Organic light emitting display device and driving method thereof that displays an image by dividing one frame into a plurality of sub-fields

The described technology relates generally to an organic light emitting display and a method for driving the same. According to an exemplary embodiment, an image is displayed by dividing one frame into a plurality of sub-fields, and a gamma curve is realized with a combination of a plurality of sub-fields respectively corresponding to a plurality of grays of image data so that image data can be compensated without adding a memory. In addition, the embodiment can extract the one combination by setting a combination of sub-fields that exceeds one frame time among the plurality of sub-fields to be an exception condition.

RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0099805 filed in the Korean Intellectual Property Office on Aug. 22, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The described technology relates generally to an organic light emitting display and a driving method thereof.

2. Description of the Related Art

A typical flat organic light emitting display includes a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), and the like.

In general, an organic light emitting display using an organic light emitting diode (OLED) among the flat organic light emitting displays is a flat-type display using electric field emission of an organic material. Light emission of the organic light emitting diode (OLED) is achieved using a mechanism in which electrons and holes are injected from electrodes, and when excitons generated by coupling the holes and electrons fall from an excited state to a ground state, light is emitted.

The organic light emitting display does not require an additional light source, and thus the thickness and weight thereof may be reduced. Since the organic light emitting display has a fast response speed and at the same time has excellent light emission efficiency, luminance, and viewing angle, the organic light emitting display can be used for electronic products such as a portable terminal or a large television.

SUMMARY

In general, an organic light emitting display compensates a luminance deviation of image data using a gamma curve. However, in order to precisely express a 2.2 gamma in low gray, about 18-bit compensation data is required. Thus, the size of a memory is increased. Therefore, an exemplary embodiment provides an organic light emitting display displaying an image by dividing one frame into a plurality of sub-fields and compensating image data without adding a memory by realizing a gamma curve with a combination of a plurality of sub-fields respectively corresponding to a plurality of grays of the image data, and a method for driving the organic light emitting display.

The organic light emitting display according to the exemplary embodiment includes: a display unit, a signal controller, a scan driver and a data driver. The display unit includes a plurality of data lines, a plurality of scan lines, and a plurality of pixels connected to the respectively corresponding data lines and scan lines. The signal controller is configured to divide externally input data by one frame unit, and configured to generate image data by arranging one frame of the input data with a plurality of sub-fields, each having a different seed value. The scan driver is configured to supply a plurality of scan signals to the plurality of scan lines for a scan period of each of the plurality of sub-fields. The data driver is configured to generate a plurality of data signals using the image data and supplies the plurality of data signals to the plurality of data lines. The signal controller is configured to arrange the sub-fields, excluding a combination including at least two sub-fields of which the sum of seed values is greater than the one frame among the plurality of sub-fields.

The signal controller may include a gamma setter setting each of a plurality of grays of the input data with a combination of sub-fields corresponding to a gamma curve. The gamma setter processes a combination that includes at least two largest seed values among the plurality of seed values as an exception condition.

Further, the gamma setter may include: a sampler, a calculator and a selector. The sampler extracts a plurality of sample combinations respectively corresponding to the plurality of grays and includes a seed value selected from a plurality of seed values. The calculator calculates a sampling luminance corresponding to the plurality of sample combinations and calculates an error value by comparing the sampling luminance and a target luminance that corresponds to the gamma curve. The selector selects a sampling combination of which an error value is included in a target error range and does not correspond to the exception condition among the plurality of sampling conditions, and stores the selected sample combination in a gamma table.

The selector selects a sample combination having the smallest error value when a plurality of sample combinations is selected. The selector adds the target luminance as a new seed value when an error value of each of the plurality of sample combinations is not included in the target error range.

In addition, according to another exemplary embodiment, a method is provided to drive an organic light emitting display. The organic light emitting display includes a display unit, a signal controller, a scan driver, and a data driver. The display unit includes a plurality of data lines, a plurality of scan lines, and a plurality of pixels connected to the corresponding data lines and the corresponding scan lines. The signal controller generates image data using externally input data. The scan driver supplies a plurality of scan signals to the plurality of scan lines for a scan period of each of a plurality of sub-fields. The data driver generates a plurality of data signals using the image data and supplies the plurality of data signals to the plurality of data lines.

The method includes: dividing the input data in one frame; setting a plurality of grays of the input data to a combination of a plurality of sub-fields, each having a different seed value; and arranging the one frame with the combination of sub-fields. The method further includes excluding a combination including at least two sub-fields of which the sum of seed values is greater than the one frame among the plurality of sub-fields.

The setting the combination of sub-fields may include: extracting a plurality of sample combinations respectively corresponding to a plurality of grays of the input data; selecting at least one sample combination among the plurality of sample combinations according to a target error range; excluding a sample combination including at least two sub-fields of which the sum of seed values is greater than the one frame among the selected sample combinations; and storing the sample combination in a gamma table.

In addition, the extracting the plurality of sample combinations may include selecting a part of the plurality of seeds values for combination. The selecting the sample combination may include: calculating a sampling luminance by adding the seed value of each of the plurality of sample combinations; calculating an error value by comparing a target luminance corresponding to a gamma curve with the sample luminance; and determining whether the error value is included in the target error range.

