Organic light emitting display and method for driving the same

This application claims priority to and the benefit of U.S. Provisional Application No. 61/079,762 filed Jul. 10, 2008, the entire content of which is incorporated herein by reference.

1. Field of the Invention

Embodiments of the present invention relate to an organic light emitting display and a method for driving the same.

2. Discussion of Related Art

Recently, various flat panel displays having a lighter weight and a smaller volume than that of a cathode ray tube, have been developed. The flat panel displays include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display, etc.

Among others, an organic light emitting display has various advantages such as an excellent color reproducibility, a slimness, etc. so that its applications are rapidly expanding to a PDA, an MP3, etc. in addition to a cellular phone.

The organic light emitting display displays an image using an organic light emitting diode (OLED) whose brightness is determined corresponding to the amount of input current.

The organic light emitting diode includes red, green, or blue light emitting layer located between an anode electrode and a cathode electrode and has brightness determined according to the amount of current flowing between the anode electrode and the cathode electrode.

At this time, the red, green and blue light emitting layer are formed of different materials, respectively, and thus a separate gamma is applied to each of them.

It is an aspect of embodiments according to the present invention to provide an organic light emitting display in which gamma can be applied in accordance with color regardless of the sequence of data output from a data driver, even if a separate gamma by color is used, and a method for driving the same.

The accompanying drawings, together with the specification illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1A is a structure view of an organic light emitting display according to an embodiment of the present invention;

FIG. 1B is a structure view of an organic light emitting display according to an embodiment of the present invention;

FIG. 2 is a structure view showing an arrangement of pixels of a pixel unit of the organic light emitting display of FIG. 1 ;

FIG. 3 is a circuit diagram showing a gamma correction unit employed in the organic light emitting display according to an embodiment of the present invention;

FIG. 4 is a circuit diagram showing a first embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention;

FIG. 5 is a circuit diagram showing a second embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention; and

FIG. 6 is a circuit diagram showing a third embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention.

Hereinafter, exemplary embodiments according to the present invention will be described with reference to the accompanying drawings.

FIGS. 1A and 1B are a structure view of an organic light emitting display according to an embodiment of the present invention. Referring to FIGS. 1 A and 1 B, the organic light emitting display includes a pixel unit 100 , a data driver 200 , a scan driver 300 , a gamma correction unit 400 , and a gamma conversion unit 500 . and the data driver 200 and the gamma conversion unit 500 are positioned above the pixel unit 100 or below the pixel unit 100 .

The pixel unit 100 includes a plurality of pixels 101 , each of which includes an organic light emitting diode (not shown) emitting light in accordance with the flow of current. Also, the pixel unit 100 includes n scan lines S 1 , S 2 , . . . , Sn−1, and Sn formed in a row direction and transferring scan signals, and m data lines D 1 , D 2 , . . . , Dm−1, and Dm formed in a column direction and transferring data signals.

Also, the pixel unit 100 is driven by receiving first power and second power. Therefore, the pixel unit 100 emits light to display an image by current flowing in an organic light emitting diode by the scan signals, the data signals, the light emitting signals, the first power, and the second power. The plurality of pixels also include red, green and blue sub-pixels.

The data driver 200 generates data signals using image signals (R, G, and B data) having red, green, and blue components. The data driver 200 is coupled to the data lines D 1 , D 2 , . . . , Dm−1, and Dm in the pixel unit 100 via output channels CH 1 , CH 2 , . . . , CHm−1, and CHm outputting data signals to apply the data signals to the pixel unit 100 . As for the output channels of the data driver to output the data signals, 1 st , 4 th , 7 th , 10 th , etc. output channels CH 1 , CH 4 , CH 7 , CH 10 , etc. are applied with red gamma, 2 nd , 5 th , 8 th , 11 th , etc. output channels CH 2 , CH 5 , CH 8 , CH 11 , etc. are applied with green gamma, and 3 rd , 6 th , 9 th , 12 th , etc. output channels CH 3 , CH 6 , CH 9 , CH 12 , etc. are applied with blue gamma.

