KR100947992B1 - Pixel and organic light emitting display device using the same - Google Patents

Abstract

The present invention relates to a pixel that can be driven stably while compensating for a threshold voltage of a driving transistor.

The pixel of the present invention includes an organic light emitting diode connected between a first power supply that is a high potential pixel power supply and a second power supply that is a low potential pixel power supply, and a gate electrode connected between the first power supply and the organic light emitting diode. A first transistor connected to a node, a second transistor connected between the first node and a drain electrode of the first transistor, and a gate electrode connected to a scan line, and connected between the first node and the second node, and having a gate A third transistor having an electrode connected to the emission control line, a fourth transistor connected between the first transistor and the organic light emitting diode and a gate electrode connected to the emission control line, and between the second node and the data line. A fifth transistor connected with a gate electrode connected to the scan line, and connected between the second node and a source electrode of the first transistor It is provided with a capacitor.

Description

Pixel and Organic Light Emitting Display Device Using the Same}

The present invention relates to a pixel and an organic light emitting display device using the same, and more particularly, to a pixel and an organic light emitting display device using the same to compensate for the threshold voltage of the driving transistor.

Recently, various flat panel display devices have been developed that are lighter in weight and smaller in volume than cathode ray tubes.

Among the flat panel displays, an organic light emitting display device (OLED) displays an image using an organic light emitting diode, which is a self-luminous device, and thus, is attracting attention as a next generation display device having excellent brightness and color purity.

Such an organic light emitting display device is classified into a passive matrix organic light emitting display device and an active matrix organic light emitting display device according to a method of driving an organic light emitting diode.

The active matrix organic light emitting display device includes a plurality of pixels positioned at intersections of scan lines and data lines. Each pixel includes an organic light emitting diode and a pixel circuit for driving the same. Here, the pixel circuit typically includes a switching transistor, a driving transistor, and a storage capacitor. Such an active matrix organic light emitting display device has an advantage of low power consumption, and thus is useful for a portable display device and the like.

However, in the active matrix organic light emitting display device, the driving transistor serves as a current source for supplying a current corresponding to the data signal to the organic light emitting diode during the light emitting period of the pixel.

Accordingly, in order for the pixels to emit light with uniform luminance corresponding to the data signal, the driving transistors of the pixels must continuously operate a stable current source while continuously supplying a constant current to the organic light emitting diode regardless of the threshold voltage deviation.

Accordingly, an object of the present invention is to provide a pixel and an organic light emitting display device using the same, which can be stably driven while compensating a threshold voltage of a driving transistor.

In order to achieve the above object, a first aspect of the present invention provides an organic light emitting diode connected between a first power supply, which is a high potential pixel power supply, and a second power supply, which is a low potential pixel power supply, and between the first power supply and the organic light emitting diode. A first transistor connected to the first node, a gate electrode connected to a first node, a second transistor connected between the first node and a drain electrode of the first transistor, and a gate electrode connected to a scan line, and the first node; A third transistor connected between a second node and a gate electrode connected to a light emission control line, a fourth transistor connected between the first transistor and the organic light emitting diode and a gate electrode connected to the light emission control line, A fifth transistor connected between a second node and a data line and having a gate electrode connected to the scan line, the second node and the first node; A pixel having a capacitor connected between a source electrode of a transistor is provided.

The first power source may be set to a first voltage VDD of a first potential or a second voltage Vref of a second potential lower than the first potential. In this case, the first power is set to the second voltage during the period in which the scan signal is supplied to the scan line, and the light emission period in which the organic light emitting diode emits light at a luminance corresponding to the data signal supplied through the data line. May be set to the first voltage.

In addition, the first to fifth transistors may be set to N-type transistors.

According to a second aspect of the present invention, there is provided a pixel unit including a plurality of pixels positioned at intersections of scan lines, emission control lines, data lines, and first power supply lines, and a scan signal and light emission using the scan lines and emission control lines. A scan driver for sequentially outputting a control signal, a data driver for outputting a data signal to the data lines, a first voltage and a second voltage used as a first power source that is a high potential pixel power of the pixels, and a low value of the pixels An organic light emitting diode including a power supply unit configured to output a second power source that is a potential pixel power source, and a power scanner to supply the first voltage or the second voltage to the first power lines using the first and second voltages Provide a display device.

