Organic light emitting diode display and method of driving the same

An organic light emitting diode display having improved display quality is disclosed. The organic light emitting diode display includes pixels positioned at intersections of scan lines and data lines, an emission control unit for controlling emission times of the pixels according to a second emission width signal indicating emission time information of the pixels, and an emission time controller for dividing the pixels into a plurality of blocks and for generating the second emission width signal according to a brightness history of the blocks.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0032869, filed on Apr. 8, 2011, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND

The disclosed technology relates to an organic light emitting diode display and a method of driving the same, and more particularly, to an organic light emitting diode display having improved display quality and a method of driving the same.

2. Description of the Related Technology

Recently, various flat panel displays having reduced weight and volume as compared to cathode ray tubes (CRT) have been developed. Flat panel technologies include liquid crystal display (LCD), field emission display (FED), plasma display panel (PDP), and an organic light emitting diode (OLED) display. Among the FPDs, the organic light emitting diode display displays an image using organic light emitting diodes (OLEDs) that generate light by re-combination of electrons and holes. The organic light emitting diode display has high response speed and is driven with low power consumption.

An OLED display includes a plurality of pixels arranged at the intersections of a plurality of data lines, scan lines, and power source lines in a matrix. The pixels generally include OLEDs and pixel circuits for controlling the amount of current that flows to them. The pixels generate voltages corresponding to data signals and supply corresponding currents to the OLEDs. Thus, light is produced with brightness corresponding to the data signals.

One significant disadvantage of OLED technology is that the diodes deteriorate over time such that the brightness for a given emission time and amount of current changes. Here, the amount of current is determined by data (that is, gray levels) so that the degree of OLED deterioration varies from pixel to pixel and overall display quality degrades.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One inventive aspect is an organic light emitting diode display. The display includes pixels positioned at intersections of scan lines and data lines, an emission control unit for controlling emission times of the pixels to correspond to a second emission width signal, and an emission time controller for dividing the pixels into a plurality of blocks and for generating the second emission width signal based on brightness history data of the blocks.

Another inventive aspect is a method of driving an organic light emitting diode display. The method includes accumulating brightness data for a plurality of blocks of pixels, and generating level data indicating brightness levels based on the accumulated brightness data of the blocks. The method also includes accumulating the level data for a plurality of frames to generate accumulated level data, comparing the accumulated level data with a threshold value to generate a first control signal if at least one of the accumulated level data is greater than the threshold value and to otherwise generate a second control signal, and incrementally reducing brightness of the pixels if the first control signal is generated.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

FIG. 1is a view illustrating an organic light emitting diode display according to an embodiment. Referring toFIG. 1, the organic light emitting diode display includes a pixel unit130including pixels140positioned at the intersections of scan lines S1to Sn, emission control lines E1to En, and data lines D1to Dm, a scan driver110for driving the scan lines S1to Sn, an emission control line driver160for driving emission control lines E1to En, a data driver120for driving the data lines D1to Dm, an emission time controller170for controlling the emission control line driver160, and a timing controller150for controlling the scan driver110, the data driver120, and the emission time controller170.

The scan driver110sequentially supplies scan signals to the scan lines S1to Sn. When the scan signals are sequentially supplied to the scan lines S1to Sn, the pixels140are selected in units of lines.

The data driver120supplies data signals to the data lines D1to Dm in synchronization with the scan signals. The data signals supplied to the data lines D1to Dm are supplied to the pixels140selected by the scan signals.

The emission control line driver160receives a second emission width signal from the emission time controller170. The emission control line driver160that received the second emission width signal generates an emission control signal having a width to correspond to emission time information on the second emission width signal and sequentially supplies the generated emission control signal to the emission control lines E1to En. Here, the pixels140that received the emission control signal are set in a non-emission state and the pixels140that did not receive the emission control signal emit light to correspond to the data signals.

