JP2008233353A - Image display device and driving method of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of suitably reducing power consumption while taking other factors except light emission efficiency into consideration when reducing the power consumption using a light emitting device of a color superior in light emission efficiency. <P>SOLUTION: An image display device includes a storage means of storing conversion information for converting first to third pieces of grayscale information constituting image data and corresponding to first to third colors into first to fourth pieces of grayscale information corresponding to first to fourth colors, and first to fourth light emitting device circuits constituted including first to fourth light emitting devices emitting light beams of first to fourth colors and first to fourth driving transistors connected to the first to fourth light emitting devices in series. A source voltage applied to the first to the fourth light emitting device circuits is set to a value relatively lower than a voltage needed to make the fourth light emitting device emit light according to a maximum grayscale. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image display device and a driving method thereof.

  Conventionally, there has been known an image display device using an organic EL (Electroluminescence) element in which the emission luminance of electroluminescence is controlled by the amount of current (for example, Patent Document 1).

  In this organic EL element, it is known that the higher the luminous efficiency (that is, the luminance with respect to the current density), the lower the power consumption.

  Therefore, a pixel that emits light of another color (for example, white (W)) with high luminous efficiency for three types of pixels that emit light of the three primary colors of red (R), green (G), and blue (B). For example, methods for reducing power consumption by adding (W pixels) have been proposed (for example, Patent Documents 2 to 5). In addition, a liquid crystal display (for example, Patent Document 6) and a plasma display (for example, Patent Document 7) in which W pixels are added to pixels of three primary colors of RGB have been proposed.

JP 2006-309258 A JP 2000-200061 A US Pat. No. 6,916,681 US Pat. No. 7,012,588 US Pat. No. 7,091,941 Japanese Examined Patent Publication No. 04-60370 US Pat. No. 4,513,281

  However, in the above prior art, the reduction of power consumption by improving the light emission efficiency was aimed at, but other factors other than the light emission efficiency with respect to the power consumption were hardly taken into consideration.

  The present invention has been made in view of the above-described problems, and when reducing the power consumption by using a light emitting element with excellent light emission efficiency, the low power consumption is taken into consideration in addition to the light emission efficiency. An object is to provide a technology capable of appropriately performing power generation.

  In order to solve the above-mentioned problems, the invention of claim 1 is an image display device, wherein the first to third gradation information corresponding to the first to third colors constituting the image data, Storage means for storing conversion information for converting the first to fourth gradation information corresponding to the first to fourth colors, and the first to fourth light emitting the first to fourth colors. A first to a fourth light emitting element circuit configured to include a light emitting element and first to fourth driving transistors connected in series to the first to fourth light emitting elements; A power supply voltage applied to the light emitting element circuit is set to a value relatively lower than a voltage necessary for causing the fourth light emitting element to emit light according to the maximum gradation.

  The invention according to claim 2 is the image display device according to claim 1, wherein the power supply voltage is a voltage required when the first to third light emitting elements emit light according to the maximum gradation. It is characterized by being set to a value equal to or greater than the maximum value.

  The invention according to claim 3 is the image display device according to claim 1 or 2, wherein the fourth gradation is included in a combination of the first to fourth gradations related to the conversion information. Is set to be smaller than the maximum gradation and equal to or less than a predetermined gradation corresponding to the power supply voltage.

  The invention according to claim 4 is the image display device according to any one of claims 1 to 3, wherein the conversion information is for each combination of the first to third gradations. It is information associated with a combination of first to fourth gradations that consumes less power than when the fourth light emitting element emits light according to the maximum gradation.

  The invention according to claim 5 is the image display device according to any one of claims 1 to 4, wherein the conversion information is for each combination of the first to third gradations. It is information associated with a combination of first to fourth gradations that minimizes power consumption.

  The invention according to claim 6 is the image display device according to any one of claims 1 to 5, wherein the light emitting element is an organic EL element.

  According to a seventh aspect of the present invention, there is provided an image display device comprising: first to fourth light emitting elements that emit light of first to fourth colors that are included in each picture element and are different from each other; A predetermined calculation for calculating a plurality of combinations of the first to fourth gradations corresponding to the first to fourth colors from the combination of the first to third gradations corresponding to the first to third colors. Rules, first to fourth gradation voltage data storing the relationship between gradation and voltage for the first to fourth colors, and gradation and current for the first to fourth colors, respectively. Storage means for storing the first to fourth gradation current data storing the relationship, and reception for receiving image data including information on the first to third gradations relating to the first to third colors And information of the first to third gradations included in the image data according to the means and the predetermined calculation rule Referring to the deriving means for deriving a plurality of combinations of the first to fourth gradations, the first to fourth gradation voltage data, and the first to fourth gradation current data, Recognizing means for recognizing one set of first to fourth gradation combinations having relatively low power consumption among a plurality of combinations of first to fourth gradations derived by the deriving means. It is characterized by.

  The invention according to claim 8 is the image display device according to claim 7, wherein the recognizing means includes the first to fourth gradation voltage data and the first to fourth gradation current data. Referring to the above, among a plurality of combinations of the first to fourth gradations derived by the deriving means, a combination of the first to fourth gradations that is a predetermined number from the lowest power consumption It is characterized by recognizing.

  The invention according to claim 9 is the image display device according to claim 8, wherein the predetermined number is the first number.

