Organic light emitting display device and method for setting gamma reference voltage thereof

An organic light emitting display device includes a gamma reference voltage setter to set a gamma reference voltage, a gamma reference voltage generator to generate a gamma reference voltage set by the gamma reference voltage setter, and a gamma voltage generator to generate a gamma voltage based on the gamma reference voltage. The gamma reference voltage setter sets the gamma reference voltage to a first temporary value, increases the first temporary value by a first delta value, searches a second temporary value at which luminance of the display panel is less than a preset value, and sets the gamma reference voltage based on the searched second temporary value.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2015-0128619, filed on Sep. 10, 2015, and entitled, “Organic Light Emitting Display Device and Method for Setting Gamma Reference Voltage Thereof,” is incorporated by reference herein in its entirety.

BACKGROUND

One or more embodiments described herein relate to an organic light emitting display device and a method for setting a gamma reference voltage for an organic light emitting device.

2. Description of the Related Art

A variety of displays have been developed. Examples include liquid crystal displays, plasma display panels, and organic light emitting displays. Organic light emitting displays are smaller, lighter, and thinner than other types of displays and have relatively low power consumption.

An organic light emitting display generates images based on data voltages applied to pixel electrodes. The data voltages are generated based on gamma voltages that reflect the gamma characteristics of the display. For example, a gray voltage corresponding to gradation of input image data may be output as a data voltage. The gray voltage may be generated based on a gamma reference voltage. However, current approaches for controlling the generation of images in an organic light emitting display degrade image quality and adversely affect reliability.

SUMMARY

In accordance with one or more embodiments, a method for setting a gamma reference voltage of an organic light emitting display device includes setting the gamma reference voltage to a first temporary value; searching a second temporary value while increasing the first temporary value by a first delta value, the second temporary value corresponding to a value at which luminance of the organic light emitting display device is less than a preset value; and setting the gamma reference voltage based on the searched second temporary value. The first temporary value may be 5V and/or the preset value may be 0.01. The first delta value may be 0.1V.

Searching the second temporary value may include measuring luminance of the organic light emitting display device when the gamma reference voltage is the first temporary value; when the measured luminance is not less than the preset value, increasing the first temporary value by the first delta value; and measuring luminance of the organic light emitting display device when the gamma reference voltage corresponds to the first temporary value increased by the first delta value.

Setting the gamma reference voltage may include setting the gamma reference voltage by adding a preset offset value to the second temporary value, where the offset value is previously set as a value to compensate a difference between the second temporary value, at which luminance of the organic light emitting display device is less than the preset value, and a third temporary value at which luminance of the organic light emitting display device is 0.

After searching the second temporary value at which luminance of the organic light emitting display device is less than the preset value, the method may include, when the luminance of the organic light emitting display device is less than the preset value, reducing the second temporary value by a second delta value and searching a forth temporary value at which luminance of the organic light emitting display device is greater than or equal to the preset value. The second delta value may be a value less than the first delta value.

The method may include setting a transistor voltage of the organic light emitting display device by adding a preset margin value to the set gamma reference voltage. The transistor voltage may be a transistor OFF voltage. The transistor may be a PMOS transistor. The gamma reference voltage may be set to be different for each of a plurality of organic light emitting display devices.

In accordance with one or more other embodiments, an organic light emitting display device includes a display panel including a plurality of pixels connected to a plurality of data lines and a plurality of scan lines intersecting the data lines; a gamma reference voltage setter to set a gamma reference voltage; a gamma reference voltage generator to generate a gamma reference voltage set by the gamma reference voltage setter; a gamma voltage generator to generate a gamma voltage based on the gamma reference voltage; and a data driver to provide a data voltage generated based on the gamma voltage to a corresponding one of the data lines, wherein the gamma reference voltage setter is to set the gamma reference voltage to a first temporary value, increase the first temporary value by a first delta value, search a second temporary value at which luminance of the display panel is less than a preset value, and set the gamma reference voltage based on the searched second temporary value. The first delta value may be 0.1V.

The gamma reference voltage setter may set the gamma reference voltage by adding a preset offset value to the second temporary value, where the offset value is previously set as a value to compensate a difference between the second temporary value, at which luminance of the organic light emitting display device is less than the preset value, and a third temporary value at which luminance of the organic light emitting display device is 0.

