KR100662987B1 - Organic light emitting display and driving method thereof - Google Patents

Abstract

A light emitting display and a driving method thereof are provided to minimize a programming error by applying initialization current to a pixel within a range of 10~50nA by setting precharge voltage before a current data signal is supplied. A light emitting display includes a scan driving unit(110) supplying a scan signal to scan lines(S1~Sn) in order and providing an emission control signal to emission control lines(E1~En) in order; a data driving unit(120) providing precharge voltage to data lines(D1~Dm) during a first period of a horizontal period and supplying a current data signal during a second period; and a pixel unit(130) including a plurality of pixels(140) selected by the scan signal to generate the light of luminance correspondent to the current data signal. A precharge voltage value is set to make initialization current of 10~50nA flow in the pixel.

Description

Light Emitting Display and Driving Method Thereof

1 illustrates a conventional light emitting display device.

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

3 is a diagram illustrating an example of a pixel illustrated in FIG. 2.

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

5 is a graph showing a relationship between an initialization current and a programming error.

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

10,110: scan driver 20,120: data driver

30,130: pixel portion 40,140: pixel

142: pixel circuit 50,150: timing controller

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device and a driving method thereof, and more particularly to a light emitting display device and a driving method thereof capable of displaying an image having a desired luminance.

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, a light emitting display, and the like.

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

1 illustrates a conventional light emitting display device.

Referring to FIG. 1, a conventional light emitting display device includes a pixel unit 30 including a plurality of pixels 40 connected to scan lines S1 to Sn and data lines D1 to Dm, and scan lines ( A timing controller for controlling the scan driver 10 for driving S1 to Sn, the data driver 20 for driving the data lines D1 to Dm, and the scan driver 10 and the data driver 20. 50 is provided.

The timing controller 50 generates a data drive control signal DCS and a scan drive control signal SCS in response to the synchronization signals supplied from the outside. The data drive control signal DCS generated by the timing controller 50 is supplied to the data driver 20, and the scan drive control signal SCS is supplied to the scan driver 10. In addition, the timing controller 50 supplies the data Data supplied from the outside to the data driver 20.

The scan driver 10 receives the scan drive control signal SCS from the timing controller 50. The scan driver 10 receiving the scan driving control signal SCS generates a scan signal and sequentially supplies the generated scan signal to the scan lines S1 to Sn.

The data driver 20 receives the data drive control signal DCS from the timing controller 50. The data driver 20 receiving the data driving control signal DCS generates a data signal and supplies the generated data signal to the data lines D1 to Dm in synchronization with the scan signal.

The pixel unit 30 receives the first power source ELVDD and the second power source ELVSS from the outside and supplies the same to the pixels 40. Each of the pixels 40 supplied with the first power supply ELVDD and the second power supply ELVSS flows from the first power supply ELVDD to the second power supply ELVSS via the organic light emitting diode in response to the data signal. By generating the light corresponding to the data signal is generated.

That is, in the conventional light emitting display device, each of the pixels 40 generates light having a predetermined luminance in response to a data signal. However, in the related art, there is a problem in that an image having a desired luminance cannot be displayed due to variations in threshold voltages and electron mobility of transistors included in each of the pixels 40. In order to overcome such a problem, a method of supplying a current as a data signal has been proposed. In fact, when the current is supplied as the data signal, the pixel unit 30 can display a uniform image even when the transistor is set to a nonuniform voltage-current characteristic.

However, when a current is supplied as the data signal, there is a concern that the desired voltage may not be charged in the pixels 30. In particular, when a low gray scale is expressed, it is difficult to charge a desired voltage to the pixels 30 within a limited time because a microcurrent is supplied. Therefore, when supplying a current as a data signal, a current deviation (programming error) occurs between the current actually flowing in the pixel 30 and the current data signal, thereby preventing display of an image having a desired brightness.

Accordingly, an object of the present invention is to provide a light emitting display device and a driving method thereof capable of displaying an image having a desired luminance.

In order to achieve the above object, the first aspect of the present invention includes a scan driver for sequentially supplying the scanning signal to the scanning lines, and sequentially supplying the emission control signal to the emission control lines; A data driver for supplying a precharge voltage to the data lines during the first period of the horizontal period, and supplying a current data signal for the second period; A pixel portion including pixels selected by the scan signal and generating light having a luminance corresponding to the current data signal; The voltage value of the precharge voltage is set to allow an initialization current of 10nA to 50nA to flow in the pixel.