  The invention of claim 10 is the image display device according to any one of claims 7 to 9, wherein the first to fourth light emitting elements and the first to fourth light emitting elements are used. 1st to 4th light emitting element circuit comprised including the 1st to 4th drive transistor connected in series, and a power supply voltage applied to the 1st to 4th light emitting element circuit is The fourth light emitting element is set to be relatively lower than a voltage required when light is emitted according to the maximum gradation.

  An eleventh aspect of the invention is the image display device according to the tenth aspect, wherein the power supply voltage is necessary when the first to third light emitting elements respectively emit light according to the maximum gradation. The value is set to a value equal to or higher than the first to third required voltages, and the predetermined calculation rule is set so that the derivation means does not derive a fourth gradation that requires a voltage exceeding the power supply voltage. It is characterized by that.

  The invention according to claim 12 is the image display device according to any one of claims 7 to 11, wherein the combination of the first to fourth gradations recognized by the recognition means, and the first And adjusting means for adjusting power supply voltages respectively applied to the first to fourth light emitting elements based on the first to fourth gradation voltage data.

  The invention of claim 13 is the image display device according to any one of claims 7 to 12, wherein the light emitting element is an organic EL element.

  According to a fourteenth aspect of the present invention, the first to fourth light emitting elements that emit light of the first to fourth colors and the first to fourth drives connected in series to the first to fourth light emitting elements. The first to fourth light emitting element circuits including transistors and the first to third gradation information corresponding to the first to third colors correspond to the first to fourth colors. A method for driving an image display apparatus having conversion information for converting to first to fourth gradation information, and receiving image data including the first to third gradation information; And B for deriving a combination of first to fourth gradations from first to third gradation information included in the image data according to the conversion information, and the first to fourth light emitting elements. The power supply voltage applied to the circuit emits light from the fourth light emitting element according to the maximum gradation. Characterized in that it is set to a relatively lower value than the voltage necessary for causing.

According to a fifteenth aspect of the present invention, there is provided a picture element including first to fourth light emitting elements that emit light of first to fourth colors, and first to third colors corresponding to the first to third colors. A predetermined calculation rule for calculating a plurality of combinations of the first to fourth gradations corresponding to the first to fourth colors from a combination of the first to third gradations; The first to fourth gradation voltage data storing the relationship between gradation and voltage for each color, and the first to fourth storing the relationship between gradation and current for each of the first to fourth colors. And a step a for receiving image data including information on the first to third gradations corresponding to the first to third colors, From the first to third gradation information included in the image data according to the predetermined calculation rule Referring to the step b for deriving a plurality of combinations of first to fourth gradations, the first to fourth gradation voltage data, and the first to fourth gradation current data, the step b Recognizing one set of first to fourth gradation combinations with relatively low power consumption among the plurality of combinations of the first to fourth gradations derived in step c.
It is characterized by providing.

  According to one aspect of the present invention, a plurality of combinations of the first to fourth gradations related to the first to fourth colors are calculated from a combination of the first to third gradations related to the first to third colors. Predetermined calculation rules, first to fourth gradation voltage data storing the relationship between gradation and voltage for the first to fourth colors, and gradation and current for the first to fourth colors, respectively. First to fourth gradation current data storing the relationship are prepared, image data including information of the first to third gradations is received, and the first included in the image data is determined according to a predetermined calculation rule. A plurality of combinations of the first to fourth gradations are derived from the information on the first to fourth gradations, and are derived with reference to the first to fourth gradation voltage data and the first to fourth gradation current data. Among the plurality of combinations of the first to fourth gradations, a combination of the first to fourth gradations with relatively low power consumption Recognizing and causing each of the first to fourth light emitting elements according to the first to fourth colors to emit light based on the combination of the first to fourth gradations, the power supply voltage in addition to the light emission efficiency. The power consumption can be reduced in consideration of the influence of the above. In other words, when reducing the power consumption by using a light emitting element having a color with excellent luminous efficiency, it is possible to appropriately reduce the power consumption in consideration of other factors besides the luminous efficiency.

  Further, among the plurality of derived combinations of the first to fourth gradations, the first to fourth colors according to the first to fourth colors based on a predetermined first to fourth gradation combination from the one with lower power consumption. By causing each of the light emitting elements 1 to 4 to emit light, it is possible to easily and appropriately reduce power consumption.

  In addition, based on the combination of the first to fourth gradations that consumes the lowest power among the derived combinations of the first to fourth gradations, the first to fourth colors 1 to 4 are associated with the first to fourth colors. By making each light emitting element emit light, the power consumption can be reduced more appropriately.

  In addition, since the power supply voltage applied to the first to fourth light emitting element circuits is set relatively lower than the voltage required for causing the fourth light emitting element to emit light according to the maximum gradation, Low power consumption can be achieved by suppressing the voltage.

  Further, the power supply voltage is set to a value higher than the voltage necessary for causing the first to third light emitting elements to emit light according to the maximum gradation, and a fourth gradation that requires a voltage exceeding the power supply voltage is derived. Therefore, it is possible to easily reduce power consumption by suppressing the power supply voltage.

  Moreover, since the power supply voltage applied to each of the first to fourth light emitting elements is adjusted based on the recognized combination of the first to fourth gradations and the first to fourth gradation voltage data, It is possible to finely reduce the power consumption by suppressing the power supply voltage.

  According to another aspect of the present invention, for each combination of the first to third gradations relating to the first to third colors, the combination of the first to fourth gradations relating to the first to fourth colors is obtained. The associated conversion information is prepared, and the power supply voltage applied to each of the first to fourth light emitting element circuits is relative to the voltage required for causing the fourth light emitting element to emit light according to the maximum gradation. Image data including information on the first to third gradations relating to the first to third colors is received and derived from the information on the first to third gradations included in the image data in accordance with the conversion information. When the first to fourth light emitting elements are caused to emit light based on the combination of the first to fourth gradations, the light emitting elements having excellent emission efficiency are used to reduce power consumption. Considering other factors other than the luminous efficiency, it is possible to appropriately reduce the power consumption.