The emission time controller170divides the pixel unit130into a plurality of blocks and accumulates data in each block to determine brightness information. The emission control line driver160generates the second emission width signal to correspond to the brightness information and supplies the generated second emission width signal to the emission control line driver160. Here, the emission time controller170generates the second emission width signal so that the deterioration of the OLEDs included in the pixels140is minimized.

In detail, the deterioration of the OLEDs is determined by the data (that is, gray levels) and emission time. The emission time controller170accumulates data for each block and determines brightness information of each block according to the accumulated data. Then, the emission time controller170generates the second emission width signal so that the emission times of the pixels are reduced when emission is performed with brightness of no less than a threshold value in at least one block. That is, when the pixels continuously emit light with high brightness in a frame period, the emission times of the pixels are reduced so that the deterioration of the OLEDs is minimized.

The timing controller150supplies a scan control signal SCS to the scan driver110and supplies data and a data control signal DCS to the data driver120. The timing controller150supplies a control signal ECS and the data to the emission time controller170. Here, block control signals, a first emission brightness signal, and a first emission width signal are included in the control signal ECS. The block control signals are for dividing the pixels140included in the pixel unit130into a plurality of blocks and the first emission brightness signal represents a brightness value that may be displayed by the pixel unit130. The first emission width signal represents time for which the pixels140emit light in one frame period.

In detail, the first emission brightness signal as a signal input from the outside (for example, a user) represents a specific brightness value among the brightness components (that is, 0% to 100%) that may be displayed by the pixel unit130. For example, the user may supply the first emission brightness signal corresponding to 80% to correspond to an external environment. The first emission width signal input from a controller that is not illustrated to correspond to the external environment includes information on the time for which the pixels140may emit light in the one frame period.

The pixel unit130includes the pixels140positioned at the intersections of the scan lines S1to Sn and the data lines D1to Dm. The pixels140receive a first power voltage ELVDD and a second power voltage ELVSS. The pixels140control the amount of currents supplied from the first power voltage ELVDD to the second power voltage ELVSS through the OLEDs to correspond to the data signals in a period where the emission control signals are not supplied.

FIG. 2is a block diagram illustrating the emission time controller ofFIG. 1. Referring toFIG. 2, the emission time controller170according to the embodiment includes a first accumulating unit171, a level determining unit172, a storage unit173, a second accumulating unit174, a stress determining unit175, and a signal generator176.

The first accumulating unit171receives the block control signals X and Y and the data from the timing controller150. The first block control signal X means the number of pixels140in a horizontal direction to be included in each block and the second block control signal Y means the number of pixels140in a vertical direction to be included in each block.

The first accumulating unit171that received the block control signals X and Y divides the pixel unit130into a plurality of blocks. Then, the first accumulating unit171accumulates the data in each block to generate accumulated data. For example, the first accumulating unit171may generate i accumulated data to correspond to i (i is a natural number no less than 2) blocks every frame.

The level determining unit172generates level data corresponding to brightness levels of the respective blocks to correspond to the accumulated data supplied from the first accumulating unit171. Therefore, a plurality of brightness data are stored in the storage unit173. For example, the plurality of brightness data including first brightness data when all of the pixels included in the blocks emit light with brightness of no less than about 95% on the average and second brightness data when all of the pixels included in the blocks emit light with brightness of no more than about 5% on the average may be stored by the storage unit173. The level determining unit172compares the accumulated data with the brightness data stored by the storage unit173and generates the level data to correspond to the comparison result.

The second accumulating unit174accumulates level data j (j is a natural number of no less than 2) frame periods to correspond to the respective blocks to generate the accumulated level data. For example, the second accumulating unit174accumulates the level data in units of 100 (that is, j=100) frames to generate the accumulated level data.

The stress determining unit175receives the accumulated level data of the blocks from the second accumulating unit174and compares the received accumulated level data with a threshold value. Here, a first control signal is generated when at least one of the input accumulated level data is larger than the threshold value and a second control signal is generated when at least one of the input accumulated level data is no more than the threshold value.

