KR20140075352A - Organic Light Emitting diode display and method of driving the same - Google Patents

Abstract

The present invention provides an organic light emitting diode display which includes an organic light emitting panel which comprises: a pixel which includes a light emitting transistor which controls the light emitting on-duty of a light emitting diode; and an image analysis part which analyzes an input image and calculates the light emitting on-duty according to the consumption current and the brightness of the input image. The light emitting on-duty is reduced according to an increase in consumption current and brightness of the input image.

Description

[0001] The present invention relates to an organic light emitting diode (OLED) display device and a method of driving the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OLED display, and more particularly, to an OLED display and a driving method thereof.

2. Description of the Related Art [0002] As an information-oriented society develops, demands for a display device for displaying an image have increased in various forms. Recently, a liquid crystal display (LCD), a plasma display panel (PDP) Various flat display devices such as organic light emitting diode (OLED) display devices have been utilized.

Of these flat panel display devices, organic light emitting element display devices have recently been widely used because they have advantages of miniaturization, weight reduction, thinness, and low power driving.

As an organic light emitting diode display device, an active matrix type organic light emitting diode display device in which a switching transistor is formed in each of pixels arranged in a matrix form is widely used.

In the organic light emitting diode display, a light emitting current is generated according to the data voltage applied to the driving transistor, and the organic light emitting diode emits light as it is applied to the organic light emitting diode. Here, the brightness of the emitted light depends on the magnitude of the light emission current, that is, the magnitude of the data voltage.

Regardless of the brightness of the image, if the same voltage or current is applied to the same gray level to emit light, it is not preferable from the viewpoint of power consumption reduction.

Accordingly, a peak luminance control method has been proposed as one of methods for reducing power consumption, and will be described with reference to FIG. 1 is a view for explaining a conventional peak luminance control method.

Referring to FIG. 1, a peak curve according to an average picture level (APL) is shown on the left, and a gamma curve is shown on the right.

Looking at the peak curve, the maximum luminance for the maximum gradation (for example, 255 gradations) of the image is set along the graph according to the APL of the input image. For example, when the APL reaches approximately 25%, the peak luminance becomes the maximum luminance. When the APL exceeds 25%, the maximum luminance decreases to the noraml luminance according to the APL. Accordingly, when the APL of the input image is calculated, the maximum brightness for the corresponding APL can be calculated.

As such, when the maximum luminance is calculated, output gamma is generated for it. Regarding the gamma curve on the right side, the gamma curve Gp with respect to the peak luminance and the gamma curve Gn with respect to the normal luminance are shown as an upper limit and a lower limit. When the maximum luminance for 255 gradations is calculated as the maximum gradation, a gamma curve with the calculated maximum luminance as the end point, that is, an output gamma curve can be generated.

The corresponding image is displayed using the gamma voltage generated through the output gamma curve thus generated.

As described above, the peak luminance and the normal luminance are set as the upper limit and the lower limit, and the power consumption can be reduced by lowering the maximum luminance as the image becomes brighter

However, the conventional peak brightness control method is a hold type method of controlling the magnitude of voltage or current, which maintains the luminance of light substantially emitted during one frame. Therefore, there is a limitation in improvement of moving picture quality as a drawback of the hold type system.

In addition, since the output gamma changes according to the input image, the white balance of the displayed image may be distorted due to a deviation.

As described above, if the conventional peak luminance control method is used, the image quality deteriorates.

Disclosure of the Invention Problems to be Solved by the Invention The present invention has a problem to provide a method for improving the image quality of an OLED display.

According to an aspect of the present invention, there is provided an organic light emitting display comprising: an organic light emitting panel including a pixel including a light emitting transistor for adjusting an on-duty of a light emitting diode; And an image analyzer for analyzing the input image and calculating the light emission on-duty according to the brightness or consumption current of the input image, wherein the light emission on- A light emitting element display device is provided.

Here, the image analyzing unit for calculating the on-duty according to the brightness of the input image may include an APL calculating unit for calculating an average image level of the input image; A luminance ratio calculating unit for calculating a maximum luminance with respect to a peak luminance according to the calculated average image level; And an emission on duty calculation unit for calculating the emission on duty according to the calculated maximum luminance with respect to the peak luminance.

An image analyzing unit for calculating an on-duty according to a consumption current of the input image includes a consumption current calculator for calculating a consumption current of the input image; A target current calculating unit for calculating a target current according to the calculated consumed current; And an emission on duty calculation unit for calculating the emission on duty according to the calculated target current.