After searching the second temporary value at which luminance of the organic light emitting display device is less than the preset value and when the luminance of the organic light emitting display device is less than the preset value, the gamma reference voltage setter may reduce the second temporary value by a second delta value and search a forth temporary value at which luminance of the organic light emitting display device is greater than or equal to the preset value. The second delta value may be a value less than the first delta value. The gamma reference voltage setter may set a transistor voltage of the organic light emitting display device by adding a preset margin value to the set gamma reference voltage. The gamma reference voltage may set to be different for each of a plurality of organic light emitting display devices.

In accordance with one or more other embodiments, a controller includes a processor to set a gamma reference voltage; a gamma reference voltage generator to generate a gamma reference voltage set by the processor; and a gamma voltage generator to generate a gamma voltage based on the gamma reference voltage, wherein the processor is to set the gamma reference voltage to a first temporary value, increase the first temporary value by a first delta value, search a second temporary value at which luminance of the display panel is less than a preset value, and set the gamma reference voltage based on the searched second temporary value.

DETAILED DESCRIPTION

FIG. 3illustrates an embodiment of an organic light emitting display device300which includes a display panel310, a scan driver320, a data driver330, a power supply unit340, a gamma reference voltage setting unit350, a gamma reference voltage generating unit360, a gamma voltage generating unit370, and a timing controller380. The organic light emitting display device300may operate, for example, in an analog driving manner. At least the a gamma reference voltage setting unit350, a gamma reference voltage generating unit360, a gamma voltage generating unit370may be considered to be a controller.

The display panel310includes a plurality of pixels P electrically connected to a plurality of scan lines SL and a plurality of data lines DL. The scan lines SL extend in a first direction and the data lines DL extend in a second direction intersecting the first direction D1.

Each pixel P may include, for example, a switching transistor, a liquid crystal capacitor (CLC) electrically connected to the switching transistor, a storage capacitor, a driving transistor, and an organic light emitting diode (OLED).

The switching transistor has a first terminal connected to one of the data lines DL1, . . . , DLm, a second terminal connected to a first node, and a gate terminal connected to one of the scan lines SL1, . . . , SLn. The storage capacitor has a first terminal connected to a first source voltage ELVDD and a second terminal connected to the first node. The driving transistor has a first terminal connected to the first source voltage ELVDD, a gate terminal connected to the first node, and a second terminal connected to an anode electrode of the OLED. The OLED has a cathode electrode connected to a second source voltage ELVSS and an anode electrode connected to the second terminal of the driving transistor. Each pixel P may have a different structure in another embodiment. The pixels P may be disposed in a matrix form.

The scan driver320provide a scan signal to the pixels P in the display panel310through the scan lines SL1, . . . , SLn. The scan driver320may include at least one scan driving integrated circuit (IC), may be positioned on at least one side surface of the display panel310, and may be connected to the display panel310, for example, in a chip-on-flexible printed circuit (COF), a chip-on-glass (COG), or a flexible printed circuit (FPC) manner.

The data driver330provide data signals corresponding to an image signal to the pixels P in the display panel310through the data lines DL1, . . . , DLm. The data driver330may include at least one data driving IC, may be positioned on at least one side surface of the display panel310, and may be connected to the display panel310, for example, in a COF, COG, or FPC manner.

The power supply unit340provides the first source voltage ELVDD and the second source voltage ELVSS to the pixels P in the display panel310. The second source voltage ELVSS may have a voltage level lower than the first source voltage ELVDD. The power supply unit340may include at least one power supply circuit. The second source voltage ELVSS may be a reference (e.g., ground) voltage.

In order to set a gamma reference voltage optimized (or predetermined) for each organic light emitting display device300, the gamma reference voltage setting unit350measures luminance of the organic light emitting display device300and sets a gamma reference voltage VREG1of the organic light emitting display device300based on the luminance measurement result.

Referring toFIG. 4, black voltages may be different for different organic light emitting display devices. Thus, the gamma reference voltage VREG1may be set to be different for different organic light emitting display devices by the gamma reference voltage setting unit350, as illustrated, for example, inFIG. 4. Also, the gamma reference voltage setting unit350may set an ON/OFF voltage of the transistor of the display panel310based on the preset gamma reference voltage VREG1. The gamma reference voltage setting unit350may be separately provided or may be in power supply unit340.

The gamma reference voltage generating unit360may generate a gamma reference voltage VREG1based on a value corresponding to the gamma reference voltage VREG1set by the gamma reference voltage setting unit350. Since the gamma reference voltage VREG1may be set to be different for different organic light emitting display devices by the gamma reference voltage setting unit350, the gamma reference voltage generating unit360may generate voltages having different values for each organic light emitting device.