In addition, the storing the sample combination in the gamma table may include updating the gamma table with a sample combination having the smallest error value among the sample combinations of which error values are included in the target error range.

When the error value of each of the plurality of sample combinations is not included in the target error range, the target luminance may be added as a new seed value.

According to the exemplary embodiment, an image is displayed by dividing one frame into a plurality of sub-fields, and a gamma curve is realized with a combination of a plurality of sub-fields respectively corresponding to a plurality of grays of image data so that image data can be compensated without adding a memory.

In addition, the exemplary embodiment can extract the one combination among the plurality of sub-fields to be an exception condition by setting a combination of sub-fields that exceeds one frame time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, the exemplary embodiments have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the exemplary embodiments. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

The exemplary embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown.

FIG. 1is a block diagram of an organic light emitting display according to an exemplary embodiment, andFIG. 2is an equivalent circuit diagram of a pixel PXij according to the exemplary embodiment.

Referring toFIG. 1, an organic light emitting display100according to the exemplary embodiment includes a display unit10, a scan driver20, a data driver30, and a signal controller40.

The display unit10is a display area including a plurality of pixels PX, and a plurality of scan lines SL[1] to SL[n], a plurality of data lines DL[1] to DL[m], and wires for applying power source voltages ELVDD and ELVSS are formed in the pixels PX.

Each of the plurality of pixels PX includes a red sub-pixel emitting red light, a green sub-pixel emitting green light, and a blue sub-pixel emitting blue light so that it can display an image with various colors.

For example, as shown inFIG. 2, a pixel PXij connected to an i-th scan line SL[i] and a j-th data line DL[j] includes a switching transistor TR1, a driving transistor TR2, a capacitor C, and an organic light emitting diode OLED.

The switching transistor TR1includes a gate electrode connected to the scan line SL[i], a source electrode connected to the data line DL[j], and a drain electrode connected to a gate electrode of the driving transistor TR2.

The driving transistor TR2includes a source electrode connected to a wire applying a power source voltage ELVDD, a drain electrode connected to an anode of a red organic light emitting diode OLED, and a gate electrode to which a voltage Vdata corresponding to a data signal D[j] is transmitted during a turn-on period of the switching transistor TR1.

The capacitor C is connected between the gate electrode and the source electrode of the driving transistor TR2. A cathode of the organic light emitting diode OLED is connected to a wire applying a power source voltage ELVSS.

In the pixel PX having such a configuration, the data voltage Vdata is transmitted to the gate electrode of the driving transistor TR2when the switching transistor TR1is turned on by the scan signal S[i]. A voltage difference between the gate electrode and the source electrode of the driving transistor TR2is maintained by the capacitor C, and a driving current Id flows to the driving transistor TR2. The organic light emitting diode OLED emits light according to the driving current Id. Meanwhile, in the exemplary embodiment, the pixel PX shown inFIG. 2is an exemplary pixel of the display, and a different type of pixel may be used.

Referring back toFIG. 1, the scan driver20is connected to the plurality of scan lines SL[1] to SL[n], and generates a plurality of scan signals S[1] to S[n] according to a first driving control signal CONT1. The scan driver20transmits the scan signals S[1] to S[n] to the respective scan lines S[1] to S[n]. The scan driver20may generate the plurality of scan signals S[1] to S[n] for every scan period of each of a plurality of sub-fields included in one frame.

The data driver30samples image data R, G, and B according to a second driving control signal CONT2, and latches the sampled data to generate a plurality of data signals D[1] to D[m]. The data driver30transmits the data signals D[1] to D[m] to the respectively corresponding data lines DL[1] to DL[m].

The signal controller40receives an external synchronization signal and processes the signal to generate the first and second driving control signals CONT1, and CONT2. Here, the synchronization signal includes a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and a main clock signal MCLK.

In addition, the signal controller40divides input data InD by every frame unit, and generates image data R, G, and B by arranging one frame of the input data InD in a plurality of sub-fields, each having a different seed value.

Thus, the signal controller40includes a gamma setter42setting a combination of a sub-field corresponding to each of a plurality of grays of the input data InD. Here, the seed value is a time weight corresponding to a gray that cannot express luminance itself with a combination of other grays among the plurality of grays of the input data InD.

The gamma setter42may exclude a combination of sub-fields that satisfy a predetermined exception condition. Here, exception condition may be set to a combination that simultaneously includes at least two sub-fields of which the sum of seed values exceeds one frame time among the plurality of sub-fields.

That is, when a combination of sub-fields includes at least two seed values which are the largest and second largest in size, the corresponding combination satisfies the exception condition. For example, when an index is assigned to each of the plurality of seed values from the largest in size, as shown inFIG. 3, a combination including a first sub-field SF1and a second sub-field SF2satisfies the exception condition if the first sub-field SF1is the largest in size and the second field SF2is the second largest in size among the plurality of sub-fields SF1to SFn. The gamma setter42may limit the number of sub-fields that exceeds half the frame to 1 or 2 among the plurality of sub-fields SF1to SFn.

In addition, the gamma setter42can reduce the seed value with a constant ratio if a total time of the corresponding combination exceeds one frame time even through the sub-field combination does not exceed the exception condition.

FIG. 4is a detailed block diagram of the gamma setter42ofFIG. 1.

Referring toFIG. 4, the gamma setter42according to the exemplary embodiment includes a sampler421, a calculator423, a selector425, and a gamma table427. Here, the sampler421extracts a plurality of sample combinations corresponding to the plurality of grays respectively of the input data InD by using the plurality of seed values. Each of the plurality of sample combinations is selected with a random number of seed values among the entire seed values, and includes a plurality of seed values regardless of the order.

The calculator423calculates a sampling luminance by adding a seed value of each of the extracted plurality of sample combinations. In addition, the calculator423calculates an error value by comparing the sampling luminance and a predetermined target luminance. Here, the target luminance corresponds to a gamma curve.

The selector425selects a sample combination of which an error value between the sampling luminance and the target luminance is included in a target error range and does not satisfy the exception condition among the plurality of sample combinations. Here, the selector425may select a sample combination of which the error value between the sampling luminance and the target luminance is the smallest among a plurality of selected sample combinations. The selector425stores the selected sample combination in the gamma table427.

In addition, when the error value between the sample luminance and the target luminance of all sample combinations is not included in the target error range, the selector425adds a target luminance of the corresponding gray as a new seed value and stores the added seed value in the gamma table427.

FIG. 5is a flowchart of a driving method of the organic light emitting display according to the exemplary embodiment.

Referring toFIGS. 4 and 5, the sampler421searches a plurality of seed values. The sampler421selects a random number of seed values among the plurality of seed values to extract a plurality of sample combinations Cset that respectively correspond to a plurality of grays (operation S1). For example, when the input data InD is 8-bit data, the sampler421extracts a plurality of sample combinations Cset that respectively correspond to 0 to 255 grays.

Then, the calculator423calculates a sampling luminance Cal_val(i) by adding a seed value of each of the extracted plurality of sample combinations Cset. In addition, the calculator423calculates an error value by comparing the sampling luminance Cal_val(i) and a predetermined target luminance target(i) (operation S2).

Then, the selector425determines whether the calculated error value (|target(i)−Cal_val(i)|) is included in a target error range (target(i)*error (%)) (operation S3). When the error value is included in the error range, the selector425determines whether the corresponding sample combination. Cset satisfies the exception condition (operation S4). For example, when a first seed value corresponds to a target luminance of gray239, a sample combination Cset of gray240may include the first seed value as a default value. In this case, a combination including both of the first seed value and a second seed value exists in a plurality of sample combinations Cset extracted corresponding to the gray240, the selector425may determine that the corresponding sample combination Cset satisfies the exception condition.

Then, when the exception condition is not satisfied according to the determination result in operation S4, the selector425stores the corresponding sample combination Cset as a random variable in the gamma table427(operation S5). In this case, when a sample combination having an error value that is smaller than an error value of the sample combination Cset stored as a variable is newly searched, the gamma table427is updated with the corresponding sample combination Cset. That is, the selector425generates the gamma table427with a sample combination having the smallest error value among error values of all sample combinations Cset.

Meanwhile, when the result of the determination in operation S3shows that the calculated error value is not included in the target error range, the selector425determines whether all available sample combinations Cset are used (operation S6). When the result of the determination shows that any value with respect to the entire extractable sample combinations Cset is not included in the target error range, the selector425adds a target luminance of the corresponding gray as a new seed value and stores the added seed value in the gamma table427(operation S7). Through such a process, the selector425can select the one sample combination Cset that corresponds to each of the plurality of grays of the input data InD.

FIG. 6toFIG. 8are provided for description of alignment of the sub-fields according to the exemplary embodiments.

Referring toFIG. 6, in one frame time, sub-fields may be divided into a first sub-field SF1and a plurality of other sub-fields OSF. For example, the first sub-field SF1is longer than half a frame and a second sub-field SF2is half a frame. If a combination of sub-fields that correspond to a specific gray includes the second sub-field SF2and the plurality of other sub-fields OSF, a dummy sub-field DSF in which light is not emitted may be arranged for a time period that corresponds to a difference between the first sub-field SF1and the second sub-field SF2.

In addition, referring toFIG. 7, when the second sub-field SF2is used instead of the first sub-field SF1, a time period that corresponds to the time period of the first sub-field SF1may be corresponded to by arranging the second sub-field SF2and other sub-fields OSF1and OSF2. As the number of arranged sub-fields is increased, the probability that the total of sub-fields exceeds one frame time may be decreased.

In addition, referring toFIG. 8, the display can be driven for one frame period by setting the first sub-field SF1as a default value and arranging a plurality of other sub-fields OSF3and OSF4. In the exemplary embodiment, the total of sub-fields may be shorter than one frame period if the combination is determined to be the best combination of sub-fields. For example, the organic light emitting display can be driven by arranging the second sub-field and a plurality of sub-fields OSF5and OSF6.