Here, each of the pixels includes an organic light emitting diode connected between a first power supply, which is a high potential pixel power supply, and a second power supply, which is a low potential pixel power supply, and a gate electrode connected between the first power supply and the organic light emitting diode. A first transistor connected to one node, a second transistor connected between the first node and a drain electrode of the first transistor, a gate electrode connected to a scan line, and connected between the first node and the second node; A third transistor having a gate electrode connected to an emission control line, a fourth transistor connected between the first transistor and the organic light emitting diode and a gate electrode connected to the emission control line, and between the second node and the data line. A fifth transistor connected to the scan line and having a gate electrode connected to the scan line, and between the second node and a source electrode of the first transistor. And a capacitor to be connected.

In addition, the potential of the second voltage may be set lower than the potential of the first voltage.

Meanwhile, the power scanner sequentially supplies the second voltage to the first power lines so as to be synchronized with the scan signal while the scan signal is supplied, and emits light at the luminance corresponding to the data signal. The first voltage may be supplied to the first power lines during the period.

In addition, the first power lines may be formed in the same direction as the scan lines and the emission control lines, and may be selected for each line by the power scanner.

According to the present invention, the pixel itself can compensate for the threshold voltage of the driving transistor, thereby displaying a uniform image regardless of the variation of the threshold voltage of the driving transistors provided in the pixels.

In addition, by maintaining the gate-source voltage Vgs of the driving transistor constant during each light emitting period of the pixel, the pixel can be driven stably.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail.

1 is a block diagram schematically illustrating an organic light emitting display device according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an organic light emitting display device according to an exemplary embodiment of the present invention includes a pixel unit 100, a scan driver 200, a data driver 300, a power scanner 400, and a power supply 500. do.

The pixel unit 100 includes a plurality of pixels positioned at intersections of the scan lines S1 to Sn, the emission control lines E1 to En, the data lines D1 to Dm, and the first power lines PL1 to PLn. 110.

Each of the pixels 110 is connected to the scan line S, the emission control line E, and the first power supply line PL arranged in the row where it is located, and the data line D arranged in the column where it is located. And a scan signal, a light emission control signal, a first power source ELVDD and a data signal are respectively supplied from them. In addition, the pixels 110 are supplied with the second power ELVSS supplied to the entire surface of the pixel unit 100.

Such pixels 110 store a data signal supplied from the data line D when the scan signal is supplied from the scan line S. FIG. At this time, the pixels 110 are not emitted by the emission control signal supplied from the emission control line E during the programming period of the data signal, and then the luminance corresponding to the data signal is changed as the voltage level of the emission control signal is shifted. Emits light. As a result, an image is displayed on the pixel portion 100.

The scan driver 200 sequentially generates a scan signal and a light emission control signal in response to a scan control signal supplied from the outside. The scan signal and the emission control signal generated by the scan driver 200 are output to the scan lines S1 to Sn and the emission control lines E1 to En, respectively, and are transmitted to the pixels 110.

The data driver 300 generates a data signal in response to data and data control signals supplied from the outside. The data signal generated by the data driver 300 is output to the data lines D1 to Dm and transferred to the pixels 110.

However, in the present invention, the first power source ELVDD is supplied line by line through the first power line PL1 formed in the same horizontal direction as the scan lines S1 to Sn and the emission control lines E1 to En.

In particular, the first power supply ELVDD is supplied with a first voltage VDD having a first potential or a second voltage Vref having a second potential, and may be supplied in a form of sequentially scanning line by line. Here, the first voltage VDD is set to a voltage capable of sufficiently emitting the pixel 110 during the light emission period. In addition, the second voltage Vref is set to a potential (second potential) lower than the potential (first potential) of the first voltage VDD. In addition, the threshold voltage of the driving transistor is set to a voltage that can be stored.