Preferably, the voltage value of the precharge voltage is set to allow an initialization current of 15nA to 25nA to flow in the pixel.

According to a second aspect of the present invention, there is provided a method of selecting pixels by sequentially supplying a scan signal every horizontal period, supplying a precharging voltage to pixels selected by the scan signal during the first period of the horizontal period; And supplying a current data signal corresponding to data to the pixels selected by the scan signal during the second period of the horizontal period, wherein the voltage value of the precharging voltage is between 10nA and 50nA in the pixel. According to an aspect of the present invention, there is provided a method of driving a light emitting display device.

Preferably, the voltage value of the precharge voltage is set to allow an initialization current of 15nA to 25nA to flow in the pixel.

Hereinafter, preferred embodiments of the present invention may be easily implemented by those skilled in the art with reference to FIGS. 2 to 5 as follows.

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

2, a light emitting display device according to an exemplary embodiment of the present invention includes a plurality of pixels 140 connected to scan lines S1 to Sn, light emission control lines E1 to En, and data lines D1 to Dm. ), A scan driver 110 for driving the scan lines S1 to Sn and emission control lines E1 to En, and data for driving the data lines D1 to Dm. The driver 120 and the timing controller 150 for controlling the scan driver 110 and the data driver 120 are provided.

The pixel unit 130 includes pixels 140 formed in regions partitioned by the scan lines S1 to Sn, the emission control lines E1 to En, and the data lines D1 to Dm. The pixels 140 receive a first power source ELVDD and a second power source ELVSS from an external source. The pixels 140 supplied with the first power supply ELVDD and the second power supply ELVSS supply current corresponding to the data signal from the first power supply ELVDD to the second power supply ELVSS via the organic light emitting diode. do.

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 scan driver 110 receives a scan driving control signal SCS. The scan driver 110 receiving the scan driving control signal SCS sequentially supplies the scan signals to the scan lines S1 to Sn every horizontal period. The scan driver 110 supplied with the scan driving control signal SCS sequentially supplies the emission control signal to the emission control lines E1 to En. Here, the width of the emission control signal is set equal to or wider than the width of the scan signal.

The data driver 120 receives the data drive control signal DCS from the timing controller 150. The data driver 120 supplied with the data driving control signal DCS supplies a predetermined precharging voltage during the first period of one horizontal period 1H and from the pixel 140 for the second period except the first period. A predetermined current (data signal) is supplied. In other words, the data driver 120 supplies a predetermined precharging voltage to the pixels selected by the scan signal during the first period of one horizontal period, and applies a predetermined current corresponding to the data Data during the second period. Sink the data signal).

3 is a circuit diagram illustrating an example of the pixel illustrated in FIG. 2. In FIG. 3, a pixel connected to the m-th data line Dm, an n-th scan line Sn, and an n-th emission control line En is shown for convenience of description.

Referring to FIG. 3, the pixel 140 of the present invention includes an organic light emitting diode OLED and a pixel circuit 142 for supplying current to the organic light emitting diode OLED.

The organic light emitting diode OLED generates light having a predetermined luminance in response to a current supplied from the pixel circuit 142. For example, the organic light emitting diode (OLED) generates color light of any one of red, green, and blue with a luminance corresponding to the amount of current in response to the current supplied thereto.

The pixel circuit 142 includes a first transistor M1, a second transistor M2, a third transistor M3, a fourth transistor M4, and a capacitor Cst.

The first electrode of the first transistor M1 is connected to the first power source ELVDD, and the second electrode is connected to the first electrode of the fourth transistor M4. The gate electrode of the first transistor M1 is connected to the first node N1. The first transistor M1 supplies a current corresponding to the voltage stored in the capacitor Cst to the first electrode of the fourth transistor M4 from the first power source ELVDD. Here, the first electrode means a source electrode or a drain electrode, and the second electrode means an electrode different from the first electrode. For example, when the first electrode is set as the source electrode, the second electrode is set as the drain electrode.

The first electrode of the second transistor M2 is connected to the data line Dm, and the second electrode is connected to the first node N1. The gate electrode of the second transistor M2 is connected to the nth scan line Sn. The second transistor M2 is turned on when a scan signal is supplied to the nth scan line Sn to electrically connect the data line Dm and the first node N1.

