JP2013228560A - Light-emitting diode control circuit and display device - Google Patents

Abstract

A light-emitting diode control circuit and a display device capable of suppressing an increase in power consumption and shortening of LED lifetime are provided.
Power consumption is calculated based on an added value of each gradation value of an input video signal. When the added value is equal to or greater than a threshold value, a determination signal is output, and based on the determination signal, At least a part of the gradation value of the input video signal is converted into a gradation value indicating lower luminance, and each of the plurality of light emitting diodes is caused to emit light.
[Selection] Figure 4

Description

  The present invention relates to a display device having a light emitting diode control circuit, and a display unit including a light emitting diode control circuit and a plurality of light emitting diodes.

  In recent years, displays in which a plurality of light emitting diodes (hereinafter referred to as LEDs) are arranged in a matrix have been actively developed.

  The LED used in these displays is a light emitting device that consumes less power and has a very high luminous efficiency when used alone. However, as described above, a display using a large number of LEDs arranged in a matrix form, Since advertising devices and the like require power consumption corresponding to the number of devices, it is necessary to consider power consumption as the size of the display device increases, as with other display devices.

  FIG. 14 is a diagram showing power consumption for each size and content with different brightness in a display using a large number of LEDs arranged in a matrix.

  As shown, when LEDs are provided at the same density per inch, the power consumption increases as the size of the display increases.

  When the brightest content (L1 in the figure) is displayed on the display, it can be seen that the power consumption increases remarkably as the size increases.

  Even when content having an intermediate brightness (L2 in the figure) and the darkest content (L3 in the figure) are displayed on the display, the power consumption is increased, but the brightest content (in the figure) Not as much as when L1) is displayed.

  This is because when a bright content (image) is displayed, a large amount of current flows, which consumes an extreme amount of power. To display a bright content (image), a large current capacity is required. This is because a current output circuit having a current is required, so that a current loss (steady current) on the circuit surface increases.

  In addition, when the light emission efficiency of the LED is high, the display becomes too bright depending on the use state of the display. As a result, excessive power consumption may be consumed, resulting in a waste of power consumption. On the other hand, in such a case, the dynamic range of the LED becomes narrow in the low gradation display region, and there is a problem that it is difficult to display a dark image.

  FIG. 15 is a diagram for explaining a conventional method for setting the gradation value and the luminance of the LED.

  As shown in the figure, conventionally, an electric current that causes an LED to emit light with a certain luminance at a gradation value of one input video signal regardless of the brightness of the input video signal. The amount was set to flow.

  Further, as shown in the figure, the entire gradation value of the input video signal is set so as to cover the entire luminance region where the LED can emit light.

  However, in such a conventional method, as shown in FIG. 15, the LED always emits light with a certain luminance according to the gradation value of a certain input video signal. Since the amount of current flows, the problem of increased power consumption that occurs when displaying bright content cannot be solved.

  On the other hand, Patent Literature 1 discloses a light-emitting advertising device that is driven while changing the brightness of an LED at predetermined time intervals.

  FIG. 16 is a diagram for explaining the method for controlling the luminance of the LED disclosed in Patent Document 1. In FIG.

  As shown in the figure, the above-mentioned Patent Document 1 discloses a mode in which the LED emits light with less than a threshold (brightness 100%) during the normal display mode, while the LED emits light with high brightness to improve visibility. In the eye-catching mode period, the LED brightness control method for causing the LED to emit light at the above threshold value (brightness 200%) is described.

  According to such an LED brightness control method, it is described that the normal display mode and the eye catch mode can be switched according to the purpose of use.

Japanese Unexamined Patent Publication No. 2004-21065 (published on January 22, 2004)

  However, the LED brightness control method disclosed in Patent Document 1 causes the LED to emit light with high brightness during the eye catch mode period, regardless of the brightness of the input video signal. .

  Therefore, when a bright image is displayed during the eye catch mode period, a current output circuit having a large current capacity is required, so that the current loss (steady current) on the circuit surface becomes large and excessive current is required. Since current is generated, there is a problem that power consumption is increased and LED life is shortened.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a light emitting diode control circuit and a display device that can suppress an increase in power consumption and a shortened life of an LED. To do.

In order to solve the above-described problems, a light-emitting diode control circuit according to the present invention is a light-emitting diode control circuit that causes each of a plurality of light-emitting diodes to emit light with a predetermined luminance based on a gradation value of an input video signal. And calculating the power consumption of the plurality of light emitting diodes based on the sum of gradation values of the input video signals, and outputting a determination signal when the sum is equal to or greater than a threshold value. A gradation value converting unit that converts at least a part of the gradation value of the input video signal into a gradation value indicating lower luminance based on the circuit and the determination signal;
And a light emitting diode driving circuit that emits light from each of the plurality of light emitting diodes based on the converted gradation value.

  According to the above configuration, the image determination circuit calculates power consumption of the plurality of light emitting diodes based on an addition value of each gradation value of the input video signal, and the addition value is equal to or greater than a threshold value. In addition, a determination signal is output.