Here, the threshold value is set as one value among the accumulated level data that may be generated by the stress determining unit175. When the threshold voltage is set to be large (that is, to correspond to high brightness), the brightness of the pixel unit130is maintained to be high and the deterioration speed of the OLEDs increases. When the threshold value is set to be low (that is, to correspond to low brightness), the brightness of the pixel unit130becomes low and the deterioration speed of the OLEDs is reduced. The threshold value may be experimentally determined in consideration of the resolution, the size, the brightness characteristic, and the deterioration characteristic of a panel.

The signal generator176generates the second emission width signal to correspond to the first control signal or the second control signal supplied by the stress determining unit175to supply the second emission width signal to the emission control line driver160. Here, the signal generator176generates the second emission width signal so that the emission times of the pixels are reduced when the first control signal is input and generates the second emission width signal so that emission is performed by a system with predetermined brightness when the second control signal is input.

That is, in some embodiments, the brightness components of the pixels are determined in the blocks in the plurality of frame periods and the emission times of the pixels are reduced when the determined brightness components are greater than the threshold value to prevent the deterioration of the OLEDs.

FIG. 3is a view illustrating the first accumulating unit illustrated inFIG. 2. Referring toFIG. 3, the first accumulating unit171according to the embodiment ofFIG. 3includes a first counter1711, a second counter1712, a third counter1713, a fourth counter1714, and a data accumulating unit1715.

The first counter1711receives the first block control signal X and the data. The first counter1711that received the first block control signal X generates a first count signal while counting the number of data supplied in a horizontal direction to correspond to the first block control signal X as illustrated inFIG. 4. When192is input to the first block control signal X, the first counter1711generates the first count signal whenever the192data are input in the horizontal direction.

The second counter1712receives the second block control signal Y and the data. The second counter1712that received the second block control signal Y generates a second count signal while counting the number of data supplied in a vertical direction to correspond to the second block control signal Y. When108is input to the second block control signal Y, the second counter1712generates the second count signal whenever the108data are input in a vertical direction.

The third counter1713receives the first count signal. The third counter1713that received the first count signal generates the third count signal when the first count signal is input. Here, the third count signal increases in the order of 0, 1, and 2, . . . and the respective numbers mean blocks divided in horizontal units.

The fourth counter1714receives the second count signal. The fourth counter1714that received the second count signal generates the fourth count signal when the second count signal is input. Here, the fourth count signal increases in the order of 0, 1, and 2, . . . and the respective numbers mean blocks divided in vertical units. For example, in the panel with the resolution of 1920×1080, when192is input to the first block control signal X and108is input to the second block control signal Y, the panel is divided into 100 blocks.

The data accumulating unit1715receives the third count signal, the fourth count signal, and the data. The data accumulating unit1715accumulates data in the blocks divided by the third count signal and the fourth count signal to generate accumulated data. For example, the data accumulating unit1715adds all of the data supplied by the respective blocks every frame to generate accumulated data in the respective blocks.

FIG. 5is a view illustrating the brightness data stored in the storage unit. Referring toFIG. 5, a plurality of (for example, 15) different brightness data are stored in the storage unit173. The brightness data may be set as one value of the accumulated data that may be generated by the first accumulating unit171.

In detail, the accumulated data generated by accumulating data include brightness information of each block. The brightness data provide a reference value so that the accumulated data may be distinguished by uniform brightness components (or gray levels). For example, the brightness data may be set to correspond to the brightness of about 95%, the brightness of about 80%, . . . , and the brightness of about 5% in the respective blocks.

The level determining unit172compares the accumulated data and the brightness data of the respective blocks supplied by the first accumulating unit171with each other to generate level data to correspond to the comparison result. For example, the level determining unit172generates fourth level data when the accumulated data of brightness data3and brightness data4are input to supply the generated fourth level data to the second accumulating unit174.

FIG. 6is a view illustrating the operation processes of the second accumulating unit and the stress determining unit. Referring toFIG. 6, the second accumulating unit174accumulates (for example, adds or integrates) level data for j frames to generate the accumulated level data of the respective blocks. The brightness information of the blocks that emit light for the j frames is included in the accumulated level data.

