JP7386035B2 - Current limiting circuit, display device, and current limiting method - Google Patents

Description

The present disclosure relates to a current limiting circuit, a display device, and a current limiting method that limit current supplied to a plurality of pixels included in a display panel.

Conventionally, display devices such as organic EL (Electro-Luminescence) display devices have been developed in which each pixel includes a self-luminous element. In such display devices, there is a demand for larger display panels. As display panels become larger, power consumption in display devices increases. Therefore, a technique for suppressing power consumption in a display device is known (see Patent Document 1). In the display device disclosed in Patent Document 1, the power consumption value in the display panel is calculated for each horizontal period (horizontal synchronization period) based on the video signal, and the current supplied to each pixel of the display panel is calculated based on the calculation result. The power consumption of the display panel is controlled by limiting the power consumption of the display panel. As a result, in the display device disclosed in Patent Document 1, it is attempted to suppress the power consumption value in the display panel to the control target power value or less.

Japanese Patent Application Publication No. 2007-212644

In the display device disclosed in Patent Document 1, in a small-area video display (that is, a state in which there are many pixels in a black display state), each pixel does not have a self-luminous element, such as a conventional liquid crystal display device. It has the same gamma characteristic (that is, the characteristic that the brightness is proportional to the 2.2 power of the pixel value). However, in large-area video displays (that is, in a state where there are many pixels that are not in a black display state), when the pixel value of each pixel is large, the current supplied to the self-emissive element of each pixel is limited, so the pixel value On the other hand, the change in brightness becomes smaller. For example, in the display device described in Patent Document 1, when a pixel value is large in a large-area video display, the brightness remains constant with respect to changes in the pixel value. For this reason, the display device described in Patent Document 1 cannot necessarily display an image with a brightness that faithfully reflects the image signal when displaying a large area image.

The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a current limiting circuit and the like that can bring gamma characteristics in a large-area video display closer to gamma characteristics in a small-area video display.

In order to achieve the above object, a current limiting circuit according to one aspect of the present disclosure limits the current supplied to a plurality of pixels of a display panel that displays an image based on a video signal. A current limiting circuit that controls a power consumption value in a pixel to be equal to or less than a control target power value, wherein each of the plurality of pixels includes a self-emitting element, and the current limiting circuit corresponds to each of the plurality of pixels. a gain determination circuit that calculates a screen power value related to the power consumption value based on the pixel value of the video signal and determines a gain based on the screen power value; and the pixel value corresponding to each of the plurality of pixels. and a gain multiplication circuit that multiplies the gain by the gain, the screen power value when a current corresponding to the upper limit of the pixel value is supplied to each of the plurality of pixels is defined as the rated power value, and The gain determined by the gain determining circuit is such that the ratio of the screen power values is the screen power ratio, and the ratio of the control target power value to the rated power value is the target power ratio. When the screen power ratio is less than or equal to the first power ratio, it is 1, and when the screen power ratio is larger than the first power ratio and is 100% or less, it decreases monotonically with respect to the screen power ratio, When the screen power ratio is greater than or equal to the target power ratio and less than 100%, the value is less than the value obtained by dividing the target power ratio by the screen power ratio, and when the screen power ratio is 100%, This is the target power ratio.

Furthermore, in order to achieve the above object, a display device according to one aspect of the present disclosure includes the current limiting circuit and the display panel.

Further, in order to achieve the above object, a current limiting method according to an aspect of the present disclosure includes a current limiting method according to an aspect of the present disclosure, by limiting the current supplied to a plurality of pixels included in a display panel that displays an image based on a video signal. A current limiting method for controlling a power consumption value in a plurality of pixels to be equal to or less than a control target power value, wherein each of the plurality of pixels includes a self-emitting element; a power calculation step of calculating a screen power value related to the power consumption value based on a pixel value of the corresponding video signal; a gain determination step of determining a gain based on the screen power value; and each of the plurality of pixels. a gain multiplication step of multiplying the pixel value corresponding to the pixel value by the gain, and the screen power value when a current corresponding to the upper limit of the pixel value is supplied to each of the plurality of pixels is set as the rated power value. , where the ratio of the screen power value to the rated power value is taken as a screen power ratio, and the ratio of the control target power value to the rated power value is taken as a target power ratio, the gain determined in the gain determining step is the screen power ratio. If the power ratio is less than or equal to a first power ratio that is less than the target power ratio, the value is 1; if the screen power ratio is greater than the first power ratio and is 100% or less, the ratio is 1 to the screen power ratio. If the screen power ratio is greater than or equal to the target power ratio and less than 100%, the value is less than the value obtained by dividing the target power ratio by the screen power ratio, and the screen power ratio is 100%. %, it is the target power ratio.

According to the present disclosure, it is possible to provide a current limiting circuit and the like that can bring gamma characteristics in a large-area video display close to gamma characteristics in a small-area video display.