  That is, when the input video signal is a bright video signal, the determination signal is output. When the input video signal is a dark video signal, the determination signal is not output.

  The gradation value conversion unit converts at least a part of the gradation value of the input video signal into a gradation value indicating lower luminance based on the determination signal, and the light emitting diode driving circuit Based on this, each of the plurality of light emitting diodes emits light.

  Therefore, in the above configuration, when the input video signal is a bright video signal, at least a part of the gradation value of the input video signal is converted into a gradation value indicating lower luminance, Since each of the plurality of light emitting diodes emits light, it is possible to suppress the occurrence of current loss and overcurrent on the circuit surface, and thus it is possible to suppress the increase in power consumption and the shortening of the LED life. .

  The image determination circuit in the light emitting diode control circuit of the present invention outputs a first determination signal when the added value is not less than the first threshold value and less than the second threshold value, and the added value is not less than the above value. If it is equal to or greater than the second threshold value, a second determination signal is output, and the gradation value conversion unit at least determines the gradation value of the input video signal based on the first determination signal. A part is converted into a first gradation value indicating lower luminance, and based on the second determination signal, at least a part of the gradation value of the input video signal is converted into the first gradation value. It is preferable to convert to a second gradation value indicating luminance lower than the gradation value.

  According to the above configuration, the gradation value of the input video signal is changed to two different gradation values according to the degree of brightness of the input video signal, that is, the calculated power consumption. Can be converted.

  Therefore, the light emitting diode control circuit can have two different conversion modes.

  In the gradation value converter in the light emitting diode control circuit of the present invention, when the determination signal is not output from the image determination circuit, at least a part of the gradation value of the input video signal is set higher. It is preferable that each of the plurality of light emitting diodes emit light by converting into a gradation value indicating luminance.

  According to the above configuration, when the calculated power consumption is not large, that is, when the input video signal is a dark video signal, at least a part of the gradation value of the input video signal is determined. Since it is converted into a gradation value indicating higher luminance and each of the plurality of light emitting diodes emits light, the visibility of dark images can be improved.

  In the light emitting diode control circuit of the present invention, the conversion of the gradation value of the input video signal into a gradation value indicating a lower luminance may be performed by a lookup table.

  According to the above configuration, since a look-up table is used, it is possible to relatively freely set a value when converting the gradation value of the input video signal to a gradation value indicating a lower luminance, for example, The gradation value can be converted only in the specific gradation value region, or the conversion value can be increased only in the specific gradation value region.

  In the light emitting diode control circuit according to the present invention, the gradation value of the input video signal is converted into a gradation value indicating a lower luminance by X being the gradation value of the input video signal. X ′ = (B / A) × X where X ′ is the tone value, A is the maximum tone value of the input video signal, and B is the target tone value smaller than the maximum tone value A. May be done by satisfying.

  According to the above configuration, since the gradation value of the input video signal can be converted into a gradation value indicating lower luminance, the dynamic range can be increased in a specific gradation value region. It can suppress becoming narrow.

  In the light emitting diode control circuit of the present invention, the conversion of the gradation value of the input video signal into a gradation value indicating higher luminance may be performed by a lookup table.

  According to the above configuration, since a lookup table is used, the setting of the value at the time of conversion to the gradation value indicating the higher luminance of the gradation value of the input video signal can be relatively freely performed. The gradation value can be converted only in the specific gradation value region, or the conversion value can be increased only in the specific gradation value region.

  In the light emitting diode control circuit of the present invention, the gradation value of the input video signal is converted into a gradation value indicating a higher luminance by X being the gradation value of the input video signal. X ′ = (A / B) × X, where X ′ is the tone value, A is the maximum tone value of the input video signal, and B is the target tone value smaller than the maximum tone value A. The light emitting diode control circuit according to claim 3, wherein the light emitting diode control circuit is performed by satisfying

  According to the above configuration, since the gradation value of the input video signal can be converted into a gradation value indicating higher luminance in an equal ratio, the dynamic range is reduced in the specific gradation value region. It can suppress becoming narrow.

  In the light emitting diode control circuit of the present invention, it is preferable that the added value of each gradation value of the input video signal is calculated for each frame of the video signal.

  According to the above configuration, it is possible to realize a light emitting diode control circuit capable of suppressing increase in power consumption and shortening of LED lifetime without causing a delay in conversion of gradation values.

  In the light-emitting diode control circuit of the present invention, it is preferable that the added value of each gradation value of the input video signal is calculated for each of a plurality of frames of the video signal.

  According to the above configuration, a rapid change in luminance can be suppressed.

  In the light emitting diode control circuit of the present invention, the addition value is L (L is a natural number) bit data, and whether the addition value is equal to or greater than the threshold value is N of the addition value (N is N ≦ L). It may be determined by whether the natural number) bit is high or low.

  In the light emitting diode control circuit of the present invention, the addition value is L (L is a natural number) bit data, and whether the addition value is greater than or equal to the first threshold value and less than the second threshold value. M (M is a natural number where M <N) is determined based on whether the bit is high or low, and whether the added value is equal to or greater than the second threshold is determined by N (N is the added value). It may be determined according to whether the bit is high or low.

