KR102435424B1 - Display Device having Duty Driving Function and Driving Method thereof - Google Patents

Abstract

A display device having a duty function according to the present invention includes a display panel, an image data reading unit, a grayscale modulation unit, and a duty variable unit. The image data reading unit reads the peak grayscale or average grayscale of the input image data in the nth frame period (n is a natural number), and outputs a duty control signal when the peak grayscale or average grayscale is less than or equal to a threshold value. The gradation modulator modulates each gradation value of the input image data in response to the duty control signal to generate a modulated gradation value. Adjust the peak modulation gradation value belonging to . In response to the duty control signal, the duty variable unit adjusts the duty ratio to reduce the emission period of the pixels during the n-th frame period.

Description

Display Device having Duty Driving Function and Driving Method thereof

The present invention relates to a display device having a duty driving function and a driving method thereof.

Flat panel displays (FPDs) are widely used in portable computers such as notebook computers, tablets, and mobile phone terminals, as well as monitors of desktop computers, due to their advantages in miniaturization and weight reduction. Such a flat panel display device is a liquid crystal display device; LCD), Plasma Display Panel (PDP), Field Emission Display; FED) and organic light emitting diode display (OLED).

In the display device, due to variations in process or luminance change characteristics due to panel characteristics, there may be problems in that the display panel shows unevenness or color deviation occurs. Pulse Width Modulation (PWM) driving technology is one of the methods for improving the luminance change characteristic of a display device. The pulse width modulation technique is a method of improving luminance characteristics by varying a period in which pixels emit light and a period in which pixels emit light in one frame according to a luminance mode. Although the pulse width modulation technique is effective in improving the display characteristics of pixels displaying high luminance, there is a limit to improving the luminance characteristics in a low grayscale region.

An object of the present invention is to provide a display device having a duty driving function capable of improving luminance characteristics even when a grayscale value of input image data is low, and a driving method thereof.

A display device having a duty function according to the present invention includes a display panel, an image data reading unit, a grayscale modulation unit, and a duty variable unit. The image data reading unit reads the peak grayscale or average grayscale of the input image data in the nth frame period (n is a natural number), and outputs a duty control signal when the peak grayscale or average grayscale is less than or equal to a threshold value. The gradation modulator modulates each gradation value of the input image data in response to the duty control signal to generate a modulated gradation value. Adjust the peak modulation gradation value belonging to . In response to the duty control signal, the duty variable unit adjusts the duty ratio to reduce the light emission period of the pixels during the n-th frame period.

A duty driving method of a display device according to the present invention includes reading a peak grayscale or an average grayscale of input image data in an nth frame period (n is a natural number). and outputting a duty control signal when the peak grayscale or the average grayscale is less than or equal to a threshold value. Then, in response to the duty control signal, each of the grayscale values of the input image data is modulated to generate a modulated grayscale value, and the peak modulated grayscale value obtained by modulating the peak grayscale among the modulated grayscale values falls within the range greater than the peak grayscale and less than the maximum grayscale. and adjusting the peak modulation grayscale value. and in response to the duty control signal, adjusting the duty ratio to decrease the light emission period of the pixels during the nth frame period.

According to the present invention, the effect of improving unevenness and color deviation of the display panel due to luminance deviation can be improved by modulating data in a low grayscale region to a high grayscale value to drive pixels. In particular, since the present invention can modulate data in a low grayscale region even when driving in the highest luminance mode, luminance deviation can be improved regardless of the luminance mode.

1 is a diagram showing the configuration of a display device according to the present invention.
2 is a block diagram showing the configuration of a duty driving unit according to the present invention.
3 is a flowchart illustrating a duty driving method according to the present invention.
4 is a diagram for explaining a grayscale modulation method.
5 is a diagram for explaining a duty variable method.
6 is a view for explaining the variation of a data voltage and a duty period by duty driving according to the present invention.
7 is a view for explaining the timing of the emission control signal according to the present invention.

Advantages and features of the present specification and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present specification is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments allow the disclosure of the present specification to be complete, and common knowledge in the technical field to which this specification belongs It is provided to fully inform the possessor of the scope of the invention, and the present specification is only defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present specification are exemplary, and thus the present specification is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in the description of the present specification, if it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present specification, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, the case in which the plural is included is included unless otherwise explicitly stated.

In interpreting the components, it is interpreted as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'beside', etc., 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal relationship is described as 'after', 'following', 'after', 'before', etc. It may include cases that are not continuous unless this is used.