FIG. 1 is a block diagram showing the functional configuration of a display device according to Embodiment 1. FIG. 2 is a block diagram showing the functional configuration of a current limiting circuit included in the display device according to the first embodiment. FIG. 3 is a schematic diagram showing the configuration of the screen data storage unit according to the first embodiment. FIG. 4 is a flowchart showing the flow of arithmetic processing in the gain determination circuit and gain multiplication circuit according to the first embodiment. FIG. 5 is a graph showing the relationship between screen power ratio and gain according to the first embodiment. FIG. 6 is a graph showing gamma characteristics when using the current limiting circuit of the comparative example. FIG. 7 is a graph showing gamma characteristics when using the current limiting circuit according to the first embodiment. FIG. 8 is a block diagram showing the functional configuration of the display device according to the second embodiment. FIG. 9 is a block diagram showing the functional configuration of a display panel included in the display device according to the second embodiment. FIG. 10 is a circuit diagram illustrating an example of the configuration of sub-pixels that constitute a pixel according to the second embodiment. FIG. 11 is a diagram illustrating an example of a write signal input to a sub-pixel according to the second embodiment. FIG. 12 is a schematic diagram showing the transition of the display state of the display unit according to the second embodiment. FIG. 13 is a graph showing gamma characteristics when using the current limiting circuit of the comparative example. FIG. 14 is a graph showing gamma characteristics when using the current limiting circuit according to the second embodiment. FIG. 15 is a block diagram showing the relationship between a current limiting circuit and a display device according to a modification. FIG. 16 is an external view of a PC incorporating a processing circuit according to a modified example. FIG. 17 is an external view of a hard disk recorder incorporating a processing circuit according to a modified example. FIG. 18 is an external view of a thin flat TV incorporating a display device according to each embodiment.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that each of the embodiments described below represents one specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and do not limit the present disclosure. do not have.

Note that each figure is a schematic diagram and is not necessarily strictly illustrated. Further, in each figure, substantially the same configurations are denoted by the same reference numerals, and overlapping explanations will be omitted or simplified.

(Embodiment 1)
The current limiting circuit and the like according to the first embodiment will be explained.

[1-1. Overall configuration of display device]
First, the overall configuration of a display device according to an embodiment will be described using FIGS. 1 and 2.

FIG. 1 is a block diagram showing the functional configuration of a display device 110 according to this embodiment. FIG. 2 is a block diagram showing the functional configuration of current limiting circuit 140 included in display device 110 according to this embodiment.

The display device 110 shown in FIG. 1 is a device that displays images based on a video signal, and includes a current limiting circuit 140 and a display panel 60.

The display panel 60 is a panel that has a plurality of pixels and displays images based on video signals. Each of the plurality of pixels includes a self-luminous element. In this embodiment, each of the plurality of pixels has a plurality of sub-pixels, and each of the plurality of sub-pixels includes a self-luminous element. In this embodiment, each of the plurality of pixels has three sub-pixels corresponding to three colors, RGB. In the present embodiment, in the display panel 60, the luminance of each sub-pixel is proportional to the pixel value input to each sub-pixel. Note that the pixel value here is a signal level that defines the gradation (brightness and darkness) of each pixel, and is also called a pixel value, gradation level, or simply signal level.

The display panel 60 is not particularly limited as long as it is a display panel whose brightness is proportional to the pixel value. For example, a plasma display panel or the like can be used as the display panel 60.

The current limiting circuit 140 is a circuit that controls the power consumption value of the plurality of pixels to be equal to or less than the control target power value by limiting the current supplied to the plurality of pixels included in the display panel 60. In this embodiment, current limiting circuit 140 calculates the power value supplied to the plurality of pixels based on the video signal, and limits the current supplied to the plurality of pixels based on the power value. Specifically, the current limiting circuit 140 limits the current supplied to the plurality of pixels by correcting each pixel value in the video signal and outputting each corrected pixel value to the display panel 60. In this embodiment, current limiting circuit 140 corrects each pixel value by multiplying each pixel value by a gain determined based on the video signal. As shown in FIG. 2, the current limiting circuit 140 includes a weighted average circuit 43, a horizontal period data calculation circuit 44, a screen data storage section 45, a gain determination circuit 148, and a gain multiplication circuit 50.

The weighted average circuit 43 is a circuit that calculates a weighted average of pixel values corresponding to each of a plurality of sub-pixels that each of a plurality of pixels has. As shown in FIG. 2, the weighted average circuit 43 multiplies each RGB pixel value by a weighting coefficient according to the power consumption characteristics of each of the plurality of sub-pixels of the display unit 70, and calculates the sum thereof. do.

The horizontal period data calculation circuit 44 calculates horizontal period power conversion data corresponding to the pixel value for each horizontal period. In the present embodiment, the horizontal period data calculation circuit 44 calculates the integrated value or average value of the weighted average outputted by the weighted average circuit 43 in the horizontal period as horizontal period power conversion data (level integrated value).

The screen data storage unit 45 stores power conversion data for one frame. In this embodiment, the screen data storage unit 45 stores one frame of power conversion data output by the horizontal period data calculation circuit 44.

The gain determination circuit 148 is a circuit that calculates a screen power value related to the power consumption value of a plurality of pixels based on a pixel value of a video signal corresponding to each of the plurality of pixels, and determines a gain based on the screen power value. be. The gain is a value greater than 0 and less than or equal to 1, which is multiplied by each pixel value by the gain multiplication circuit 50. The gain is determined to be a value less than 1 at least when the screen power value exceeds the control target power value. By multiplying each pixel value by such a gain, power consumption in the display panel 60 is limited.

The gain determination circuit 148 calculates a screen power value related to the power consumption value for one frame in a plurality of pixels based on the power conversion data stored in the screen data storage section 45. In this embodiment, the gain determination circuit 148 has a lookup table (LUT) 149 that indicates the relationship between the value corresponding to the calculated screen power value and the value corresponding to the gain. Gain determination circuit 148 determines a gain corresponding to the calculated screen power value based on lookup table 149. Details of the gain determined by the gain determining circuit 148 will be described later.