  In the light emitting diode control circuit of the present invention, the Nth bit of the added value may be the most significant bit.

  According to the above configuration, it can be determined relatively easily whether the added value of the gradation values of the input video signals is equal to or greater than the threshold value.

  In order to solve the above-described problems, a display device according to the present invention includes the light-emitting diode control circuit and a display unit including a plurality of light-emitting diodes.

  According to the said structure, the display apparatus which can suppress the increase in power consumption and the lifetime reduction of LED is realizable.

  As described above, the light emitting diode control circuit of the present invention calculates the power consumption of the plurality of light emitting diodes based on the added value of the gradation values of the input video signals, and the added value is a threshold value. In the above case, an image determination circuit for outputting a determination signal and a level for converting at least a part of the gradation value of the input video signal into a gradation value indicating lower luminance based on the determination signal. In this configuration, a tone value conversion unit and a light emitting diode driving circuit that causes each of the plurality of light emitting diodes to emit light based on the converted gradation value are provided.

  In addition, as described above, the display device of the present invention is configured to include the light emitting diode control circuit and the display unit including a plurality of light emitting diodes.

  Therefore, it is possible to realize a light-emitting diode control circuit and a display device that can suppress an increase in power consumption and shortening of the LED lifetime.

It is a figure for demonstrating conversion of the gradation value performed with the LED drive circuit with which the display apparatus of one embodiment of this invention was equipped. It is a figure for demonstrating conversion of the gradation value performed by the look-up table A for default modes with the LED drive circuit with which the display apparatus of one embodiment of this invention was equipped. It is a figure for demonstrating conversion of the gradation value performed by the look-up table B for low power consumption modes with the LED drive circuit with which the display apparatus of one embodiment of this invention was equipped. It is a figure which shows schematic structure of the display apparatus of one embodiment of this invention. How the determination circuit provided in the display device according to the embodiment of the present invention determines whether the added value obtained by adding all the gradation values included in the video data for one frame exceeds a predetermined threshold. It is a figure for demonstrating. It is a figure which shows schematic structure of the display apparatus of other one Embodiment of this invention. It is a figure for demonstrating the conversion of the gradation value performed by the coefficient multiplier A for low power consumption modes with which the display apparatus of further another embodiment of this invention was equipped. It is a figure for demonstrating conversion of the gradation value performed with the LED drive circuit with which the display apparatus of further another embodiment of this invention was equipped. FIG. 9 is a diagram showing a low power consumption mode 1 look-up table B and a low power consumption mode 2 look up table C used for realizing low power consumption provided in the LED drive circuit shown in FIG. 8. is there. It is a figure which shows schematic structure of the display apparatus of further another embodiment of this invention. The determination circuit provided in the display device of still another embodiment of the present invention adds two threshold values (first threshold values) obtained by adding all the gradation values included in one frame of video data. (Second threshold) is a diagram for explaining how to determine whether it is larger or smaller. The gradation value conversion performed by the low power consumption mode 1 coefficient integrator A and the low power consumption mode 2 coefficient integrator B provided in the display device according to another embodiment of the present invention is performed. It is a figure for demonstrating. To explain the conversion of gradation values performed by the low power consumption mode 1 coefficient multiplier A and the low power consumption mode 2 coefficient multiplier B provided in the display device of still another embodiment of the present invention. FIG. In the display which uses many LED arrange | positioned at matrix form, it is a figure which shows each power consumption in the classification according to the size and the content from which brightness differs. It is a figure for demonstrating the conventional method of setting a gradation value and the brightness | luminance of LED. It is a figure for demonstrating the control method of the brightness | luminance of LED described in patent document 1. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are merely one embodiment, and the scope of the present invention should not be construed as being limited thereto.

  In the following embodiment, a display device including a light emitting diode control circuit and a display unit in which a plurality of LEDs are arranged in a matrix will be described. As an example of this display device, for example, A television receiver, a monitor, a light-emitting advertising device, etc. can be mentioned.

[Embodiment 1]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 4 is a diagram illustrating a schematic configuration of the display device 1 including the light emitting diode control circuit 2 and the LED display unit 3 in which a plurality of LEDs are arranged in a matrix.

  As shown in the figure, the light-emitting diode control circuit 2 includes an image determination circuit 4 and an LED drive circuit 7, and the LED display unit 3 according to the present embodiment has 100 × 100 pieces as an example. LEDs are arranged in a matrix.

  Each LED provided in the LED display unit 3 may be a white LED, and a configuration having a plurality of colors of LEDs, for example, a red LED, a green LED, and a blue LED are packaged together, and for each color. The structure which can be controlled may be sufficient.

  When performing black and white display on the LED display unit 3, a white LED may be used. When performing full color display, a configuration having a plurality of LEDs or a combination of a white LED and a plurality of color filters is used. Etc. can be used.

  The image determination circuit 4 includes an input adder 5 and a determination circuit 6.