For example, in the present embodiment, the first power source ELVDD of the second voltage Vref is configured to be synchronized with the scan signal during the period in which the scan signals are sequentially supplied to the scan lines S1 to Sn. To PLn, the first power lines PL1 to PLn of the first voltage VDD during periods other than a period in which the signal is sequentially supplied through the lines and the scan signal is supplied for each line, in particular, during the light emission period. Power source ELVDD can be supplied.

To this end, the organic light emitting display device according to the present embodiment uses the first voltage VDD and the second voltage Vref supplied from the power supply unit 500 to supply the first power ELVDD during a period in which the scan signal is supplied. And a power scanner 400 scanning with the pixels 110.

The power scanner 400 sequentially supplies the second voltage Vref to the first power lines PL1 to PLn so as to be synchronized with the scan signal. Otherwise, the power scanner 400 supplies the first voltage to the first power lines PL1 to PLn. (VDD) can be supplied.

The power supply unit 500 outputs the first voltage VDD and the second voltage Vref used as the first power ELVDD to the power scanner 400, as well as the second power ELVSS that is a low potential pixel power. ) Is output to the pixel unit 100. Here, the first and second power sources ELVDD and ELVSS are driving powers of the pixels 110, the first power source ELVDD is a high potential pixel power source, and the second power source ELVSS is a low potential pixel power source. In this case, the potential of the second power supply ELVSS may be set to a potential lower than the second voltage Vref as well as the first voltage VDD of the first power supply ELVDD.

The aforementioned organic light emitting display device shown in FIG. 1 is provided as an example for applying the pixel of FIG. 2 to be described below, and the organic light emitting display device of the present invention is not necessarily limited thereto. That is, the driving circuit capable of generating the driving waveforms of FIG. 3 for driving the pixels of FIG. 2 may be changed and designed while employing the pixels shown in FIG. 2 by applying the technical idea of the present invention.

FIG. 2 is a circuit diagram illustrating a pixel according to an exemplary embodiment of the present invention. The pixel of FIG. 2 may be employed in the organic light emitting display device of FIG. 1. For convenience, FIG. 2 illustrates pixels arranged in the nth row mth column.

Referring to FIG. 2, the pixel 110 according to an exemplary embodiment of the present invention includes an organic light emitting diode OLED, N-type first to fifth transistors M1 to M5, and a capacitor C1 for driving the same. It includes.

The organic light emitting diode OLED is connected between the first power supply ELVDD and the second power supply ELVSS, and emits light with luminance corresponding to a current supplied thereto.

The first transistor M1 is connected between the first power supply ELVDD and the organic light emitting diode OLED, and the gate electrode of the first transistor M1 is connected to the first node N1. The first transistor M1 generates a current corresponding to the voltage supplied to its gate electrode (that is, the voltage of the first node N1). That is, the first transistor M1 is a driving transistor, and serves as a current source for generating a current corresponding to the voltage of the first node N1 during the light emitting period of the pixel 110.

The second transistor M2 is connected between the first node N1 and the first power supply ELVDD, and the gate electrode of the second transistor M2 is connected to the scan line Sn. That is, the second transistor M2 is connected between the gate electrode and the drain electrode of the first transistor M1 to diode-connect the first transistor M1 when a scan signal is supplied from the scan line Sn.

The third transistor M3 is connected between the first node N1 and the second node N2, and the gate electrode of the third transistor M3 is connected to the emission control line En. Here, the second node N2 is a node through which the data signal is transferred from the data line Dm into the pixel 110 when the scan signal is supplied to the scan line Sn. The third transistor M3 is turned off when a low-level emission control signal for preventing emission of the organic light emitting diode OLED is turned off to insulate the first node N1 from the second node N2. In other cases, it is turned on to connect the first node N1 to the second node N2.

The fourth transistor M4 is connected between the first transistor M1 (particularly, the third node N3 to which the source electrode of the first transistor M1 is connected) and the organic light emitting diode OLED. The gate electrode of M4 is connected to the light emission control line En. The fourth transistor M4 is turned off when the low-level emission control signal is supplied to block the current from the first transistor M1 from being supplied to the organic light emitting diode OLED. In addition, the fourth transistor M4 is turned on by the light emission control signal that transitions to a high level after the data signal is programmed in the pixel 110, thereby transferring the current from the first transistor M1 to the organic light emitting diode ( OLED).