Although the first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present specification.

Each feature of the various embodiments of the present specification may be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be independently implemented with respect to each other or may be implemented together in a related relationship. may be

Although this specification has been mainly described with respect to an organic light emitting display device, the technical spirit of the present invention is not limited thereto and may be applied to other display devices.

1 is a diagram showing the configuration of a display device according to the present invention.

Referring to FIG. 1 , an organic light emitting diode display according to the present invention includes a display panel 100 in which pixels P are arranged in a matrix form, a data driver 120 , gate drivers 130 and 140 , and a timing controller 110 . be prepared

The display panel 100 includes a display unit 100A in which pixels P are arranged to display an image, and a non-display unit 100B in which a shift register 140 is arranged and does not display an image.

The display unit 100A includes a plurality of pixels P, and displays an image based on a gray level displayed by each pixel P. The pixels P are arranged along the first to nth pixel lines HL1 to HL[n]. Each pixel P is connected to a data line DL arranged along a column line, and connected to a gate line GL arranged along a pixel line HL. That is, pixels disposed on the same pixel line share the same gate line GL and are driven simultaneously. In addition, when pixels disposed on the first pixel line HL1 are defined as first pixels P1 and pixels disposed on the nth pixel line HLn are defined as nth pixels Pn, the first pixel From (P1) to n-th pixels (Pn) are sequentially driven. In addition, a sampling period for writing data in one scan line may be defined as one horizontal period (1H). The gate line GL may include a plurality of emission lines and a plurality of scan lines according to a pixel structure.

The timing controller 110 controls driving timings of the data driver 120 and the gate drivers 130 and 140 . The timing controller 110 rearranges the image data RGB input from the outside to match the resolution of the display panel 100 . The timing controller 110 generates a data control signal DDC for controlling the operation timing of the data driver 120 and a gate control signal GDC for controlling the operation timing of the gate driver 130 and 140 . The timing controller 110 provides the image data DATA, the data control signal DDC, and the gate control signal GDC to the duty driver 10 .

The duty driver 10 receives the image data DATA from the timing controller 110 and reads a grayscale value of the image data DATA in units of frames. The duty driver 10 detects a peak grayscale among the image data DATA within one frame, and increases the grayscale value of the image data when the peak grayscale is less than or equal to a threshold value to generate a modulated grayscale value. The duty driver supplies the modulated image data MDATA having the modulated grayscale value to the data driver 120 and varies the timing of the gate control signal GDC. A detailed description of the duty driving unit 10 will be described later.

The data driving unit 120 is for driving the data line unit DL. The data driver 120 converts the image data DATA or modulated image data MDATA input from the duty driver 10 into analog data voltages based on the data control signal DDC and supplies them to the data lines DL. do.

The gate drivers 130 and 140 include a level shifter 130 and a shift register 140 . The level shifter 130 is formed on a printed circuit board (not shown) connected to the display panel 100 in the form of an IC, and the shift register 140 is a gate formed in the non-display area 100B of the display panel 100 . -It is formed in a gate-in-panel (GIP) method.

The level shifter 130 provides the shift register 140 after level-shifting the clocks and the start signal VST. The shift register 140 is formed by a combination of a plurality of thin film transistors (hereinafter, transistors) in the non-display area 100B of the display panel 100 by the GIP method. In particular, the gate drivers 130 and 140 control the timing of gate pulses applied to the gate lines GL according to the gate control signal GDC of the duty driver 10 .

2 is a view showing the configuration of the duty driving unit according to the present invention.

Referring to FIG. 2 , the duty driver 10 includes an image data reading unit 11 , a grayscale modulator 14 , and a duty variable unit 15 .

The image data reading unit 11 outputs a duty control signal when a peak gradation among input image data or an average gradation of the input image data is less than or equal to a threshold value.

The grayscale modulator 14 modulates each grayscale value of the input image data DATA in response to the duty control signal S_d to generate a modulated grayscale value. The duty variable unit 15 adjusts the peak modulated grayscale value obtained by modulating the peak grayscale among the modulated grayscale values to a peak modulated grayscale value that is greater than the peak grayscale and falls within the maximum grayscale range.

In response to the duty control signal S_d, the duty variable unit 15 adjusts a duty ratio to reduce the emission period of pixels during one frame period.

3 is a flowchart illustrating the operation of the duty driver according to the present invention.

Referring to FIGS. 1 to 3 , the operation of the duty driver is as follows.