The first electrode of the third transistor M3 is connected to the data line Dm, and the second electrode is connected to the second electrode of the first transistor M1. The gate electrode of the third transistor M3 is connected to the nth scan line Sn. 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 electrode of the first transistor M1.

The first electrode of the fourth transistor M4 is connected to the second electrode of the first transistor M1, and the second electrode is connected to the anode electrode of the organic light emitting diode OLED. The gate electrode of the fourth transistor M4 is connected to the nth emission control line En. The fourth transistor M4 is turned off when the emission control signal is supplied to the nth emission control line En and is turned on when the emission control signal is not supplied. Here, the emission control signal supplied to the nth emission control line En is supplied to overlap with the scan signal supplied to the nth scan line Sn. Therefore, the fourth transistor M4 is turned off when the scan signal is supplied to the nth scan line Sn and the capacitor Cst is charged with a predetermined voltage, and in other cases, the fourth transistor M4 is turned on and the first transistor M4 is turned on. The organic light emitting diode OLED is electrically connected to M1). In FIG. 3, for convenience of description, the transistors M1 to M4 are illustrated in a PMOS type, but the present invention is not limited thereto.

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

4, one horizontal period 1H of the present invention is driven by dividing into a first period T1 and a second period T2. The precharge voltage Vp is supplied to the data lines D1 to Dm during the first period T1, and the current data signal Idata is supplied during the second period.

3 and 4, the operation process will be described in detail. First, a scan signal is supplied to the nth scan line Sn. When the scan signal is supplied to the nth scan line Sn, the second transistor M2 and the third transistor M3 are turned on. When the second transistor M2 is turned on, the first node N1 and the data line Dm are electrically connected to each other. Then, the precharging voltage Vp supplied to the data line Dm is supplied to the first node N1 via the second transistor M2 during the first period T1. At this time, the capacitor Cst is charged with a voltage corresponding to the difference between the first node N1 and the first power source ELVDD.

On the other hand, when the third transistor M3 is turned on, the second electrode of the first transistor M1 and the data line Dm are electrically connected to each other. Then, during the second period T2, the current corresponding to the current data signal Idata is transmitted from the first power source ELVDD to the data driver 120 through the first transistor M1 and the third transistor M3. Is supplied. At this time, the capacitor Cst is additionally charged with a voltage corresponding to the current flowing in the first transistor M1. Here, since the predetermined voltage is charged in the capacitor Cst by the precharging voltage Vp during the first period T1, the time for which the voltage is charged in the capacitor Cst during the second period T2 is shortened. Can be. Since the parasitic caps of the data line D are precharged when the precharging voltage Vp is supplied, the parasitic cap charging time of the data line D is adjusted when the current data signal is supplied during the second period T2. It can be shortened.

Meanwhile, the emission control signal is supplied to the nth emission control line En during the period in which the scan signal is supplied to the nth scan line Sn. Then, the fourth transistor M4 is turned off during the period in which the scan signal is supplied to the nth scan line Sn so that a predetermined voltage is charged in the capacitor Cst so that an unwanted current flows to the organic light emitting diode OLED. Can be prevented. After the predetermined voltage is charged in the capacitor Cst, the supply of the emission control signal supplied to the nth emission control line En is stopped and the fourth transistor M4 is turned on. Then, the first transistor M1 controls the current flowing to the organic light emitting diode OLED in response to the voltage charged in the capacitor Cst to generate light having a predetermined luminance.

In the present invention as described above, the voltage charged in the capacitor Cst is controlled by using the current data signal. In other words, the charging voltage of the capacitor Cst is controlled by using the amount of current flowing in the first transistor M1, and thus, the non-uniform voltage-current of the first transistor M1 included in each of the pixels 140. A uniform image can be displayed regardless of the characteristic.

On the other hand, the current data signal (Idata) can be expressed as shown in equation (1).

In Equation 1, C denotes a parasitic capacitor of the data line D, and I _M1 denotes a current flowing in the first transistor M1. And, V _G means the gate voltage (or the voltage charged in the capacitor Cst) of the first transistor M1. As described in Equation 1, the current data signal Idata is determined by the current I _M1 flowing in the first transistor M1. Here, the current I _M1 flowing in the first transistor M1 may be expressed by Equation 2 below.