In displaying the input image, the same gamma voltage may be used irrespective of the brightness or current consumption of the input image.

In another aspect, the present invention includes a step of analyzing an input image and calculating an on-duty of the light-emitting diode according to brightness or current consumption of the input image, wherein the on- And the driving voltage of the organic light emitting diode display decreases as the current increases.

The calculating the light emission on duty according to the brightness of the input image may include calculating an average image level of the input image; Calculating a maximum luminance with respect to a peak luminance according to the calculated average image level; And calculating the light emission on duty according to the calculated maximum luminance with respect to the peak luminance.

The step of calculating an on-duty according to the consumption current of the input image may include calculating a consumption current of the input image; Calculating a target current according to the calculated consumed current; And calculating the light emission on duty according to the calculated target current.

In displaying the input image, the same gamma voltage may be used irrespective of the brightness or current consumption of the input image.

According to the present invention, the light emission on-duty is adjusted according to the brightness of the image and the consumption current. Accordingly, it can be driven in an impulse manner unlike the conventional hold mode. Therefore, it is possible to improve the picture quality in moving picture display.

In addition, since a single gamma curve is used, a change in white balance does not substantially occur.

In addition, when the light emission on-duty is adjusted according to the consumption current, the consumption current can be improved.

As a result, according to the present invention, image quality is improved and current consumption can be improved.

1 is a view for explaining a conventional peak luminance control method
BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]
3 is a circuit diagram schematically illustrating a pixel structure of an OLED display according to a first embodiment of the present invention.
4 is a view schematically showing an image analysis unit according to an embodiment of the present invention.
FIG. 5 is a waveform diagram showing a state in which the light emission on duty is adjusted according to the first embodiment of the present invention; FIG.
FIG. 6 is a diagram showing a change in color according to an image in the related art and the first embodiment of the present invention. FIG.
7 is a view schematically showing an image analysis unit according to a second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic view illustrating an OLED display according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing a pixel structure of an OLED display according to a first embodiment of the present invention Circuit diagram.

2 and 3, the organic light emitting diode display 100 according to the first embodiment of the present invention may include an organic luminescent panel 110 and a driving circuit for driving the organic luminescent panel 110 .

The driving circuit may include a data driving circuit 120, a scan driving circuit 130, a timing control circuit 140, a gamma voltage generating circuit 150, and an image analysis unit 200.

The timing control circuit 140 receives a vertical / horizontal synchronizing signal, a clock signal, a data enable signal, and the like from an external system through an interface such as a Low Voltage Differential Signaling (LVDS) interface or a Transition Minimized Differential Signaling As shown in FIG.

Using such a timing signal, the timing control circuit 140 can generate a data control signal DCS for controlling the data driving circuit 120 and a scan control signal SCS for controlling the scan driving circuit 200 have.

On the other hand, the timing control circuit 140 receives a digital data signal (RGB) for image display from an external system, processes it, and supplies the digital data signal RGB to the data driving circuit 120.

The data driving circuit 120 may be formed of a plurality of driving ICs or may be formed directly on the organic light emitting panel 110, for example. The data driving circuit 120 is connected to the organic light emitting panel 110 through a COG (Chip On Glass) process or a COF (Chip On Film) process and connected to the corresponding data line DL .

The data driving circuit 120 receives the data signal and the data control signal DCS from the timing control circuit 140 and outputs the analog data voltage to the corresponding data line DL in response thereto.

The gamma voltage generating circuit 150 generates a gamma voltage and supplies it to the data driving circuit 120. The data voltage corresponding to the data signal RGB can be output using the gamma voltage thus supplied .

The scan driver circuit 130 may include a plurality of driver ICs or may be formed directly on the organic light emitting panel 110. [ The scan driving circuit 130 is connected to the organic luminescent panel 110 through a COG (Chip On Glass) process or a COF (Chip On Film) process, And can be connected to the control wiring EL.

The scan driving circuit 130 can sequentially scan the gate wiring GL and the light emission control wiring EL in response to the scan control signal SCS supplied from the timing control circuit 140. [

For example, each of the gate wiring GL and the light emission control wiring EL is sequentially scanned along the column direction for each frame. On the other hand, in each row line, the gate wiring GL and the light emission control wiring EL are scanned in accordance with the driving timing of the corresponding row line. That is, the gate wiring GL and the emission control wiring EL are scanned in accordance with the data writing process and the timing of the light emission process.

When the gate wiring GL and the light emission control wiring EL are selected and scanned, a gate signal and a light emission control signal for turning on the transistor corresponding to the wiring are outputted.