  In addition, since the power supply voltage is set to a value equal to or higher than the maximum value of the voltage necessary for causing the first to third light emitting elements to emit light according to the maximum gradation, the maximum order of the first to third gradations is set. The power consumption can be reduced by suppressing the power supply voltage within a range in which monochromatic light emission of the first to third colors according to the tone is possible.

  In the combination of the first to fourth gradations related to the conversion information, the fourth gradation is set to be lower than the maximum gradation and equal to or less than a predetermined gradation corresponding to the power supply voltage. Low power consumption can be achieved by suppressing the voltage.

  Further, the conversion information is converted into the first to fourth floors that consume less power than the case where the fourth light emitting element emits light according to the maximum gradation for each combination of the first to third gradations. By using information associated with key combinations, it is possible to reduce power consumption by suppressing power supply voltage.

  Further, the conversion information is information in which the combination of the first to fourth gradations that minimizes the power consumption is associated with each combination of the first to third gradations, thereby reducing the power consumption. Can be performed more appropriately.

<Glossary>
The “gradation” of each color referred to in this specification is used as a parameter indicating the degree of brightness of each color. For example, in gradation representation of a predetermined bit (for example, 8 bits), the gradation of each color is The minimum value (for example, 0 gradation) means that it is reproduced darkest on the screen, and the maximum value (for example, 255 gradation) means that it is reproduced brightest on the screen. Yes. The first gradation is the gradation of the first color, the second gradation is the gradation of the second color, the third gradation is the gradation of the third color, The fourth gradation means the gradation of the fourth color.

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

<Basic technology>
Before describing an embodiment, an image display device (an image display device according to a basic technique) serving as a basis of an image display device according to an embodiment of the present invention to be described later will be described with reference to FIGS. Here, the image display device is configured to include an organic EL display that adjusts light emission luminance by a so-called current value. In this image display device, a large number of pixels are arranged, and an organic EL element is arranged in each pixel.

<Configuration of pixel circuit>
FIG. 1 is a diagram illustrating a configuration example of a pixel circuit (driving circuit) 7 for one pixel constituting the image display device according to the basic technology.

  The pixel circuit 7 includes an organic EL element 1, a drive transistor 2, a threshold compensation transistor 3, and a capacitor 4. The pixel circuit 7 has a one-to-one correspondence with one pixel.

  The organic EL element 1 is a light-emitting element that is made of an organic material and the like, and whose emission luminance varies depending on the amount of current (current amount) flowing through the light-emitting layer. The organic EL element 1 has an anode electrode 1a and a cathode electrode 1b. The anode electrode 1a is a VDD line Lvd as a power supply line that is on the high potential side when the organic EL element 1 emits light among the power supply lines. Is electrically connected. On the other hand, the cathode electrode 1b is electrically connected via the drive transistor 2 to a VSS line Lvs as a power supply line that is on the low potential side when the organic EL element 1 emits light in the power supply line.

  The drive transistor 2 is a transistor that is electrically connected in series to the organic EL element 1 and controls the light emission luminance of the organic EL element 1 by adjusting the amount of current in the organic EL element 1. Here, the drive transistor 2 is a thin film transistor (TFT: Thin Film Transistor) which is a type of field effect transistor (FET) that employs a type (n-type) MIS (Metal Insulator Semiconductor) structure in which carriers are electrons. ), I.e., an n-MISFET TFT.

  The drive transistor 2 has first to third electrodes 2ds, 2sd, and 2g. The first electrode 2ds is electrically connected to the cathode electrode 1b of the organic EL element 1, and when the organic EL element 1 emits light, that is, when a forward current flows through the organic EL element 1, the drain electrode (Hereinafter abbreviated as “drain”). On the other hand, when a current flows in the reverse direction with respect to the organic EL element 1, it functions as a source electrode (hereinafter abbreviated as “source”). The second electrode 2sd is electrically connected to the VSS line Lvs, and functions as a source electrode (source) when a forward current flows through the organic EL element 1. On the other hand, when a current flows in the reverse direction with respect to the organic EL element 1, it functions as a drain electrode (drain). Further, the third electrode 2 g is a so-called gate electrode (hereinafter abbreviated as “gate”), and is electrically connected to one electrode (seventh electrode 4 a) of the capacitor 4.

  In the driving transistor 2, a potential applied to the third electrode 2g, more specifically, applied between the first electrode 2ds or the second electrode 2sd and the third electrode 2g (that is, between the gate and the source). By adjusting the voltage value, the amount of current (current amount) flowing between the first electrode 2ds and the second electrode 2sd (hereinafter also referred to as “between the first and second electrodes”) is adjusted. Then, the potential applied to the third electrode (gate) 2g causes the drive transistor 2 to have a state in which a current can flow between the first and second electrodes (that is, between the drain and the source) (conducting state), Is selectively set to a state in which the current cannot flow (non-conducting state).

  The Vth compensation transistor 3 detects the lower limit (predetermined threshold voltage Vth) of the potential of the third electrode 2g with respect to the second electrode 2sd of the drive transistor 2 when the drive transistor 2 is energized, and the drive transistor 2 2 is a transistor that adjusts the gate voltage of 2 to a threshold voltage Vth (hereinafter abbreviated as “threshold Vth”). Here, the Vth compensation transistor 3 is also composed of an n-MISFET TFT in the same manner as the drive transistor 2.

