KR101048951B1 - Organic light emitting display - Google Patents

Abstract

The present invention relates to an organic light emitting display device capable of compensating a threshold voltage of a driving transistor.

An organic light emitting display device according to the present invention includes: a scan driver for sequentially supplying scan signals to scan lines and sequentially supplying emission control signals to emission control lines; A data driver for supplying a data signal to data lines when the scan signal is supplied; Pixels positioned at intersections of the scan lines, the emission control lines, and the data lines; Each of the pixels includes an organic light emitting diode having a cathode electrode connected to a second power source; A first transistor for controlling the amount of current supplied to the organic light emitting diode; A second transistor connected between the first electrode and the gate electrode of the first transistor and turned on when a scan signal is supplied to an n-1 (n is a natural number) scan line; A first capacitor having a first terminal connected to the gate electrode of the first transistor; A third transistor connected between the data line and the second terminal of the first capacitor and turned on when a scan signal is supplied to the nth scan line; A fourth transistor connected between the second terminal of the first capacitor and a reference power supply and turned on when a scan signal is supplied to the n-th scan line; A fifth transistor connected between the first electrode of the first transistor and a first power source and turned off when the emission control signal is supplied to the nth emission control line; And a second capacitor connected between the anode electrode of the organic light emitting diode and the first terminal of the first capacitor.

Description

Organic Light Emitting Display Device

The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device capable of compensating a threshold voltage of a driving transistor.

Recently, various flat panel displays have been developed to reduce weight and volume, which are disadvantages of cathode ray tubes. The flat panel display includes a liquid crystal display, a field emission display, a plasma display panel, and an organic light emitting display.

Among flat panel displays, an organic light emitting display device displays an image using an organic light emitting diode that generates light by recombination of electrons and holes. Such an organic light emitting display device is advantageous in that it has a fast response speed and is driven with low power consumption.

1 is a circuit diagram illustrating a pixel of a general organic light emitting display device. In FIG. 1, transistors included in pixels are set to NMOS.

Referring to FIG. 1, a pixel 4 of a conventional organic light emitting display device is connected to an organic light emitting diode OLED, a data line Dm, and a scanning line Sn to control the organic light emitting diode OLED. The pixel circuit 2 is provided.

The anode electrode of the organic light emitting diode OLED is connected to the pixel circuit 2, and the cathode electrode is connected to the second power source ELVSS. Such an organic light emitting diode (OLED) generates light having a predetermined brightness in response to a current supplied from the pixel circuit 2.

The pixel circuit 2 controls the amount of current supplied to the organic light emitting diode OLED corresponding to the data signal supplied to the data line Dm when the scan signal is supplied to the scan line Sn. To this end, the pixel circuit 2 may include a second transistor M2 (ie, a driving transistor), a second transistor M2, and a data line connected between the first power supply ELVDD and the organic light emitting diode OLED. A first transistor M1 connected between Dm) and a scan line Sn, and a storage capacitor Cst connected between a gate electrode and a second electrode of the second transistor M2 are provided.

The gate electrode of the first transistor M1 is connected to the scan line Sn, and the first electrode is connected to the data line Dm. The second electrode of the first transistor M1 is connected to one terminal of the storage capacitor Cst. Here, the first electrode is set to any one of a source electrode and a drain electrode, and the second electrode is set to an electrode different from the first electrode. For example, when the first electrode is set as the drain electrode, the second electrode is set as the source electrode. The first transistor M1 connected to the scan line Sn and the data line Dm is turned on when a scan signal is supplied from the scan line Sn to receive a data signal supplied from the data line Dm to the storage capacitor Cst. ). In this case, the storage capacitor Cst charges a voltage corresponding to the data signal.

The gate electrode of the second transistor M2 is connected to one terminal of the storage capacitor Cst, and the first electrode is connected to the first power source ELVDD. The second electrode of the second transistor M2 is connected to the other terminal of the storage capacitor Cst and the anode electrode of the organic light emitting diode OLED. The second transistor M2 controls the amount of current flowing from the first power source ELVDD to the second power source ELVSS via the organic light emitting diode OLED in response to the voltage value stored in the storage capacitor Cst.