In the first step S301, the peak gradation reading unit 12 or the average gradation reading unit 13 reads the input image data DATA. The peak gradation reading unit 12 reads the image data DATA frame by frame, and detects the peak gradation of the image data DATA belonging to one frame. As for the peak gray level, the highest gray level among the image data DATA in one frame may be detected as the peak gray level. The average grayscale reading unit 13 reads the image data DATA in units of frames, and detects the average grayscale of the image data DATA belonging to one frame. The peak gradation reading section 12 and the average gradation reading section 13 can be selectively driven.

In the second step S303, the peak gradation reading unit 12 compares the magnitude of the peak gradation with a preset first threshold. The first threshold is for determining low-grayscale image data to be improved in the luminance characteristic. The peak grayscale reading unit 12 outputs the duty control signal S_d when the peak grayscale level is equal to or less than the first threshold.

The average gradation reading unit 13 compares the magnitude of the average gradation with a preset second threshold. The size of the first threshold value and the second threshold value may be the same or may be set differently. Hereinafter, in the present specification, the first and second thresholds will be unified as thresholds.

In the third step (S305). In a state in which the image data reading unit 11 does not output the duty control signal S_d, the display device maintains normal driving. The normal driving refers to a driving method in which the light emission period is continuously maintained during the frame period according to the luminance mode or the light emission period is reduced according to the luminance mode selected by the user.

In the fourth step S307, the grayscale modulator 14 modulates the grayscale value of the image data in response to the duty control signal S_d. A method in which the grayscale modulator 14 modulates the grayscale value of the image data DATA will be described as follows.

4 is a diagram illustrating a method of modulating a grayscale value of image data according to a peak luminance. In FIG. 4 , the reference gamma curve gamma_R refers to a gamma curve of 2.2 in the maximum luminance mode. In FIG. 4 , the reference gamma curve gamma_R shows a gamma curve in which the maximum grayscale G_max is 255 grayscales and the maximum luminance L_max is set to 1000 nits.

The first to fourth data data1, data2, data3, and data4 represent examples of image data belonging to an arbitrary frame. When the duty control signal S_d is output by the peak gray level reading unit 12, the peak gray level G_peak refers to the largest gray level among image data belonging to one frame. Alternatively, when the duty control signal S_d is output by the average grayscale reading unit 13, the peak grayscale G_peak refers to the largest grayscale among the grayscales within the average grayscale among image data belonging to one frame.

4 shows an example in which 127 grayscales corresponding to the grayscale values of the fourth data data4 are regarded as peak grayscales. When it is assumed that the luminance displayed by 127 grayscales is 200 nits in the maximum luminance mode, each pixel in the nth frame displays the luminance within the range of 0 nits to 200 nits.

The grayscale modulator 14 modulates the peak grayscale G_peak in the nth (n is a natural number) frame image data to the maximum grayscale G_max on the reference gamma curve gamma_R. The grayscale modulator 14 modulates the grayscale values of the nth frame image data to have the same change rate as the change rate of the peak grayscale G_peak. As a result, the grayscale modulator 14 rescales the grayscale range of the nth frame image data having the range from 0 grayscale to the peak grayscale G_peak from 0 grayscale to the maximum grayscale G_max.

A method of rescaling the n-th frame image data may use a change rate of the peak grayscale (G_peak). An arbitrary grayscale value (Gx) and a rescaled modulation grayscale value (G_mod) within the range of 0 grayscale to peak grayscale (G_peak) have a relationship of "G_peak:G_max = Gx:Gmod". Accordingly, the grayscale modulator 14 may calculate the modulated grayscale value G_mod for an arbitrary grayscale value Gx belonging to the nth frame by using [Equation 1].

[Equation 1]

G_mod = (G_max/G_peak)×Gx

The grayscale modulator 14 provides the modulated grayscale values G_mod to the data driver 120 . The data driver 120 generates a data voltage using the modulated grayscale values G_mod.

In the fifth step ( S309 ), the duty variable unit 15 adjusts the duty ratio in response to the duty control signal S_d. A method for the duty variable unit 15 to adjust the duty ratio will be described as follows.

5 is a diagram illustrating a method of adjusting a duty ratio according to peak luminance. Since the data driver 120 generates a data voltage using the modulated grayscale value G_mod, if the light emission period of the nth frame is maintained the same, the luminance of the image displayed in the nth frame is increased as a whole. Accordingly, the duty variable unit 15 varies the light emission period of the n-th frame according to the size of the modulation grayscale value G_mod.