  Based on Vsync (vertical synchronization signal) input from the outside, the input adder 5 adds the gradation value included in the video data (Digital Video Data) for one frame as needed, and this addition value is determined by the determination circuit 6. Send to.

  The input adder 5 resets the addition result for each frame, and the determination circuit 6 repeats the determination for each frame.

  In the LED display unit 3 of the present embodiment, 100 × 100 LEDs are arranged in a matrix, and assuming that the gradation value data included in the video data is 8-bit data, one frame. The maximum number of digits obtained by adding all the gradation values included in the video data for 22 minutes is 22 bits.

  FIG. 5 is a diagram for explaining how the determination circuit 6 determines whether the addition value obtained by adding all the gradation values included in the video data for one frame exceeds a predetermined threshold value. .

  FIG. 5A shows a case where the 22nd bit data of the addition value is in the L (low) state, and FIG. 5B shows a case where the 22nd bit data of the addition value is in the H (high) state. The case is shown.

  In this embodiment, since the 22nd bit of the added value is set to MSB (Most Significant Bit), the 22nd bit of the added value is set to L (low) as shown in FIG. ) State, the determination circuit 6 outputs a determination flag L as a determination signal. On the other hand, as shown in FIG. 5B, the 22nd bit of the added value is in the H (high) state. In some cases, a determination flag H is output from the determination circuit 6 as a determination signal.

  When the determination signal output from the determination circuit 6 is the determination flag L, a default mode, which will be described later in detail, is selected, and the gradation value conversion according to this mode is performed by the LED drive circuit 7.

  On the other hand, when the determination signal output from the determination circuit 6 is the determination flag H, a low power consumption mode, which will be described in detail later, is selected, and gradation value conversion in accordance with this mode is performed by the LED drive circuit 7. The

  When the 22nd bit of the addition value is in the H (high) state, the addition value is 2097152 or more, and since 2097152 ÷ (100 × 100) ≈210, the average gradation value per pixel of one frame is 210 or more. In this case, a determination flag H is output from the determination circuit 6 so that the low power consumption mode is selected.

  In the present embodiment, the 22nd bit of the added value is set as the MSB and is used as a threshold value. However, the present invention is not limited to this, and the MSB bit can be set as appropriate. The determination may be made by a combination of the above.

  As shown in FIG. 4, the gradation value included in the video data (Digital Video Data) input from the outside is input to the LED drive circuit 7 in addition to the input adder 5.

  Although not shown, the image determination circuit 4 or the LED drive circuit 7 may be provided with a frame memory that can store the gradation value data of the frame that is determined by the determination circuit 6.

  Although not shown, the LED drive circuit 7 includes a lookup table A used for converting the gradation value when the default mode is selected, and a level when the low power consumption mode is selected. And a lookup table B used to convert the key values.

  In the present embodiment, a lookup table A and a lookup table B are provided as gradation value conversion units, and the lookup table A and the lookup table B are LED driven. Although provided in the circuit 7, the present invention is not limited to this, and may be provided as appropriate in the light emitting diode control circuit 2.

  The LED drive circuit 7 includes a VI conversion circuit, a constant current circuit, a D / A converter, a D / F converter, and the like.

  Then, each LED included in the LED display unit 3 is driven based on the converted gradation value by the lookup table A or the lookup table B.

  Further, the luminance control of each LED by the LED drive circuit 7 can be performed by either a PWM (Pulse Width Modulation) method or a current value control method.

  Hereinafter, the look-up table A used for converting the gradation value when the default mode provided in the LED driving circuit 7 is selected, and the gradation value when the low power consumption mode is selected. The lookup table B used for this purpose will be described in detail.

  FIG. 1 is a diagram for explaining the gradation value conversion performed by the LED drive circuit 7.

  FIG. 1A is a diagram showing the relationship between the gradation value after conversion by the default mode look-up table A and the luminance of the LED, and the relationship between the gradation value set by the conventional method and the luminance of the LED. It is.

  As shown in the figure, after the conversion by the default mode lookup table A, the luminance of the LED becomes higher than that in the case of setting by the conventional method indicated by the dotted line in all gradation values of 0 to 255. Is set to

  Depending on the look-up table A for the default mode, when the input gradation value (input data X) is 204, conversion is performed so that the luminance of the LED becomes 100% that is the Max value.

  In addition, as for the gradation value of the circled area indicated by the dotted line in the figure, the determination flag H is output from the determination circuit 6 when the average gradation value per pixel of one frame is 210 or more, and the low power consumption Since the mode is selected, it is not actually input.

  On the other hand, FIG. 1B shows the relationship between the gradation value converted by the low power consumption mode look-up table B and the luminance of the LED, the gradation value set by the conventional method, and the luminance of the LED. It is a figure which shows a relationship.

  As shown in the figure, after conversion by the low power consumption mode look-up table B, the brightness of the LED is higher than that in the conventional method indicated by the dotted line in all gradation values of 0 to 255. It is set to be low.