One terminal of the storage capacitor Cst is connected to the gate electrode of the second transistor M2, and the other terminal of the storage capacitor Cst is connected to the anode electrode of the organic light emitting diode OLED. The storage capacitor Cst charges a voltage corresponding to the data signal.

The conventional pixel 4 displays an image having a predetermined brightness by supplying a current corresponding to the voltage charged in the storage capacitor Cst to the organic light emitting diode OLED. However, such a conventional organic light emitting display device has a problem in that it is not possible to display an image of uniform luminance due to the deviation of the threshold voltage of the second transistor M2.

In fact, when the threshold voltages of the second transistor M2 are set differently for each of the pixels 4, each of the pixels 4 generates light of different luminance in response to the same data signal. Can't display video.

Accordingly, an object of the present invention is to provide an organic light emitting display device capable of compensating a threshold voltage of a driving transistor.

An organic light emitting display device according to the present invention includes: a scan driver for sequentially supplying scan signals to scan lines and sequentially supplying emission control signals to emission control lines; A data driver for supplying a data signal to data lines when the scan signal is supplied; Pixels positioned at intersections of the scan lines, the emission control lines, and the data lines; Each of the pixels includes an organic light emitting diode having a cathode electrode connected to a second power source; A first transistor for controlling the amount of current supplied to the organic light emitting diode; A second transistor connected between the first electrode and the gate electrode of the first transistor and turned on when a scan signal is supplied to an n-1 (n is a natural number) scan line; A first capacitor having a first terminal connected to the gate electrode of the first transistor; A third transistor connected between the data line and the second terminal of the first capacitor and turned on when a scan signal is supplied to the nth scan line; A fourth transistor connected between the second terminal of the first capacitor and a reference power supply and turned on when a scan signal is supplied to the n-th scan line; A fifth transistor connected between the first electrode of the first transistor and a first power source and turned off when the emission control signal is supplied to the nth emission control line; And a second capacitor connected between the anode electrode of the organic light emitting diode and the first terminal of the first capacitor.

Preferably, the reference power supply is set to a voltage lower than the data signal. The reference power supply is set to the same voltage as the second power supply. The scan driver partially overlaps the scan signal supplied to the n-th scan line, and supplies the emission control signal to the n-th emission control line to completely overlap the scan signal supplied to the n-th scan line.

According to the organic light emitting display device of the present invention, an image having a uniform luminance can be displayed regardless of the threshold voltage of the driving transistor.

Hereinafter, the present invention will be described in detail with reference to FIGS. 2 to 8 in which preferred embodiments of the present invention may be easily implemented by those skilled in the art.

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

Referring to FIG. 2, an organic light emitting display device according to an exemplary embodiment of the present invention includes pixels positioned to be connected to scan lines S0 to Sn, emission control lines E1 to En, and data lines D1 to Dm. 140, the scan driver 110 for driving the scan lines S0 to Sn and the emission control lines E1 to En, the data driver 120 for driving the data lines D1 to Dm, The timing controller 150 is configured to control the scan driver 110 and the data driver 120.

The scan driver 110 receives the scan driving control signal SCS from the timing controller 150. The scan driver 110 receiving the scan driving control signal SCS generates a scan signal and sequentially supplies the generated scan signal to the scan lines S0 to Sn. In addition, the scan driver 110 receiving the scan driving control signal SCS generates an emission control signal and sequentially supplies the generated emission control signal to the emission control lines E1 to En. Here, the light emission control signal supplied to the i (i is a natural number) th light emission control line Ei overlaps the scan signal supplied to the i-1 th scan line Si-1 for a period of time (other than the initial period). It is supplied so as to completely overlap with the scan signal supplied to the i-th scan line Si.

The data driver 120 receives the data drive control signal DCS from the timing controller 150. The data driver 120 receiving the data driving control signal DCS supplies the data signals to the data lines D1 to Dm when the scan signal is supplied.