The gain multiplication circuit 50 is a circuit that multiplies a video signal by a gain. That is, the gain multiplication circuit 50 multiplies the pixel value of the video signal corresponding to each of the plurality of sub-pixels by the gain determined by the gain determination circuit 148. Thereby, when the screen power value exceeds the control target power value, the video signal is multiplied by a gain of less than 1, so that the brightness of the video signal can be reduced. Therefore, the current supplied to the plurality of pixels of the display panel 60 is limited.

[1-2. Operation of current limit circuit]
Next, the operation of current limiting circuit 140 will be explained.

First, the configuration and operation of the screen data storage section 45 included in the current limiting circuit 140 will be described using FIG. 3. FIG. 3 is a schematic diagram showing the configuration of the screen data storage section 45 according to this embodiment. As shown in FIG. 3, the screen data storage unit 45 stores horizontal period power conversion data for each horizontal line on the display screen of the display unit 70 as signal information written to the display unit 70. For example, the horizontal period power conversion data of the i-th line is stored in the screen data storage unit 45 as the power value of the i-th line. When rewriting of the next field begins, the screen data storage unit 45 also rewrites the stored power value and stores it as a power value corresponding to the signal written on the display screen.

Next, the arithmetic processing in the gain determination circuit 148 and the gain multiplication circuit 50 will be explained using FIG. 4. FIG. 4 is a flowchart showing the flow of arithmetic processing in gain determination circuit 148 and gain multiplication circuit 50 according to the present embodiment.

As shown in FIG. 4, first, the gain determination circuit 148 calculates a screen power value related to the power consumption value based on the pixel value of the video signal corresponding to each of the plurality of pixels (S10). In the present embodiment, the gain determination circuit 148 calculates the screen power value based on the horizontal period power conversion data stored in the screen data storage section 45. Specifically, the sum of the horizontal period power conversion data of the number of horizontal lines stored in the screen data storage unit 45 is calculated as the screen power value.

Subsequently, the gain determination circuit 148 determines a gain based on the screen power value calculated in step S10 (S11). Specifically, the gain determination circuit 148 determines the gain corresponding to the calculated screen power value based on a lookup table 149 indicating the relationship between the value corresponding to the calculated screen power value and the value corresponding to the gain. do.

The gain calculated by the gain determining circuit 148 as described above is input to the gain multiplication circuit 50, and the gain multiplication circuit 50 multiplies the video signal by the gain (S12). More specifically, the gain multiplication circuit 50 multiplies each pixel value of the video signal by a gain. As a result, each pixel value is reduced at least when the screen power value exceeds the control target power value, so the current supplied to the plurality of pixels of the display panel 60 is limited.

[1-3. Operation example]
Next, an example of the operation of the display device 110 according to the present embodiment will be described using FIG. 5 while comparing it with the operation of a display device of a comparative example. FIG. 5 is a graph showing the relationship between screen power ratio and gain according to this embodiment. In FIG. 5, the horizontal axis shows the screen power ratio, and the vertical axis shows the gain. Further, FIG. 5 also shows the relationship between the screen power ratio and the gain in the current limiting circuit of the comparative example. The solid line and broken line graphs shown in FIG. 5 represent the gains of this embodiment and the comparative example, respectively.

Here, the screen power value when a current corresponding to the upper limit of the pixel value is supplied to each of the plurality of pixels of the display panel 60 is defined as the rated power value, and the ratio of the screen power value to the rated power value is defined as the screen power ratio. do. The pixel value of all the pixels of the display panel 60 is the upper limit value, and the screen power value when the current is not limited is the rated power value. Further, the ratio of the control target power value to the rated power value is set as the target power ratio. The graph shown in FIG. 5 shows an example of a graph when the target power ratio is 0.4.

In the current limiting circuit of the comparative example using the gain shown by the broken line in FIG. 5, the gain is 1 when the screen power ratio is less than or equal to the target power ratio (40%), and when the screen power ratio is greater than 40%. In this case, the gain is inversely proportional to the screen power ratio. Gamma characteristics when the current limiting circuit of the comparative example and the current limiting circuit 140 according to the present embodiment are used in a display device will be described with reference to FIGS. 6 and 7. 6 and 7 are graphs showing gamma characteristics when using the current limiting circuit of the comparative example and the current limiting circuit 140 according to the present embodiment, respectively. A solid line and a broken line shown in FIGS. 6 and 7 indicate gamma characteristics in the case of large-area video display and small-area video display, respectively. 6 and 7 show gamma characteristics when all pixels are displayed in white as an example of a large-area image display, and gamma characteristics are shown in a case where 10% of pixels are displayed in white as an example of a small-area image display. The gamma characteristics when the other 90% of pixels display black are shown. The horizontal axes of the graphs in FIGS. 6 and 7 indicate pixel values, and the vertical axes indicate the brightness of each pixel.

As shown in FIG. 6, in the current limiting circuit of the comparative example, since the gain is 1 in the case of small-area video display, a gamma characteristic in which the luminance is proportional to the pixel value is obtained. On the other hand, in a large-area video display, a gamma characteristic in which the brightness is proportional to the pixel value is obtained in a range where the pixel value is small, but the brightness remains constant in a range where the pixel value is close to the upper limit (255). . In this way, in the case of large-area video display, the gamma characteristic is significantly different from the gamma characteristic in which the luminance is proportional to the pixel value.

