of the present invention, the compensation transistor is diode-connected, and the first voltage is a threshold voltage of the compensation transistor.

In an image display device according to an aspect of the present invention, the pixel circuit includes a display element for displaying an image corresponding to an amount of current applied thereto, a first terminal, a second terminal connected to a power supply, and the display element. A driving transistor having a third terminal connected thereto and controlling a current flowing from the second terminal to the third terminal according to a voltage applied to the first terminal, the first terminal and the second terminal of the driving transistor; And a first switching element configured to transfer a voltage applied to the data line to the first terminal of the driving transistor in response to the selection signal.

In the image display device according to an aspect of the present invention, the pixel circuit further includes a second switching element for applying a precharge voltage to the first terminal of the driving transistor in response to a first control signal.

In the image display device according to one aspect of the present invention, the first control signal is a selection signal applied before the selection signal applied to the pixel circuit.

In the image display device according to an aspect of the present invention, the pixel circuit further includes a third switching element configured to transfer or block a current flowing through the driving transistor to the display device in response to a second control signal.

In the image display device according to one aspect of the present invention, the second control signal is a selection signal applied before the selection signal applied to the pixel circuit.

An image display device according to an aspect of the present invention, wherein the pixel circuit is configured to apply a precharge voltage to the first terminal of the driving transistor in response to a first control signal, and a second control signal. And a third switching element configured to transfer or block a current flowing through the driving transistor to the display device in response to the change.

In the image display device according to an aspect of the present invention, the driving transistor is formed to have substantially the same characteristics as that of the compensation transistor included in the deviation compensating unit.

In the image display device according to one aspect of the present invention, the driving transistor is a transistor having a P-type channel, the first terminal is a gate, the second terminal is a source, and the third terminal is a drain.

According to another aspect of the present invention, an image display apparatus includes: a pixel circuit including a display element displaying an image corresponding to an amount of current applied and a driving transistor configured to control an amount of current applied to the display element in accordance with an image signal; A data driver for supplying a data voltage corresponding to the image signal; And a deviation compensator connected between the data driver and the pixel circuit to drop the data voltage by a first voltage and apply the data voltage to the pixel circuit.

According to one aspect of the present invention, there is provided a method of driving an image display device, comprising: a plurality of data lines for transmitting an image signal, a plurality of scan lines for transmitting a selection signal, a plurality of pixel circuits electrically connected to the data lines and the scan lines; A driving method of an image display device, comprising: a driving transistor configured to form a capacitor between a first terminal and a second terminal, and output a current corresponding to a voltage charged in the capacitor to a third terminal; And a display element for displaying an image in correspondence with the amount of output current therefrom, the driving method comprising: transferring a precharge voltage to the first terminal of the driving transistor in response to a control signal for a first period of time; And transferring a voltage applied to the data line to the first terminal of the driving transistor in response to the selection signal for a second period, wherein the voltage applied to the data line corresponds to the image signal. Minus the first voltage.

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, it includes not only the case where it is directly connected but also the case where it is electrically connected with another element between them. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

3 is a schematic plan view of an organic EL display device according to an embodiment of the present invention.

As shown in FIG. 3, the organic EL display device according to the exemplary embodiment of the present invention includes an organic EL display panel 100, a scan driver 200, a data driver 300, and a deviation compensator 400. do.

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

In addition, the deviation compensator 400 is connected to the output terminal of the data driver 300, and drops the data voltage output from the data driver 300 by a predetermined voltage and applies the data voltage to the data lines D1 -Dm.

The scan driver 200, the data driver 300, and / or the deviation compensator 400 may be electrically connected to the display panel 100 or may be bonded to the display panel 100 and electrically connected to the tape carrier package. (tape carrier package, TCP) may be mounted in the form of a chip or the like. Alternatively, the display panel 100 may be mounted on 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, the data driver 300, and / or the deviation compensator 400 may be directly mounted on the glass substrate of the display panel, or may have the same layers as the scan line, the data line, and the thin film transistor on the glass substrate. It may be replaced with or directly mounted to the driving circuit formed with a.

Hereinafter, the pixel circuit 10 and the deviation compensator 40 of the organic EL display device according to the first embodiment of the present invention will be described in detail with reference to FIGS. 4 and 5. 4 is an equivalent circuit diagram of a pixel circuit according to a first exemplary embodiment of the present invention, and FIG. 5 is a driving waveform diagram for driving the pixel circuit of FIG. 4. 4 illustrates only the pixel circuit connected to the m-th data line Dm and the n-th scan line Sn, the deviation compensator 40 connected to the m-th data line Dm, and the data driver 40. It was. When the terms relating to the scan lines are defined, the scan lines to which the current selection signal is to be transmitted are referred to as "current scan lines", and the scan lines to which the selection signal is transmitted before the current selection signal is transmitted are referred to as "previous scan lines".