The timing controller 150 generates a data drive control signal DCS and a scan drive control signal SCS in response to external synchronization signals. The data driving control signal DCS generated by the timing controller 150 is supplied to the data driver 120, and the scan driving control signal SCS is supplied to the scan driver 110. The timing controller 150 supplies the data Data supplied from the outside to the data driver 120.

The pixel unit 130 receives the first power source ELVDD, the second power source ELVSS, and the reference power source Vref from the outside, and supplies them to the pixels 140. Each of the pixels 140 supplied with the first power source ELVDD, the second power source ELVSS, and the reference power source Vref generates light corresponding to the data signal.

Here, the first power supply ELVDD is set to a higher voltage value than the second power supply ELVSS to supply a predetermined current to the organic light emitting diode. The reference power supply Vref is set to a voltage lower than that of the data signal.

On the other hand, the pixel 140 positioned in the i-th horizontal line (i is a natural number) is connected to the i-1th scan line, the i-th scan line, and the i-th emission control line Ei. The pixel 140 includes a plurality of NMOS transistors, and supplies a current to the organic light emitting diode to compensate for the threshold voltage of the driving transistor.

3 is a diagram illustrating a pixel according to a first embodiment of the present invention. In FIG. 3, for convenience of description, the pixel 140 connected to the m-th data line Dm is illustrated when positioned on the n-th horizontal line.

Referring to FIG. 3, the pixel 140 according to the first exemplary embodiment of the present invention is connected to the organic light emitting diode OLED, the data line Dm, and the scan lines Sn−1 and Sn to form an organic light emitting diode ( Pixel circuit 142 for controlling the OLED).

The anode electrode of the organic light emitting diode OLED is connected to the pixel circuit 142, and the cathode electrode is connected to the second power source ELVSS. The organic light emitting diode OLED generates light having a predetermined luminance in response to a current supplied from the pixel circuit 142.

The pixel circuit 142 charges a voltage corresponding to the threshold voltage of the first transistor M1 (ie, the driving transistor) during the period in which the scan signal is supplied to the n−1 th scan line Sn−1, and the n th scan line In Sn, a voltage corresponding to the data signal is charged during the period in which the scan signal is supplied. The pixel circuit 142 charged with a predetermined voltage supplies a current corresponding to the charged voltage to the organic light emitting diode OLED. To this end, the pixel circuit 142 includes first to fifth transistors M1 to M5, a first capacitor C1, and a second capacitor C2.

The gate electrode of the first transistor M1 is connected to the first terminal of the first capacitor C1 (that is, the first node N1), and the first electrode is connected to the second electrode of the fifth transistor M5. do. The second electrode of the first transistor M1 is connected to the anode electrode (ie, the third node N3) of the organic light emitting diode OLED. The first transistor M1 controls the amount of current supplied from the first power source ELVDD to the second power source ELVSS via the organic light emitting diode OLED in response to the voltage applied to the first node N1. do.

The gate electrode of the second transistor M2 is connected to the n-th scan line Sn-1, and the first electrode is connected to the second electrode of the fifth transistor M5. The second electrode of the second transistor M2 is connected to the first node N1. The second transistor M2 is turned on when the scan signal is supplied to the n-1 th scan line Sn-1 to electrically connect the gate electrode of the first transistor M1 and the first node N1. Let's do it. In this case, the first transistor M1 is connected in the form of a diode.

The gate electrode of the third transistor M3 is connected to the nth scan line Sn, and the first electrode is connected to the data line Dm. The second electrode of the third transistor M3 is connected to the second terminal of the first capacitor C1 (ie, the second node N2). The third transistor M3 is turned on when a scan signal is supplied to the nth scan line Sn to electrically connect the data line Dm and the second node N2.

The gate electrode of the fourth transistor M4 is connected to the n-1 th scan line Sn-1, and the first electrode is connected to the reference power source Vref. The second electrode of the fourth transistor M4 is connected to the second node N2. The fourth transistor M4 is turned on when the scan signal is supplied to the n-th scan line Sn- 1 to supply the voltage of the reference power supply Vref to the second node N2. Here, the reference power supply Vref is set to a voltage lower than the voltage of the data signal, for example, the same voltage as the second power supply ELVSS.

