KR20080061753A - Flat panel display and method for driving the same - Google Patents

Abstract

A flat panel display device and a method for driving the same are provided to prevent image sticking due to data signals of a previous frame by refreshing pixel circuits before inputting data signals corresponding to a current frame when a screen is transferred. A flat panel display device includes signal lines, a display unit(110), scan and data drivers(120,130), and a scene change detection unit(180). The signal lines include scan, data, and first and second power lines. The display unit includes plural pixel circuits positioned at areas which are defined by the signal lines. The scan driver applies scan signals to the pixel circuits through the scan lines. The data driver applies data signals to the pixel circuit receiving the scan signals through the data lines. The scene change detection unit refreshes the pixel circuits according to the transition of images which are displayed in the display unit.

Description

Flat Panel Display and method for driving the same

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

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

3 is a block diagram illustrating a screen change measuring unit according to an exemplary embodiment of the present invention.

4 is a graph illustrating an image image and an image histogram thereof for explaining an embodiment of the present invention.

5 is a block diagram illustrating a screen switching measurement unit according to another exemplary embodiment of the present invention.

6A and 6B are photographs illustrating an image image and an inverted image image thereof for explaining an embodiment of the present invention.

7 is a timing diagram illustrating an operation of an organic light emitting display device according to an embodiment of the present invention.

The present invention relates to a flat panel display and a driving method thereof.

Recently, the importance of flat panel displays (FPDs) has increased with the development of multimedia. In response, a number of liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), organic light emitting displays (Organic Light Emitting Displays), etc. Branch-type flat panel displays have been put into practical use.

Among them, the liquid crystal display device has better visibility than the cathode ray tube, the average power consumption and the heat generation amount are small, and the organic light emitting display device has a fast response time with a response speed of 1 ms or less, and a low power consumption. Because it is self-luminous, there is no problem in viewing angle, and thus, it is attracting attention as a next-generation flat panel display element.

The flat panel display displays various images according to the data signal input through the data line. When the image is expressed, the scene is changed, such as displaying a bright screen image and a dark screen image. It may happen.

In this case, an afterimage remains on the screen due to the data signal applied to the previous frame due to the rapid switching of the screen, which causes a problem of degrading the quality of the screen.

Accordingly, an object of the present invention is to provide a flat panel display device and a driving method thereof having improved image quality by preventing afterimages.

In order to achieve the above object, the present invention provides a display device including signal lines including scan lines and data lines, a display unit including a plurality of pixel circuits positioned in an area defined by the signal lines, and through the scan lines. A scan driver for applying a scan signal to the pixel circuits; a data driver for applying a data signal to the pixel circuit to which the scan signal is applied; Provided is a flat panel display including a screen switching measurement unit for refreshing.

In addition, the present invention, receiving the gray level signals corresponding to the current frame from the outside, extracting the image histogram of the current frame from the gray level signal, comparing the image histogram of the current frame and the image histogram of the previous frame And refreshing pixel circuits formed at the intersections of the scan lines and the data lines according to the comparison result.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, an organic light emitting display device will be described as an example of a flat panel display device.

1 is a block diagram illustrating an organic light emitting display device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram illustrating a pixel circuit of an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 1, the organic light emitting display device includes a display panel 110, a scan driver 120, a data driver 130, a controller 140, a power supply unit 150, and a screen switching measuring unit 160. do.

The display panel 110 includes the data lines D1 -Dm arranged in the first direction and the scan lines S1 -Sn and the data lines (D1 -Dm crossing the first direction and arranged in the second direction). )) And the pixel circuits P11 -Pnm positioned in the region where the scan lines S1 -Sn cross each other.

The control unit 140 outputs a control signal to the scan driver 120, the data driver 130, and the power supply unit 150, and the power supply unit 150 controls the first power lines in accordance with the control signal of the control unit 140. A voltage necessary for driving the display panel 110 is output through 160: VDD1-VDDm and the second power lines 170: VSS1-VSSn.