The scan driver 300 generates scan signals and is coupled to the scan lines S 1 , S 2 , . . . Sn−1, and Sn to transfer the scan signals to a specific row of the pixel unit 100 . A pixel 101 having received a scan signal receives a data signal output from the data driver 200 , so that the pixel 101 receives voltage corresponding to the data signal.

The gamma correction unit 400 adjusts the voltage ratio of a data signal to a gray scale. Also, a separate gamma is employed for each of red, green, and blue because of different light emitting efficiencies of red, green, and blue light emitting layers. For example, as for expressing gray scales from 0 to 63, the voltage of a data signal corresponding to a 30 gray scale is set to 3.0V in red, 3.1 V in green, and 3.2V in blue because of different efficiencies of red, green, and blue.

The gamma conversion unit 500 allows a red gamma to be applied to red data signals transferred to a red pixel, a green gamma to be applied to green data signals transferred to a green pixel, and a blue gamma to be applied to blue data signals transferred to a blue pixel. That is, a data signal applied with the red gamma is transferred to the red pixel of the pixel unit, a data signal applied with the green gamma is transferred to the green pixel thereof, and a data signal applied with the blue gamma is transferred to the blue pixel thereof, regardless of the output channels of the data driver 200 , outputting the data signals. The gamma conversion unit 500 operates according to gamma conversion signals gs.

FIG. 2 is a structure view showing an arrangement of pixels of a pixel unit of the organic light emitting display of FIGS. 1A and 1B . Referring to FIG. 2 , one pixel 101 of the pixel unit 100 includes three sub-pixels, which include red, green, and blue sub-pixels 101 R, 101 G, and 101 B. The respective sub-pixels 101 R, 101 G, and 101 B are coupled to the data lines to receive the data signals.

Also, the red, green, and blue sub-pixels 101 R, 101 G, and 101 B are positioned in each pixel 101 in order from left to right.

The data driver 200 is coupled to the pixel unit 100 and outputs data signals in two manners: a first case in which red, green, and blue data signals are output by the sequence of 1 st , 2 nd , 3 rd , etc. output channels CH 1 , CH 2 , CH 3 , etc. of the data driver 200 ; and a second case in which blue, green, and red data signals are output by the sequence of 1 st , 2 nd ,3 rd , etc. output channels CH 1 , CH 2 , CH 3 , etc. of the data driver 200 . One of the two cases as above is selected according to whether the data driver 200 is positioned above the pixel unit 100 or below the pixel unit 100 , or whether the pixel unit 100 is a front light-emitting type or a rear light-emitting type.

In the first case, a first output channel is coupled with a pixel applied with a red gamma, receiving a red data signal, and expressing red. A second output channel is coupled with a pixel applied with a green gamma, receiving a green data signal, and expressing green. A third output channel is coupled with a pixel applied with a blue gamma, receiving a blue data signal, and expressing blue. In the second case, a first output channel is coupled with a pixel applied with a red gamma, receiving a blue data signal, and expressing blue. A second output channel is coupled with a pixel applied with a green gamma, receiving a green data signal, and expressing green. A third output channel is coupled with a pixel applied with a blue gamma, receiving a red data signal, and expressing red.

Therefore, in the first case, the pixels expressing red, green and blue are applied with a red, green and blue gamma, thereby displaying brightness proper for each color. In the second case, however, the pixels expressing red, green and blue are applied with a blue, green and red gamma, and thus the brightness proper for each color is not expressed.

In order to solve the problem, the gamma conversion unit 500 is coupled between the data driver 200 and the pixel unit 100 , thereby allowing a data signal applied with a red gamma to be transferred to the pixel expressing red, allowing a data applied with green gamma to be transferred to the pixel expressing green, and allowing a data signal applied with blue gamma to be transferred to the pixel expressing blue.

