KR100688799B1 - Light emitting display, and method for driving light emitting display and pixel circuit - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device, a method of driving a light emitting display device, and a method of driving a pixel circuit, and more particularly, to a light emitting display device capable of improving the uniformity of luminance, a method of driving a light emitting display device, and a method of driving a pixel circuit. will be.

According to an embodiment of the present invention, a scan driver sequentially applies a scan signal to a plurality of scan lines for each subframe among a plurality of subframes included in one frame, and a plurality of subframes in at least one light emitting subframe period among a plurality of subframes included in one frame. A data driver for applying a data voltage to a data line of the data line and applying a voltage corresponding to a black gray level to the plurality of data lines in at least one non-light-emitting subframe period of the plurality of subframes included in one frame; A light emitting display device is provided that includes an image display portion for displaying an image in accordance with a scan signal applied to a scan line and a voltage applied to the plurality of data lines.

The present invention has the advantage of improving the uniformity of the luminance of the light emitting display device.

Description

LIGHT EMITTING DISPLAY, AND METHOD FOR DRIVING LIGHT EMITTING DISPLAY AND PIXEL CIRCUIT}             

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, a method of driving a light emitting display device, and a method of driving a pixel circuit, and more particularly, to a light emitting display device capable of improving the uniformity of luminance, a method of driving a light emitting display device, and a method of driving a pixel circuit. will be.

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, it is an object of the present invention to provide a light emitting display device, a method of driving a light emitting display device, and a method of driving a pixel circuit, which emit light in only a part of one frame, thereby improving the uniformity of luminance.

As a technical means for achieving the above object, the first aspect of the present invention is a scan driver for sequentially applying a scan signal to a plurality of scan lines for each subframe of a plurality of subframes included in one frame, included in one frame A data voltage is applied to a plurality of data lines in at least one light emitting subframe period of a plurality of subframes, and blacked in the plurality of data lines in at least one non-light emitting subframe period of a plurality of subframes included in one frame. A light emitting display device includes a data driver for applying a voltage corresponding to a gray level, and an image display unit for displaying an image according to scan signals applied to the plurality of scan lines and voltages applied to the plurality of data lines.

According to a second aspect of the present invention, a scan driver for applying a scan signal to a plurality of scan lines, a data driver for applying a voltage to a plurality of data lines, and an image according to a scan signal applied to the scan line and a voltage applied to the data line A method of driving a light emitting display device having an image display unit for displaying a light source, the method comprising: (a) sequentially applying a scan signal to a plurality of scan lines and applying a data voltage to a plurality of data lines within one frame period; and ( and b) sequentially applying a scan signal to a plurality of scan lines and applying a predetermined voltage to the plurality of data lines. Preferably, the predetermined voltage is a voltage corresponding to black gradation.

According to a third aspect of the present invention, a first transistor transfers a voltage applied to a data line according to a scan signal applied to a scan line, a capacitor to store a voltage corresponding to the transferred voltage, and a current corresponding to a voltage stored in the capacitor. A method of driving a pixel circuit including a second transistor for transmitting a light emitting device to a light emitting device, the method comprising: at least one light emitting subframe and at least one non-light emitting subframe within one frame period, wherein the light emitting subframe is connected to the scan line. Storing a voltage corresponding to a data voltage applied to the data line while the scan signal is applied to the capacitor; And transmitting a current corresponding to a voltage stored in the capacitor to the light emitting device, wherein the non-light emitting subframe receives a voltage corresponding to a black gray applied to the data line while a scan signal is applied to the scan line. A method of driving a pixel circuit, the method comprising: storing the capacitor and transferring a current corresponding to the voltage stored in the capacitor to the light emitting device.

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 to Dm. The data driver 20 generates data voltages in response to the data driver control signals DCS and the video data Data, and supplies the generated data voltages to the data lines D1 to Dm. The data driver 20 supplies a data voltage to the data lines D1 to Dm during the light emitting subframe period among the plurality of subframes constituting one frame, and the non-light emitting subframe period among the plurality of subframes constituting one frame. The voltage corresponding to the black gray level is applied to the data lines D1 to Dm. Such an 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 may also perform video data corresponding to the black gray level. It may be performed by receiving from the timing controller 50. In particular, when the latter method is performed, the timing controller 50 delivers 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.

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 video data Data and outputs the data data to the D / A converter 23 in parallel. 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 outputs the output voltage of the D / A converter 23 to the data line in the light emitting subframe period, and outputs the voltage V _black corresponding to the black gray level as the data line in the non-light emitting subframe period.