The gamma voltage generating unit370generates gamma voltages VGAM based on the gamma reference voltage VREG1and provides the gamma voltages to the data driver330. Since the gamma voltage generating unit370generates the gamma voltages VGAM based on the gamma reference voltage VREG1, the gamma voltages VGAM may be changed according to a change in the gamma reference voltage VREG1. For example, when the gamma reference voltage VREG1is increased, the gamma voltages VGAM may be increased. Also, when the gamma reference voltage VREG1is reduced, the gamma voltages VGAm may be reduced.

The data driver330generate data signals for the pixels P in the display panel310based on the gamma voltages VGAM from the gamma voltage generating unit370. The data driver330outputs the data signals to corresponding ones of the data lines DL.

A method for setting the gamma reference voltage VREG1of the organic light emitting display device300by the gamma reference voltage setting unit350according to one embodiment will now be described.

FIG. 5illustrates an embodiment of the gamma reference voltage setting unit350which includes a black voltage searching unit351, a gamma reference voltage determining unit352, a margin value setting unit353, an adding unit354, and a transistor voltage determining unit355.

The black voltage searching unit351measures a black voltage of the organic light emitting display device300and outputs the black voltage to the gamma reference voltage determining unit352. In one embodiment, the black voltage searching unit351may measure luminance of the organic light emitting display device300in order to measure black voltage.

The gamma reference voltage determining unit352determines a gamma reference voltage VREG1for the organic light emitting display device300based on the black voltage from the black voltage searching unit351. The gamma reference voltage determining unit352may determine the gamma reference voltage VREG1, for example, by adding a preset offset value to the measured black voltage from the black voltage searching unit351. The gamma reference voltage determining unit352may then set the determined gamma reference voltage VREG1in the display device300.

The margin value setting unit353may determine a margin value for setting a transistor ON/OFF voltage of the organic light emitting display device300. The margin value may be set to a predetermined value, e.g., 0.1V or 0.2V.

The adding unit354adds the gamma reference voltage VREG1determined by the gamma reference voltage determining unit352and the margin value determined by the margin value setting unit353and outputs the added value to the transistor voltage determining unit355.

The transistor voltage determining unit355may determine an OFF voltage of a transistor as, or based on, the value resulting from adding the margin value to the gamma reference voltage VREG1from the adding unit354. For a PMOS transistor, for example, the OFF voltage may correspond to VGH. The transistor voltage determining unit355may set the determined transistor OFF voltage in the organic light emitting display device300.

The transistor voltage determining unit355may also determine an ON voltage of the transistor. In one embodiment, the transistor voltage determining unit355may perform a separate algorithm for determining the ON voltage of the transistor using the gamma reference voltage VREG1. A calculation module other than the adding unit354may be provided in the gamma reference voltage setting unit350to determine the transistor ON voltage.

An embodiment of a method for setting the gamma reference voltage VREG1of the gamma reference voltage setting unit350will be described using a more specific example of a method for searching for a black voltage of the black voltage searching unit351. The gamma reference voltage setting unit350may perform all of the operations of the method. In another embodiment, one or more of the operations of the method may be performed by components provided, for example, in the gamma reference voltage setting unit350or a separate unit.

FIG. 6illustrates an embodiment of a method for setting a gamma reference voltage. In this method, the gamma reference voltage setting unit350determines the gamma reference voltage VREG1individually set for the organic light emitting display device300. The gamma reference voltage setting unit350measures a black voltage of the organic light emitting display device300and sets the gamma reference voltage VREG1with respect to the corresponding organic light emitting display device300according to the measured black voltage.

Referring toFIG. 6, first, the gamma reference voltage setting unit350sets a temporary value (VREG1_TEMP) of a gamma reference voltage (operation601). The temporary value may be set to a sufficiently low value such that a black voltage may be properly measured with respect to the organic light emitting display device300. In one embodiment, the gamma reference voltage setting unit350may set the temporary value (VREG1_TEMP) of the gamma reference voltage to 5V.

Next, when the gamma reference voltage VREG1is set to a temporary value, the gamma reference voltage setting unit350determines whether luminance of the organic light emitting display device300is less than a preset value (operation602).