FIG. 3 is a circuit diagram showing a gamma correction unit employed in an organic light emitting display according to an embodiment of the present invention. Referring to FIG. 3 , there are three gamma correction units 400 to be applied to red, green and blue data signals.

Each gamma correction unit 400 includes a register unit 60 , a ladder resistor 61 , an amplitude control register 62 , a curve control register 63 , a first selector 64 to sixth selector 69 , and a gray scale voltage amplifier 70 .

The register unit 60 stores a proper resister set value for red if the gamma correction unit 400 is a red gamma correction unit, stores a proper resister set value for green if the gamma correction unit 400 is a green gamma correction unit, and stores a proper resister set value for blue if the gamma correction unit 400 is a blue gamma correction unit. In other words, when the gamma correction unit 400 is coupled to the red pixel to perform gamma correction, the register unit 60 stores a register set value proper for the red pixel. When the gamma correction unit 400 is coupled to the green pixel to perform gamma correction, the register unit 60 stores a register set value proper for the green pixel. When the gamma correction unit 400 is coupled to the blue pixel to perform gamma correction, the register unit 60 stores a register set value proper for the blue pixel.

Among the register values stored in the register unit 60 , the upper 10 bits are input to the amplitude control register 62 and the lower 16 bits are input to the curve control register 63 , respectively, thereby being selected as a register set value.

The ladder resistor 61 has a configuration in which a plurality of variable resistors are coupled to each other in series between the uppermost level voltage VHI and the lowermost level voltage VLO, and a plurality of gray scale voltages are generated through the ladder resistor 61 .

The amplitude control register 62 outputs 3-bit register set values to the first selector 64 , and 7-bit register set values to the second selector 65 . At this time, the number of selectable gray scales may be increased by increasing the number of the set bits, and a different gray scale voltage may be selected by changing the register set values.

The curve control register 63 outputs 4-bit register set values to the third selector 66 to the sixth selector 69 , respectively. At this time, the register set values may be changed, and the selectable gray voltage may be controlled according to the register set values.

The amplitude control register 62 is input with the upper 10 bits register signals, and the curve control register 63 is input with the lower 16 bits register signals.

The first selector 64 selects a gray scale voltage corresponding to a 3-bit register set value in the amplitude control register 62 , among a plurality of gray scale voltages distributed through the ladder resistor 61 , and outputs the gray scale voltage as the uppermost gray scale voltage.

The second selector 65 selects a gray scale voltage corresponding to a 7-bit register set value in the amplitude control register 62 , among a plurality of gray scale voltages distributed through the ladder resistor 61 , and outputs the gray scale voltage as the lowermost gray scale voltage.

The third selector 66 distributes a voltage between the gray scale voltage output from the first selector 64 and the gray scale voltage output from the second selector 65 into a plurality of gray scale voltages through a plurality of resistance columns and selects a gray scale voltage corresponding to a 4-bit register set value to be output.

The fourth selector 67 distributes a voltage between the gray scale voltage output from the first selector 64 and the gray scale voltage output from the third selector 66 into a plurality of gray scale voltages through a plurality of resistance columns and selects a gray scale voltage corresponding to a 4-bit register set value to be output.

The fifth selector 68 selects and outputs a gray scale voltage corresponding to a 4-bit register set value among gray scale voltages between the first selector 64 and the fourth selector 67 .

The sixth selector 69 selects and outputs a gray scale voltage corresponding to a 4-bit register set value among gray scale voltages between the first selector 64 and the fifth selector 68 . A curve of an intermediate gray scale can be adjusted according to the register set values of the curve control register 63 through the operations as above, making it possible to adjust gamma properties with ease according to respective properties of light emitting elements. In order to allow the gamma curve property to become convex downwardly, a potential difference between gray scales is set to increase as a lower gray scale is represented. To the contrary, in order to allow the gamma curve property to become convex upwardly, the resistance value of each ladder resistor 61 is set to allow a potential difference between gray scales to be reduced as a lower gray scale is represented.