In the current limiting circuit 140 according to the present embodiment, the gain determined by the gain determining circuit 148 is 1 when the screen power ratio is 10% or less, and 100% when the screen power ratio is greater than 10%. In the following cases, the screen power ratio decreases monotonically. Furthermore, when the screen power ratio is equal to or higher than the target power ratio and less than 100%, the gain is a value less than the value obtained by dividing the target power ratio by the screen power ratio, and when the screen power ratio is 100%, This is the target power ratio. In other words, when the screen power ratio is greater than 10% and the screen power ratio is less than the target power ratio, the gain according to the present embodiment is less than or equal to the gain of the comparative example, and the screen power ratio is greater than or equal to the target power ratio. , less than 100%, it is smaller than the gain of the comparative example, and when the screen power ratio is 10% or less and 100%, it is the same as the gain of the comparative example.

In this embodiment, since the gain can be arbitrarily set using the lookup table 149, the optimal gain can be set for the screen power value.

Here, the statement that the gain monotonically decreases includes not only the case where the gain always decreases as the screen power ratio increases, but also the case where the gain remains constant as the screen power ratio increases. Also included. For example, a case where the gain decreases stepwise with respect to an increase in the screen power ratio is also included in the case where the gain decreases monotonically.

In the example shown in FIG. 5, the gain is 1 in the range where the screen power ratio is 10% or less, and the gain with respect to the screen power ratio is monotonous in the range where the screen power ratio is greater than 10% and 100% or less. decreases to In the example shown in FIG. 5, when the screen power ratio is greater than 10% and less than 100%, the gain graph becomes a downwardly convex curve (that is, the rate of change in the slope of the graph is positive). ). More specifically, in at least a part of the range where the screen power ratio is larger than a predetermined value, the gain G is expressed by the following equation 1 using the screen power ratio P.

G=a×P ^b-1 (0<a<1, b<1) (Formula 1)

In the present embodiment, the gain G is expressed by the following equation 2 in a range where the screen power ratio P is greater than 10% and less than 100%.

G=0.4P ^{(1.325/2.2-1)} (Formula 2)

Gamma characteristics when using current limiting circuit 140 according to this embodiment will be explained using FIG. 7.

As shown in FIG. 7, in the case of small-area video display, since the gain is 1, a gamma characteristic in which the brightness is proportional to the pixel value is obtained. In addition, in large-area video display, a gamma characteristic in which the brightness is proportional to the pixel value is obtained in a range where the pixel value is small (a range of 89 or less), and a gamma characteristic where the pixel value is close to the upper limit (255) (a range greater than 89) is obtained. 255 or less), the slope of the graph showing the brightness for each pixel value of a plurality of pixels is greater than zero at any pixel value. More specifically, according to the current limiting circuit 140 according to the present embodiment, a gamma characteristic represented by a curve close to a curve proportional to the pixel value is obtained even in a range where the pixel value is close to the upper limit value. In other words, when using the value Y that normalizes the brightness by the maximum value and the value X that normalizes the pixel value by the maximum value, the following formula 3 holds true in the range where the pixel value is 89 or less.

Y=a1×X ^b1 (Formula 3)

Further, in a range where the pixel value is greater than 89, the following formula 4 holds true.

Y=a2×X ^b2 (Formula 4)

Here, in this embodiment, a1=1>a2=0.4>0, and b1=1>b2>0.

As described above, according to the current limiting circuit 140 according to the present embodiment, the gamma characteristic in a large-area video display can be brought close to the gamma characteristic in a small-area video display.

Furthermore, in current limiting circuit 140 according to the present embodiment, the gain is less than 1 when the screen power ratio is greater than 10%. As a result, the gain can be increased more slowly than in the current limiting circuit of the comparative example in a range where the screen power ratio is greater than 10%. Therefore, the gamma characteristics in large area video display can be brought closer to the gamma characteristics in small area video display.

Note that in the description of the current limiting circuit 140 according to the present embodiment, an example in which the target power ratio is 40% is shown, but the target power ratio is not limited to 40%, and may be greater than 0% or 100%. It is sufficient if it is less than

Further, in the current limiting circuit 140 according to the present embodiment, the gain is 1 when the screen power ratio is 10% or less, but the value of 10% is a value less than the target power ratio. This is just an example of a power ratio. In other words, the first power ratio is not limited to 10%, but may be greater than 0% and less than the target power ratio. The gain determined by the gain determining circuit 148 of the current limiting circuit 140 according to the present embodiment is 1 when the screen power ratio is equal to or less than the first power ratio that is less than the target power ratio; When the power ratio is greater than 1 and less than 100%, it decreases monotonically with respect to the screen power ratio, and when the screen power ratio is greater than or equal to the target power ratio and less than 100%, the target power ratio is changed to the screen power ratio. If the screen power ratio is 100%, it is the target power ratio.

[1-4. Effects, etc.]
As described above, current limiting circuit 140 according to the present embodiment calculates the screen power value related to the power consumption value based on the pixel value of the video signal corresponding to each of the plurality of pixels, and calculates the screen power value related to the power consumption value based on the screen power value. and a gain multiplication circuit 50 that multiplies a pixel value corresponding to each of a plurality of pixels by a gain. The gain determined by the gain determination circuit 148 is 1 when the screen power ratio is less than or equal to the first power ratio that is less than the target power ratio, and is 1 when the screen power ratio is greater than the first power ratio and 100% or less. decreases monotonically with respect to the screen power ratio, and if the screen power ratio is greater than or equal to the target power ratio but less than 100%, the value is less than the value obtained by dividing the target power ratio by the screen power ratio, and the screen power When the ratio is 100%, it is the target power ratio.