In Equation 2, k denotes a coefficient of the first transistor M1, and Vth denotes a threshold voltage of the first transistor M1. In Equations 1 and 2, the time when the current data signal Idata is supplied may be expressed as Equation 3.

In Equation 3, Io denotes an initialization current flowing in the first transistor M1 by the precharging voltage Vp, and ΔI represents a deviation of the current. In other words, ΔI means a difference value between the current data signal Idata and the current flowing in the first transistor M1. In Equation 3, a programming error may be expressed as Equation 4.

Referring to Equation 4, when expressing a high gradation, the initialization current Io does not act as an important factor for a programming error. In other words, when a high current flows through the current data signal Idata, the initialization current Io does not have a great influence on the programming error. However, when expressing low gradation, the initialization current Io is an important factor of programming error. In practice, a programming error generated corresponding to the initialization current Io is represented by a graph as shown in FIG. 5.

Referring to FIG. 5, it can be seen that the value of the programming error changes according to the value of the initialization current Io flowing by the precharging voltage Vp. Here, when expressing a high gradation, a programming error hardly occurs regardless of the initialization current Io value. However, when the low gradation is expressed, it can be seen that the programming error value is greatly changed according to the initialization current Io value.

Therefore, in the present invention, the precharging voltage Vp is set to allow the initialization current Io of 10 nA to 50 nA, more specifically 15 to 25 nA, to flow in the pixels 140. As such, when the precharging voltage Vp is set such that the initialization current Io of 10 nA to 50 nA flows in the pixels 140, the programming error value generated at low gray levels can be minimized as shown in the graph of FIG. 5. Thus, an image of desired luminance can be displayed. On the other hand, the voltage value of the precharging voltage Vp that is set such that the initialization current Io of 10 nA to 50 nA flows in the pixels 140 may vary depending on various conditions such as the resolution of the pixel unit 130 and the structure of the pixel 140. Are set differently. Accordingly, the programming error is minimized by setting the precharging voltage Vp so that the initialization current Io of 10nA to 50nA can flow regardless of the resolution of the pixel unit 130 and the structure of the pixel 140.

The above detailed description and drawings are merely exemplary of the present invention, but are used only for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention as defined in the meaning or claims. Accordingly, 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 protection 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.

As described above, according to the light emitting display device and the driving method thereof according to the exemplary embodiment of the present invention, a programming error is set by setting a precharge voltage such that an initialization current flows between 10nA and 50nA in a pixel before the current data signal is supplied. Can be minimized. As such, when a programming error is minimized, an image having a desired luminance can be displayed on the light emitting display device.

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 precharge voltage to the data lines during the first period of the horizontal period, and supplying a current data signal for the second period; A pixel portion including pixels selected by the scan signal and generating light having a luminance corresponding to the current data signal; And a voltage value of the precharging voltage is set such that an initialization current of 10nA to 50nA flows in the pixel. The method of claim 1, The voltage value of the precharging voltage is set such that an initialization current of 15nA to 25nA flows in the pixel. The method of claim 1, The pixel is An organic light emitting diode; A capacitor for charging a voltage corresponding to the precharging voltage and current data signal; A first transistor for supplying current to the organic light emitting diode in response to the voltage charged in the capacitor; A second transistor connected between the first node, which is a common terminal of the first transistor and the capacitor, and the data line, and turned on when a scan signal is supplied to the scan line; A third transistor connected between the second electrode of the first transistor and the data line and turned on when a scan signal is supplied to the scan line; And a fourth transistor connected between the organic light emitting diode and the second electrode of the first transistor and turned off when the emission control signal is supplied. The method of claim 3, wherein And the precharging voltage is supplied to the first node during the first period when the second transistor is turned on. The method of claim 4, wherein And when the third transistor is turned on, the current data signal is supplied to the data driver through the first transistor and the third transistor during the second period. Selecting pixels by sequentially supplying scanning signals for each horizontal period; Supplying a precharge voltage to the pixels selected by the scan signal during the first period of the horizontal period; Supplying a current data signal corresponding to data to pixels selected by the scan signal during the second period of the horizontal period, And a voltage value of the precharging voltage is set to allow an initialization current of 10nA to 50nA to flow in the pixel. The method of claim 6, And a voltage value of the precharging voltage is set to allow an initialization current of 15nA to 25nA to flow in the pixel.

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