The screen switching measuring unit 180 receives gray level signals from the outside and determines whether the current frame is a screen switching frame to determine whether to refresh the pixel circuits P11 -Pnm. In this case, the controller 140 may receive the enable signal for the refresh from the screen switching measurement unit 160 and apply the control signal for the refresh to the scan driver 120 and the data driver 130. This will be described later in detail.

The scan driver 120 outputs a scan signal to scan lines S1 -Sn connected to the scan driver 120 according to a control signal of the controller 140. As a result, the pixel circuits P11 -Pnm located in the display panel 110 are selected in response to the scan signals S1 -Sn.

The data driver 130 receives grayscale signals from the outside according to a control signal of the controller 140, converts the grayscale signals into analog data signals, and applies them to the pixel circuits 110 through the data lines D1 to Dm. .

Accordingly, the display panel 110 displays an image image by emitting light from the pixel circuits P1 -Pnm in response to the data signals.

Referring to FIG. 2, the pixel circuit transmits a data signal from the data line Dm in response to a selection signal from the scan line Sn, and a data signal received through the switching transistor T2. A capacitor Cst for storing the voltage, a driving transistor T2 for generating a driving current according to the data signal stored in the capacitor Cst, and a light emitting operation according to the driving current, and connected to the first power line VDD. Organic light emitting diodes (OLED).

The gate electrode of the driving transistor T2 is connected to the drain electrode of the switching transistor T1 to receive a data signal, and the driving transistor T2 is the difference between the data signal and the second power line VSS connected to the source electrode. A driving current corresponding to the driving current is generated and supplied to the organic light emitting diode OLED connected to the drain electrode.

The amount of current flowing through the organic light emitting diode OLED can be expressed as follows.

t

t

Here, K is a constant, Vgs is the difference between the source-gate voltage of the driving transistor, and Vth is the threshold voltage of the driving transistor.

Accordingly, the organic light emitting display device displays a desired image image by a data signal input to the pixel circuit.

3 is a block diagram illustrating a screen switching measurement unit according to an embodiment of the present invention. FIG. 4 is a graph illustrating an image image and an image histogram extracted for explaining an embodiment of the present invention. FIGS. 5A and 5B Images illustrating a video image and an inverted image thereof for explaining an embodiment of the present invention.

1 and 3, a flat panel display device according to an embodiment of the present invention includes a scene change detection block 180.

The screen switching measurement unit 180 includes a data processor 181, a memory unit 183, and a comparison unit 185.

The data processor 181 receives the gray level signals corresponding to one frame from the outside, extracts an image histogram, and stores the extracted image histogram in the memory unit 183. Here, the video image and the resulting image histogram may be represented as shown in FIG. 4.

Then, the data processor 181 sums the image histogram of the current frame and the image histogram of the previous frame stored in the memory unit 183.

Histo_error is a result of summing two histograms, n is an order of frames, and gray is a gray value of all pixel circuits of the corresponding frame.

When the result value obtained by the sum is obtained as described above, the data processor 181 transfers the result value to the comparator 185, and the comparator 185 is provided with a predetermined reference value (Ref.value). Compare.

When the result value is lower than the reference value, the comparison unit 185 determines that the screen of the current frame is a continuous screen frame.

On the contrary, when the result value is higher than the reference value, the comparator 185 determines the screen of the current frame as the screen change frame and transmits an enable signal for refresh to the controller 140.

Here, the comparator 185 determines whether to refresh the pixel circuits by comparing the value obtained by dividing the result value with the reference value, and here, by performing sufficient refresh to eliminate afterimages and to realize the display image for the implementation of the image image. In order to ensure the reference value may be in the range of 0.7 to 1.

When the enable signal for refresh is transmitted from the comparator 185 to the controller 140, the controller 140 turns on all scan lines and applies the black data through the data lines to the scan driver 120. The control signal is applied to the data driver 130.