The fifth transistor M5 is connected between the data line Dm and the second node N2, and the gate electrode of the fifth transistor M5 is connected to the scan line Sn. The fifth transistor M5 is a switching transistor. When the scan signal is supplied from the scan line Sn, the fifth transistor M5 is turned on to transfer the data signal supplied from the data line Dm to the second node N2.

The capacitor C1 is connected between the second node N2 and the third node N3. The capacitor C1 charges a voltage corresponding to the data signal and the threshold voltage of the first transistor M1 during the programming period in which the scan signal is supplied, and maintains the charged voltage during the subsequent light emission period to maintain the first voltage. Stabilize the operation of M1).

In FIG. 2, all of the first to fifth transistors M1 to M5 are designed as N type transistors, but the present invention is not limited thereto. For example, the first to fifth transistors M1 to M5 may be set to P-type transistors, and the pixels may be deformed to meet the type change of the transistors.

3 is a waveform diagram illustrating a driving method of the pixel illustrated in FIG. 2. 4A through 4C are circuit diagrams sequentially illustrating a driving process of the pixel illustrated in FIG. 2.

Hereinafter, the driving method of the pixel illustrated in FIG. 2 will be described in detail with reference to FIGS. 3 to 4C in conjunction with FIG. 2.

First, the scan signal Scan, the emission control signal em, and the second voltage, When the first power ELVDD of Vref is supplied, the second to fifth transistors M2 to M5 are turned on by the high level scan signal scan and the emission control signal em. The first transistor M1 is diode-connected while the second voltage Vref is supplied to the drain electrode and the gate electrode by the turn-on of the second transistor M2.

During this first period t1, as shown in FIG. 4A, the voltage of the third node N3 is initialized by turning on the fourth transistor M4. That is, the first period t1 may be an initialization period, and the duration of the first period t1 may be experimentally determined to be a period in which the voltage of the third node N3 can be sufficiently initialized.

Thereafter, when the low level emission control signal em is supplied to the emission control line En during the second period t2, as shown in FIG. 4B, the third and fourth transistors M3 and M4 are turned on. -Off.

During the second period t2, the data signal from the data line Dm is supplied to the second node N2 by the fifth transistor M5 during the period in which the scan signal scan is supplied. The voltage V (N2) of the node becomes the voltage (hereinafter, data voltage) Vdata of the data signal. In addition, since the first transistor M1 is diode-connected in the forward direction during the second period t2, the voltage V (N3) of the third node is the threshold voltage Vth of the first transistor at the second voltage Vref. Is reduced to Vref-Vth.

)이 충전된다. Therefore, during the second period t2, the capacitor C1 has the difference voltage between the voltage V (N2) of the second node and the voltage V (N3) of the third node.

) Is charged.

That is, the second period t2 may be a programming period, and the duration of the second period t2 may be experimentally determined as a period in which the data voltage Vdata is sufficiently charged in the capacitor C1.

Subsequently, when the supply of the scan signal scan is stopped during the third period t3 (that is, when the voltage level of the scan signal scans to a low level), as shown in FIG. 5 transistors M2 and M5 are turned off. When the supply of the low level emission control signal em is stopped during the third period t3 and the voltage level of the emission control signal em changes to a high level, the third and fourth transistors M3 and M4 In this case, the first voltage VDD is supplied to the first power line PLn.

During the third period t3, the gate-source voltage of the first transistor M1 is connected while the first node N1 and the second node N2 are connected by the turn-on of the third transistor M3. Vgs is kept constant at the value charged by the capacitor C1 for the second period t2.

Since the first transistor M1 and the organic light emitting diode OLED are connected by the turn-on of the fourth transistor M4, current from the first transistor M1 is supplied to the organic light emitting diode OLED. . That is, since the current path is formed from the first power supply ELVDD to the second power supply ELVSS through the first transistor M1 and the organic light emitting diode OLED during the third period t3, the organic light emitting diode ( OLED) emits light (unless emitting black data signal)

That is, the third period t3 may be an emission period, and may be experimentally determined as a period in which the pixel 110 can sufficiently express gray scales during the corresponding frame.