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

Referring to FIG. 3, a pixel includes an OLED and a pixel circuit. The 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.

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.

The first subframe SF1 is a light emitting subframe, and when the scan signal of the first subframe SF1 is applied, the data voltages V _data 1 to V _data n are applied to the data line Dm. Therefore, the image display unit 30 emits light corresponding to the data voltages V _data 1 to V _data n applied in the first subframe SF1 period.

The second to fourth subframes SF2, SF3, SF4 are non-emission subframes, and are blocked on the data line Dm when a scan signal of the second to fourth subframes SF2, SF3, SF4 is applied. The voltage V _black corresponding to the gray level is applied. Therefore, the image display unit 30 displays an image corresponding to the black gray level according to the voltage corresponding to the black gray level applied in the second to fourth subframes SF2, SF3, SF4.

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, in FIG. 4, only the first subframe SF1 is a light emitting subframe, and the remaining subframes SF2, SF3, SF4 are non-light emitting subframes, but one or more subframes among the plurality of subframes are light emitting subframes. If more than one subframe is a non-light emitting subframe, the object of the present invention can be achieved. In the case of the light emitting subframe in two or more subframes, the data voltage transmitted to one pixel may be the same for all light emitting subframes included in one frame or may be different for each light emitting subframe. 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 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 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.

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 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 per 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 prior art and an average error E ( _{ΔI OLED2} ) of a current 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, the light emitting display device according to the present invention has an effect of improving the uniformity 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, the method of driving the light emitting display device, and the method of driving the pixel circuit 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, the method of driving the light emitting display device, and the method of driving the pixel circuit according to an exemplary embodiment of the present invention increase the operating frequency of the scan driver, which is widely used in the related art, thereby reducing the light emission period and the non-light emission period within a frame. It has the advantage of being distinguishable.

Claims (10)

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; A data voltage is applied to a plurality of data lines in at least one light emitting subframe period among a plurality of subframes included in one frame, and the data voltage is applied in at least one non-light emitting subframe period of a plurality of subframes included in one frame. A data driver for applying a voltage corresponding to the black gray level to the data line of the data line; And An image display unit for displaying an image according to a scan signal applied to the plurality of scan lines and a voltage applied to the plurality of data lines, 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 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 A light emitting display device including a selector for outputting an output voltage of the D / A converter to the data line in the light emitting subframe period, and a voltage corresponding to the black gray level to the data line in the non-light emitting subframe period . delete The method of claim 1, Transfers a scan driver control signal to the scan driver, transmits a data driver control signal to the data driver, transfers video data corresponding to the input video data to the data driver for a predetermined period, and to a black gray level for the remaining period. And a timing controller configured to transfer corresponding video data. 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 the one frame have the same period. A scan driver for applying a scan signal to the plurality of scan lines, a data driver for applying a voltage to the plurality of data lines, and an image display unit for displaying an image according to the scan signal applied to the scan line and the voltage applied to the data line In a method of driving a light emitting display device, Within one frame (a) sequentially applying scan signals to the plurality of scan lines, and selecting a data voltage by the data driver to apply data voltages to the plurality of data lines; And and (b) sequentially applying scan signals to the plurality of scan lines, and applying a predetermined voltage to the plurality of data lines by selecting a predetermined voltage by the data driver. The method of claim 7, wherein And the predetermined voltage is a voltage corresponding to black gradation. A first transistor for transmitting a voltage applied to the data line according to a scan signal applied to the scan line, a capacitor for storing a voltage corresponding to the transferred voltage, and a current for transmitting a current corresponding to the voltage stored in the capacitor to the light emitting device. In a method of driving a pixel circuit comprising two transistors, At least one light emitting subframe and at least one non-light emitting subframe within one frame period, The light emitting subframe may include: storing a data voltage applied to the data line by selecting the data voltage by the data driver while the scan signal is applied to the scan line; And transmitting a current corresponding to the voltage stored in the capacitor to the light emitting device. The non-light emitting subframe may include: storing the black gray voltage applied to the data line by selecting the black gray voltage by the data driver while the scan signal is applied to the scan line in the capacitor; And transmitting a current corresponding to the voltage stored in the capacitor to the light emitting device. The method of claim 9, A first power supply voltage is applied to the source of the second transistor, And a voltage corresponding to the black gray level is the first power supply voltage.

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