The gate electrode of the fifth transistor M5 is connected to the emission control line En, and the first electrode is connected to the first power source ELVDD. The second electrode of the fifth transistor M5 is connected to the first electrode of the first transistor M1. The fifth transistor M5 is turned off when the emission control signal is supplied to the emission control line En, and is otherwise turned on.

The first capacitor C1 is connected between the first node N1 and the second node N2. The first capacitor C1 charges a voltage corresponding to the threshold voltage of the first transistor M1.

The second capacitor C2 is connected between the second node N2 and the third node N3. The second capacitor C2 charges a voltage corresponding to the data signal.

4 is a diagram illustrating a waveform diagram for driving the pixel illustrated in FIG. 3.

3 and 4, the operation process is described in detail. First, a scan signal is supplied to the n−1 th scan line Sn−1. When the scan signal is supplied to the n-1 th scan line Sn-1, the fourth transistor M4 and the second transistor M2 are turned on.

When the fourth transistor M4 is turned on, the reference power supply Vref is supplied to the second node N2. When the second transistor M2 is turned on, the voltage of the first node N1 increases to the voltage of the first power source ELVDD. In other words, the fifth transistor M5 is set to be turned on during the initial period in which the scan signal is supplied to the n-th scan line Sn-1, and thus the voltage of the first node N1 is approximately The voltage rises to the voltage of the first power supply ELVDD.

Thereafter, the emission control signal is supplied to the nth emission control line En so that the fifth transistor M5 is turned off. When the fifth transistor M5 is turned off, the voltage of the first node N1 is set to the sum of the threshold voltage Vth of the first transistor M1 and the threshold voltage of the organic light emitting diode OLED.

In detail, when the fifth transistor M5 is turned off, the first power ELVDD is not supplied to the first node N1. When the fifth transistor M5 is turned off, the second transistor M2 maintains a turn-on state. That is, the first transistor M1 is connected in the form of a diode. If this is expressed as an equivalent circuit, as shown in FIG. 5, the first transistor M1 is implemented as a diode. In this case, the voltage of the first node N1 is reduced to the sum of the threshold voltage Vth of the first transistor M1 and the threshold voltage Vto of the organic light emitting diode OLED.

At this time, the first capacitor C1 is charged with a voltage corresponding to the difference between the first node N1 and the second node N2. That is, the voltage corresponding to the threshold voltage of the first transistor M1 is charged in the first capacitor C1.

Thereafter, the supply of the scan signal to the n-th scan line Sn-1 is stopped, and the scan signal is supplied to the n-th scan line Sn. When the supply of the scan signal to the n−1 th scan line Sn−1 is stopped, the second transistor M2 and the fourth transistor M4 are turned off. When the scan signal is supplied to the nth scan line Sn, the third transistor M3 is turned on.

When the third transistor M3 is turned on, the data signal from the data line Dm is supplied to the second node N2. At this time, the voltage of the second node N2 increases from the voltage of the reference power supply Vref to the voltage of the data signal. At this time, the voltage of the first node N1 set to the floating state is also increased in correspondence with the voltage increase amount of the second node N2. Thus, the first capacitor C1 maintains the voltage charged in the previous period.

Meanwhile, a voltage corresponding to a difference between the voltage of the data signal applied to the first node N1 and the threshold voltage Vto of the organic light emitting diode OLED applied to the third node N3 is applied to the second capacitor C2. Is charged. That is, the second capacitor C2 charges a voltage corresponding to the data signal.

Thereafter, the supply of the scan signal to the nth scan line Sn is stopped, and the supply of the emission control signal to the nth emission control line En is stopped. When the supply of the scan signal to the nth scan line Sn is stopped, the third transistor M3 is turned off. When supply of the emission control signal to the nth emission control line En is stopped, the fifth transistor M5 is turned on.