Here, the control unit 140 or the data driver 130 has a MUX circuit therein to selectively select the black data signal and the data signal according to the gray level according to the enable signal from the screen switching measurement unit 180. Can be supplied to the display unit 110.

As described above, the screen switching measuring unit 180 of the organic light emitting display device according to an embodiment of the present invention extracts and sums the histogram of the previous frame and the histogram of the current frame, thereby determining whether to refresh the pixel circuits. do. Therefore, since the pixel circuits can be refreshed only when the screen is switched, the quality of the screen can be improved by reducing the afterimage of the screen while ensuring sufficient time necessary for the display.

5 is a block diagram illustrating a screen switching measurement unit according to another exemplary embodiment of the present invention, and FIGS. 6A and 6B are photographs showing an image image and an inverted image image thereof.

In the above-described exemplary embodiment of the present invention, when the pixel circuits are refreshed, the black data, that is, the data signal corresponding to gray 0 is applied to the pixel circuits. However, the pixel circuits may be applied as inverted data.

For example, if the video image implemented in the previous frame is the image shown in FIG. 6A, the refresh frame is configured to implement an inverted video image of the video image implemented in the previous frame, that is, the video image as shown in FIG. 6B. Signal can be applied.

This may be performed by applying the enable signal to the control unit 140 or the data driver 130 by applying the inverted gray level signal of the gray level signal of the previous frame when the screen change measuring unit 180 determines that the refresh is necessary. have.

The inverted gray level signal may be expressed by subtracting the previous gray level signal from the highest gray. For example, when the highest gray is 255 and the previous gray level signal is 10, 245 grays of 255-10 may be represented in the refresh frame. .

Therefore, the organic light emitting display device according to another embodiment of the present invention selectively supplies the gray scale signal for representing the image and the inverted gray scale signal to the display unit 110 according to the enable signal of the screen switching measuring unit 180. A mux circuit (MUX) 190 may be included, and the inverter 195 may further include an inverted gray level signal.

As described above, when the inverted gray level signal is input to the pixel circuits instead of uniformly applying black data to the pixel circuits during the refresh period, the pixel circuits are refreshed in view of the state of the pixel circuits according to the gray level signal applied to the previous frame. Data can be entered. Thus, refreshing of the pixel circuits can be performed more effectively.

7 is a timing diagram illustrating an operation of an organic light emitting display device according to an embodiment of the present invention. Hereinafter, an operation of the organic light emitting display device described above will be described with reference to FIGS. 1, 3, and 7.

First, the screen change measuring unit 180 receives and stores grayscale signals from the outside according to a control signal of the controller 140. Then, the screen switching measurement unit 180 compares the gray level signal of the previous frame and the gray level signal of the current frame to determine whether the current frame corresponds to the screen switching frame.

If it is determined by the screen switching measuring unit 180 that the current frame is not a screen switching frame, the screen switching measuring unit 180 applies a low level enable signal En to the controller 140. The controller 140 receiving the low level enable signal En outputs a control signal to the scan driver 120 and the data driver 130 to represent an image on the display 110.

Accordingly, the scan driver 120 applies a selection signal to the pixel circuits through the scan lines, and the data driver 130 receives the gray scale signals from the outside according to a control signal from the controller 140 and receives the analog data signal. The conversion is performed to the pixel circuits P11-Pnm. In addition, the pixel circuits P11 -Pnm receive the analog data signal and represent a video image corresponding thereto.

If the screen change measuring unit 180 determines that the current frame is the screen change frame, the screen change measuring unit 180 applies the high level enable signal En to the controller 140. The controller 140 receiving the high level enable signal En outputs an enable signal for refreshing the pixel circuits P11 -Pnm to the controller 140.