The organic light emitting panel 110 is a display panel for displaying an image, and a plurality of pixels P are arranged in a matrix form.

In the organic luminescent panel 110, a plurality of gate lines GL extend in the first direction along the row direction. The plurality of data lines DL extend in a column direction as a second direction crossing the first direction. The gate lines GL and the data lines DL intersecting with each other define a plurality of pixels P arranged in a matrix form.

On the other hand, in the organic luminescent panel 110, a light emission control wiring EL extending along the row direction corresponding to the gate wiring GL is formed for each row line.

Referring to FIG. 3, a plurality of transistors T1 to T3, a capacitor C, and an organic light emitting diode (OLED) may be formed in each pixel P.

The plurality of transistors T1 to T3 may include, for example, a switching transistor T1, a driving transistor T2, and a light emitting transistor T3.

As the transistors T1 to T3, a crystalline silicon transistor, an amorphous silicon transistor, an oxide transistor, or the like using silicon crystallized through, for example, a low-temperature crystallization process may be used, but the present invention is not limited thereto.

On the other hand, for the sake of convenience of explanation, a case where, for example, a P-type transistor is used as these transistors T1 to T3 will be described as an example.

The switching transistor Tl is connected to the corresponding gate wiring and data lines GL and DL. That is, the gate terminal and the source terminal of the switching transistor Tl are connected to the gate wiring and the data wiring GL and DL, respectively.

The driving transistor T2 is connected to the switching transistor T1. That is, the gate terminal of the driving transistor T2 is connected to the drain terminal of the switching transistor T1. On the other hand, the source terminal of the driving transistor T2 is connected to the high power supply voltage (Vdd) source.

The capacitor C is connected between the gate terminal of the driving transistor T2 and the source of the high power supply voltage (Vdd) to function as a storage capacitor.

The light emitting transistor T3 is connected between the driving transistor T2 and the light emitting diode OLED. Thus, the light emitting transistor T3 controls the light emitting current generated by the driving transistor T2 to be supplied to the light emitting diode OLED. That is, when the light emitting transistor T3 is turned on, a light emitting current is supplied to the light emitting diode OLED to have a light emitting state.

The turn-on / off operation of the light-emitting transistor T3 is applied through the light-emission control line EL to follow the light emission control signal. For example, when the emission control signal is at the low level, the light emitting transistor T3 is turned on, and when the light emission control signal is at the high level, the light emitting transistor T3 is turned off.

Meanwhile, according to the first embodiment of the present invention, the turn-on time of the light emitting transistor T2, that is, the light emission on duty is controlled according to the brightness of the image, which will be described in detail below.

FIG. 4 is a schematic diagram of an image analysis unit according to an exemplary embodiment of the present invention, and FIG. 5 is a waveform diagram illustrating a state in which light emission on duty is adjusted according to the first exemplary embodiment of the present invention.

Referring to FIG. 4, the image analysis unit 200 according to an exemplary embodiment of the present invention analyzes an input image and calculates an on-duty of the input image. The image analysis unit 200 may be included in the timing control circuit 140, but the present invention is not limited thereto. In the embodiment of the present invention, for convenience of explanation, a case where the image analysis unit 200 is configured in the timing control circuit 140 will be described as an example.

When the emission on-duty is calculated as the analysis result of the image analysis unit 200, a control signal reflecting the emission on-duty is transmitted to the scan driving circuit 130, and the output timing of the emission control line EL, that is, the emission on- .

The image analysis unit 200 may include an APL calculation unit 210, a luminance ratio calculation unit 220, and an emission on duty calculation unit 230.

The APL calculation unit 210 calculates an APL for an input image, that is, an average image level. The APL corresponds to the information indicating the brightness of the input image. For example, if the luminance and gradation of all the pixels are summed and then divided by the number of pixels, the APL can be calculated.

The calculated APL is input to the brightness ratio calculating unit 220. [ The luminance ratio calculating unit 220 calculates the ratio of the peak luminance to the maximum luminance. This can be referred to the conventional FIG. For example, when the APL is calculated, the maximum luminance for the APL of the input image can be determined through the peak curve. Therefore, the ratio of the peak luminance to the maximum luminance can be calculated.

The peak contrast information, that is, the luminance ratio information is input to the light emission on duty calculation unit 230. The light emission on duty calculation unit 230 calculates the light emission on duty according to the luminance ratio, that is, the maximum luminance.

In this regard, a relatively high APL image, that is, a bright image, has a low luminance ratio, and a relatively low APL image, that is, a dark image, has a high luminance ratio.