The stress determining unit175receives the accumulated level data of the respective blocks to determine if the input accumulated level data are greater than the threshold value. The stress determining unit175generates the first control signal when one of the input accumulated level data is greater than the threshold value and generates the second control signal to supply the generated second control signal to the signal generator176when the input accumulated level data is no more than the threshold value.

FIG. 7is a view illustrating an embodiment of a signal generator. Referring toFIG. 7, the signal generator176according to the embodiment includes a brightness controller1761, a weight value generator1762, and a width controller1763.

The weight value generator1762receives a first control signal or a second control signal from the stress determining unit175. The weight value generator1762incrementally reduces the weight value if the first control signal is input and incrementally increases the weight value if the second control signal is input.

Here, the weight value generator1762includes information on the largest weight value (for example, 1) and the smallest weight value (for example, 0.3) and reduces or increases the weight value between the largest weight value and the smallest weight value. In particular, the weight value generator1762reduces or increases the weight value in the form of an incremental step so that a change in brightness is not recognized by an observer.

The brightness controller1761receives the weight value from the weight value generator1762and receives a first emission brightness signal from the timing controller150. The brightness controller1761that received the first emission brightness signal and the weight value changes the first emission brightness signal to correspond to the weight value to generate a second emission brightness signal. For example, the brightness controller1761multiplies the brightness of the first emission brightness signal by the weight value to generate the brightness information of the second emission brightness signal. In one embodiment, as illustrated in TABLE 1, the second emission brightness signal is generated to correspond to the first emission brightness signal and the weight value.

In table 1, the brightness controller1761generates the second emission brightness signal so that brightness information of 30% is included regardless of the weight value when the first emission brightness signal is set to have the brightness of 30%. That is, the minimum brightness information is included in the brightness controller1761and the second emission brightness signal is generated so that brightness information of no less than the minimum brightness is included.

The width controller1763receives the second emission brightness signal and the first emission width signal. The width controller1763that received the second emission brightness signal and the first emission width signal changes the first emission width signal to correspond to the brightness information of the second emission brightness signal to generate the second emission width signal. For example, when the first emission width signal includes emission time information of 10,000 clocks and the second emission brightness signal includes the brightness information of 50%, the width controller1763multiplies the time (10,000 clocks) by the brightness (0.5) to generate the second emission width signal so that the emission time information of 5,000 clocks is included. Therefore, the width controller1763changes the brightness information (%) of the second emission brightness signal into a value between 1 and 0 and multiplies the clock information by the brightness information. The emission control line driver160generates the emission control signals so that the pixels140emit light for the time of 5,000 clocks.

FIG. 8is a view illustrating the weight value generator according to the embodiment of the present invention. Referring toFIG. 8, the weight value generator according to this embodiment includes a main weight value controller1762aand a sub weight value controller1762b.

The main weight value controller1762areceives a main step (MS) signal and a main interval (MI) signal. The MS signal represents the changed values (reduction width and increase width) of the weight value and the MI signal represents change intervals. That is, the main weight value controller1762generates the weight value that changes by the MS every MI to correspond to the first or second control signal as illustrated inFIG. 9.

The sub weight value controller1762breceives a sub step (SS) signal and a sub interval (SI) signal. The SS signal represents the changed values (reduction width and increase width) of the weight value and the SI signal represents change intervals. Here, the SS represents change width between the MS and is set as smaller width (or number) than the MS. The SS signal represents change intervals between the MI and is set as smaller time (or number). The SS signal represents change intervals between the MI and is set as smaller time (or number) than the MI.

FIG. 10is a flowchart illustrating the operation processes of the main weight value controller. Referring toFIG. 10, the main weight value controller1762adetermines whether the first control signal or the second control signal is input from the stress determining unit175(S1). When it is determined that the first control signal (high) is input in S1, the main weight value controller1762adetermines whether the first weight value is a value of no more than the minimum weight value (S2). When it is determined that the first weight value is no more than the minimum weight value in S2, the main weight value controller1762aoutputs the value of the minimum weight value as the first weight value (S4). When the first weight value is larger than the minimum weight value in S2, the first weight value is reduced by the MS (S5).