When the fifth transistor M5 is turned on, the first electrode of the first transistor M1 and the first power source ELVDD are electrically connected to each other. In this case, the first transistor M1 supplies a current corresponding to the voltage applied to the first node N1 from the first power supply ELVDD to the second power supply ELVSS via the organic light emitting diode OLED. . Here, the voltage applied to the first node N1 is set to a voltage corresponding to the threshold voltage and the data signal of the first transistor M1, and thus is supplied from the first transistor M1 to the organic light emitting diode OLED. The current to be set is set regardless of the threshold voltage of the first transistor M1. Therefore, in the present invention, an image of uniform luminance can be displayed.

Meanwhile, in the present invention, when the current is supplied from the first transistor M1 to the organic light emitting diode OLED, the second node N2 and the first node N1 are set to the floating state. Therefore, even if the voltage of the third node N3 is changed by the current supplied from the first transistor M1, the voltages charged in the first capacitor C1 and the second capacitor C2 do not change during the previous period.

6 is a diagram illustrating a pixel according to a second exemplary embodiment of the present invention. 6, the same components as in FIG. 3 are assigned the same reference numerals, and detailed description thereof will be omitted.

Referring to FIG. 6, in the pixel 140 according to the second exemplary embodiment of the present invention, the gate electrode of the fourth transistor M4 ′ is connected to the n−1 th scan line Sn−1, and the first electrode is formed of the first electrode. It is connected to n scanning line Sn. The second electrode of the fourth transistor M4 'is connected to the second node N2. The fourth transistor M4 'is turned on when the scan signal is supplied to the n-1 th scan line Sn-1, and supplies the voltage supplied to the n th scan line Sn to the second node N2. do.

Here, when the scan signal is supplied to the n-th scan line Sn-1, the scan signal (that is, the high voltage) is not supplied to the n-th scan line Sn, but a low voltage is supplied. Here, the low voltage is set to a voltage lower than the voltage of the data signal. That is, in the second embodiment of the present invention, when the fourth transistor M4 'is turned on, the low voltage is supplied to the nth scan line Sn instead of the reference power supply Vref. Other operations are the same as the first embodiment of the present invention, so detailed description thereof will be omitted.

7 is a diagram illustrating a pixel according to a third exemplary embodiment of the present invention. Referring to FIG. 7, the same components as in FIG. 3 are assigned the same reference numerals, and detailed description thereof will be omitted.

Referring to FIG. 7, in the pixel 140 according to the third embodiment of the present invention, the second capacitor C2 ′ is connected between the first node N1 and the third node N3. In the third embodiment of the present invention as described above, only the position of the second capacitor C2 'is changed, and the configuration and operation of the other components are set as in the first embodiment of the present invention.

4 and 7, an operation process will be briefly described. First, a scan signal is supplied to the n−1 th scan line Sn−1 so that the fourth transistor M4 and the second transistor M2 are turned on. .

When the fourth transistor M4 is turned on, the reference power supply Vref is supplied to the second node N2, and when the second transistor M2 is turned on, the first power supply ELVDD is supplied to the first node N1. ) Is supplied. Thereafter, the emission control signal is supplied to the nth emission control line En so that the fifth transistor M5 is turned off. When the fifth transistor M5 is turned off, the voltage of the first node N1 is set to the sum of the threshold voltage Vth of the first transistor M1 and the threshold voltage Vto of the organic light emitting diode OLED. do. At this time, the first capacitor C1 is charged with a voltage corresponding to the difference between the first node N1 and the second node N2. That is, the voltage corresponding to the threshold voltage of the first transistor M1 is charged in the first capacitor C1.

The scan signal is supplied to the nth scan line Sn to turn on the third transistor M3. When the third transistor M3 is turned on, the data signal from the data line Dm is supplied to the second node N2. At this time, the voltage of the second node N2 increases from the voltage of the reference power supply Vref to the voltage of the data signal. At this time, the voltage of the first node N1 set to the floating state is also increased in correspondence with the voltage increase amount of the second node N2. Thus, the first capacitor C1 maintains the voltage charged in the previous period.

The second capacitor C2 ′ charges the voltage applied to the first node N1 and the difference voltage between the third node N3. Here, the voltage of the first node N1 is determined by the voltage of the data signal. In other words, the voltage rise of the second node N1 is determined by the data signal, and thus the voltage rise of the first node N1 is also determined by the data signal. Therefore, the voltage corresponding to the data signal is charged in the second capacitor C2 '.