The scan driver 120 applies a selection signal to all scan lines according to the control signal of the controller 140, and the data driver 130 is synchronized with the scan signal to the pixel circuits P11-Pnm through all the data lines. Output the refresh data signal. The refresh data signal may be a black signal, that is, an analog data signal corresponding to gray level 0.

The pixel circuits P11-Pnm receive an analog data signal corresponding to gray level 0 and do not represent an image during the corresponding frame, thereby refreshing the pixel circuits P11-Pnm.

When the refresh is completed, the controller 140 applies a control signal for displaying a video image to the scan driver 120 and the data driver 130, and the pixel circuits P11-Pnm correspond to the grayscale data of the current frame. A light emitting operation is performed. The screen change measurement unit 180 and the controller 140 repeat the above-described operation, whereby the pixel circuits P11-Pnm repeatedly perform the expression and refresh of the image image.

As described above, in the organic light emitting display device according to the exemplary embodiment of the present invention, when the screen switching measuring unit 180 determines that the current frame is the screen switching frame, the pixel circuit is refreshed. That is, a refresh frame is inserted. When the screen is switched, the pixel circuits may be refreshed before inputting the data signal corresponding to the current frame, thereby preventing an afterimage according to the data signal of the previous frame.

In one embodiment of the present invention, the refresh frame is described as one frame, but the present invention is not limited thereto, and the refresh frame may be set to a plurality of frames as long as the display time can be sufficiently secured.

 While the invention has been shown and described with reference to certain preferred embodiments, the invention is not so limited, and the invention is not limited to the scope and spirit of the invention as defined by the following claims. It will be readily apparent to one of ordinary skill in the art that various modifications and variations can be made.

According to the present invention, it is possible to secure the display time and to prevent afterimages, thereby improving the screen quality of the flat panel display.

Claims (12)

Signal lines including scan lines, data lines, first and second power lines; A display unit including a plurality of pixel circuits positioned in an area defined by the signal lines; A scan driver which applies a scan signal to the pixel circuits through scan lines; And A data driver for applying a data signal to the pixel circuit to which the scan signal is applied through the data line; And a screen switching measuring unit for refreshing the pixel circuits according to the switching of the video image implemented in the display unit. The method of claim 1, And the screen change measuring unit determines whether to refresh the pixel circuits by comparing the gray level signals corresponding to the current frame and the gray level signals corresponding to the previous frame. The method of claim 2, The screen change measurement unit is configured to compare the image histogram of the previous frame and the image histogram of the current frame with a data processor for extracting an image histogram by applying the signal signals corresponding to the current frame, a memory unit for storing the image histogram extracted by the data processor, and an image histogram of the previous frame. Flat panel display device comprising a comparison unit. The method of claim 3, The scan driver turns on all scan lines and the data driver applies refresh data according to a comparison result of the comparison unit. The method of claim 4, wherein And the refresh data is black data. The method of claim 4, wherein And the refresh data is an inversion data signal of a data signal of a previous frame. The method of claim 1, The pixel circuit may include a switching transistor that transfers a data signal from the data line according to a scan signal from a scan line, a capacitor that receives the data signal from the switching transistor and stores the data signal, and is driven according to the data signal stored in the capacitor. And a light emitting diode connected between the driving transistor and the first power line to generate a current, the light emitting diode receiving the driving current to perform a light emitting operation. The method of claim 1, The pixel circuit includes a thin film transistor, a capacitor, and a liquid crystal layer. Receiving grayscale signals corresponding to a current frame from the outside; Extracting an image histogram of the current frame from the gray level signals; Comparing the image histogram of the current frame with the image histogram of a previous frame; And refreshing pixel circuits formed at the intersections of the scan lines and the data lines according to the comparison result. The method of claim 9, The refreshing of the pixel circuit may include turning on the scan lines and applying refresh data through the data lines. The method of claim 10, And the refresh data is black data. The method of claim 10, And the refresh data is inverted data of data applied to a previous frame.

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