According to the current limiting circuit 140 having such a configuration, the brightness can be monotonically increased over the entire range of pixel values even in a large area video display, so that the gamma characteristic in the large area video display can be adjusted to the same level as that in the small area video display. The gamma characteristic can be approached to that of .

In the current limiting circuit 140 according to the present embodiment, in a range where the pixel value is less than or equal to a predetermined first value, the pixel value is normalized by the maximum value X, and a plurality of Between the value Y, which is the luminance of each pixel normalized by the maximum value,
Y=a1×X ^b1 (a1>0, b1>0) (Formula 5)
holds true, and in the range where the pixel value is larger than a predetermined value,
Y=a2×X ^b2 (Formula 6)
holds true, and furthermore, a1>a2>0 and b1>b2>0 may hold true.

Furthermore, in the current limiting circuit 140 according to the present embodiment, in at least a part of the range where the screen power ratio is larger than the predetermined second value, there is a difference between the gain G and the screen power ratio P.
G=a×P ^b-1 (0<a<1, b<1) (Formula 7)
may hold true.

Furthermore, in the current limiting circuit 140 according to the present embodiment, the gain determining circuit 148 may include a lookup table 149 indicating the relationship between the value corresponding to the screen power value and the value corresponding to the gain.

Thereby, according to the gain determination circuit 148, the gain can be set arbitrarily, so that the optimum gain can be set for the screen power value.

Further, in the current limiting circuit 140 according to the present embodiment, the gain determined by the gain determining circuit 148 may be less than 1 if the screen power ratio is larger than the first power ratio which is less than the target power ratio. good.

As a result, the current limiting circuit according to the present embodiment can increase the gain more gently than the current limiting circuit of the comparative example in a range where the screen power ratio is greater than the first power ratio that is less than the target power ratio. Therefore, the gamma characteristics in large area video display can be brought closer to the gamma characteristics in small area video display.

Furthermore, in the current limiting circuit 140 according to the present embodiment, the slope of the graph showing the luminance for each pixel value of a plurality of pixels may be greater than zero at any pixel value.

Furthermore, the display device 110 according to the present embodiment includes a current limiting circuit 140 and a display panel 60.

Since the display device 110 according to the present embodiment includes the current limiting circuit 140, it is possible to make the gamma characteristic in a large-area video display close to the gamma characteristic in a small-area video display.

Further, the current limiting method according to the present embodiment includes a power calculation step of calculating a screen power value related to a power consumption value based on a pixel value of a video signal corresponding to each of a plurality of pixels; and a gain multiplication step of multiplying a pixel value corresponding to each of a plurality of pixels by a gain. The gain determined in the gain determination step is 1 when the screen power ratio is less than or equal to the first power ratio that is less than the target power ratio, and is 1 when the screen power ratio is greater than the first power ratio and 100% or less. decreases monotonically with respect to the screen power ratio, and when the screen power ratio is greater than or equal to the target power ratio and less than 100%, it is a value that is less than the value obtained by dividing the target power ratio by the screen power ratio, and the screen power ratio When is 100%, it is the target power ratio.

The current limiting method having such a configuration provides the same effects as the current limiting circuit 140 described above.

(Embodiment 2)
Next, a display device according to Embodiment 2 will be described. This embodiment differs from Embodiment 1 in the gamma characteristics of the display panel used. The display device according to this embodiment will be described below, focusing on the differences from the display device 110 according to Embodiment 1.

[2-1. Overall configuration of display device]
First, the overall configuration of the display device according to this embodiment will be described using FIG. 8.

FIG. 8 is a block diagram showing the functional configuration of the display device 110a according to this embodiment.

The display device 110a shown in FIG. 8 is a device that displays images based on a video signal, and includes an inverse gamma correction circuit 151, a current limit circuit 140, a gamma correction circuit 152, and a display panel 160.

The inverse gamma correction circuit 151 is a circuit that corrects the relationship between the pixel value included in the video signal and the luminance of each sub-pixel included in the display panel 160 into a proportional relationship. In this embodiment, the inverse gamma correction circuit 151 corrects the gamma characteristic in which the brightness is proportional to the 2.2 power of the pixel value to the gamma characteristic in which the brightness is proportional to the pixel value by converting the pixel value. The inverse gamma correction circuit 151 outputs a video signal including the converted pixel value to the current limiting circuit 140.

Current limiting circuit 140 according to this embodiment has the same configuration as current limiting circuit 140 according to Embodiment 1.

The gamma correction circuit 152 is a circuit that corrects the relationship between the pixel value included in the video signal and the luminance of each sub-pixel included in the display panel 160 from a proportional relationship to a predetermined relationship. In this embodiment, the gamma correction circuit 152 corrects the gamma characteristic in which the brightness is proportional to the pixel value to the gamma characteristic in which the brightness is proportional to the 2.2 power of the pixel value by converting the pixel value. Gamma correction circuit 152 outputs a video signal including the converted pixel values to display panel 160.

As described above, by using the inverse gamma correction circuit 151 and the gamma correction circuit 152, even when using the display panel 160 whose brightness is proportional to the 2.2 power of the pixel value, the current limiting circuit according to the first embodiment 140 can be used.

Display panel 160, like display panel 160 according to Embodiment 1, is a panel that has a plurality of pixels and displays video based on a video signal. Each of the plurality of pixels has a plurality of sub-pixels, and each of the plurality of sub-pixels includes a self-luminous element. Each of the plurality of pixels has three sub-pixels corresponding to three colors of RGB. In the present embodiment, in the display panel 160, the luminance of each sub-pixel is proportional to the 2.2 power of the pixel value input to each sub-pixel.

The display panel 160 is not particularly limited as long as it is a display panel whose brightness is proportional to the 2.2 power of the pixel value. For example, an organic EL display panel or the like can be used as the display panel 160. The configuration of display panel 160 according to this embodiment will be described below using FIG. 9.

FIG. 9 is a block diagram showing the functional configuration of display panel 160 included in display device 110a according to this embodiment.

As shown in FIG. 9, the display panel 160 includes a display section 70, a write processing section 62, a source driver 68, and a write shift register 64. The display section 70 has a plurality of pixels and displays an image corresponding to a video signal. The write processing unit 62 outputs a control signal and a data signal for writing pixel values corresponding to display data to the display unit 70. Source driver 68 outputs a data signal to display section 70 . The write shift register 64 outputs a write signal, which is a control signal for writing a data signal to the display section 70, to the display section 70.

A plurality of pixels included in the display panel 160 will be explained using FIG. 10. FIG. 10 is a circuit diagram illustrating an example of the configuration of sub-pixels that constitute the pixel according to this embodiment. FIG. 10 shows a sub-pixel that uses an organic EL element as a self-luminous element. The pixel according to this embodiment includes three sub-pixels corresponding to three colors, RGB. The subpixel shown in FIG. 10 is a subpixel for emitting red (R) light. Note that the sub-pixels for emitting green and blue light also have the same circuit configuration as the circuit shown in FIG. 10.

As shown in FIG. 10, the sub-pixel includes a TFT (Thin Film Transistor) 81, a capacitor 84, a TFT 82, and a self-luminous element 85r.

A data signal, which is an output signal of the source driver 68, is input to one end of the TFT 81. Capacitor 84 is connected to TFT 81 . A control terminal of the TFT 82 is connected to a connection point between the TFT 81 and the capacitor 84 . The self-luminous element 85r is connected to the TFT 82.

The TFT 81 is switched on/off based on a write signal, which is a control signal output from the write shift register 64. When the TFT 81 is turned on by a write signal within one horizontal period, a data signal which is a source driver output signal corresponding to the signal level written to the pixel is held in the capacitor 84.

After the write signal is turned off, a current corresponding to the voltage held in the capacitor 84 flows through the TFT 82, and the self-luminous element 85r lights up.

First, signals input to the sub-pixels shown in FIG. 10 will be explained using FIG. 11. FIG. 11 is a diagram illustrating an example of a write signal input to a sub-pixel according to this embodiment. The display device 110a writes the data signal output from the source driver 68 into the display section 70 using a write signal, and emits light in units of horizontal lines (hereinafter also simply referred to as "lines").

Next, the transition of the display state of the display section 70 will be explained using FIG. 12. FIG. 12 is a schematic diagram showing the transition of the display state of the display unit 70 according to the present embodiment. In FIG. 12, the display screen transitions from time T1 to time T2, and from time T2 to time T3. At time T1, which corresponds to the end of the m-th field shown in FIG. 12, the screen of the m-th field is displayed. Here, the write shift register 64 that outputs a write signal, which is a control signal for writing a data signal to each pixel, scans from the top to the bottom of the screen starting from the top of the display area of the display unit 70. Outputs a write signal. Therefore, at time T2, which corresponds to the middle of the n-th field (that is, the m+1 field), which is the next field after the m-th field, the upper half of the screen becomes the n-th field screen, and the lower half becomes the m-th field screen. The screen remains. At time T3, which corresponds to the end of the n-th field, the display area is scanned to the bottom, and the entire screen becomes the n-th field screen.

[2-2. Operation example]
Next, an example of the operation of the display device 110a according to the present embodiment will be described while comparing it with the operation of a display device of a comparative example. The relationship between the screen power ratio and the gain according to the present embodiment and the comparative example is as shown in FIG. 5, as in the first embodiment.

Gamma characteristics when the current limiting circuit of the comparative example and the current limiting circuit 140 according to the present embodiment are used in a display device will be described with reference to FIGS. 13 and 14. 13 and 14 are graphs showing gamma characteristics of the display device 110a when using the current limiting circuit of the comparative example and the current limiting circuit 140 according to the present embodiment, respectively. A solid line and a broken line shown in FIGS. 13 and 14 indicate gamma characteristics in the case of large-area video display and small-area video display, respectively. 13 and 14 show gamma characteristics when all pixels are displayed in white as an example of a large-area image display, and gamma characteristics are shown in a case where 10% of pixels are displayed in white as an example of a small-area image display. The gamma characteristics when the other 90% of pixels display black are shown. The horizontal axis of the graphs in FIGS. 13 and 14 indicates the pixel value input to the display device 110a (that is, the pixel value before inverse gamma correction), and the vertical axis indicates the brightness of each pixel.

As shown in FIG. 13, in the current limiting circuit of the comparative example, since the gamma is 1 in the case of small-area video display, a gamma characteristic in which the luminance is proportional to the 2.2 power of the pixel value is obtained. It will be done. On the other hand, in a large-area video display, in a range where the pixel value is small, a gamma characteristic in which the brightness is proportional to the 2.2 power of the pixel value is obtained, but in a range where the pixel value is close to the upper limit (255), the brightness decreases. It remains constant. In this way, in the case of large-area video display, the gamma characteristic is significantly different from the gamma characteristic in which the luminance is proportional to the 2.2 power of the pixel value.

In the current limiting circuit 140 according to the present embodiment, the gain determined by the gain determining circuit 148 is 1 when the screen power ratio is 10% or less, and 100% when the screen power ratio is greater than 10%. In the following cases, the screen power ratio decreases monotonically. Furthermore, when the screen power ratio is equal to or higher than the target power ratio and less than 100%, the gain is a value less than the value obtained by dividing the target power ratio by the screen power ratio, and when the screen power ratio is 100%, This is the target power ratio. In other words, when the screen power ratio is greater than 10% and the screen power ratio is less than the target power ratio, the gain according to the present embodiment is less than or equal to the gain of the comparative example, and the screen power ratio is greater than or equal to the target power ratio. , less than 100%, it is smaller than the gain of the comparative example, and when the screen power ratio is 10% or less and 100%, it is the same as the gain of the comparative example.

The gamma characteristics of the display device 110a when using the current limiting circuit 140 according to this embodiment will be explained using FIG. 14.

As shown in FIG. 14, in the case of small-area video display, since the gain is 1, a gamma characteristic in which the luminance is proportional to the 2.2 power of the pixel value is obtained. In addition, in large-area video display, in a range where the pixel value is small (range of 89 or less), a gamma characteristic in which the brightness is proportional to the 2.2 power of the pixel value is obtained, and the pixel value is close to the upper limit value (255). Even within the range (a range greater than 89 and less than or equal to 255), the slope of the graph showing the luminance for each pixel value of a plurality of pixels is greater than zero at any pixel value. More specifically, according to the current limiting circuit 140 according to the present embodiment, even in a range where the pixel value is close to the upper limit value, a gamma characteristic shown by a curve close to a curve proportional to the 2.2 power of the pixel value can be obtained. ing. In other words, when using the value Y that normalizes the brightness by the maximum value and the value X that normalizes the pixel value by the maximum value, the following formula 8 holds true in a range where the pixel value is 89 or less.

Y=a1×X ^b1 (Formula 8)

Further, in a range where the pixel value is greater than 89, the following formula 9 holds true.

Y=a2×X ^b2 (Formula 9)

Here, in this embodiment, a1=1>a2=0.4>0, and b1=2.2>b2≈1.325>0.

As described above, according to the current limiting circuit 140 according to the present embodiment, the gamma characteristic in a large-area video display can be brought close to the gamma characteristic in a small-area video display.

Further, in current limiting circuit 140 according to the present embodiment, the gain is less than 1 when the screen power ratio is greater than 10%. As a result, the gain can be increased more slowly than in the current limiting circuit of the comparative example in a range where the screen power ratio is greater than 10%. Therefore, the gamma characteristics in large area video display can be brought closer to the gamma characteristics in small area video display.

Note that in the current limiting circuit 140 according to the description of this embodiment, an example is shown in which the target power ratio is 40%, but the target power ratio is not limited to 40%, and may be greater than 0% and less than 100%. That's fine.

Further, in the current limiting circuit 140 according to the present embodiment, the gain is 1 when the screen power ratio is 10% or less, but the value of 10% is a value less than the target power ratio. This is just an example of a power ratio. In other words, the first power ratio is not limited to 10%, but may be greater than 0% and less than the target power ratio.

(Other embodiments)
Although the current limiting circuit and the like according to the present disclosure have been described above based on the embodiments, the current limiting circuit and the like according to the present disclosure are not limited to the above embodiments. Other embodiments realized by combining arbitrary components in each embodiment, and modifications obtained by making various modifications to each embodiment that a person skilled in the art can think of without departing from the gist of the present disclosure. The present disclosure also includes various devices incorporating the current limiting circuit and the like according to the examples and embodiments.

For example, in each of the above embodiments, the current limiting circuit is provided in the display device, but the current limiting circuit does not necessarily need to be provided in the display device. Such a modification will be explained using FIG. 15. FIG. 15 is a block diagram showing the relationship between the current limiting circuit 140 and the display device 210 according to this modification. As shown in FIG. 15, the current limiting circuit 140 is included in a GPU (Graphics Processing Unit) 212. The GPU 212 is an arithmetic unit for image processing, receives a video signal, and outputs a video signal processed by the current limiting circuit 140. The GPU 212 is placed outside the display device 210 and outputs the video signal processed by the processing circuit 20 to the display device 210. The GPU 212 may be included in a PC (Personal Computer) 804 as shown in FIG. 16, for example. The PC 804 is operated using a keyboard 806, a mouse 807, and the like. Display device 210 may be included in monitor 805 shown in FIG. 16. The monitor 805 includes a display device 210 and displays the video signal from the PC 804. Further, the GPU 212 may be included in a hard disk recorder 808 as shown in FIG. 17.

As described above, even when the display device is not equipped with the current limiting circuit 140, the same effects as the current limiting circuit 140 according to the embodiment described above can be achieved.

Further, the display device according to each of the above embodiments may be built into a thin flat TV 802 as shown in FIG. 18. In this case as well, the same effects as in each of the above embodiments can be achieved.

Furthermore, in each of the above embodiments, in order to simplify the explanation, an example was shown in which the brightness is proportional to the pixel value input to the current limit circuit 140, but the brightness is proportional to the pixel value input to the current limit circuit 140. may not necessarily be proportional. For example, even if the brightness is proportional to the 2.2 power of the pixel value input to the current limiting circuit, the same effect as the current limiting circuit according to each of the above embodiments can be achieved by converting the data included in the LUT. It is possible to realize a current limiting circuit that performs well.

Further, in the second embodiment, the display panel 160 whose luminance is proportional to the 2.2 power of the pixel value is used, but the display panel is not limited to this. For example, an organic EL display panel whose luminance is proportional to the 2.4th power or more and the 2.6th power or less of the pixel value may be used.

Further, in the above embodiment, a pixel included in the display panel includes three sub-pixels corresponding to each of the three colors RGB, but the pixel configuration is not limited to this. For example, a pixel may include four sub-pixels, each corresponding to four RGBW colors.

Further, in the above embodiment, the video signal is an RGB signal, but the video signal may include a signal other than the RGB signal. In other words, the video signal may include RGB signals.

Further, in the above embodiment, an example is shown in which a discharge cell of a plasma display panel and an organic EL element are used as the self-luminous elements, but the self-luminous elements are not limited thereto. For example, an inorganic EL element or the like may be used as the self-luminous element.

The present disclosure is useful for organic EL flat panel displays, and is particularly suitable for use in large-screen displays that consume large amounts of power.

43 Weighted average circuit 44 Horizontal period data calculation circuit 45 Screen data storage section 50 Gain multiplication circuit 60, 160 Display panel 62 Writing processing section 64 Writing shift register 68 Source driver 70 Display section 81, 82 TFT
84 capacitor 85r self-luminous element 110, 110a, 210 display device 140 current limiting circuit 148 gain determining circuit 149 look-up table (LUT)
151 Reverse gamma correction circuit 152 Gamma correction circuit 212 GPU
802 Thin flat TV
804 PC
805 Monitor 806 Keyboard 807 Mouse 808 Hard disk recorder

Claims (7)

A current limiting circuit that controls the power consumption value of the plurality of pixels to be equal to or less than the control target power value by limiting the current supplied to the plurality of pixels of a display panel that displays images based on a video signal. ,
Each of the plurality of pixels includes a self-emitting element,
The current limiting circuit is
a gain determination circuit that calculates a screen power value related to the power consumption value based on a pixel value of the video signal corresponding to each of the plurality of pixels, and determines a gain based on the screen power value;
a gain multiplication circuit that multiplies the pixel value corresponding to each of the plurality of pixels by the gain;
The screen power value when a current corresponding to the upper limit of the pixel value is supplied to each of the plurality of pixels is a rated power value, and the ratio of the screen power value to the rated power value is a screen power ratio,
The ratio of the control target power value to the rated power value is set as a target power ratio,
The gain determined by the gain determining circuit is
when the screen power ratio is equal to or less than a first power ratio that is less than the target power ratio, it is 1;
When the screen power ratio is greater than the first power ratio and less than 100%, it monotonically decreases with respect to the screen power ratio,
When the screen power ratio is greater than or equal to the target power ratio and less than 100%, the value is less than the value obtained by dividing the target power ratio by the screen power ratio,
When the screen power ratio is 100%, it is the target power ratio,
In a range where the pixel value is equal to or less than a predetermined first value, a value Between the converted value Y,
Y=a1×X ^b1
holds true, and in the range where the pixel value is larger than a predetermined value,
Y=a2×X ^b2
holds true,
Furthermore, a1>a2>0 and b1>b2>0 hold.
Current limit circuit. In at least a part of the range where the screen power ratio is larger than a predetermined second value, there is a relationship between the gain G and the screen power ratio P: G=a×P ^b−1 (0<a< 1, b<1)
The current limiting circuit according to claim 1, wherein the following holds true. The current limiting circuit according to claim 1 or 2 , wherein the gain determining circuit includes a look-up table indicating a relationship between a value corresponding to the screen power value and a value corresponding to the gain. The gain determined by the gain determining circuit is
The current limiting circuit according to any one of claims 1 to 3 , wherein when the screen power ratio is larger than the first power ratio, it is less than 1. The current limiting circuit according to any one of claims 1 to 4 , wherein a slope of a graph showing luminance with respect to the pixel value of each of the plurality of pixels is greater than zero at any pixel value. The current limiting circuit according to any one of claims 1 to 5 ,
A display device comprising the display panel. A current limiting method for controlling a power consumption value in a plurality of pixels to a control target power value or less by limiting a current supplied to a plurality of pixels of a display panel that displays an image based on a video signal, the method comprising: ,
Each of the plurality of pixels includes a self-emitting element,
The current limiting method includes:
a power calculation step of calculating a screen power value related to the power consumption value based on a pixel value of the video signal corresponding to each of the plurality of pixels;
a gain determining step of determining a gain based on the screen power value;
a gain multiplication step of multiplying the pixel value corresponding to each of the plurality of pixels by the gain;
The screen power value when a current corresponding to the upper limit of the pixel value is supplied to each of the plurality of pixels is a rated power value, and the ratio of the screen power value to the rated power value is a screen power ratio,
The ratio of the control target power value to the rated power value is set as a target power ratio,
The gain determined in the gain determining step is:
when the screen power ratio is equal to or less than a first power ratio that is less than the target power ratio, it is 1;
When the screen power ratio is greater than the first power ratio and less than 100%, it monotonically decreases with respect to the screen power ratio,
When the screen power ratio is greater than or equal to the target power ratio and less than 100%, the value is less than the value obtained by dividing the target power ratio by the screen power ratio,
When the screen power ratio is 100%, it is the target power ratio,
In a range where the pixel value is equal to or less than a predetermined first value, a value Between the converted value Y,
Y=a1×X ^b1
holds true, and in the range where the pixel value is larger than a predetermined value,
Y=a2×X ^b2
holds true,
Furthermore, a1>a2>0 and b1>b2>0 hold.
Current limiting method.

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