As shown in FIG. 4, the pixel furnace 10 according to the first embodiment of the present invention includes an organic EL element OLED, transistors M1, M3, and M4, and a capacitor Cst. The driving transistor M1 transfers a current corresponding to the voltage between the gate and the source to the organic EL element OLED, and the capacitor Cst is connected between the gate and the source of the driving transistor M1 so that the driving transistor M1 is connected to the organic EL element OLED. The gate-source voltage V _GS is maintained for a period of time. The switching transistor M3 transfers the compensation voltage from the data line Dm to the transistor M2 in response to the selection signal from the current scan line Sn. The transistor M4 transfers the precharge voltage Vp to the transistor M1 in response to the selection signal from the immediately preceding scan line Sn-1.

In the organic EL element OLED, a cathode is connected to the reference voltage VSS and emits light corresponding to an applied current. The reference voltage VSS is a voltage having a level lower than that of the power supply voltage VDD, and a ground voltage or the like may be used.

The deviation circuit 40 according to the exemplary embodiment of the present invention is connected between the data driver 40 and the transistor M3 of the pixel circuit 10, and drops the data voltage output from the data driver 40 by a predetermined voltage. The compensation voltage is transferred to the transistor M3.

Hereinafter, operations of the pixel circuit and the deviation compensator 40 according to the first embodiment of the present invention will be described in detail with reference to FIGS. 4 and 5.

First, during the precharge period T1, the selection signal from the immediately preceding scan line Sn-1 is at a low level so that the transistor M4 is turned on and the precharge voltage Vp is transferred to the gate of the transistor M1.

Next, in the state where the selection signal from the current scan line Sn is kept at the high level during the blanking period T2, the selection signal from the previous scan line Sn-1 is at the high level. In this period T2, the data voltage from the data line Dm is changed to the data voltage corresponding to the pixel circuit currently connected to the scan line Sn.

Next, in the data charge period T3, the selection signal from the current scan line Sn becomes low level, and the transistor M3 is turned on. Then, the data voltage from the data driver 30 is applied to the drain of the transistor M3 through the compensation transistor M2. At this time, since the transistor M2 is diode-connected, the compensation voltage applied to the drain of the transistor M3 becomes a voltage corresponding to the difference between the threshold voltage V _TH2 of the compensation transistor M2 and the data voltage. The compensation voltage is transferred to the gate of the driving transistor M1 through the transistor M3, charged in the capacitor Cst, and maintained for a predetermined time. The transistor M5 is turned on because the selection signal from the previous scanning line Sn-1 is at a high level.

During the light emission period T4, the current I _OLED corresponding to the gate-source voltage V _GS of the transistor M1 is supplied to the organic EL element OLED, and the organic EL element OLED emits light. . This current I _OLED becomes as shown in equation (1).

Here, V _TH1 is the threshold voltage of the transistor M1, V _DATA is the data voltage from the data line Dm, and β represents a constant value.

At this time, if the threshold voltage V _TH1 of the driving transistor M1 and the threshold voltage V _TH2 of the compensation transistor M2 are the same, Equation 1 is expressed by Equation 2 below.

Therefore, a current corresponding to the data voltage flows through the organic EL element OLED regardless of the threshold voltage V _TH1 of the transistor M1.

As described above, according to the first embodiment of the present invention, by disposing the compensation transistor M2 for compensating for the variation in the threshold voltage of the driving transistor M1 outside the pixel, the pixel circuit is made up of a small number of transistors. In this configuration, variation in the threshold voltage of the driving transistor M1 can be compensated for.

In addition, as shown in FIG. 6, since the data voltage applied from the data driver 300 is transferred to each pixel circuit through the compensation transistor M2, all pixel circuits connected to one data line Dm are one. The compensation transistor may compensate for the deviation of the driving transistor. Therefore, although the variation of the driving voltage is conventionally compensated by using m x n compensation transistors, according to the first embodiment of the present invention, the threshold voltage variation of the driving transistors of all the pixels may be compensated only by the m compensation transistors. .

In the pixel circuit according to the first embodiment of the present invention, the immediately preceding scan line Sn-1 is used to control the transistor M4, but a control signal capable of turning on the transistor M4 during the precharge period T1 is provided. A separate control line (not shown) for transmitting may be used.

7 shows an equivalent circuit diagram of a pixel circuit according to a second embodiment of the present invention. The pixel circuit shown in FIG. 7 differs from the pixel circuit shown in FIG. 4 in that it further includes a transistor M5.

Specifically, the transistor M5 transmits or blocks the current flowing through the transistor M1 to the organic EL element OLED by the selection signal from the immediately preceding scan line Sn-1, thereby correcting black. Allows black gradation to be expressed. In addition, since unnecessary current is prevented from flowing, power consumption can be reduced.

8 is an organic EL display device employing a pixel circuit according to a second embodiment of the present invention.

As shown in FIG. 8, in the organic EL display device according to the second embodiment of the present invention, similarly to the first embodiment, all data voltages applied to one data line are connected to the data line through one compensation transistor. Since it is applied to the pixel circuit, the deviation of the threshold voltages of the driving transistors of the n pixel circuits can be compensated with one compensation transistor.

In the above description, a description has been given of an embodiment in which the concept of the present invention is optimally applied to a specific pixel circuit. However, it is apparent to those skilled in the art that the scope of the present invention is not limited to the pixel circuit described above, and the present invention can be applied using the concept of the present invention as it is in all display devices in which the variation of the threshold voltage of the driving transistor is a problem. That is, in the pixel circuit shown in FIG. 4, the transistor M4 may be removed, and the pixel circuit may be configured by only the transistors M1 and M3.

