Method for compensating voltage drop of display device, system for voltage drop compensation and display device including the same

The present invention relates to a method for compensating voltage drop of a display device, a system for voltage drop compensation, and a display device including the same. A method for compensating a voltage drop of a display device including a display panel, a maximum compensation voltage table MLEC LUT for voltage compensation when a voltage drop is a maximum in the display panel, and a voltage drop coefficient table LEC LUT representing voltage drop coefficients with respect to total output currents during one frame according to an embodiment of the present invention comprises: receiving an input image signal; gamma-converting the input image signal to obtain a pre-compensation data voltage; obtaining a first total output current flowing in all pixels PX of the display panel during one frame based on the input image signal; obtaining a first voltage drop compensation voltage V_LEC based on the voltage drop coefficient table LEC LUT and the maximum compensation voltage table MLEC LUT; and adding the first voltage drop compensation voltage V_LEC to the pre-compensation data voltage to obtain the post-compensation data voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0126768 filed in the Korean Intellectual Property Office on Dec. 12, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method for compensating a voltage drop of a display device, a system for voltage drop compensation and a display device including the same.

(b) Description of the Related Art

In general, an active matrix flat panel display includes a plurality of pixels arranged in a matrix, a thin film transistor (TFT), which is a three terminal element, for switching a voltage applied to each pixel, and an electro-optic converting element for converting an electrical signal to light. A display device displays images by controlling luminance of each pixel, which is outputted through the electro-optic converting element, according to given luminance information. Each pixel displays one of primary colors, red (R), green (G), and blue (B), and expresses a predetermined color by a spatial or temporal sum of the primary colors.

A display device includes a display panel provided with several voltage lines for driving. However driving voltages may not be uniformly transmitted according to positions on the display panel because of influences such as resistances of the driving voltage lines and RC delay, and a voltage drop may increase as the position is further away from a driver. Particularly, in a case of an organic light emitting device which is driven by a current, the difference of the voltage drop according to positions on the display panel appears as non-uniform luminance and color, thereby decreasing the display quality.

SUMMARY OF THE INVENTION

A method for compensating a voltage drop of a display device including a display panel, a maximum compensation voltage table MLEC LUT for voltage compensation when a voltage drop is maximum in the display panel, and a voltage drop coefficient table LEC LUT representing voltage drop coefficients with respect to total output currents during one frame according to an embodiment of the present invention, includes: receiving an input image signal; gamma-converting the input image signal to obtain a pre-compensation data voltage; obtaining a first total output current flowing in all pixels PX of the display panel during one frame based on the input image signal; obtaining a first voltage drop compensation voltage V_LEC based on the voltage drop coefficient table LEC LUT and the maximum compensation voltage table MLEC LUT; and adding the first voltage drop compensation voltage V_LEC to the pre-compensation data voltage to obtain a post-compensation data voltage.

The obtaining of the first voltage drop compensation voltage V_LEC may comprise obtaining a first voltage drop coefficient LEC corresponding to the first total output current from the voltage drop coefficient table LEC LUT, obtaining a first maximum compensation voltage V_MLEC from the maximum compensation voltage table MLEC LUT, and multiplying the first maximum compensation voltage V_MLEC by the first voltage drop coefficient LEC.

Obtaining the XY coordinates of the input image signal in the display panel may be further included.

The obtaining of the first maximum compensation voltage V_MLEC may comprise obtaining the first maximum compensation voltage V_MLEC corresponding to the XY coordinates of the input image signal using the maximum compensation voltage table MLEC LUT.

The maximum compensation voltage table MLEC LUT may comprise a maximum compensation voltage for a position of a portion of the display panel.

The obtaining of the first maximum compensation voltage V_MLEC corresponding to the XY coordinates of the input image signal may comprise using interpolation.

Providing gamma data may be further comprised, and the obtaining of the pre-compensation data voltage based on the input image signal may comprise using the gamma data.

The gamma data may be separately provided for each primary color including red, green, and blue.

At least one of the maximum compensation voltage table MLEC LUT and the voltage drop coefficient table LEC LUT may be separately provided for each primary color including red, green, and blue.