When the gamma reference voltage VREG1is set to a temporary value, the gamma reference voltage setting unit350may measure luminance of the organic light emitting display device300and determine whether the measured luminance is less than a preset value. The preset value, as a reference for comparison, may be a value at which measured luminance is sufficiently low to display black, e.g., when a black voltage is reached, e.g., 0.01.

When the measured luminance is not less than the preset value, the gamma reference voltage setting unit350increases the temporary value (VREG1_TEMP) of the gamma reference voltage by a delta value (operation603). The delta value may be a value previously set to determine whether luminance of the organic light emitting display device300is less than a preset value, while increasing the temporary value (VREG1_TEMP) of the gamma reference voltage. As the delta value decreases, the accuracy of the measured black voltage increases and black voltage measurement time is lengthened. Conversely, as the delta value increases, the accuracy of the black voltage decreases and the black voltage measurement time is shortened. Thus, the delta value may be set by taking into consideration the accuracy of black voltage measurement and a measurement time. The delta value may be set to 0.1 V, for example, or another value.

Based on the temporary value (VREG1_TEMP) of the gamma reference voltage increased by the delta value, the gamma reference voltage setting unit350measures luminance of the organic light emitting display device300again and then determines whether the luminance is less than a preset value. By repeating the foregoing operation, the gamma reference voltage setting unit350searches for a temporary value having a luminance that is less than the preset value. When operation602determines that a current or second temporary value, which is the initial or first temporary value that has been increased due to operation603, has a luminance that is less than the preset value, that current temporary value is output to operation604to set the gamma reference voltage.

When the measured luminance is less than the preset value, the gamma reference voltage setting unit350adds the preset offset value to the temporary value at the time and determines the resultant value as reference voltage VREG1(operation604).

In at least one embodiment, a black voltage refers to a voltage when luminance of the organic light emitting display device300is 0. In some circumstances, it may be difficult to measure whether luminance of the organic light emitting display device300is 0. Thus, in actually measuring the black voltage, the black voltage may be measured using a certain value (e.g., the preset value mentioned above), not 0, determined as a state in which measured luminance is sufficiently low so the black voltage is reached. Thus, the measured black voltage may have a difference value compared with the black voltage that exists when luminance is 0. Thus, in one embodiment, in order to compensate for the difference in the black voltage generated due to the foregoing reason, the gamma reference voltage VREG1may be determined by adding a preset offset value to a temporary value.

In addition, the gamma reference voltage setting unit350determines a transistor voltage by adding a preset margin value to the determined gamma reference voltage VREG1(operation605). In one embodiment, the gamma reference voltage setting unit350may determine an OFF voltage of the transistor. When the transistor is a PMOS transistor, the OFF voltage of the transistor may correspond to VGH.

FIG. 7illustrates another embodiment of a method for setting a gamma reference voltage. Referring toFIG. 7, first, the gamma reference voltage setting unit350sets a temporary value (VREG1_TEMP) of a gamma reference voltage (operation701). The temporary value may be set to a sufficiently low value such that a black voltage may be properly measured with respect to the organic light emitting display device300. In one embodiment, the gamma reference voltage setting unit350may set the temporary value (VREG1_TEMP) of the gamma reference voltage to a predetermined voltage, e.g., 5V.

Next, when the gamma reference voltage VREG1is set to a temporary value, the gamma reference voltage setting unit350determines whether luminance of the organic light emitting display device300is less than a preset value (operation702).

When the gamma reference voltage VREG1is set to a temporary value, the gamma reference voltage setting unit350may measure luminance of the organic light emitting display device300and determine whether the measured luminance is less than a preset value. The preset value, as a reference for comparison, may be a value at which measured luminance is sufficiently low to display black (e.g., when a black voltage is reached) such as, for example, 0.01.

When the measured luminance is not less than the preset value, the gamma reference voltage setting unit350increases the temporary value (VREG1_TEMP) of the gamma reference voltage by a first delta value (operation703). The first delta value is a value previously set to summarize and measure a black voltage, while rapidly increasing the temporary value (VREG1_TEMP) of the gamma reference voltage. The first delta value may be set to a value greater than 0.1 V or another predetermined value.

Based on the temporary value (VREG1_TEMP) of the gamma reference voltage increased by the first delta value, the gamma reference voltage setting unit350measures luminance of the organic light emitting display device300again and determines whether the luminance is less than the preset value. By repeating the foregoing operation, the gamma reference voltage setting unit350searches for a temporary value having a luminance that is less than the preset value. When operation702determines that a current or second temporary value, which is the initial or first temporary value that has been increased due to operation703, has a luminance that is less than the preset value, that current temporary value is output to operation704to set the gamma reference voltage.