  FIG. 2 is a diagram for explaining the gradation value conversion performed by the default mode lookup table A. FIG.

  In the default mode look-up table A, based on a graph showing the relationship between the gradation value set by the conventional method shown in the left diagram of FIG. Conversion is performed.

  According to the graph shown in the left diagram of FIG. 2A, the luminance of the LED is 60% at the gradation value 204, but the input gradation value is determined by the default mode lookup table A shown in FIG. 204 (input data X) is converted and output with an output gradation value 255 (output data X ′). According to the graph shown in the left diagram of FIG. Since the luminance is 100%, when the gradation values are converted by the default mode lookup table A shown in FIG. 2B for all gradation values, the solid line in FIG. 1A and FIG. The graph is as shown in the right figure of a).

  As shown in FIG. 1 (a), after conversion by the default mode lookup table A, the LED is compared with the case where it is set by the conventional method indicated by the dotted line in all gradation values of 0 to 255. Since the brightness is set to be high, the visibility of dark images can be improved.

  In this embodiment, in order to improve the visibility of dark images, a look-up table A for default mode is provided, but when the default mode is selected without providing look-up table A, Alternatively, the gradation value may not be converted.

  Further, in the present embodiment, a case has been described in which tone value conversion is performed using a lookup table when the default mode is selected. For the conversion to the tone value, the gradation value of the input video signal is X, the converted gradation value is X ′, and the input video signal is the same as the method described later in Embodiment 3 in detail. Is the maximum gradation value A (255 in the present embodiment), and the target gradation value smaller than the maximum gradation value A is B (204 in the present embodiment), X ′ = ( A / B) × X may be satisfied.

  By performing the gradation value conversion in this way, the gradation value conversion can be performed in an equal ratio, so that the dynamic range can be prevented from becoming narrow in the specific gradation value region. .

  FIG. 3 is a diagram for explaining the gradation value conversion performed by the low power consumption mode lookup table B. FIG.

  In the low power consumption mode look-up table B, the gradation is determined based on the graph showing the relationship between the gradation value set by the conventional method shown in the left diagram of FIG. Value conversion is performed.

  According to the graph shown in the left diagram of FIG. 3A, the luminance of the LED becomes 100% at the gradation value 255, but the input floor is determined by the low power consumption mode lookup table B shown in FIG. The tone value 255 (input data X) is converted into an output tone value 229 (output data X ′). According to the graph shown in the left diagram of FIG. Therefore, when the gradation values are converted for all gradation values by the low power consumption mode lookup table B shown in FIG. 3B, the solid line in FIG. 1B and FIG. ) On the right.

  As shown in FIG. 1B, after conversion by the low power consumption mode lookup table B, all gradation values from 0 to 255 are set by the conventional method indicated by the dotted line. Furthermore, since the brightness of the LED is set to be low, it is possible to suppress the occurrence of current loss and overcurrent on the circuit surface, thereby suppressing the increase in power consumption and the shortening of the LED life. can do.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the addition value is calculated for each of a plurality of frames (for example, 5 frames), and the addition value is calculated for each frame in that the determination is made for each of the plurality of frames (for example, 5 frames). This is different from the first embodiment in which the determination is performed for each frame. Other configurations are as described in the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 6 is a diagram showing a schematic configuration of a display device 1a including a light emitting diode control circuit 2a and an LED display unit 3 in which a plurality of LEDs are arranged in a matrix.

  As illustrated, the light emitting diode control circuit 2a includes an image determination circuit 4a and an LED driving circuit 7.

  The input adder 5 provided in the image determination circuit 4a includes video data (Digital Video Data) for a plurality of frames (for example, 5 frames) based on Vsync (vertical synchronization signal) input from the outside. The gradation values to be added are added as needed, and this added value is sent to the determination circuit 6.

  The input adder 5 resets the addition result every 5 frames, and the determination circuit 6 repeats the determination every 5 frames.

  In the LED display unit 3 of the present embodiment, 100 × 100 LEDs are arranged in a matrix, and the gradation value data included in the video data is 8-bit data. The maximum number of digits obtained by adding all the gradation values included in the video data of the minute is from 100 × 100 × 8 bits × 5 to 24 bits.

  Then, the determination circuit 6 determines whether the addition value obtained by adding all the gradation values included in the video data for five frames exceeds a predetermined threshold value.

  In this embodiment, since the 24th bit of the added value is set to MSB (Most Significant Bit), when the 24th bit of the added value is in the L (low) state, the determination circuit 6 The determination flag L is output as a determination signal, and when the 24th bit of the added value is in the H (high) state, the determination circuit 6 outputs the determination flag H as the determination signal.

  As shown in the figure, in the present embodiment, it is determined whether or not the addition value obtained by adding all the gradation values included in the video data for five frames exceeds a predetermined threshold value. Since the time required for the determination becomes longer than that in the first embodiment, the image determination circuit 4a is provided with an N frame memory 8 capable of storing the gradation values included in the video data for five frames.

  The position where the N frame memory 8 is provided is not limited to the image determination circuit 4a, and can be provided in the light emitting diode control circuit 2a such as the LED drive circuit 7.

  In such a configuration, the display itself is delayed by 5 frames, but a rapid luminance change can be suppressed.

[Embodiment 3]
Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the gradation value is converted by using the coefficient accumulator A instead of the lookup table B used for converting the gradation value when the low power consumption mode is selected. This is different from the first embodiment. Other configurations are as described in the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 7 is a diagram for explaining the gradation value conversion performed by the low power consumption mode coefficient multiplier A. FIG.

  Also in the low power consumption mode coefficient accumulator A, the gradation based on the graph showing the relationship between the gradation value set by the conventional method shown in the left diagram of FIG. Value conversion is performed.

  According to the graph shown in the left diagram of FIG. 7A, the luminance of the LED is 100% at the gradation value 255, but the input floor is reduced by the low power consumption mode coefficient integrator A shown in FIG. The tone value 255 (input data X) is converted into an output tone value 229 (output data X ′). According to the graph shown in the left diagram of FIG. Therefore, when the gradation values are converted by the low power consumption mode coefficient integrator A shown in FIG. 7B for all gradation values, a graph as shown in the right diagram of FIG. It becomes.

  As shown in FIG. 7B, the gradation value conversion by the low power consumption mode coefficient integrator A is performed by converting the gradation value of the input video signal to X and the converted gradation value. X ′, the maximum gradation value of the input video signal is A (255 in the present embodiment), and the target gradation value smaller than A which is the maximum gradation value is B (229 in the present embodiment). ), X ′ = (B / A) × X is satisfied.

  According to the above configuration, the gradation value can be converted in an equal ratio, so that it is possible to suppress the dynamic range from being narrowed in the specific gradation value region.

[Embodiment 4]
Next, a fourth embodiment of the present invention will be described based on FIGS. The present embodiment is different from the first embodiment in that a plurality (two) of low power consumption modes are provided and a plurality (two) of low power consumption mode lookup tables are provided. . Other configurations are as described in the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 10 is a diagram showing a schematic configuration of a display device 1b including a light emitting diode control circuit 2b and an LED display unit 3 in which a plurality of LEDs are arranged in a matrix.

  As illustrated, the light emitting diode control circuit 2b includes an image determination circuit 4b and an LED drive circuit 7a. The image determination circuit 4b includes an input adder 5 and a determination circuit 6a. ing.

  The LED drive circuit 7a includes a default mode lookup table A, a low power consumption mode 1 lookup table B, and a low power consumption mode 2 lookup table C as a low power consumption mode lookup table. Is provided.

  FIG. 11 shows whether the addition value obtained by adding all the gradation values included in the video data for one frame by the determination circuit 6a is larger or smaller than two different threshold values (first threshold value / second threshold value). It is a figure for demonstrating how to determine.

  In the present embodiment, as shown in the figure, when the 21st bit of the addition value is in the H (high) state, the addition value is 1048576 or more, and 1048576 ÷ (100 × 100) ≈105, The case where the average gradation value per pixel of the frame is 105 or more is set as the first threshold value. When the 22nd bit of the addition value is in the H (high) state, the addition value is 2097152 or more, and 2097152 ÷ ( Since 100 × 100) ≈210, the second threshold value is a case where the average gradation value per pixel of one frame is 210 or more.

  Therefore, in the present embodiment, the 21st bit of the addition value and the 22nd bit of the addition value are set in the MSB.

  As shown in FIG. 11A, when both the 21st bit of the added value and the 22nd bit of the added value are in the L (low) state, the average gradation per pixel of one frame Since the value is less than 105, the determination circuit 6a outputs the determination flag LL as a determination signal, and the default mode is selected.

  As shown in FIG. 11B, when the 21st bit of the added value is in the H (high) state and the 22nd bit of the added value is in the L (low) state, one frame is obtained. Since the average gradation value per pixel is 105 or more and exceeds the first threshold value, the determination circuit 6a outputs a determination flag HL as a determination signal, and the low power consumption mode 1 is selected.

  Then, as shown in FIG. 11C and FIG. 11D, when the 22nd bit of the added value is in the H (high) state, the average gradation value per pixel of one frame Is 210 or more and exceeds the second threshold value, the determination circuit 6a outputs the determination flag LH or the determination flag HH as the determination signal, and the luminance of the LED is lower than that in the low power consumption mode 1. The low power consumption mode 2 set as described above is selected.

  In the present embodiment, in order to simplify the determination, the case where the determination is performed using only the 21st bit and the 22nd bit is given as an example, but the present invention is not limited to this. It is also possible to perform determination using an arbitrary average gradation value as a threshold value by changing the combination pattern using these bits.

  FIG. 8 is a diagram for explaining the gradation value conversion performed in the LED drive circuit 7a.

  FIG. 8A is the same as FIG. 1A of the first embodiment, and since it has already been described in the first embodiment, the description thereof is omitted here.

  FIG. 8B is also the same as FIG. 1B of the first embodiment, and since it has already been described in the first embodiment, the description thereof is omitted here. However, the low power consumption mode in the first embodiment is the low power consumption mode 1 in the present embodiment.