A system for a voltage drop compensation according to an embodiment of the present invention comprises: a current adder receiving an input image signal and obtaining a first total output current flowing in all pixels PX of a display panel during one frame; a coefficient calculator obtaining a first voltage drop coefficient LEC corresponding to the first total output current using a voltage drop coefficient table LEC LUT representing voltage drop coefficients with respect to total output currents during one frame; a maximum compensation voltage calculator obtaining a first maximum compensation voltage V_MLEC using a maximum compensation voltage table MLEC LUT for voltage compensation when a voltage drop of the display panel is a maximum; a multiplier multiplying the first maximum compensation voltage V_MLEC by the first voltage drop coefficient LEC to obtain a first voltage drop compensation voltage V_LEC; and an adder receiving a pre-compensation data voltage and adding the first voltage drop compensation voltage V_LEC to the pre-compensation data voltage to obtain a post-compensation data voltage.

An XY position calculator receiving the input image signal to obtain XY coordinates of the input image signal in the display panel may be further comprised.

The first maximum compensation voltage V_MLEC may be a maximum compensation voltage corresponding to the XY coordinates of the input image signal.

The maximum compensation voltage table MLEC LUT may comprise a maximum compensation voltage for a position of a portion of the display panel.

The maximum compensation voltage calculator may obtain the first maximum compensation voltage V_MLEC through interpolation using the maximum compensation voltage table MLEC LUT.

The current adder may use gamma data.

At least one of the maximum compensation voltage table MLEC LUTF and the voltage drop coefficient table LEC LUT may be separately provided for each primary color including red, green, and blue.

A display device according to an embodiment of the present invention comprises: a display panel; a data driver transmitting a data voltage to the display panel; a memory storing a voltage drop coefficient table LEC LUT representing voltage drop coefficients with respect to total output currents during one frame, and a maximum compensation voltage table MLEC LUT for voltage compensation when a voltage drop of the display panel is a maximum; a gamma converter receiving an input image signal and gamma-converting the input image signal into a pre-compensation data voltage; a voltage drop compensation system obtaining a first voltage drop compensation voltage (V_LEC) according to an XY position in the display panel using the voltage drop coefficient table LEC LUT and the maximum compensation voltage table MLEC LUT, and adding the first voltage drop compensation voltage V_LEC to the pre-compensation data voltage to generate a post-compensation data voltage; and a signal controller processing the post-compensation data voltage to generate a data voltage and outputting the data voltage to the data driver.

The voltage drop compensation system may comprise: a current adder receiving an input image signal and obtaining a first total output current flowing in all pixels PX of the display panel during one frame; a coefficient calculator obtaining a first voltage drop coefficient LEC corresponding to the first total output current using a voltage drop coefficient table LEC LUT representing voltage drop coefficients with respect to the total output currents during one frame; a maximum compensation voltage calculator obtaining a first maximum compensation voltage V_MLEC using a maximum compensation voltage table MLEC LUT for voltage compensation when a voltage drop of the display panel is a maximum; a multiplier multiplying the first maximum compensation voltage V_MLEC by the first voltage drop coefficient LEC to obtain a first voltage drop compensation voltage V_LEC; and an adder receiving the pre-compensation data voltage and adding the first voltage drop compensation voltage V_LEC to the pre-compensation data voltage to obtain a post-compensation data voltage.

The voltage drop compensation system may further comprise an XY position calculator receiving the input image signal to obtain XY coordinates of the input image signal in the display panel.

The memory may further store gamma data for converting the input image signal into the pre-compensation data voltage.

At least one of the maximum compensation voltage table MLEC LUT and the voltage drop coefficient table LEC LUT may be separately provided for each primary color including red, green, and blue.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Now, a display device according to an embodiment of the present invention will be described with reference toFIG. 1toFIG. 8.

FIG. 1is a block diagram of a display device according to an embodiment of the present invention,FIG. 2is a block diagram showing a voltage drop compensation system of a display device according to an embodiment of the present invention,FIG. 3is a graph showing gamma data for red, green, and blue,FIG. 4andFIG. 5are graphs showing a maximum compensation voltage table (MLEC LUT) according to XY positions of a display device according to an embodiment of the present invention, respectively, andFIG. 6is a graph showing a voltage drop coefficient table (LEC LUT) with respect to total output currents of one frame of a display device according to an embodiment of the present invention.

Referring toFIG. 1, a display device according to an embodiment of the present invention includes a display panel300, a scan driver400, a data driver500, an input signal input section550, a voltage drop compensation system600, a memory700, a gamma converter800, and a signal controller900.

From the viewpoint of an equivalent circuit, the display panel300includes a plurality of signal lines G1-Gnand D1-Dmand a plurality of pixels PX that are connected to the signal lines and arranged in an approximate matrix form.