On the other hand, when the second control signal (low) is input in S1, the main weight value controller1762adetermines whether the first weight value is no less than the maximum weight value (S3). When it is determined that the first weight value is no less than the minimum weight value in S3, the main weight value controller1762aoutputs the value of the maximum weight value as the first weight value (S6). When the first weight value is set to be less than the maximum weight value in S3, the first weight value is increased by the MS (S7).

The main weight value controller1762aincreases or reduces the first weight value to correspond to the first control signal or the second control signal as illustrated inFIG. 9while repeating S1to S7.

FIGS. 11 and 12are views illustrating the operation processes of the sub weight value controller. Referring toFIGS. 11 and 12, the sub weight value controller1762breceives a current first weight value n from the main weight value controller1762a. The sub weight value controller1762bthat received the current first weight value n compares a previous first weight value n−1 with the current first weight value n (S10).

When it is determined that the previous first weight value n−1 is greater than the current first weight value n in S10, it is determined that the current weight value is no more than the current first weight value n (S11). When it is determined in S11that the current weight value is no more than the current first weight value n, the value of the current first weight value is output as the current weight value (S13). When it is determined in S11that the current weight value is greater than the current first weight value n, the current weight value is reduced by the SS to be output (S14).

When it is determined in S10that the previous first weight value n−1 is less than the current first weight value n, it is determined whether the current weight value is no less than the current first weight value n (S12). When it is determined in S12that the current weight value is no less than the current first weight value n, the value of the current first weight value is output as the current weight value (S15). When it is determined in S12that the current weight value is less than the first weight value n, the current weight value is increased by the SS to be output (S16). The current weight value output in S13, S14, S15, and S16is supplied to the brightness controller1761as the weight value.

FIG. 13is a view illustrating the second emission brightness signal corresponding to the first and second control signals. Referring toFIG. 13, the second emission brightness signal is generated according to the control signal, the weight value, and the first emission brightness signal. Here, the second emission brightness signal is set to be gradually reduced when the first control signal is input and to be gradually increased to the value of the original first emission brightness signal when the second control signal is input. That is, when brightness of a high gray level is realized in units of blocks, that is, when the first control signal is input, the brightness of a panel is reduced so that it is possible to prevent the OLEDs from being rapidly deteriorated.

FIG. 14is a view illustrating an organic light emitting diode display according to another embodiment. WhenFIG. 14is described, the same elements asFIG. 1are generally denoted by the same reference numerals and detailed description thereof may be omitted. Referring toFIG. 14, a power source unit200for supplying the first power voltage ELVDD or the second power voltage ELVSS to power source lines VL1formed in units of horizontal lines is provided.

The power source unit200controls the emission times of the pixels140to correspond to the second emission width signal supplied from the emission time controller170. That is, the power source unit200controls the emission and non-emission states of the pixels140while controlling the voltage of the first power voltage ELVDD or the second power voltage ELVSS supplied to the power source lines VL1to VLn.

In detail, according to the embodiment ofFIG. 1, the emission of the pixels140is controlled using the widths of the emission control signals. When the emission control signals are used, transistors coupled to the emission control line (one of E1to En) must be included in the pixels140.

However, some embodiments of pixels140may have circuit structures in which transistors are not coupled to the emission control lines E1to En. In addition, various embodiments of driving methods of supplying the power voltages ELVDD or ELVSS using the power source lines VL1to VLn in units of horizontal lines may be used.

In this case, as illustrated inFIG. 14, the emission of the pixels140may be controlled by controlling the voltage of the first power voltage ELVDD or the second power voltage ELVSS. Other aspects of this embodiment may be similar to the embodiment ofFIG. 1.

While various aspects have been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements.