KR100600284B1 - Light emitting display, and method for driving the same - Google Patents

Abstract

The present invention relates to a light emitting display device and a driving method thereof capable of improving the uniformity of luminance and achieving white balance.

The present invention provides a plurality of red pixels connected to a plurality of scan lines and a red data line, a plurality of green pixels connected to the plurality of scan lines and a green data line, and a plurality of blue pixels connected to the plurality of scan lines and a blue data line. An image display unit, a scan driver for sequentially applying a scanning signal to the plurality of scan lines for each subframe among a plurality of subframes included in one frame, and data for a red light emitting subframe among one frame to the plurality of red data lines Applies a signal corresponding to a black gray level to the remaining subframes, applies a data signal to a green light emitting subframe among one frame to the plurality of green data lines, and applies a signal corresponding to the black gray level to the remaining subframes A blue light emitting subp of one frame on the plurality of blue data lines And a data driver for applying a data signal and applying a signal corresponding to a black gray level in the remaining subframes, the number of the red light emitting subframes included in one frame and the number of the green light emitting subframes included in one frame. And at least one of the number of the blue light emitting subframes included in one frame is different from the others.

Description

LIGHT EMITTING DISPLAY, AND METHOD FOR DRIVING THE SAME}             

1 illustrates a light emitting display device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a data driver employed in the light emitting display device of FIG. 1.

3 is a circuit diagram illustrating an example of a pixel employed in the light emitting display device of FIG. 1.

4 is a signal diagram illustrating a driving method for driving the light emitting display device of FIG. 1.

<Explanation of symbols for the main parts of the drawings>

10: scan driver 20: data driver

30: image display unit 40: pixel

50: timing controller 21: shift register

22: data latch 23: D / A converter

24: selector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device and a driving method thereof, and more particularly, to a light emitting display device and a method of driving the same, which can improve the uniformity of luminance and achieve a white balance.

Recently, various flat panel displays have been developed to reduce weight and volume, which are disadvantages of cathode ray tubes. The flat panel display includes a liquid crystal display, a field emission display, a plasma display panel, a light emitting display, and the like.

Among the flat panel displays, a light emitting display device is a self-light emitting device that emits a fluorescent material by recombination of electrons and holes, and includes an inorganic light emitting display device including an inorganic light emitting layer and an organic light emitting layer according to materials and structures. It is roughly divided into. Organic light emitting displays are sometimes referred to as organic electroluminescent displays. Such a light emitting display device has an advantage of having a fast response speed, such as a cathode ray tube, compared to a passive light emitting device requiring a separate light source like a liquid crystal display device.

The driving method of the light emitting display device is a passive matrix method and an active matrix method. Among these, the passive matrix method is a method in which the anode and the cathode are formed to be orthogonal and the lines are selected and driven. The active matrix method is a method of controlling the amount of current flowing through the light emitting device using the active device. As the active device, a transistor is mainly used. The active matrix method is somewhat complicated but has the advantage of low current consumption and long light emission time.

However, when the threshold voltage of the transistor is not uniform, there is a problem that the light emitting display device using the active matrix method does not have a uniform screen. In particular, when the light emitting device emits light continuously during one frame period, there is a problem in that uniformity is further deteriorated due to the accumulation of the influence of the error of the threshold voltage.

Accordingly, an object of the present invention is to provide a light emitting display device and a method of driving the same, which can improve the uniformity of luminance by emitting light only in a part of one frame.

Another object of the present invention is to provide a light emitting display and a driving method thereof capable of matching white balance.

As a technical means for achieving the above object, the first aspect of the present invention provides a plurality of red pixels connected to a plurality of scan lines and a red data line, a plurality of green pixels connected to the plurality of scan lines and a green data line, and the plurality of And a plurality of blue pixels connected to the scan line and the blue data line of the image display unit, wherein the image display unit displays one image in one frame, and scan signals are transmitted to the plurality of scan lines in each of the plurality of subframes included in one frame. A scan driver sequentially applying a data signal to a red light emitting subframe among one frame to the plurality of red data lines, a signal corresponding to a black gray level to the remaining subframes, and one frame to the plurality of green data lines The data signal is applied to the green light emitting subframe, and the black And a data driver for applying a signal corresponding to the plurality of blue data lines, applying a data signal to a blue light emitting subframe among one frame, and applying a signal corresponding to a black gray level to the other subframes. At least one of the number of the red light emitting subframes included, the number of the green light emitting subframes included in one frame, and the number of the blue light emitting subframes included in one frame may be different from the rest.