The amount of current flowing through the organic light emitting diode OLED during the light emission period is expressed by Equation 1 below.

Here, Cox is the capacitance per unit area of the parallel plate capacitor formed by the gate electrode and the channel of the first transistor M1, and μ is the electron mobility in the channel. W / L is an aspect ratio of the first transistor M1, that is, a ratio of the channel width W to the channel length L.

Referring to Equation 1, it can be seen that the threshold voltage element Vth of the first transistor M1 is canceled during the light emission period so that the current flowing through the organic light emitting diode OLED is not affected. That is, the pixel 110 of the present invention can compensate for the threshold voltage Vth of the first transistor M1 by itself.

In addition, the gate-source voltage Vgs of the first transistor M1 is kept constant by the capacitor C1 during the light emission period. That is, even if the voltage of the source node of the first transistor M1 is changed by the voltage-current characteristic deviation of the OLED during the light emission period, the gate-source voltage Vgs of the first transistor M1 is equal to the capacitor C1. Is kept constant. Therefore, since the first transistor M1 is driven with a stable current source having a size corresponding to the data voltage Vdata, the operation of the pixel 110 can be stabilized.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various modifications are possible within the scope of the technical idea of the present invention.

1 is a block diagram schematically illustrating an organic light emitting display device according to an exemplary embodiment of the present invention.

2 is a circuit diagram showing a pixel according to an embodiment of the present invention;

3 is a waveform diagram illustrating a driving method of the pixel illustrated in FIG. 2.

4A through 4C are circuit diagrams sequentially illustrating a driving process of the pixel illustrated in FIG. 2.

<Explanation of symbols for the main parts of the drawings>

100: pixel portion 110: pixel

200: scan driver 300: data driver

400: power scanner 500: power supply

Claims (10)

An organic light emitting diode having an anode electrode connected to a first power supply that is a high potential pixel power supply, and a cathode electrode connected to a second power supply that is a low potential pixel power supply; A first transistor connected between the first power supply and an anode electrode of the organic light emitting diode, and a gate electrode connected to a first node; A second transistor connected between the first node and the first power source and having a gate electrode connected to a scan line; A third transistor connected between the first node and the second node, and a gate electrode connected to a light emission control line; A fourth transistor connected between the first transistor and an anode electrode of the organic light emitting diode, and a gate electrode connected to the emission control line; A fifth transistor connected between the second node and a data line and having a gate electrode connected to the scan line; And a capacitor connected between the connection node of the first and fourth transistors and the second node. The method of claim 1, And the first power supply is set to a first voltage VDD of a first potential or a second voltage Vref of a second potential lower than the first potential. The method of claim 2, And the first power source is set to the second voltage during a period in which a scan signal is supplied to the scan line. The method of claim 2, And the first power source is set to the first voltage during a light emitting period in which the organic light emitting diode emits light at a luminance corresponding to a data signal supplied through the data line. The method of claim 1, The first to fifth transistors are N-type transistors. A pixel portion including a plurality of pixels positioned at an intersection of scan lines, light emission control lines, data lines, and first power lines; A scan driver which sequentially outputs a scan signal and a light emission control signal to the scan lines and the light emission control lines; A data driver for outputting a data signal to the data lines; A power supply unit configured to output a first voltage and a second voltage used as a first power source that is a high potential pixel power of the pixels and a second power source that is a low potential pixel power of the pixels; A power scanner configured to supply the first voltage or the second voltage to the first power lines using the first and second voltages; Each of the pixels is a pixel according to claim 1, wherein the organic light emitting display device. The method of claim 6, And the potential of the second voltage is set lower than that of the first voltage. The method of claim 6, And the power scanner sequentially supplies the second voltage to the first power lines so as to be synchronized with the scan signal while the scan signal is supplied. The method of claim 6, And the power scanner supplies the first voltage to the first power lines during a light emitting period in which the pixels emit light at a luminance corresponding to the data signal. The method of claim 6, The first power lines are formed in the same direction as the scan lines and the light emission control lines, and are selected for each line by the power scanner.

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