The signal lines G1-Gnand D1-Dminclude a plurality of scanning signal lines G1-Gntransferring a scan signal and approximately extending in an X direction, and a plurality of data lines D1-Dmtransferring a data signal and approximately extending in a Y direction.

Each pixel PX may include a switching element (not shown) connected to the corresponding scanning signal lines G1-Gnand the corresponding data lines D1-Dm, and an electro-optic converting element (not shown). The switching element (not shown) transmits a data voltage applied to the data lines D1-Dmto the electro-optic converting element in response to a scanning signal applied to the scanning signal lines G1-Gn. The electro-optic converting element (not shown) converts the data voltage into light, thereby displaying images having a desired luminance. An example of the electro-optic converting element is a liquid crystal capacitor of a liquid crystal display, or an organic light emitting diode of an organic light emitting device (OLED).

XY coordinates of the pixel PX in the display panel300may be determined by the scanning signal lines G1-Gnand the data lines D1-Dmconnected to each pixel PX. For example, the XY coordinates of the pixel PX connected to the i-th scanning signal line Gi(i=1, 2, . . . , n) and the j-th data line Dj(j=1, 2, . . . , m) may be referred to as (i, j).

For color display, each pixel PX uniquely displays one of three primary colors (spatial division) or each pixel PX alternately displays the three primary colors (temporal division) as time passes, and a desired color is recognized by a spatial or temporal sum of the primary colors. For example, the primary colors are three primary colors of red, green, and blue.

The scan driver400is connected to the scanning signal line G1to Gnof the display panel300, and applies gate signals obtained by combining a high voltage and a low voltage to the scanning signal lines G1to Gn.

The data driver500is connected to the data lines D1to Dmof the display panel300, and applies data voltages from the signal controller900to the data line D1-Dm.

The signal controller900controls the operation of the scan driver400and the data driver500.

The signal input section550is supplied with input image signal Din for R, G, and B and input control signal ICON for controlling the display thereof from the outside to respectively transfer them to the gamma converter800and the voltage drop compensation system600. The input image signals Din contain luminance information of each pixel PX. The luminance has a predetermined number of grays, such as 1024=210, 256=28, or 64=26. The input control signals ICON include, for example, a vertical synchronization signal, a horizontal synchronization signal, a main clock signal, and a data enable signal.

The gamma converter800converts the gray of the input image signal Din from the signal input section550into pre-compensation data voltages Vd′ assuming that there is no voltage drop in the display panel300, and outputs the pre-compensation data voltages Vd′ to the voltage drop compensation system600.

The voltage drop compensation system600calculates data voltage drop values according to the XY positions of the display panel300, and adds the data voltage drop values to the pre-compensation data voltages Vd′ from the gamma converter800to generate post-compensation data voltages Vd″.

The memory700stores gamma data GM for each of red R, green G, and blue B, a maximum compensation voltage table MLEC LUT, and a voltage drop coefficient table LEC LUT. The memory700supplies the gamma data GM to the gamma converter800and the maximum compensation voltage table MLEC LUT and the voltage drop coefficient table LEC LUT to the voltage drop compensation system600. The memory700may be an EEPROM, and the gamma data GM, the maximum compensation voltage table MLEC LUT, and the voltage drop coefficient table LEC LUT may be stored as a lookup table LUT.

The gamma data GM is information representing the pre-compensation data voltages Vd′ or currents for all grays without consideration of any voltage drop in the display panel300. The gamma data GM is previously determined suitably for the characteristics of the display panel300so that the luminance of an image displayed by the display device may have a desired value. The gamma data GM are input to the gamma converter800and the voltage drop compensation system600.FIG. 3is one example of the gamma data GM for each of the red R, the green G, and the blue B. The gamma data GM for each of the red R, the green G, and the blue B may be different from each other.

The maximum compensation voltage table MLEC LUT represents voltage drop values for a predetermined portion of the display panel300when the data voltage drop according to the positions of the predetermined portion of the display panel300is a maximum, such as the case in which the maximum output currents flow in the display panel300. Referring toFIG. 4, the value of the maximum compensation voltage table MLEC LUT may be positive with respect to a reference voltage such as the common voltage, or may be negative as shown inFIG. 5, and may be different according to red R, green G, and blue B. InFIG. 4andFIG. 5, even though the values of the maximum compensation voltage table MLEC LUT are shown to be continuous according to the XY coordinates, values for a predetermined portion of the display panel300may be included so as to thereby reduce the size of the memory700. Referring toFIG. 4andFIG. 5, the value of the maximum compensation voltage table MLEC LUT generally becomes greater going from the edge portion to the central portion of the display panel300. The maximum compensation voltage table MLEC LUT may depend on characteristics of the display panel300, and is previously determined.