According to a second aspect of the present invention, there is provided a method of driving a light emitting display device that displays one image in one frame, wherein one frame sequentially applies a scan signal to a plurality of scan lines, the data line connected to a red pixel, and a blue pixel. Applying a data voltage to the data line connected to the data line connected to the green pixel, and sequentially applying a scan signal to the plurality of scan lines, the data line connected to the red pixel, the data line connected to the blue pixel, and the green pixel Applying a data voltage to some of the data lines connected to the data lines and applying a predetermined voltage to the remaining data lines; and sequentially applying a scan signal to the plurality of scan lines, wherein the data lines are connected to the red pixels, The predetermined voltage on a data line connected to a blue pixel and a data line connected to the green pixel; It provides a method of driving a light emitting display including the step of applying.

Hereinafter, preferred embodiments of the present invention may be easily implemented by those skilled in the art with reference to FIGS. 1 to 4 as follows.

1 illustrates a light emitting display device according to an embodiment of the present invention.

Referring to FIG. 1, the light emitting display device includes a scan driver 10, a data driver 20, an image display unit 30, and a timing controller 50. The light emitting display device displays an image on the image display unit 30 in units of frames. One frame is composed of a plurality of subframes.

The scan driver 10 drives the scan lines S1 to Sn. The scan driver 10 generates a scan signal in response to the scan driver control signals SCS, and sequentially supplies the generated scan signal to the scan lines S1 to Sn. The scan driver 10 sequentially applies the scan signals S1 to Sn to the plurality of scan lines every subframe.

The data driver 20 drives the data lines D1 (R), D1 (G), D1 (B) to Dm (R), Dm (G), and Dm (B). The data driver 20 generates data voltages in response to the data driver control signals DCS and the video data, and generates the data voltages in the data lines D1 (R), D1 (G), and D1. (B) to Dm (R), Dm (G), and Dm (B)). The data driver 20 may include data lines D1 (R), D1 (G), D1 (B) to Dm (R), Dm (G), and Dm (e) in light emitting subframes among a plurality of subframes constituting one frame. B)) and supplies a data voltage, and the data lines D1 (R), D1 (G), D1 (B) to Dm (R), Dm ( G), Dm (B)) applies a voltage corresponding to black gradation. The operation may be performed by the data driver 20 having a function of selecting a data voltage and a voltage corresponding to the black gray level, and the data driver 20 timing the video data corresponding to the black gray level. It may be performed by receiving from the control unit 50. In particular, when the latter method is performed, the timing controller 50 transmits the video data corresponding to the video data input to the timing controller 50 in the predetermined period to the data driver 20 and the black gray level in the remaining period. It must be possible to deliver the corresponding video data.

The image display unit 30 includes a plurality of pixels 40 defined by the scan lines S1 to Sn and the data lines D1 to Dm. In addition, the image display unit 30 receives the first power supply voltage VDD and the second power supply voltage VSS from the outside. Here, the first power supply voltage VDD and the second power supply voltage VSS are transferred to the respective pixels 40. Each of the pixels 40 displays an image corresponding to the data signal supplied thereto.

The timing controller 50 supplies the scan driver control signal SCS to the scan driver 10, and supplies the data driver control signal DCS and video data Data to the data driver. The video data may include red, green, and blue video data. In addition, the video data may additionally include white video data.

On the other hand, the light emitting device of the light emitting display generates light having different luminance even when the same data signal is applied due to material characteristics. For example, the luminous efficiency of the green light emitting device may be relatively lower than that of the blue light emitting device and the red light emitting device. As such, when light having different efficiencies is generated for each light emitting device, white balance is not matched to display an image having a desired color. Accordingly, in the light emitting display device according to the exemplary embodiment of the present invention, the number of light emitting subframes among the subframes constituting one frame varies depending on the red light emitting device, the green light emitting device, and the blue light emitting device in consideration of white balance. In other words, in one embodiment of the present invention, the largest number of light emitting subframes of the data lines D_G1 to D_Gm transferring the data voltage to the green pixel is set to the largest value, and the data line D1 transferring the data voltage to the blue pixel. The number of light emitting subframes of (B) to Dm (B) and the data lines D1 (R) to Dm (R) for transmitting the data voltage to the red pixel is set small. Then, the white balance of the red pixels, the green pixels, and the blue pixels can be matched to some extent, thereby improving the display quality.