  The Vth compensation transistor 3 includes fourth to sixth electrodes 3ds, 3sd, and 3g. The fourth electrode 3ds is conductively connected to a wiring that electrically connects the first electrode 2ds of the drive transistor 2 and the cathode electrode 1b of the organic EL element 1. That is, the fourth electrode 3ds is electrically connected to the first electrode 2ds of the drive transistor 2. Further, the fifth electrode 3sd is conductively connected to a wiring electrically connecting the third electrode (gate) 2g of the driving transistor 2 and the capacitor 4 at the connection point T1. That is, it is electrically connected to the gate 2g of the driving transistor 2. Further, the sixth electrode 3g is a so-called gate electrode and is electrically connected to the scanning signal line Lss.

  In the Vth compensation transistor 3, the potential applied to the sixth electrode 3g, more specifically, between the fourth electrode 3ds or the fifth electrode 3sd and the sixth electrode 3g (that is, between the gate and the source). The amount of current (current amount) flowing between the fourth electrode 3ds and the fifth electrode 3sd (hereinafter also referred to as “between the fourth and fifth electrodes”) is adjusted by adjusting the voltage value applied to The Then, the potential applied to the sixth electrode (gate) 3g causes the Vth compensation transistor 3 to have a state in which a current can flow between the fourth and fifth electrodes (between the drain and the source) (conduction state), It is selectively set to a state where current cannot flow (non-conducting state).

  Here, since the light emission luminance of the organic EL element 1 is controlled by the current value, the light emission luminance fluctuates sensitively to fluctuations in the gate voltage of the drive transistor 2 during light emission. In particular, when the driving transistor 2 is configured using amorphous silicon, the threshold Vth tends to be different for each driving transistor 2. Therefore, if a function for compensating a different threshold Vth for each pixel (Vth compensation function) is not provided, there is a slight difference between the desired light emission luminance and the actual light emission luminance. Unevenness occurs.

  Therefore, the Vth compensation transistor 3 is provided to realize a Vth compensation function that compensates for variations in the threshold Vth in the drive transistor 2 by matching the gate voltage of the drive transistor 2 to the threshold Vth for each pixel before light emission. It has been.

  The capacitor 4 includes a seventh electrode 4a electrically connected to the third electrode 2g of the drive transistor 2 and an eighth electrode 4b electrically connected to the image signal line Lis. ing. The holding capacity of the capacitor 4 is set to a predetermined value Cs.

  By the way, the organic EL element 1 functions as a capacitor when a voltage opposite to that at the time of light emission is applied, and this capacitance (EL element capacitance) is set to a predetermined value Co. The driving transistor 2 includes a parasitic capacitance CgsTd between the second electrode 2sd and the third electrode 2g (hereinafter also referred to as “between the second and third electrodes”), and between the first electrode 2ds and the third electrode 2g. And a parasitic capacitance CgdTd (hereinafter also referred to as “between the first and third electrodes”). Further, the Vth compensation transistor 3 includes a parasitic capacitance CgsTth between the fifth electrode 3sd and the sixth electrode 3g (hereinafter also referred to as “between the fifth and sixth electrodes”), the fourth electrode 3ds, and the sixth electrode 3g. (Hereinafter also referred to as “between the 4th and 6th electrodes”) parasitic capacitance CgdTth. The parasitic capacitances CgsTd, CgdTd, CgsTth, and CgdTth are capacitances having predetermined values determined by the configurations of the drive transistor 2 and the Vth compensation transistor 3, respectively.

  FIG. 2 shows a circuit configuration (indicated by a thin line in the figure) related to parasitic capacitances CgsTth, CgdTth, CgsTd, CgdTd and an EL element capacitance Co, compared to the circuit configuration of the pixel circuit 7 shown in FIG. It is the schematic diagram which added description.

  As shown in FIG. 2, in the pixel circuit 7, a capacitor 1 c having an EL element capacitance Co exists between both electrodes of the organic EL element 1, and a parasitic capacitance CgsTd is provided between the second and third electrodes of the driving transistor 2. While the capacitor 2gs is present, the capacitor 2gd having the parasitic capacitance CgdTd exists between the first and third electrodes of the driving transistor 2, and further, the parasitic capacitance is provided between the fifth and sixth electrodes of the Vth compensation transistor 3. While the capacitor 3gs having CgsTth exists, a state equivalent to the state in which the capacitor 3gd having the parasitic capacitance CgdTth exists between the fourth and sixth electrodes of the Vth compensation transistor 3 occurs.

  Here, the description has been made focusing on one pixel circuit 7, but there are a large number of pixel circuits 7 in the entire organic EL display. For this reason, there are many scanning signal lines Lss. Therefore, in the following, a large number of scanning signal lines Lss are appropriately referred to as “Nth scanning signal line (N is a natural number) Lss”.

<Driving method for light emission of organic EL element>
FIG. 3 is a timing chart showing signal waveforms (drive waveforms) when the organic EL element 1 emits light. In FIG. 3, the horizontal axis indicates time, and in order from the top, (a) the potential applied to the VDD line Lvd (potential Vdd), (b) the potential applied to the VSS line Lvs (potential Vss), (c) The potential of the signal applied to the first scanning signal line Lss (potential Vls1), (d) the potential of the signal applied to the second scanning signal line Lss (potential Vls2), (e) applied to the image signal line Lis. The waveform of the potential of the signal (potential Vlis) is shown.