Therefore, the emission on-duty is short in the case of a relatively bright image, and the emission on-duty is long in the case of a relatively dark image. That is, as the image becomes brighter, the light emission on duty becomes shorter.

As described above, according to the first embodiment of the present invention, the light emission on duty is adjusted according to the brightness of the image, which can be referred to FIG. Referring to FIG. 5, on-duty of a low level is shortened as a turn-on level of a light emission control signal for a relatively bright image, and on-duty of a light emission control signal is increased for a relatively dark image. On the other hand, conventionally, the turn-on level of the emission control signal is fixed.

On the other hand, in the first embodiment of the present invention, it is preferable to use a single gamma voltage as the gamma voltage. For example, the gamma voltage generating circuit 150 may be configured to generate a gamma voltage according to a gamma curve implementing peak luminance. Accordingly, the same gamma voltage is generated regardless of the brightness of the image.

As described above, according to the first embodiment of the present invention, a single gamma voltage is used and the luminous on-duty is adjusted according to the brightness of the image.

Accordingly, it can be driven in an impulse mode different from the conventional hold mode in which light is emitted for the same time irrespective of the brightness of an image. Therefore, it is possible to improve the picture quality in moving picture display.

In this regard, reference may be made to Table 1 below. Table 1 is a table showing simulation results of MPRT (Motion Picture Response Time) of the OLED display according to the first embodiment of the present invention.

0 31 63 95 127 159 191 223 225 0 - 1.0 1.0 1.0 1.0 2.1 2.5 2.9 3.4 31 1.0 - 1.0 1.0 2.1 2.5 2.9 3.4 3.8 63 1.0 1.0 - 2.1 2.5 2.9 3.4 3.8 4.2 95 1.0 1.0 2.1 - 2.9 3.4 3.8 4.2 4.6 127 1.0 2.1 2.5 2.9 - 3.8 4.2 4.6 5.0 159 2.1 2.5 2.9 3.4 3.8 - 4.6 5.0 5.4 191 2.5 2.9 3.4 3.8 4.2 4.6 - 5.4 5.8 223 2.9 3.4 3.8 4.2 4.6 5.0 5.4 - 6.3 225 3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.3 -

In Table 1, the upper row and left adiabatic are the tone values respectively.

Referring to Table 1, it can be seen that the MPRT at the 120 Hz drive has an average of about 4 ms or less. On the other hand, in the conventional case, MPRT has approximately 8 ms. As described above, according to the embodiment of the present invention, the effect of driving at 240 Hz is demonstrated by 120 Hz driving, and the video quality is improved to a considerable extent.

In addition, since a single gamma curve is used, a change in white balance does not substantially occur. In this regard, reference can be made to Fig. FIG. 6 is a diagram illustrating a change in color according to an image according to the related art and the first embodiment of the present invention, and is based on a CIE coordinate system.

6, changes of R (red), G (green), B (blue), and gray color according to an image are conventionally large, whereas according to the present invention, Able to know.

Therefore, according to the embodiment of the present invention, the white balance according to the image is substantially the same.

As a result, according to the first embodiment of the present invention, considerable improvements can be made in terms of image quality as well as power consumption reduction.

7 is a view schematically showing an image analysis unit according to a second embodiment of the present invention.

The OLED display according to the second embodiment of the present invention is substantially similar to the first embodiment except for the image analysis unit. Therefore, a detailed description of a similar configuration to the first embodiment can be omitted.

Referring to FIG. 7, the image analyzer 300 according to the second embodiment of the present invention analyzes the consumption current of the input image and calculates the on-duty of the input image. The image analysis unit 300 may be configured in a timing control circuit (see 140 in FIG. 2), but the present invention is not limited thereto.

When the emission on-duty is calculated as the analysis result of the image analysis unit 300, the control signal reflecting the emission on-duty is transmitted to the scan driving circuit (see 130 in FIG. 2) Timing or emission on-duty is adjusted.

The image analyzing unit 300 according to the second embodiment may include a consumption current measuring unit 310, a target current calculating unit 320, and an emission on duty calculating unit 330.

The consumption current calculator 310 calculates consumption current for the input image.

The consumption current calculated in this manner is input to the target current calculation unit 320, and the target current corresponding to the consumption current is calculated. The target current calculation process is substantially similar to the maximum brightness calculation process for the APL in the first embodiment described above.