FIG. 2 is a diagram illustrating an example of a data driver employed in the light emitting display of FIG. 1, in particular, when the data driver 20 has a function of selecting a data voltage and a voltage corresponding to a black gray level.

Referring to FIG. 2, the data driver includes a shift register 21, a data latch 22, a D / A converter 23, and a selector 24. The shift register 21 controls the data latch 22 in response to the horizontal clock signal HCLK and the horizontal synchronization signal HSYNC. The horizontal clock signal HCLK and the horizontal synchronization signal HSYNC are one of the data driver control signals DCS of FIG. 1. The data latch 22 sequentially receives the red video data R, the green video data G, and the blue video data B, and outputs them in parallel to the D / A converter 23. The data latch 22 is controlled by a control signal output from the shift register 21. The D / A converter 23 converts a signal output in parallel from the data latch and converts the signal into an analog voltage. The selector 24 sets the output voltage of the D / A converter 23 in the light emitting subframe period to the data lines D1 (R), D1 (G), D1 (B) to Dm (R), Dm (G) and Dm. (B)), and outputs a voltage V _black corresponding to the black gradation to the data line in the non-emission subframe period. In this case, the number of light emitting subframes among the subframes constituting one frame varies depending on the red light emitting device, the green light emitting device, and the blue light emitting device in consideration of the white balance.

3 is a circuit diagram illustrating an example of a red pixel, a blue pixel, and a green pixel employed in the light emitting display device of FIG. 1.

Referring to FIG. 3, the red pixel 40 (R) includes a red light emitting element OLED (R) and a pixel circuit, and the green pixel 40 (G) includes a green light emitting element OLED (G) and A pixel circuit is included, and the blue pixel 40 (B) includes a blue light emitting element OLED (B) and a pixel circuit. Each pixel circuit includes a switching transistor M1, a driving transistor M2, and a capacitor Cst.

The switching transistor M1 transfers the data voltage applied to the data line Dm to the capacitor Cst according to the scan signal applied to the scan line Sn. The capacitor Cst stores the transferred data voltage in a period during which the scan signal is applied and maintains it for a period during which the scan signal is not applied. The driving transistor M2 transfers a current corresponding to the voltage of the capacitor Cst to the light emitting device OLED. The light emitting device OLED emits light according to the transmitted current. The first power supply voltage VDD is applied to the source of the second transistor, and the second power supply voltage VSS is applied to the light emitting device OLED.

4 is a signal diagram illustrating a driving method for driving the light emitting display device of FIG. 1. This signal diagram is an example of a case where white balance is achieved by extending the light emission period of the green light emitting device because the light emitting efficiency of the green light emitting device is the lowest.

1 and 4, one frame includes four subframes SF1, SF2, SF3, and SF4 as an example of a plurality of subframes. Scan signals are sequentially applied to the scan lines S1 to Sn in each subframe period.

In the red data line Dm (R) that applies a data voltage to the red pixel, the first subframe SF1 is a light emitting subframe, and the red data line is applied when the scan signal of the first subframe SF1 is applied. Data voltages V _data 1 (R) to V _data n (R) are applied to Dm (R). Therefore, the red pixels connected to the red data line Dm (R) emit light in response to the data voltages V _data 1 (R) to V _data n (R) applied in the first subframe SF1 period. do. The second to fourth subframes SF2, SF3, SF4 are non-emission subframes, and when the scan signals of the second to fourth subframes SF2, SF3, SF4 are applied, the red data line Dm (R )) Is applied a voltage V _black (R) corresponding to the black gradation. Accordingly, the red pixels connected to the red data line Dm (R) may be disposed according to the voltage V _black (R) corresponding to the black gray level applied in the second to fourth subframes SF2, SF3, SF4. The image corresponding to the black gradation is displayed.

In the case of the green data line Dm (G) that applies a data voltage to the green pixel, the first and second subframes SF1 and SF2 are light emitting subframes and are connected to the green data line Dm (G). The green pixels are applied to the data voltages V _data 1 (G) to V _data n (G) applied to the green data line Dm (G) when the scan signals of the first and second subframes SF1 and SF2 are applied. Will emit light. The third and fourth subframes SF3 and SF4 are non-emission subframes. The green pixels connected to the green data line Dm (G) have scan signals of the third and fourth subframes SF3 and SF4. When applied, an image corresponding to the black gray level is displayed according to the voltage V _black (G) corresponding to the black gray applied to the green data line Dm (G).

In the case of the blue data line Dm (B) that applies a data voltage to the blue pixel, the first subframe SF1 is a light emitting subframe, and the blue pixels connected to the blue data line Dm (B) are firstly formed. When the scan signal of the subframe SF1 is applied, light is emitted corresponding to the data voltages V _data 1 (B) to V _data n (B) applied to the blue data line Dm (B). The second to fourth subframes SF2, SF3, SF4 are non-emission subframes, and the blue pixels connected to the blue data line Dm (B) are the second to fourth subframes SF2, SF3, SF4. When the scan signal is applied, the image corresponding to the black gray level is displayed in response to the voltage V _black (B) corresponding to the black gray applied to the blue data line Dm (B).

As described above, one frame may be divided into light emitting subframes and non-light emitting subframes to improve luminance nonuniformity, and white balance may be achieved by increasing driving time of a green light emitting device having a relatively low luminous efficiency.

In FIG. 4, if the number of subframes is four, but the number of subframes is two or more, the object of the present invention can be achieved. In addition, although the lengths of the four subframes are the same in FIG. 4, even if the lengths of the subframes constituting one frame are different, the object of the present invention can be achieved. In FIG. 4, only the case where the number of light emitting subframes of the green data line Dm (G) is different from the number of light emitting subframes of the remaining data lines Dm (R) and Dm (B) is represented. The case where the data Dm (R), the green data Dm (G), and the blue data Dm (B) are different from each other is also included in the scope of the present invention. In addition, although the light emitting subframe is located in front of one frame in FIG. 4, the object of the present invention can be achieved even if the light emitting subframe is located at the middle or the back of one frame.

The voltage corresponding to the black gradation is a voltage that causes the pixel to represent the black gradation. However, an error in the threshold voltage V _TH of the transistor may occur in each pixel, so that a voltage corresponding to the black gray level in one pixel may have a gray gray level instead of black in another pixel having a large error in the threshold voltage. Can be. Therefore, preferably, the voltage corresponding to the black gradation is a voltage such that all the pixels included in the image display unit 30 express the black gradation. The voltage corresponding to the black gray may be, for example, the first power voltage VDD. In addition, the red data line (Dm (R)) is applied voltage (V _black (R)) corresponding to a black gradation, a green data line (Dm (G)) V _black (voltage corresponding to the black gradation to be applied (in which the G)) and the voltages V _black (B) corresponding to the black gray applied to the blue data line Dm (B) may be different from each other or may be the same.

Hereinafter, the error _{ΔV th} of the threshold voltage of the light emitting display device according to the related art and the light emitting display device according to the first embodiment of the present invention is the average of the error of luminance, that is, the average of the current flowing through the light emitting device ( Let's examine the effect on E (△ I _OLED )).

The current flowing through the light emitting device OLED according to the related art, that is, continuously emitting light for one frame period is represented by Equation 1.

I _OLED1 = I _D = (β / 2) (V _GS1 -V _TH ) ²

Here, I _OLED1 is a current flowing through the light emitting device OLED in the case of the prior art, I _D is a current flowing in the drain direction from the source of the drive transistor M2, and V _GS1 is the driving transistor M2 in the case of the prior art. The voltage between the gate and the source, V _TH is the threshold voltage of the driving transistor M2, β represents the gain factor.

When an error _{ΔV th} occurs in the threshold voltage in the light emitting display device according to the related art, the error _{ΔI OLED1} of the current flowing through the light emitting device may be expressed by Equation 2.

_{ΔI OLED1} = (β / 2) (V _GS1 -V _TH + ΔV _th ) ^2- (β / 2) (V _GS1 -V _TH ) ²

= (β / 2) ( _{2ΔV th} (V _GS1 -V _TH ) + ΔV _th ² )

In the conventional light emitting display device, since the same current flows for one frame period, the average E ( _{ΔI OLED1} ) of the current flowing through the light emitting device is equal to the error ( _{ΔI OLED1} ) flowing through the light emitting device. Has a value. That is, the average E of the currents flowing through the light emitting device E ( _{ΔI OLED1} ) may be expressed by Equation 3 below.

E ( _{ΔI OLED1} ) = _{ΔI OLED1} = (β / 2) ( _{2ΔV th} (V _GS1 -V _TH ) + ΔV _th ² )

In the case of the light emitting display device according to the present invention, when an error _{ΔV th} occurs in the threshold voltage, the error _{ΔI OLED2} of the current flowing through the light emitting device may be expressed by Equation 4 below.

_{ΔI OLED2} = (β / 2) (V _GS2 -V _TH + _{ΔV th} ) ^2- (β / 2) (V _GS2 -V _TH ) ²

In Equation 4, V _GS2 represents a voltage between the gate and the source of the driving transistor M2 of the light emitting display according to the present invention. In a light emitting display device according to an embodiment of the present invention, one frame has N subframes, and only the first subframe of the subframes emits light according to the data voltage V _data , and the remaining subframes emit light according to the off-state voltage. If it is assumed that the luminance of the black gradation is displayed, and the luminance is proportional to the current flowing through the light emitting device, it should be V _GS2 -V _TH = (V _GS1 -V _TH ) √N in the first subframe. The driving method according to the first embodiment of the invention and the driving method according to the prior art display the same luminance on an average on one frame. Where √N is the square root of N. Therefore, _{ΔI OLED2} may be expressed as in Equation 5.

ΔI _OLED2 = (β / 2) ((V _GS1 -V _TH ) √N + ΔV _th ) ^2- (β / 2) ((V _GS1 -V _TH ) √N) ²

= (β / 2) (2 △ V _th (V _GS1 -V _TH ) √N + ΔV _th ² )

Since the light emitting device emits light only in the first subframe period in one frame period and is off in the remaining (N-1) subframe period, the average E of the currents flowing through the light emitting device (E ( _{ΔI OLED2} )) is expressed by the following equation. It can be expressed as 6.

E ( _{ΔI OLED2} ) = ΔI _OLED2 / N = (β / 2) (2ΔV _th (V _GS1 -V _TH ) / √N + ΔV _th ² / N)

Equation 3 expressing an average error E ( _{ΔI OLED1} ) of a light emitting display device according to the related art and an average current error E ( _{ΔI OLED2} ) of a light emitting display device according to an embodiment of the present invention. In comparison with Equation (6), it can be seen that the average E ( _{ΔI OLED2} ) of the error of the current of the light emitting display according to the embodiment of the present invention becomes much smaller as N increases. Accordingly, in the light emitting display device according to the present invention, the uniformity can be improved by reducing the influence of the error of the threshold voltage V _TH on the luminance.

In a driving method having a similar effect, by adding one transistor that operates according to the emission control signal between the driving transistor M2 and the light emitting element OLED of FIG. 3, a current is applied to the light emitting element OLED according to the emission control signal. It is conceivable to think of a driving method for controlling the supply of. That is, a method of distinguishing the light emission period from the non-light emission period in one frame according to the light emission control signal can be considered. However, according to this driving method, one more transistor operating in accordance with the light emission control signal has to be added, so the complexity increases and the light emission control signal needs to be additionally generated. Since the light emission control line to be transmitted to is added, there is a fear that the aperture ratio of the display device is reduced. On the contrary, the light emitting display device according to the present invention does not require the addition of a transistor operating in accordance with the light emission control signal and the light emission control line for transmitting the light emission control signal, or the design of a new scan driver. By increasing, there is an advantage that the light emission period and the non-light emission period can be distinguished in one frame.