The gray scale voltage amplifier 70 outputs a plurality of gray scale voltages each corresponding to a plurality of gray scales to be displayed on the pixel unit 100 . In FIG. 2 , the output of the gray scale voltages corresponding to 64 gray scales has been represented.

FIG. 4 is a circuit diagram showing a first embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention. Referring to FIG. 4 , a gamma conversion unit 500 includes a first transistor M 1 , a second transistor M 2 , a third transistor M 3 , and a fourth transistor M 4 . It is illustrated that the first transistor M 1 and the fourth transistor M 4 are implemented as PMOS transistors, and the second transistor M 2 and the third transistor M 3 are implemented as NMOS transistors. However, if the first transistor M 1 and the fourth transistor M 4 are implemented as NMOS transistors, the second transistor M 2 and the third transistor M 3 may be implemented as PMOS transistors.

A source of the first transistor M 1 is coupled to a first channel CH 1 of a data driver 200 , and a drain thereof is coupled to a first data line D 1 . A gate thereof is coupled to a gamma conversion signal line GS.

A source of the second transistor M 2 is coupled to the first channel CH 1 of the data driver 200 , and a drain thereof is coupled to a third data line D 3 . A gate thereof is coupled to the gamma conversion signal line GS.

A source of the third transistor M 3 is coupled to a third channel CH 3 of the data driver 200 , and a drain thereof is coupled to the first data line D 1 . A gate thereof is coupled to the gamma conversion signal line GS.

A source of the fourth transistor M 4 is coupled to the third channel CH 3 of the data driver 200 , and a drain thereof is coupled to the third data line D 3 . A gate thereof is coupled to the gamma conversion signal line GS.

A second channel CH 2 of the data driver 200 is directly coupled to a second data line D 2 .

If a gamma conversion signal in a low state is transferred through the gamma conversion signal line GS, the first transistor M 1 and the fourth transistor M 4 turn on, and the second transistor M 2 and the third transistor M 3 turn off. In other words, the first channel CH 1 of the data driver 200 is coupled to the first data line D 1 , the second channel CH 2 of the data driver 200 is coupled to the second data line D 2 , and the third channel CH 3 of the data driver 200 is coupled to the third data line D 3 .

If a gamma conversion signal in a high state is transferred through the gamma conversion signal line GS, the first transistor M 1 and the fourth transistor M 4 turn off, and the second transistor M 2 and the third transistor M 3 turn on. In other words, the first channel CH 1 of the data driver 200 is coupled to the third data line D 3 , the second channel CH 2 of the data driver 200 is coupled to the second data line D 2 , and the third channel CH 3 of the data driver 200 is coupled to the first data line D 1 .

Therefore, if the gamma conversion signal transferred through the gamma conversion signal line GS is in a low state, a red data is transferred to the first data line D 1 , a green data is transferred to the second data line D 2 , and a blue data is transferred to the third data line D 3 . If the gamma conversion signal transferred through the gamma conversion signal line GS is in a high state, a blue data is transferred to the first data line D 1 , a green data is transferred to the second data line D 2 , and a red data is transferred to the third data line D 3 .

Through the operations as above, a red sub-pixel 101 R of the pixel unit 100 receives a data signal applied with the red gamma, a green sub-pixel 101 G thereof receives a data signal applied with the green gamma, and a blue sub-pixel 101 B thereof receives a data signal applied with the blue gamma.