The voltage drop coefficient table LEC LUT represents coefficients representing the degree of a loading effect, that may be a voltage drop, for a total output current Itot flowing in the display panel300per one frame. The voltage drop coefficient LEC is 0 when the total output current Itot of the display panel300is 0, and it is 1 when the total output current Itot is a maximum Imax. The curves H1, H2, and H3ofFIG. 6respectively show examples of the voltage drop coefficient table LEC LUT for different display panels300, and may be variously changed according to the characteristics of the display panel300such as the characteristics of the thin film transistor and the emitting light efficiency. The voltage drop coefficient LEC may be also different according to each primary color of red R, green G, and blue B.

Next, the voltage drop compensation system600will be described with reference toFIG. 2.

Referring toFIG. 2, the voltage drop compensation system600includes a current adder610, an XY position calculator620, a coefficient calculator640, a maximum compensation voltage calculator650, a multiplier660, and an adder670.

The current adder610converts the input image signals Din for all pixels PX that are input from the signal input section550during one frame into currents and adds them up to obtain a total output current Itot, and outputs the total output current Itot to the coefficient calculator640. In the case of an organic light emitting device, the total output current Itot may be a sum of driving currents flowing through organic light emitting diodes each of which is included in each pixel PX.

The XY position calculator620obtains the information Fxy for the XY coordinates of the display panel300corresponding to the input image signal Din input from the signal input section550to output it to the maximum compensation voltage calculator650. The XY coordinates corresponding to the input image signal Din as the XY coordinates of the corresponding pixel PX may be determined by the scanning signal lines G1-Gnand the data lines D1-Dmconnected to the corresponding pixel PX, as described above.

The maximum compensation voltage calculator650obtains the maximum compensation voltages V_MLEC, which are voltage drop values when the voltage drop is a maximum at all positions of the display panel300, using the maximum compensation voltage table MLEC LUT for a predetermined portion of the display panel300that is input from the memory700. Here, the maximum compensation voltages V_MLEC for the remaining positions of the display panel300may be obtained through interpolation using the maximum compensation voltage table MLEC LUT.

The coefficient calculator640obtains a voltage drop coefficient LEC for the corresponding frame based on the total output current Itot for one frame input from the current adder610and the voltage drop coefficient table LEC LUT input from the memory700.

The multiplier660respectively multiplies the maximum compensation voltage V_MLEC for red R, green G, and blue B from the maximum compensation voltage calculator650by the voltage drop coefficient LEC for red R, green G, and blue B from the coefficient calculator640to obtain the voltage drop compensation voltages V_LEC of the corresponding frame.

The adder670receives the voltage drop compensation voltages V_LEC from the multiplier660to add them to the pre-compensation data voltages Vd′ from the gamma converter800. Accordingly, changes such as a voltage drop due to a loading effect according to the positions of the display panel300may be compensated in one frame.

Next, a display operation including the voltage drop compensation method of a display device will be described.

The signal input section550receives the input image signal Din and the input control signal ICON from an external graphics controller (not shown), and outputs them to the current adder610and the XY position calculator620of the gamma converter800and the voltage drop compensation system600.

The memory700supplies the gamma data GM to the gamma converter800and the current adder610, the voltage drop coefficient table LEC LUT to the coefficient calculator640, and the maximum compensation voltage table MLEC LUT to the maximum compensation voltage calculator650.

The gamma converter800converts the input image signal Din as a digital signal into a pre-compensation data voltage {Vd′=GM(Din)} according to each gamma data GM for red R, green G, and blue B, and outputs it to the multiplier660of the voltage drop compensation system600.

The current adder610converts the input image signal Din to a current according to each gamma data GM for red R, green G, and blue B and adds up the currents to obtain the total output current Itot for all pixels PX for one frame, and to output the total output current Itot to the coefficient calculator640.

The coefficient calculator640obtains the voltage drop coefficient {LEC=LEC LUT(Itot)} corresponding to the total output current Itot for the corresponding frame from the voltage drop coefficient table LEC LUT, and outputs the voltage drop coefficient LEC to the multiplier660.