According to the present invention, by providing the deviation compensator, the pixel circuit is composed of a small number of transistors, and the deviation of the threshold voltage of the driving transistor of the pixel circuit can be compensated.

Furthermore, the configuration of the pixel circuit can be simplified to ensure a high aperture ratio, and a display device with high resolution can be provided.

1 is a conceptual diagram of an organic electroluminescent device.

2 is an equivalent circuit diagram of a pixel circuit according to the prior art.

3 is a schematic plan view of an organic EL display device according to an embodiment of the present invention.

4 illustrates a pixel circuit and a deviation compensator according to the first exemplary embodiment of the present invention.

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

6 illustrates an organic EL display device to which a pixel circuit and a deviation compensation unit according to a first embodiment of the present invention are applied.

FIG. 7 illustrates a pixel circuit and a deviation compensator according to a second embodiment of the present invention.

8 illustrates an organic EL display device to which a pixel circuit and a deviation compensator are applied according to the second embodiment of the present invention.

Claims (18)

An image display apparatus comprising a plurality of data lines for transmitting an image signal, a plurality of scanning lines for transmitting a selection signal, and a plurality of pixel circuits electrically connected to the data lines and the scanning lines. A data driver for supplying a data voltage corresponding to the image signal; A deviation compensator for dropping the data voltage by a first voltage to apply the data voltage to the plurality of data lines; And A scan driver for supplying the selection signal to the scan line Image display device comprising a. The method of claim 1, And the deviation compensator comprises a plurality of compensation transistors respectively connected between the plurality of data lines and the data driver. The method of claim 2, And the compensation transistor is diode connected, and the first voltage is a threshold voltage of the compensation transistor. The method according to any one of claims 1 to 3, The pixel circuit A display element for displaying an image in correspondence with the amount of current applied; A first terminal, a second terminal connected to a power supply, and a third terminal connected to the display element, and controlling a current flowing from the second terminal to the third terminal by a voltage applied to the first terminal. Driving transistor, A capacitor connected between the first terminal and the second terminal of the driving transistor, and A first switching element transferring a voltage applied to the data line to the first terminal of the driving transistor in response to the selection signal Image display device comprising a. The method of claim 4, wherein And the pixel circuit further comprises a second switching element for applying a precharge voltage to the first terminal of the driving transistor in response to a first control signal. The method of claim 5, And the first control signal is a selection signal applied before the selection signal applied to the pixel circuit. The method of claim 4, wherein And the pixel circuit further includes a third switching element configured to transfer or block a current flowing through the driving transistor to the display device in response to a second control signal. The method of claim 7, wherein And the second control signal is a selection signal applied before the selection signal applied to the pixel circuit. The method of claim 4, wherein The pixel circuit may include a second switching element configured to apply a precharge voltage to the first terminal of the driving transistor in response to a first control signal, and a current flowing through the driving transistor in response to a second control signal to the display device. An image display device further comprising a third switching element for transmitting or blocking. The method of claim 4, wherein And the driving transistor is configured to have substantially the same characteristics as the compensation transistor included in the deviation compensator. The method of claim 4, wherein And the driving transistor is a transistor having a P-type channel, the first terminal is a gate, the second terminal is a source, and the third terminal is a drain. A pixel circuit including a display element for displaying an image corresponding to the amount of current applied and a driving transistor for controlling the amount of current applied to the display element in accordance with the image signal; A data driver for supplying a data voltage corresponding to the image signal; And A deviation compensator connected between the data driver and the pixel circuit to drop the data voltage by a first voltage and apply it to the pixel circuit Image display device comprising a. The method of claim 12, And the deviation compensator comprises a diode-connected compensation transistor, and wherein the first voltage is a threshold voltage of the compensation transistor. The method of claim 13, And the compensation transistor is formed to have substantially the same characteristics as the driving transistor. A driving method of an image display apparatus comprising a plurality of data lines for transmitting an image signal, a plurality of scanning lines for transmitting a selection signal, and a plurality of pixel circuits electrically connected to the data lines and the scanning lines. In the pixel circuit, a capacitor is formed between a first terminal and a second terminal, the driving transistor outputting a current corresponding to the voltage charged in the capacitor to the third terminal, and an image corresponding to the amount of output current from the driving transistor. Including a display element to display, The driving method, Transferring a precharge voltage to the first terminal of the driving transistor in response to a control signal for a first period of time; And Transferring a voltage applied to the data line to the first terminal of the driving transistor in response to the selection signal for a second period of time; And a voltage applied to the data line is a value obtained by subtracting a first voltage from a voltage corresponding to the image signal. The method of claim 15, And the first voltage is substantially equal to a threshold voltage of the driving transistor. The method according to claim 15 or 16, And the first transistor and the light emitting element are electrically cut off in at least one of the first period and the second period. The method according to claim 15 or 16, And the control signal is a selection signal applied before the selection signal is applied to the pixel circuit.