  In addition, FIG. 3 shows a drive waveform for causing the organic EL element 1 to emit light once, and a period related to one light emission is a Cs initialization period P1 (time t11 to t12) in time sequence. Preparation period P2 (time t12 to t13), Vth compensation period P3 (time t13 to t14), writing period P4 (time t14 to t15), element initialization period P5 (time t15 to t16), and light emission period P6 (time) t16-). Since the potential Vlis in the writing period P4 is an arbitrary value determined by the light emission luminance of each organic EL element 1, in FIG. 3, hatched hatching is attached for convenience in the range where the potential can exist. .

  4 to 8 are diagrams illustrating the current flow of the pixel circuit 7 generated in each period, focusing on the pixel circuit 7 when driving the image display device according to the basic technology. 4 to 8, among the pixel circuits 7, circuits that contribute to the current flow are indicated by thick lines, and circuits that hardly contribute to the current flow are indicated by thin lines.

  Hereinafter, a method for driving the image display device according to the basic technique will be described with reference to FIGS. 3 and 4 to 8 as appropriate.

○ Cs initialization period P1:
FIG. 4 illustrates the flow of current in the pixel circuit 7 in the Cs initialization period P1 (hereinafter abbreviated as “period P1” as appropriate).

  In the period P1, a predetermined positive high potential VDD (for example, 15V) is applied to the VDD line Lvd and the VSS line Lvs, respectively, and a predetermined positive high potential VgH (for example, 15V) is applied to all the scanning signal lines Lss. A predetermined reference potential (0 V in this case) is applied to the signal line Lis.

  At this time, the Vth compensation transistor 3 is turned on by applying a high potential VgH on the scanning signal line Lss to apply a positive potential corresponding to the high potential VgH to the sixth electrode (gate) 3g. On the other hand, for the drive transistor 2, since the VDD line Lvd and the VSS line Lvs are substantially at the same potential, the drive transistor 2 is substantially turned off and becomes non-conductive.

  Therefore, in the period P1, current flows from the VDD line Lvd to the capacitor 4 via the fourth and fifth electrodes 3ds and 3sd of the Vth compensation transistor 3, as indicated by the white arrow in FIG. A predetermined amount of charge (for example, a charge amount corresponding to 15 V) is accumulated in 4.

  If the amount of charge accumulated in the capacitor 4 increases with the passage of time in the period P1, a positive potential exceeding a predetermined value may be applied to the third electrode (gate) 2g in the driving transistor 2 and the conductive state may be established. obtain. However, since the VDD line Lvd and the VSS line Lvs are both set to the same potential VDD, no current flows between the first and second electrodes of the drive transistor 2.

○ Preparation period P2:
FIG. 5 illustrates the flow of current in the pixel circuit 7 in the preparation period P2 (hereinafter abbreviated as “period P2” as appropriate).

  In the period P2, a negative predetermined potential −Vp (for example, −7V) is applied to the VDD line Lvd, a predetermined reference potential (here, 0V) is applied to the VSS line Lvs, and a predetermined low potential is applied to all the scanning signal lines Lss. VgL (for example, −10 V) is applied, and a predetermined high potential VdH (for example, 10 V) is applied to the image signal line Lis.

  At this time, the Vth compensation transistor 3 is in a non-conductive state because almost no positive potential is applied to the sixth electrode (gate) 3g due to the application of the low potential VgL in the scanning signal line Lss. On the other hand, the drive transistor 2 is turned on by applying a high potential VdH to the image signal line Lis and applying a positive potential (for example, 15 + 10 = 25 V) corresponding to the high potential VdH to the third electrode (gate) 2g. .

  Since the potential of the VSS line Lvs is higher by Vp than that of the VDD line Lvd, the second and first electrodes 2sd and 2ds of the drive transistor 2 are connected from the VSS line Lvs as shown by a white arrow in FIG. Therefore, a current flows toward the organic EL element 1. As a result, a predetermined amount of electric charge (for example, electric charge corresponding to 7 V) corresponding to the potential difference between the VDD line Lvd and the VSS line Lvs is accumulated in the organic EL element 1, that is, the element capacitor 1c.

○ Vth compensation period P3:
FIG. 6 illustrates the flow of current in the pixel circuit 7 in the Vth compensation period P3 (hereinafter abbreviated as “period P3” as appropriate).

  In the period P3, a predetermined reference potential (here, 0V) is applied to the VDD line Lvd and the VSS line Lvs, the high potential VgH is applied to all the scanning signal lines Lss, and the high potential VdH (for example, 10V) is applied to the image signal line Lis. ) Is applied.

  At this time, the Vth compensation transistor 3 is turned on by applying a high potential VgH on the scanning signal line Lss to apply a positive potential corresponding to the high potential VgH to the sixth electrode (gate) 3g. Further, the driving transistor 2 becomes conductive at the beginning of the period P3 due to the electric charge accumulated in the capacitor 4 and the potential VdH applied to the image signal line Lis.

  Therefore, at the beginning of the period P3, as indicated by the white arrow in FIG. 6, the current accompanying the charge accumulated in the capacitor 4 is supplied from the capacitor 4 to the fifth and fourth electrodes 3sd, 3ds of the Vth compensation transistor 3. Furthermore, it flows toward the VSS line Lvs via the first and second electrodes 2ds and 2sd of the driving transistor 2. In addition, a current associated with the charge accumulated in the element capacitor 1c flows toward the VSS line Lvs via the first and second electrodes 2ds and 2sd of the driving transistor 2.