FIG. 5 is a circuit diagram showing a second embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention. Referring to FIG. 5 , a gamma conversion unit 500 includes a first transistor M 11 , a second transistor M 21 , a third transistor M 31 , a fourth transistor M 41 , and a fifth transistor M 51 . Also, the first transistor M 11 , the third transistor M 31 , and the fifth transistor M 51 are implemented as PMOS transistors, and the second transistor M 21 and the fourth transistor M 41 are implemented as NMOS transistors. Also, if the first transistor M 11 , the third transistor M 31 , and the fifth transistor M 51 are implemented as NMOS transistors, the second transistor M 21 and the fourth transistor M 41 may be implemented as PMOS transistors.

A source of the first transistor M 11 is coupled to a first channel CH 1 of a data driver 200 , and a drain thereof is coupled to a first node N 1 . A gate thereof is coupled to a gamma conversion signal line GS 1 .

A source of the second transistor M 21 is coupled to a third channel CH 3 of the data driver 200 , and a drain thereof is coupled to a second node N 2 . A gate thereof is coupled to the gamma conversion signal line GS 1 .

A source of the third transistor M 31 is coupled to the first node N 1 , and a drain thereof is coupled to a first data line D 1 . A gate thereof is coupled to a second gamma conversion signal line GS 2 .

A source of the fourth transistor M 41 is coupled to the second node N 2 , and a drain thereof is coupled to a third data line D 3 . A gate thereof is coupled to the second gamma conversion signal line GS 2 .

A source of the fifth transistor M 51 is coupled to the first node N 1 , and a drain thereof is coupled to the second node N 2 . A gate thereof is coupled to a third gamma conversion signal line GS 3 .

A second channel CH 2 of the data driver 200 is directly coupled to a second data line D 2 .

If red, green, and blue data are output from the first channel CH 1 , the second channel CH 2 , and the channel CH 3 , and red, green, and blue pixels are coupled to the first data line D 1 , the second data line D 2 , and the third data line D 3 , the transistors operate as follows.

First, if a first gamma conversion signal and a second gamma conversion signal are in a low state, and a third gamma conversion signal is in a high state, the first transistor M 11 and the third transistor M 31 turn on, and the second transistor M 21 , the fourth transistor M 41 , and the fifth transistor M 51 turn off. In such a state, the red data output from the first channel CH 1 is transferred to the first data line D 1 . Then, the red data is transferred to the red pixel.

If a first gamma conversion signal, a second gamma conversion signal, and a third gamma conversion signal are in a high state, the first transistor M 11 , the third transistor M 31 , and the fifth transistor M 51 turn off, and the second transistor M 21 and the fourth transistor M 41 turn on. In such a state, the blue data output from the third channel CH 3 is transferred to the third data line D 3 . Then, the blue data is transferred to the blue pixel.

At this time, the second channel CH 2 is directly coupled to the second data line D 2 , so that the green data is transferred to the green pixel.

If blue, green, and red data are output from the first channel CH 1 , the second channel CH 2 , and the channel CH 3 , and red, green, and blue pixels are coupled to the first data line D 1 , the second data line D 2 , and the third data line D 3 , the transistors operate as follows.

First, if a first gamma conversion signal and a third gamma conversion signal are in a low state, and a second gamma conversion signal is in a high state, the first transistor M 11 , the fourth transistor M 41 , and the fifth transistor M 51 turn on, and the second transistor M 21 and the third transistor M 31 turn off. In such a state, the blue data output from the first channel CH 1 is transferred to the third data line D 3 via the first transistor M 11 , the fifth transistor M 51 , and the fourth transistor M 41 . Then, the blue data is thereby transferred to the blue pixel.

If a first gamma conversion signal is in a high state, and a second gamma conversion signal and a third gamma conversion signal are in a low state, the second transistor M 21 , the third transistor M 31 , and the fifth transistor M 51 turn on, and the first transistor M 11 and the fourth transistor M 41 turn off. In such a state, the red data output from the third channel CH 3 is transferred to the first data line D 1 via the second transistor M 21 , the fifth transistor M 51 , and the third transistor M 31 . Then, the red data is thereby transferred to the red pixel.