  FIG. 8C is a diagram for explaining the low power consumption mode 2.

  The gradation value conversion in the low power consumption mode 2 is also based on the graph showing the relationship between the gradation value set by the conventional method shown by the dotted line in FIG. 8C and the luminance of the LED. A key value conversion is performed.

  According to the dotted line graph shown in FIG. 8C, the luminance of the LED is 100% at the gradation value 255, but the input gradation value 255 (input data) is determined by the low power consumption mode 2 lookup table C described later. X) is converted, and an output gradation value 187 (output data X ′) is output.

  According to the dotted line graph shown in FIG. 8C, since the luminance of the LED is 50% at the gradation value 187, all the gradation values are determined according to the lookup table C for low power consumption mode 2 described later. When the gradation value is converted, a graph like the solid line in FIG. 8C is obtained.

  Then, the graph showing the relationship between the converted gradation value and the luminance of the LED by the lookup table C for low power consumption mode 2 shown by the solid line in FIG. 8C, and the solid line in FIG. 8B. Compared with the graph indicating the relationship between the converted gradation value and the luminance of the LED by the low power consumption mode 1 look-up table B shown in FIG. 8, it is shown by a solid line in FIG. It can be seen that lower power consumption can be realized by conversion using the lookup table C for low power consumption mode 2.

  FIG. 9 is a diagram showing a low power consumption mode 1 look-up table B and a low power consumption mode 2 look up table C that are used to realize low power consumption in the present embodiment. .

  FIG. 9A shows a lookup table B for the low power consumption mode 1. For example, the input tone value 255 (input data X) is converted by this lookup table B, and the output tone value 229 is converted. Output as (output data X ′).

  FIG. 9B shows a lookup table C for the low power consumption mode 2, and for example, the input gradation value 255 (input data X) is converted by this lookup table C, and the output gradation value 187 is converted. Output as (output data X ′).

  According to the above configuration, the look-up table B for the low power consumption mode 1 or the look for the low power consumption mode 2 depending on the brightness level of the input video signal, that is, the calculated power consumption level. The up table C is selected.

  When the degree of brightness of the input video signal, that is, when the calculated power consumption is relatively large, the low power consumption mode 2 lookup table C that can realize lower power consumption is provided. It is to be selected.

[Embodiment 5]
Next, a fifth embodiment of the present invention will be described based on FIG. 12 and FIG. In the present embodiment, when the low power consumption mode 1 or the low power consumption mode 2 is selected, the coefficient integrator A and the coefficient integrator B are used instead of using the look-up table to convert the gradation value. Unlike the first, second, and fourth embodiments, in that tone value conversion is performed using, and different from the third embodiment in that a plurality of coefficient integrators are used. Other configurations are as described in the third embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the third embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 12 is a diagram for explaining the gradation value conversion performed by the low power consumption mode 1 coefficient multiplier A and the low power consumption mode 2 coefficient multiplier B.

  In both the low power consumption mode 1 coefficient integrator A and the low power consumption mode 2 coefficient integrator B, the gradation value and the LED brightness set by the conventional method shown in the left diagram of FIG. The gradation value is converted based on the graph showing the relationship.

  In the present embodiment, the low power consumption mode coefficient multiplier A already described with reference to FIG. 7 of the third embodiment is used as the low power consumption mode 1 coefficient multiplier A as it is.

  According to the graph shown in the left diagram of FIG. 12, the luminance of the LED is 100% at the gradation value 255. However, the input gradation value 255 (input data X ) Is converted into an output gradation value 229 (output data X ′). According to the graph shown in the left diagram of FIG. 12, the luminance of the LED is 80% at the gradation value 229. When the gradation value is converted by the low-power consumption mode 1 coefficient integrator A, a graph as shown in the upper right diagram of FIG. 12 is obtained.

  On the other hand, the input tone value 255 (input data X) is converted by the coefficient multiplier B for low power consumption mode 2 described later to become the output tone value 217 (output data X ′), which is shown in the left diagram of FIG. According to the graph, since the luminance of the LED becomes 70% at the gradation value 217, when the gradation value is converted by the coefficient multiplier B for the low power consumption mode 2 for all gradation values, FIG. The graph will be as shown in the lower right figure.

  FIG. 13 is a diagram for explaining the coefficient multiplier A for low power consumption mode 1 and the coefficient multiplier B for low power consumption mode 2.

  In the present embodiment, as in the case of the above-described fourth embodiment, the addition value obtained by adding all the gradation values included in the video data for one frame by the determination circuit 6a is two different threshold values (first 1 threshold value / second threshold value), and if the added value is less than the first threshold value, the default mode is selected, and the default mode lookup table A determines the gradation value. Conversion is performed.

  If the added value is not less than the first threshold value and less than the second threshold value, the low power consumption mode 1 is selected, and the gradation value is converted by the low power consumption mode 1 coefficient multiplier A. If the added value is equal to or greater than the second threshold value, the low power consumption mode 2 is selected, and the gradation value is converted by the low power consumption mode 2 coefficient multiplier B.