  However, as the current accompanying the charge accumulated in the capacitor 4 flows from the capacitor 4 toward the VSS line Lvs, the charge accumulated in the capacitor 4 decreases. When the potential Vgs of the third electrode 2g with respect to the second electrode 2sd of the drive transistor 2 (hereinafter also referred to as “between the third and second electrodes”) decreases substantially to the threshold value Vth, the drive transistor 2 becomes non-conductive. Become. At this time, the capacitor 4 is in a state where charges according to the threshold value Vth are accumulated. As described above, in the period P3, the electric charge corresponding to the threshold value Vth is accumulated in the capacitor 4, and the variation in the threshold value Vth that is different for each pixel is compensated.

○ Writing period P4:
FIG. 7 illustrates the flow of current in the pixel circuit 7 in the writing period P4 (hereinafter abbreviated as “period P4” as appropriate).

  In the period P4, the reference potential 0V is applied to the VDD line Lvd and the VSS line Lvs, respectively, and the scanning signal line Lss in the target pixel of the process (data writing process) for accumulating charges according to the pixel data signal. Is applied with a high potential VgH, and a potential (VdH−Vdata) is applied to the image signal line Lis. Note that the potential Vdata is a potential of the pixel data signal and is a potential corresponding to a value corresponding to the luminance gradation of the pixels constituting the image.

  At this time, the Vth compensation transistor 3 becomes conductive by applying a high potential VgH to the scanning signal line Lss to apply a positive potential according to the high potential VgH to the gate. On the other hand, the driving transistor 2 is turned off because a potential (VdH−Vdata) equal to or lower than the potential VdH in the period P3 is applied to the image signal line Lis and the gate voltage is equal to or lower than the threshold value Vth.

  Therefore, in the period P4, as indicated by the white arrow in FIG. 7, the capacitor 4 is connected from the organic EL element 1 (that is, the element capacitor 1c) to the capacitor 4 via the fourth and fifth electrodes 3ds and 3sd of the Vth compensation transistor 3. An electric current flows toward. As a result, the charge corresponding to the potential Vdata is added to the charge corresponding to the threshold value Vth already stored in the capacitor 4 and stored. That is, in the period P4, electric charges corresponding to the light emission luminance of the organic EL element 1 are accumulated in the capacitor 4. In other words, charges corresponding to the pixel data signal are accumulated in the capacitor 4 in the pixel circuit 7 in the period P4.

  Note that the amount of change in the potential of the seventh electrode 4a of the capacitor 4 (gate potential of the driving transistor 2) is the amount of change in the potential of the image signal line Lis, the holding capacity Cs of the capacitor 4, and the EL element capacity Co of the element capacitor 1c. And the ratio (capacity ratio). That is, in this embodiment, when the potential of the image signal line Lis changes from VdH to Vdata, the gate potential of the driving transistor 2 changes by (Vdata−VdH) · Cs / (Cs + Co). For example, when VdH = 10 V, Vdata = 5 V, and Cs: Co = 1: 2, the potential of the image signal line Lis changes by −5 V, and the gate potential of the driving transistor 2 is changed from the organic EL element 1 to the capacitor 4. (5-10) · 1 / (1 + 2) = − 5 / 3V is changed by the movement of the electric charge with respect to. Thus, the change in the potential of the image signal line Lis is reflected in the gate potential of the driving transistor 2 due to the movement of the charge accumulated in the capacitor 4.

○ Element initialization period P5:
In the element initialization period P5 (hereinafter abbreviated as “period P5” as appropriate), a predetermined negative potential −Vp is applied to the VDD line Lvd and the VSS line Lvs, respectively, and a low potential VgL is applied to all the scanning signal lines Lss. The high potential VdH is applied to the image signal line Lis. At this time, the Vth compensation transistor 3 is turned off and the driving transistor 2 is turned on. Since there is no potential difference between the VDD line Lvd and the VSS line Lvs and the VSS line Lvs is set to the negative potential −Vp, the charge accumulated in the organic EL element 1 (that is, the element capacitor 1c) is reduced to VSS. The charge accumulated in the organic EL element 1 is wiped out through the line Lvs.

○ Light emission period P6:
FIG. 8 illustrates the flow of current in the pixel circuit 7 in the light emission period P6 (hereinafter abbreviated as “period P6” where appropriate).

  In the period P6, the positive high potential VDD is applied to the VDD line Lvd, while the reference potential 0V is applied to the VSS line Lvs, the low potential VgL is applied to the scanning signal line Lss, and the high potential is applied to the image signal line Lis. VdH is applied.

  At this time, the Vth compensation transistor 3 becomes non-conductive due to the application of the low potential VgL to the scanning signal line Lss. On the other hand, for the driving transistor 2, since the high potential VdH is applied to the image signal line Lis, only the potential corresponding to the amount of charge accumulated in the capacitor 4 (the amount of charge corresponding to the potential Vdata) in the period P4. Vgs becomes higher than the threshold value Vth, and a conductive state is established.

  For example, when Vdata = 5V and Cs: Co = 1: 2, the potential accumulated in the capacitor 4 in the period P4 is lower than the threshold value Vth by 5 / 3V ([Vth-5 / 3] V ). In the period P6, a potential higher than the period P4 by Vdata (= 5V) is applied to the image signal line Lis, and the third electrode (gate) 2g is higher by 10 / 3V than the threshold value Vth. A potential ([Vth + 10/3] V = [Vth− (5/3) +5] V) is applied.