A method of adjusting the duty ratio will be described with reference to FIG. 5 . In FIG. 5 , the reference gamma curve gamma_R and the first to fourth data data4 are the same as the example shown in FIG. 4 .

When the luminance displayed by the fourth data data4 having 127 grayscales in the reference gamma curve gamma_R is 200 nits, the fourth modulated grayscale value G_mod in which the fourth data data4 is modulated has 255 grayscales.

The duty variable unit 15 reduces the light emission period within the n-th frame period so that the n-th frame image does not display high luminance as a whole. When the ratio occupied by the light emitting period in one frame period is defined as a duty ratio, the overall luminance displayed by the display panel 100 during one frame period is linearly proportional to the duty ratio. Accordingly, the duty variable unit 15 may adjust the duty ratio using the following [Equation 2].

[Equation 2]

Duty_m=(L_max / L_peak)×100

In [Equation 2], the modulation duty ratio (Duty_m) refers to a duty ratio set as the ratio of the peak gray level (G_peak) to the maximum gray level (G_max). Accordingly, if the duty ratio is adjusted based on [Equation 2], the n-th frame image displays the luminance corresponding to the maximum luminance mode. The display device may be in a state in which duty driving has already been performed according to the luminance mode. For example, the display device may vary the maximum luminance of 255 grayscales by varying the duty ratio according to a user or a preset condition. For example, if a luminance mode in which a luminance value of 255 grayscale is set to 50% of the maximum luminance L_max is set, the duty driver 10 sets the duty ratio to 50% regardless of the pit grayscale or the average grayscale is in one state When a duty ratio preset by a user selection is referred to as a set duty ratio (Duty_set), the duty driver 10 may lower the modulation duty ratio (Duty_m) to a ratio of the set duty ratio (Duty_set). That is, when the set duty ratio (Duty_set) is a% and the modulation duty ratio (Duty_m) is b%, the duty driver 10 calculates the modulation duty ratio in the luminance mode setting state as “{(a/100)×( b/100)}100". For example, if the set duty ratio (Duty_set) is 50% and the modulation duty ratio (Duty_m) is 20%, the modulation duty ratio in the 50% luminance mode setting state is (20×50)/100=10(%). can be set.

6 is a diagram comparing data voltages by the duty driver of the present invention.

In FIG. 6 , the 100% duty driving voltage Duty_100 is the data voltage of the n-th frame image described with reference to FIGS. 4 and 5 when operating in the general maximum luminance mode. The 20% duty driving voltage Duty_20 represents a data voltage of the gradation value G_mod modulated by the duty driving unit 10 of the present invention. In particular, the data voltages shown in FIG. 6 represent the data voltage of the fourth data data4, and the fourth data data4 represents the same value in the nth frame and the (n+1)th frame.

Referring to FIG. 6 , in the maximum luminance mode state in which duty driving is not performed, the fourth data data4 maintains a constant 127 grayscale voltage V_127G. The 127 gradation voltage V_127G is a data voltage applied to the pixels P to display 200 nits of luminance corresponding to 127 gradations in the maximum luminance mode.

According to the duty driving of the present invention, the gray level corresponding to the fourth data data4 is modulated to 255 gray levels by the gray level modulator. As a result, the pixel P to which the fourth data data4 is applied is in the maximum luminance mode. It emits light using the 255 gradation voltage (V_255G). The 255 gradation voltage V_255G is a data voltage applied to the pixels P to display a luminance of 1000 nits corresponding to the 255 gradation in the maximum luminance mode. In addition, according to the duty driving of the present invention, the pixels P are driven at a duty ratio of 20% during the n-th frame period. As a result, light emission is maintained for a period of 20% in the nth frame period and light emission is stopped for a period of 80%.

7 is a diagram showing the timing of the emission control signal for controlling the emission period. 7A and 7B are illustrated based on an embodiment in which pixels emit light when the emission control signal is a turn-on voltage.

Referring to FIG. 7A , the emission control signal EM applied to the pixels P maintains a turn-on voltage during the n-th frame period in the maximum luminance mode state in which duty driving is not performed.

On the other hand, referring to FIG. 7B , when the duty driving according to the present invention is performed, the light emission control signal EM maintains the turn-on voltage for 20% of the n-th frame period, and the n-th frame period is During 80% of the frame period, the light emission control signal EM maintains a turn-off voltage.