  FIG. 13 shows a case where the added value is equal to or greater than the second threshold, the low power consumption mode 2 is selected, and the gradation value is converted by the low power consumption mode 2 coefficient multiplier B. .

  As shown in the figure, the gradation value conversion by the low-power consumption mode 2 coefficient integrator B is performed by converting the gradation value (input data) of the input video signal to X and the converted gradation value (output data). ) Is X ′, the maximum gradation value of the input video signal is A (255 in this embodiment), and the target gradation value smaller than A, which is the maximum gradation value, is B (in this embodiment). 217), X ′ = (B / A) × X is satisfied.

  According to the above configuration, the gradation value can be converted in an equal ratio, so that it is possible to suppress the dynamic range from being narrowed in the specific gradation value region.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the present invention can be obtained by appropriately combining technical means disclosed in different embodiments. Embodiments are also included in the technical scope of the present invention.

  The present invention can be suitably used for a light emitting diode control circuit and a display device including a plurality of light emitting diodes.

DESCRIPTION OF SYMBOLS 1, 1a, 1b Display apparatus 2, 2a, 2b Light emitting diode control circuit 3 LED display part (display part)
4, 4a, 4b Image determination circuit 5 Input adder 6, 6a Determination circuit 7, 7a LED drive circuit (light emitting diode drive circuit)
8 N frame memory

Claims (13)

A light-emitting diode control circuit that emits each of a plurality of light-emitting diodes with a predetermined luminance based on a gradation value of an input video signal;
An image determination circuit that calculates power consumption of the plurality of light emitting diodes based on an addition value of each gradation value of the input video signal, and outputs a determination signal when the addition value is equal to or greater than a threshold; ,
A gradation value conversion unit that converts at least a part of the gradation value of the input video signal into a gradation value indicating lower luminance based on the determination signal;
A light emitting diode control circuit comprising: a light emitting diode driving circuit that causes each of the plurality of light emitting diodes to emit light based on the converted gradation value. When the addition value is not less than the first threshold and less than the second threshold, the image determination circuit outputs a first determination signal, and the addition value is not less than the second threshold. Outputs a second determination signal,
In the gradation value conversion unit, based on the first determination signal, at least a part of the gradation value of the input video signal is converted into a first gradation value indicating lower luminance, Based on the second determination signal, at least a part of the gradation value of the input video signal is converted into a second gradation value indicating luminance lower than the first gradation value. The light-emitting diode control circuit according to claim 1, wherein:   The gradation value conversion unit converts at least a part of the gradation value of the input video signal into a gradation value indicating higher luminance when the determination signal is not output from the image determination circuit. The light emitting diode control circuit according to claim 1, wherein each of the plurality of light emitting diodes emits light.   3. The light emitting diode control circuit according to claim 1, wherein the conversion of the gradation value of the input video signal into a gradation value indicating lower luminance is performed by a lookup table.   The conversion of the gradation value of the input video signal to a gradation value indicating lower luminance is performed by inputting the gradation value of the input video signal as X and the converted gradation value as X ′. When the maximum gradation value of the video signal is A and the target gradation value smaller than the maximum gradation value A is B, X ′ = (B / A) × X is satisfied. The light-emitting diode control circuit according to claim 1 or 2.   4. The light emitting diode control circuit according to claim 3, wherein the conversion of the gradation value of the input video signal into a gradation value indicating higher luminance is performed by a lookup table.   The conversion of the input video signal into a gradation value indicating higher luminance is performed by inputting the input image signal with the gradation value X and the converted gradation value X 'with the input value. When the maximum gradation value of the video signal is A and the target gradation value smaller than the maximum gradation value A is B, X ′ = (A / B) × X is satisfied. The light-emitting diode control circuit according to claim 3.   The light emitting diode control circuit according to any one of claims 1 to 7, wherein an added value of gradation values of each of the input video signals is calculated for each frame of the video signal. .   8. The light emitting diode control circuit according to claim 1, wherein an added value of gradation values of each of the input video signals is calculated for each of a plurality of frames of the video signal. . The added value is L (L is a natural number) bit data,
2. The determination as to whether or not the added value is greater than or equal to the threshold value is based on whether the Nth bit (N is a natural number where N ≦ L) of the added value is high or low. The light-emitting diode control circuit according to any one of 1 to 9. The added value is L (L is a natural number) bit data,
Whether the added value is greater than or equal to the first threshold value and less than the second threshold value is determined by whether the M bit (M is a natural number where M <N) of the added value is high or low. And
Whether the added value is greater than or equal to the second threshold value is determined by whether the Nth bit (N is a natural number where N ≦ L) of the added value is high or low. The light-emitting diode control circuit according to claim 2.   12. The light emitting diode control circuit according to claim 10, wherein the Nth bit of the added value is the most significant bit.   A display device comprising: the light-emitting diode control circuit according to claim 1; and a display unit including a plurality of light-emitting diodes.

Images