At this time, the second channel CH 2 is directly coupled to the second data line D 2 , so that the green data is transferred to the green pixel.

Through the operations as above, a red sub-pixel 101 R of the pixel unit 100 receives a data signal applied with the red gamma, a green sub-pixel 101 G thereof receives a data signal applied with the green gamma, and a blue sub-pixel 101 B thereof receives a data signal applied with the blue gamma.

FIG. 6 is a circuit diagram showing a third embodiment of a gamma conversion unit employed in the organic light emitting display according to an embodiment of the present invention. Referring to FIG. 6 , a gamma conversion unit 500 includes a first transistor M 21 , a second transistor M 22 , a third transistor M 23 , and a fourth transistor M 24 . Although it is illustrated that the first transistor M 21 to the fourth transistor M 24 are implemented as PMOS transistors, the first transistor M 21 to the fourth transistor M 24 may also be implemented as NMOS transistors.

A source of the first transistor M 21 is coupled to a first channel CH 1 of a data driver 200 , and a drain thereof is coupled to a first data line D 1 . A gate thereof is coupled to a second gamma conversion signal line GS 2 .

A source of the second transistor M 22 is coupled to the first channel CH 1 of the data driver 200 , and a drain thereof is coupled to a third data line D 3 . A gate thereof is coupled to a first gamma conversion signal line GS 1 .

A source of the third transistor M 23 is coupled to a third channel CH 3 of the data driver 200 , and a drain thereof is coupled to the first data line D 1 . A gate thereof is coupled to the first gamma conversion signal line GS 1 .

A source of the fourth transistor M 24 is coupled to the third channel CH 3 of the data driver 200 , and a drain thereof is coupled to the third data line D 3 . A gate thereof is coupled to the second gamma conversion signal line GS 2 .

A second channel CH 2 of the data driver 200 is directly coupled to a second data line D 2 .

If a gamma conversion signal in a low state is transferred through the second gamma conversion signal line GS 2 , the first transistor M 21 and the fourth transistor M 24 turn on. If a gamma conversion signal in a high state is transferred through the first gamma conversion signal line GS 1 , the second transistor M 22 and the third transistor M 23 turn off. In other words, the first channel CH 1 of the data driver 200 is coupled to the first data line D 1 , the second channel CH 2 of the data driver 200 is coupled to the second data line D 2 , and the third channel CH 3 of the data driver 200 is coupled to the third data line D 3 .

If a gamma conversion signal in a high state is transferred through the second gamma conversion signal line GS 2 , the first transistor M 21 and the fourth transistor M 24 turn off, and if a gamma conversion signal in a low state is transferred through the first gamma conversion signal line GS 1 , the second transistor M 22 and the third transistor M 23 turn on. In other words, the first channel CH 1 of the data driver 200 is coupled to the third data line D 3 , the second channel CH 2 of the data driver 200 is coupled to the second data line D 2 , and the third channel CH 3 of the data driver 200 is coupled to the first data line D 1 .

Therefore, if the gamma conversion signal transferred through the second gamma conversion signal line GS 2 is in a low state and the gamma conversion signal transferred through the first gamma conversion signal line GS 1 is in a high state, a red data is transferred to the first data line D 1 , a green data is transferred to the second data line D 2 , and a blue data is transferred to the third data line D 3 . If the gamma conversion signal transferred through the second gamma conversion signal line GS 2 is in a high state and the gamma conversion signal transferred through the first gamma conversion signal line GS 1 is in a low state, a blue data is transferred to the first data line D 1 , a green data is transferred to the second data line D 2 , and a red data is transferred to the third data line D 3 .

Through the operations as above, a red sub-pixel 101 R of the pixel unit 100 receives a data signal applied with the red gamma, a green sub-pixel 101 G thereof receives a data signal applied with the green gamma, and a blue sub-pixel 101 B thereof receives a data signal applied with the blue gamma.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.