As described above, according to the present invention, the effect of improving the unevenness and color deviation of the display panel due to the luminance deviation can be improved by driving the pixels by modulating data in the low grayscale region to a high grayscale value. In particular, since the present invention can modulate data in a low grayscale region even when driving in the highest luminance mode, luminance deviation can be improved regardless of the luminance mode.

Although the present specification has been described focusing on an embodiment in which the duty driving unit 10 is disposed outside the timing controller 110 , the duty driving unit may be disposed inside the timing controller.

Those skilled in the art from the above description will be able to see that various changes and modifications can be made without departing from the technical spirit of the present invention. Accordingly, the technical 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.

10: duty driver 100: display panel
110: timing controller 120: data driver
130,140: gate driver

Claims (12)

a display panel including a plurality of pixels;
an image data reading unit for reading a peak gradation or an average gradation of input image data in an nth frame period (n is a natural number) and outputting a duty control signal when the peak gradation or average gradation is less than or equal to a threshold value;
A modulated gradation value is generated by modulating each gradation value of the input image data in response to the duty control signal. a gradation modulator for adjusting a peak modulated gradation value belonging to a range of ; and
In response to the duty control signal, comprising a duty variable for adjusting a duty ratio (duty ratio) to reduce the light emission period of the pixels during the n-th frame period,
The gradation modulator
The display device modulates each of the grayscale values of the input image data into a modulated grayscale value that falls within the maximum grayscale range from the 0 grayscale when the input image data has a grayscale value that falls within the peak grayscale range from zero grayscale. The method of claim 1,
The image data reading unit
The display device compares each of the input image data in units of a frame period, and sets a highest grayscale value among the input image data as the peak grayscale. The method of claim 1,
The image data reading unit
The display device calculates an average grayscale of the image data belonging to the nth frame, and outputs the duty control signal when the average grayscale is equal to or less than the threshold. delete 3. The method of claim 2,
The gradation modulator
Any input image within the nth frame so that the ratio of the peak modulated grayscale value to the peak grayscale is equal to the ratio of the modulated grayscale value to the input image data grayscale value in the nth frame A display device for modulating a data grayscale value with the modulated grayscale value. 6. The method of claim 5,
The gradation modulator
A modulated gradation value (G_mod) in which an arbitrary gradation value (Gx) belonging to the peak gradation range from 0 gradation is modulated is calculated using the following [Equation 1],
[Equation 1]
G_mod = (G_max/G_peak)×Gx
In this case, G_max is the maximum gray scale of the display device, and G_peak is the gray scale value of the peak gray scale. The method of claim 1,
The duty variable part
The ratio of the luminance value corresponding to the peak grayscale to the luminance value corresponding to the peak modulated grayscale value is equal to the ratio of the duty ratio of the nth frame to the duty ratio of 100%. A display device that controls the duty ratio of a frame period. 8. The method of claim 7,
The duty variable part
By adjusting the duty ratio using [Equation 2] as shown below, duty driving is performed with the modulation duty ratio (Duty_m),
[Equation 2]
Duty_m=(L_max / L_peak)×100
In this case, L_max is a luminance value corresponding to the maximum grayscale in the maximum luminance mode, and L_peak is a luminance value corresponding to the peak grayscale in the maximum luminance mode. The method of claim 1,
and a data driver configured to receive the modulated gradation value and supply a data voltage to the pixels based on the modulated gradation value. A duty driving method for controlling a light emission period of pixels disposed on a display panel, the method comprising:
reading a peak gradation or an average gradation of input image data in an nth (n is a natural number) frame period;
outputting a duty control signal when the peak grayscale or the average grayscale is less than or equal to a threshold value;
A modulated gradation value is generated by modulating each gradation value of the input image data in response to the duty control signal. adjusting to a peak modulation grayscale value belonging to a range of ; and
In response to the duty control signal, comprising the step of adjusting the duty ratio to decrease the light emission period of the pixels during the n-th frame period,
The step of generating the modulated gradation value includes:
and modulating each of the grayscale values of the input image data to a modulated grayscale value falling within the maximum grayscale range from the 0 grayscale when the input image data has a grayscale value that falls within the peak grayscale range from the zero grayscale. driving method. 11. The method of claim 10,
After generating the modulated gradation value,
and generating a data voltage by using the modulated grayscale value. 11. The method of claim 10,
After adjusting the duty ratio,
and adjusting the timing of the emission control signal applied to the pixels.

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