When the measured luminance is less than the preset value, the gamma reference voltage setting unit350reduces the temporary value (VREG1_TEMP) of the gamma reference voltage by a second delta value (operation704). The second delta value may be a value set to accurately measure a black value summarized and searched by the first delta value, while reducing the temporary value (VREG1_TEMP) of the gamma reference voltage. The second delta value may be set to a value less than the first delta value.

Thus, under some circumstances, the method for setting a gamma reference voltage value according to this embodiment may measure a black voltage accurately at a faster rate than the previous embodiment.

Thereafter, based on the temporary value (VREG1_TEMP) of the gamma reference voltage increased by the second delta value, the gamma reference voltage setting unit350determines whether the luminance of the organic light emitting display device300is greater than or equal to a preset value (operation705).

When the measured luminance is not greater than or equal to the preset value, the gamma reference voltage setting unit350measures luminance of the organic light emitting display device300again, while reducing the temporary value (VREG1_TEMP) of the gamma reference voltage by the second delta value, and determines whether the luminance is greater than or equal to the preset value. While repeating the operation, the gamma reference voltage setting unit350searches a temporary value of luminance greater than or equal to the preset value.

When the measured luminance is greater than or equal to the preset value, the gamma reference voltage setting unit350adds the preset offset value to the temporary value at the time and determines the resultant value as a reference voltage VREG1(operation706).

In addition, the gamma reference voltage setting unit350determines a transistor voltage by adding a preset margin value to the determined gamma reference voltage VREG1(operation707). In one embodiment, the gamma reference voltage setting unit350may determine an OFF voltage of the transistor. For a PMOS transistor, the OFF voltage may correspond to VGH.

FIG. 8is a graph illustrating an example of driving power consumption of an organic light emitting display device when a gamma reference voltage is set according to a gamma reference voltage setting method according to one or more embodiments described herein.

Referring toFIG. 8, it may be confirmed that, compared with a case in which the same gamma reference voltage VREG1is collectively set for a plurality of organic light emitting display devices300, when the optimal gamma reference voltage VREG1is set for each organic light emitting display device300according to one or more embodiments described herein, driving power consumption of the organic light emitting display device300is reduced by about 5%. The driving power consumption may be a different percentage on other embodiments.

The controllers, units, and other processing features may be implemented in logic which, for example, may include hardware, software, or both. When implemented at least partially in hardware, the controllers, units, and other processing features may be, for example, any one of a variety of integrated circuits including but not limited to an application-specific integrated circuit, a field-programmable gate array, a combination of logic gates, a system-on-chip, a microprocessor, or another type of processing or control circuit.

By way of summation and review, an organic light emitting display generates images based on data voltages applied to pixel electrodes. The data voltages are generated based on gamma voltages that reflect the gamma characteristics of the display. For example, a gray voltage corresponding to gradation of input image data may be output as a data voltage. The gray voltage may be generated based on a gamma reference voltage.

FIG. 1illustrates an example of a gamma reference voltage and an ON/OFF voltage of a transistor (e.g., VGL/VGH in case of using PMOS) in one type of an organic light emitting display. The gamma reference voltage and ON/OFF voltage of the transistor determine the width of a voltage swing according to Equation 1 and thus are direct factors in determining dynamic power.
Dynamic power=C×ΔV2×f(1)
In Equation 1, C denotes capacitance, V denotes a set voltage, and f denotes a frequency.

In one type of device, a single gamma reference voltage is commonly set on grounds that all the organic light emitting display devices (cells) have the same gamma characteristics. However, due to various factors, the gamma characteristics of organic light emitting displays have variations. Thus, the gamma reference voltage may be set based on an expected worst condition of an organic light emitting display.

FIG. 2illustrates an example of a gamma reference voltage set to an overload value based on the understanding that luminance dispersions are different because organic light emitting displays have different black voltages. Also, the ON/OFF voltage of each transistor is set by adding a margin value of 0.1 to 0.2V to the gamma reference voltage. As a result, image quality is degraded and reliability of the organic light emitting display is adversely affected.

In accordance with one or more of the aforementioned embodiments, an organic light emitting display device is provided in which an optimal or other predetermined gamma reference voltage and a transistor ON/OFF voltage are individually and differently set for each of a plurality of organic light emitting display devices. A method for setting a gamma reference voltage of the organic light emitting display device is also provided.