  Then, the VDD line Lvd is higher than the VSS line Lvs by the potential VDD, and the driving transistor 2 is in a conductive state in which current flows between the first and second electrodes according to the potential Vdata. For this reason, as indicated by a white arrow in FIG. 8, a current corresponding to the potential Vdata flows through the organic EL element 1. As a result, the organic EL element 1 emits light with a luminance corresponding to the potential Vdata. That is, in the period P6, light having a luminance corresponding to the pixel data signal is emitted from each pixel.

  Here, regarding the drive transistor 2 when the organic EL element 1 emits light, the following equation (1) is established between Vgs, Vdata, and Vth.

  In the above formula (1), a and d are constants.

  Further, when the current flowing between the first and second electrodes (between the drain and source) of the driving transistor 2 is Ids, the following expression (2) is established.

  Since the light emission luminance of the organic EL element 1 is substantially proportional to the current density (current density) flowing through the organic EL element 1, a desired light emission luminance can be obtained in each pixel by the control using the drive waveform shown in FIG. It is done.

  In the light emission period P6, a predetermined voltage Voled that is uniquely determined by the current Ids expressed by the above equation (2) is applied to the organic EL element 1. The potential of the first electrode 2ds with respect to the second electrode 2sd of the drive transistor Td, that is, the voltage between the first and second electrodes (hereinafter also referred to as “drain voltage”) Vds is VDD−Voled.

  Here, when the driving transistor Td is, for example, a TFT using amorphous silicon, current control is difficult if the driving transistor Td is used in a linear region, that is, in a condition that satisfies the relationship of Vgs−Vth> Vds. There is a possibility that the threshold Vth shift (Vth shift) occurs rapidly. Note that the Vth shift is a phenomenon in which the threshold value Vth increases and causes deterioration in luminance. Therefore, it is necessary to use the drive transistor Td in a saturation region, that is, a condition that satisfies the relationship of Vgs−Vth ≦ Vds. Therefore, the relationship of VDD ≧ Voled + Vgs−Vth is established, that is, Voled + Vgs−Vth is the minimum power supply voltage (hereinafter also referred to as “required power supply voltage”) necessary for light emission of the organic EL element 1.

<Improvement of luminous efficiency using W pixels>
Conventionally, the luminous efficiency of each pixel (R pixel, G pixel, B pixel) that emits red (R) green (G) blue (B) light when expressing light of the same chromaticity as white (W) ( A technique is known in which the light emission efficiency (unit [cd / A]) of a pixel emitting W light (W pixel) is always better than the combined value of the unit [cd / A]). Therefore, a technique for maximizing the light emission of the W pixel has been proposed by configuring each picture element by adding W pixels to RGB three-color pixels.

  Table 1 below illustrates the maximum emission luminance Y of the R, G, B, and W pixels, the chromaticity coordinates of the emitted light chromaticity (CIE color system chromaticity), and the luminous efficiency at the maximum emission luminance.

  FIG. 9 is a diagram showing the relationship between the necessary power supply voltage (Voled + Vgs−Vth) of R, G, B, and W pixels and the gradation of RGBW. Here, the gradation of each color for causing the R, G, B, and W pixels to emit light at the maximum luminance is 255 gradations. In FIG. 9, the horizontal axis indicates the necessary power supply voltage of the R, G, B, and W pixels, and the vertical axis indicates the gradation of each color. Specifically, the relationship between the necessary power supply voltage and the gradation relating to the R pixel is a curve Lr (thin line), and the relationship between the necessary power supply voltage and the gradation relating to the G pixel is related to the curve Lg (thick broken line) and the B pixel. The relationship between the necessary power supply voltage and the gradation is indicated by a curve Lb (thin broken line), and the relationship between the necessary power supply voltage and the gradation related to the W pixel is indicated by a curve Lw (thick line).

  Here, the chromaticity of white of the image display device is chromaticity coordinates (x, y) = (0.3127, 0.329), the gamma characteristic is γ = 2.2, and the number of picture elements composed of RGBW pixels is. If it is 320 × 240, for example, if white is expressed without using W pixels in an 8-bit gradation, the gradation of R is 255, the gradation of G is 255, and the gradation of B is 255. . Hereinafter, white realized by this gradation is represented as “Ws”. On the other hand, if the same white is expressed using W pixels as much as possible, the gradation of R is 211, the gradation of G is 0, the gradation of B is 106, and the gradation of W is 255.

  FIG. 10 shows the ratio of W pixels used (that is, white pixels) from the combination of RGBW pixels that do not use W pixels at all to the combination of RGBW pixels that use W pixels to the maximum when displaying white (Ws). It is the figure which showed the relationship between the light emission luminance of each pixel of RGBW, and the ratio of the light emission luminance of W pixel which occupies luminance. In FIG. 10, the horizontal axis represents the W pixel usage ratio, and the vertical axis represents the light emission luminance of each color pixel. Specifically, the relationship between the usage ratio of the W pixel related to the R pixel and the light emission luminance is a curve Pr (thin line), and the relationship between the usage ratio of the W pixel related to the G pixel and the light emission luminance is a curve Pg (thick broken line). The relationship between the usage ratio of the W pixel related to the B pixel and the light emission luminance is indicated by a curve Pb (thin broken line), and the relationship between the usage ratio of the W pixel related to the W pixel and the light emission luminance is indicated by a curve Pw (thick line).