Thereafter, the supply of the scan signal to the nth scan line Sn is stopped, the third transistor M3 is turned off, and the supply of the emission control signal to the nth emission control line En is stopped, so that the fifth transistor M5 is stopped. ) Is turned on. In this case, the first transistor M1 supplies a current corresponding to the voltage applied to the first node N1 to the organic light emitting diode OLED. Here, the voltage applied to the first node N1 is set to a voltage corresponding to the threshold voltage and the data signal of the first transistor M1, and thus is supplied from the first transistor M1 to the organic light emitting diode OLED. The current to be set is set regardless of the threshold voltage of the first transistor M1. Therefore, in the present invention, an image of uniform luminance can be displayed.

8 is a diagram illustrating a pixel according to a fourth embodiment of the present invention. 8, the same components as those in FIG. 7 are assigned the same reference numerals, and detailed description thereof will be omitted.

Referring to FIG. 8, in the pixel 140 according to the fourth exemplary embodiment of the present invention, the gate electrode of the fourth transistor M4 ″ is connected to the n−1 th scan line Sn−1, and the first electrode It is connected to the nth scan line Sn. And, the second electrode of the fourth transistor M4 " is connected to the second node N2. The fourth transistor M4 ″ is turned on when the scan signal is supplied to the n−1 th scan line Sn−1 to supply a voltage supplied to the n th scan line Sn to the second node N2. Supply.

Here, when the scan signal is supplied to the n-th scan line Sn-1, a low voltage is supplied to the n-th scan line Sn. Here, the low voltage is set to a voltage lower than the voltage of the data signal. That is, in the fourth embodiment of the present invention, when the fourth transistor M4 ″ is turned on, the low voltage supplied to the nth scan line Sn is supplied instead of the reference power supply Vref. Other operations are the same as the third embodiment of the present invention, so detailed description thereof will be omitted.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

1 is a view showing a conventional pixel.

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

3 is a diagram illustrating a pixel according to a first embodiment of the present invention.

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

FIG. 5 is a diagram illustrating an equivalent circuit of the first transistor illustrated in FIG. 3.

6 is a diagram illustrating a pixel according to a second exemplary embodiment of the present invention.

7 is a diagram illustrating a pixel according to a third exemplary embodiment of the present invention.

8 is a diagram illustrating a pixel according to a fourth embodiment of the present invention.

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

2,142: pixel circuit 4,140: pixel

110: scan driver 120: data driver

130: pixel portion 150: timing controller

Claims (7)

A scan driver for sequentially supplying scan signals to scan lines and sequentially supplying light emission control signals to light emission control lines; A data driver for supplying a data signal to data lines when the scan signal is supplied; Pixels positioned at intersections of the scan lines, the emission control lines, and the data lines; Each of the pixels An organic light emitting diode having a cathode electrode connected to the second power source; A first transistor for controlling the amount of current supplied to the organic light emitting diode; A second transistor connected between the first electrode and the gate electrode of the first transistor and turned on when a scan signal is supplied to an n-1 (n is a natural number) scan line; A first capacitor having a first terminal connected to the gate electrode of the first transistor; A third transistor connected between the data line and the second terminal of the first capacitor and turned on when a scan signal is supplied to the nth scan line; A fourth transistor connected between the second terminal of the first capacitor and a reference power supply and turned on when a scan signal is supplied to the n-th scan line; A fifth transistor connected between the first electrode of the first transistor and a first power source and turned off when the emission control signal is supplied to the nth emission control line; And a second capacitor connected between the anode electrode of the organic light emitting diode and the first terminal of the first capacitor. The method of claim 1, And the reference power supply is set at a voltage lower than that of the data signal. 3. The method of claim 2, And the reference power source is set to the same voltage as the second power source. delete delete delete The method of claim 1, The scan driver partially overlaps the scan signal supplied to the n-th scan line, and supplies the emission control signal to the n-th emission control line so as to completely overlap the scan signal supplied to the n-th scan line. Organic electroluminescent display.

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