The XY position calculator620obtains the information Fxy for the XY coordinates of the input image signal Din and outputs it to the maximum compensation voltage calculator650.

The maximum compensation voltage calculator650obtains the maximum compensation voltages V_MLEC of all positions of the display panel300corresponding to the input image signal Din through interpolation using the maximum compensation voltage table MLEC LUT for a predetermined portion of the display panel300, and outputs the maximum compensation voltages V_MLEC to the multiplier660.

The multiplier660multiplies the maximum compensation voltages V_MLEC of all positions of the display panel300corresponding to the input image signals Din by the voltage drop coefficient LEC to obtain the voltage drop compensation voltages V_LEC, and outputs the voltage drop compensation voltages V_LEC to the adder670.

The adder670adds the voltage drop compensation voltage V_LEC to the pre-compensation data voltage Vd′ from the gamma converter800to generate the post-compensation data voltage Vd″, and outputs the post-compensation data voltage Vd″ to the signal controller900along with the input control signal ICON.

The process of obtaining the post-compensation data voltage Vd″ from the input image signal Din may be represented by the following Equation 1.
Vd″=GM(Din)+V—MLEC(X, Y)*LEC LUT(Itot)  (Equation 1)

Next, the signal controller900appropriately processes the post-compensation data voltages Vd″ based on the post-compensation data voltages Vd″ and the input control signals ICON according to the structure of the display panel300and the operating conditions thereof to generate data voltages Vd, and generates the scan control signals CONT1and the data control signals CONT2. The signal controller900outputs the scan control signal CONT1to the scan driver400, and the data control signal CONT2and the data voltage Vd to the data driver500.

The data driver500applies the data voltage Vd to the data line D1-Dmaccording to the data control signals CONT2, and the scan driver400applies the scanning signal to the scanning signal line G1-Gnaccording to the scan control signals CONT1, and thereby the data voltage Vd is applied to each pixel PX.

The voltage applied to each pixel PX is converted to light of a corresponding gray through the electro-optic converting element, thereby displaying images on the display panel300.

According to an embodiment of the present invention, the voltage that will be dropped according to positions of the display panel300is previously calculated and the calculated voltages are added to the gamma converted pre-compensation data voltages, and therefore, loading effects such as voltage drops according to positions of the display panel300by RC delay or the like may be compensated, thereby displaying uniform luminance with respect to position. Voltage drop compensation as described above is separately executed for each of the primary colors of the red R, the green G, and the blue B such that uniform color may be displayed according to position of the display panel300. In an embodiment of the present invention, since the maximum compensation voltage table MLEC LUT for a portion of the display panel300when a maximum current flows in the display panel300is used, the capacity of the memory700may be reduced. When a current that is not a maximum flows through the display panel300, the voltage drop coefficient LEC is used for obtaining the voltage drop compensation voltage. The voltage drop compensation voltage for the position which is not included in the maximum compensation voltage table MLEC LUT may be simply calculated through interpolation such that the voltage drop compensation method may be more quickly executed and the capacity of the memory700may be reduced.

FIG. 7is a view showing an image display screen of a display device without a voltage drop compensation system, andFIG. 8is a view showing an image display screen of a display device including a voltage drop compensation system according to an embodiment of the present invention.

Referring toFIG. 7, when a voltage drop compensation method according to an embodiment of the present invention is not applied, the images of the non-uniform luminance or the non-uniform color are displayed according to the positions on the display panel300, although the display panel300displays the images having the same luminance. Particularly, as the position approaches the central portion of the display panel300far away from the data driver500, the loading effect, that is the voltage drop, is relatively high. However, referring toFIG. 8, when the voltage drop compensation system using the voltage drop compensation method according to an embodiment of the present invention is used, uniform luminance and color are displayed regardless of the XY positions of the display panel300.

In the present embodiment, a loading effect such as a voltage drop due to an RC delay in a display panel300was explained. However the present invention is not limited thereto, and any voltage rise or drop according to positions of a display panel300may be compensated through the same method as described above so that uniform luminance and color may be displayed.

The display device according to an embodiment of the present invention may be various display devices such as an organic light emitting device or a liquid crystal display.

According to an embodiment of the present invention, the luminance and color of the display device may be made uniform throughout a display device. Also, the capacity of a memory of a voltage drop compensation system may be reduced.