The above detailed description and drawings are merely exemplary of the present invention, which are used only for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention as defined in the claims or the claims. Accordingly, those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical protection scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

As described above, the light emitting display device and the driving method thereof according to the exemplary embodiment of the present invention have an advantage of improving the uniformity of luminance of the light emitting display device.

In addition, the light emitting display device and the driving method thereof according to an exemplary embodiment of the present invention have an advantage in that the light emission period and the non-light emission period can be distinguished within one frame by increasing only the operating frequency of a scan driver widely used.

In addition, the light emitting display device and the driving method thereof according to the embodiment of the present invention have an advantage that white balance can be adjusted.

Claims (11)

A plurality of red pixels connected to a plurality of scan lines and a red data line, a plurality of green pixels connected to the plurality of scan lines and a green data line, and a plurality of blue pixels connected to the plurality of scan lines and a blue data line, An image display unit for displaying one image in one frame; A scan driver sequentially applying a scan signal to each of the plurality of scan lines among the plurality of subframes included in one frame; The data signal is applied to the red light emitting subframe of one frame to the plurality of red data lines, and the signal corresponding to the black gray level is applied to the remaining subframes. Applies a signal corresponding to a black gray level to the remaining subframes, applies a data signal to a blue light emitting subframe among one frame to the plurality of blue data lines, and applies a signal corresponding to the black gray level to the remaining subframes It includes a data driver to And at least one of the number of the red light emitting subframes included in one frame, the number of the green light emitting subframes included in one frame, and the number of the blue light emitting subframes included in one frame are different from the others. The method of claim 1, The data driver A shift register configured to output a latch control signal in response to a clock signal and a synchronization signal; A data latch sequentially receiving red, green, and blue video data according to the latch control signal and outputting the video data in parallel; A D / A converter for outputting a voltage obtained by analog converting the output of the data latch; And And a selector for selectively outputting an output voltage of the D / A converter and a voltage corresponding to a black gray level. The method of claim 2, The selector The output voltage of the D / A converter is output to the red data line in the red light emitting subframe of one frame, and the voltage corresponding to the black gray level is output to the red data line in the other subframe. The output voltage of the D / A converter is output to the green data line in a green light emitting subframe of one frame, and the voltage corresponding to the black gray level is output to the green data line in a remaining subframe. The blue light emitting display device outputs the output voltage of the D / A converter to the blue data line in one blue frame, and the voltage corresponding to the black gray level to the blue data line in the other subframe. The method of claim 1, Transmitting a scan driver control signal to the scan driver, transmitting a data driver control signal to the data driver, and selectively transmitting video data corresponding to the input video data and video data corresponding to the black gradation to the data driver. A light emitting display further comprising a timing controller. The method of claim 1, A first power supply voltage and a second power supply voltage are applied to the image display unit. The voltage corresponding to the black gradation is one voltage selected from the group consisting of the first power supply voltage and the second power supply voltage. The method of claim 1, And a voltage corresponding to the black gradation is a voltage which causes the pixels included in the image display unit to express the black gradation. The method of claim 1, A plurality of subframes included in one frame have the same period. The method of claim 1, The light emitting display device having the largest number of light emitting subframes included in one frame of the red, green, and blue pixels having the lowest luminous efficiency. In the driving method of a light emitting display device which displays one image in one frame, one frame (a) sequentially applying a scan signal to the plurality of scan lines, and applying a data voltage to a data line connected to a red pixel, a data line connected to a blue pixel, and a data line connected to a green pixel; (b) sequentially applying a scan signal to the plurality of scan lines, and applying a data voltage to a data line of a portion of a data line connected to the red pixel, a data line connected to the blue pixel, and a data line connected to the green pixel; Applying a predetermined voltage to the remaining data lines; And (c) sequentially applying a scan signal to the plurality of scan lines, and applying the predetermined voltage to a data line connected to the red pixel, a data line connected to the blue pixel, and a data line connected to the green pixel. A method of driving a light emitting display device. The method of claim 9, And the predetermined voltage is a voltage corresponding to black gradation. The method of claim 9, In the step (b), the light emitting efficiency of the pixel connected to the data line to which the data voltage is applied is lower than the light emitting efficiency of the remaining pixels.

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