That is, in the first embodiment, the target current with respect to the consumption current can be determined through the so-called current peak curve, as the maximum luminance with respect to the APL is determined through the peak curve. Here, the current peak curve has a shape similar to the peak curve of the first embodiment. As the consumption current increases, the target current decreases. The peak current and the normal current can be set as the upper and lower limits.

The target current information is input to the light emission on duty calculation unit 330. The light emission on duty calculation unit 330 calculates the light emission on duty according to the target current. That is, the light emission on duty can be calculated according to the ratio of the target current to the peak current.

Therefore, in the case of an image with a relatively high current consumption, the emission on-duty is short, and in the case of an image with a relatively low current consumption, the emission on-duty is long. That is, as the consumption current of the image increases, the luminous on-duty becomes shorter.

As described above, according to the second embodiment of the present invention, the luminous on-duty is adjusted according to the consumption current of the image, which can be referred to FIG. 5 of the first embodiment.

On the other hand, in the second embodiment of the present invention, it is preferable to use a single gamma voltage as the gamma voltage. For example, the gamma voltage generating circuit (see 150 in FIG. 2) may be configured to generate a gamma voltage according to a gamma curve that implements peak current, i.e., peak brightness. Accordingly, the same gamma voltage is generated regardless of the consumption current of the image.

As described above, according to the second embodiment of the present invention, a single gamma voltage is used and the emission on-duty is adjusted according to the consumption current of the image.

Accordingly, it can be driven in an impulse manner unlike the conventional hold mode. Therefore, it is possible to improve the picture quality in moving picture display.

In addition, since a single gamma curve is used, a change in white balance does not substantially occur.

In addition, the consumption current can be improved. In this regard, for example, in realizing the luminance of 87 nits, the light emission on duty is set to 100% in the conventional case at 150 gradations, and a current of about 4.1 A is consumed in such a case. On the other hand, according to the second embodiment, the light emission on duty is set to 50% at 255 gradations, and in this case, a current of approximately 3.7 A is consumed. As described above, according to the embodiment of the present invention, a consumption current reduction effect also occurs.

The embodiment of the present invention described above is an example of the present invention, and variations are possible within the spirit of the present invention. Accordingly, the invention includes modifications of the invention within the scope of the appended claims and equivalents thereof.

200: image analysis unit 210: APL calculation unit
220: luminance ratio calculating unit 230: light emission on duty calculating unit

Claims (8)

An organic light emitting display comprising: a pixel including a light emitting transistor for controlling an on-duty of a light emitting diode;
And an image analyzer for analyzing the input image and calculating the light emission on-duty according to the brightness or current consumption of the input image,
The light emission on duty decreases as the brightness or current consumption of the input image increases
(OLED) display device.
The method according to claim 1,
The image analyzing unit calculates an on-duty according to the brightness of the input image,
An APL calculation unit for calculating an average image level of the input image;
A luminance ratio calculating unit for calculating a maximum luminance with respect to a peak luminance according to the calculated average image level;
And a light emission on duty calculation unit for calculating the light emission on duty according to the calculated maximum luminance with respect to the peak luminance
(OLED) display device.
The method according to claim 1,
Wherein the image analyzing unit calculates an on-duty according to the consumption current of the input image,
A consumption current calculation unit for calculating a consumption current of the input image;
A target current calculating unit for calculating a target current according to the calculated consumed current;
And an emission on duty calculation unit for calculating the emission on duty according to the calculated target current
(OLED) display device.
The method according to claim 1,
In displaying the input image, the same gamma voltage is used regardless of the brightness of the input image or the current consumption
(OLED) display device.
Analyzing the input image and calculating an on-duty of the light-emitting diode according to the brightness or current consumption of the input image,
The light emission on duty decreases as the brightness or current consumption of the input image increases
A method of driving an organic light emitting diode display device.
6. The method of claim 5,
Wherein the step of calculating the light emission on duty according to the brightness of the input image comprises:
Calculating an average image level of the input image;
Calculating a maximum luminance with respect to a peak luminance according to the calculated average image level;
And calculating the light emission on duty according to the calculated maximum luminance with respect to the peak luminance
A method of driving an organic light emitting diode display device.
6. The method of claim 5,
Wherein the calculating the light emission on duty according to the consumption current of the input image comprises:
Calculating a consumption current of the input image;
Calculating a target current according to the calculated consumed current;
And calculating the light emission on duty according to the calculated target current
A method of driving an organic light emitting diode display device.
6. The method of claim 5,
In displaying the input image, the same gamma voltage is used regardless of the brightness of the input image or the current consumption
A method of driving an organic light emitting diode display device.

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