  FIG. 11 shows the usage ratio of the W pixel and the organic EL display from the combination of RGBW pixels that do not use any W pixels to the combination of RGBW pixels that use the maximum W pixels when displaying white (Ws). It is the figure which showed the relationship with the total value of the electric current which flows by all the pixels. In FIG. 11, the horizontal axis indicates the W pixel usage ratio, and the vertical axis indicates the current value.

  As shown in FIG. 11, when no W pixel is used, a current of 77.5 mA flows through the entire organic EL display, and when the W pixel is used to the maximum, the entire organic EL display displays 64.5 mA. Current flows. Therefore, compared to the case where no W pixel is used, when the W pixel is used to the maximum, if the same power supply voltage is applied to all the organic EL elements, the power consumption is about 16.7%. (= [77.5-64.5] /77.5×100%).

  By the way, color image data generally includes RGB gradation information, and it is necessary to convert RGB gradations to RGBW gradations in order to emit light from W pixels. Various gradation conversion methods have been proposed (for example, Japanese Patent Application Laid-Open Nos. 2001-147666, 2004-295086, 2004-334199, and 2006-133711). No. 2006-163067, JP-A 2006-267148, US Pat. No. 6,885,380, US Pat. No. 6,987,876, etc.) are all essentially using matrix operations.

  Hereinafter, an example of a method of converting from RGB gradations to RGBW gradations that use the maximum number of W pixels will be briefly described. The XYZ vectors of the CIE color system at the maximum gradation of R, G, B, and W pixels are Ar, Ag, Ab, and Aw, respectively, and a combination of ρ, γ, and β that satisfies the relationship of Aw = ρAr + γAg + βAb is obtained. Here, since Ar, Ag, and Ab are independent vectors, there always exists a combination of ρ, γ, and β that satisfies the relationship of Aw = ρAr + γAg + βAb. Here, if the luminance (Y) of the XYZ vector of the CIE color system at the maximum gradation of R, G, B, W pixels is Yr, Yg, Yb, Yw, respectively, the relationship of Yw = ρYr + γYg + βYb is established. Since ρ, γ, and β are unique to the organic EL display, they can be obtained in advance.

  Then, if the luminances of R, G, and B pixels of an arbitrary display color are Yr ′, Yg ′, and Yb ′, then Yr ′ / (ρYr), Yg ′ / (γYg), Yb ′ / ( The smallest one of βYb) is obtained, and this is defined as ω. Here, assuming that the luminance of the W pixel is ωYw, the relationship of ωYw = ωρYr + ωγYg + ωβYb is established, and the luminance of the R, G, B pixels after gradation conversion is Yr′−ωρYr, Yg′−ωγYg, Yb′−ωβYb. It becomes. The luminances of the R, G, and B pixels are all 0 or more, and any one of them is 0. By calculating the luminance ωYw of the W pixel that satisfies such a relationship, it is possible to derive RGBW gradations that make maximum use of the W pixel.

<Problems found by the present inventor>
When the W pixel is used to the maximum, the current flowing through the entire organic EL display is concentrated on the W pixel, so that a high voltage is required. For example, as shown in FIG. 9, the necessary power supply voltage (Voled + Vgs−Vth) for performing light emission corresponding to the maximum gradation in the W pixel is 12.5 V, which is higher than the necessary power supply voltages related to pixels of other colors. high.

  With respect to this point, in the conventionally proposed technology, since a constant power supply voltage is applied to the RGBW pixels, it has been considered that the more W pixels are used, the more effective the reduction of power consumption is. . However, from the viewpoint of both current and voltage, the inventor of the present application has found that the maximum use of W pixels is not necessarily optimal for the effect of reducing power consumption.

  Therefore, the present inventor can appropriately reduce the power consumption in consideration of other factors other than the light emission efficiency when using the light emitting element having the excellent light emission efficiency to reduce the power consumption. An image display device that can be used and a driving method thereof have been created. This will be described below.

<First Embodiment>
<Schematic configuration of image display device>
FIG. 12 is a diagram illustrating a schematic configuration of the image display apparatus according to the first embodiment of the invention. In the present embodiment, the first color is R (red), the second color is G (green), the third color is B (blue), and the fourth color is a color other than RGB, for example, white ( An example of using W) will be described.

  The mobile phone 10 is a portable electronic device that includes a main body unit 100 and a display unit 200, and functions as an image display device that displays various images such as moving images and still images on the display unit 200. For this reason, hereinafter, the mobile phone is also referred to as an “image display device” as appropriate.

  The main unit 100 includes a communication function, a power supply function such as a battery, an operation unit, and the like.

  The display unit 200 includes, for example, an organic EL display (organic electroluminescence display) having a substantially rectangular outline, and driver means to which various signals supplied from the main body unit 100 are input. An organic EL display is a self-luminous image display device having a self-luminous light-emitting element that emits light by flowing current through the organic material.

  The organic EL display is provided with an image signal line for supplying a data signal (pixel data signal) corresponding to light emission luminance to each pixel, and substantially orthogonal to the image signal line. And a scanning signal line for supplying a scanning signal. The scanning signal is a signal that controls the timing of supplying a pixel data signal to each pixel via an image signal line.

  On the other hand, the driver means is electrically connected to the image signal line and is electrically connected to the scanning signal line and an X driver (image signal line driving circuit) for controlling the timing of supplying the pixel signal to the image signal line. And a Y driver (scanning signal line driving circuit) for controlling the timing of supplying the scanning signal to the scanning signal line. For example, in the mobile phone 1, the X driver is disposed along the short side of the organic EL display, and the Y driver is disposed along the long side of the organic EL display.

<Functional configuration of image display device>
FIG. 13 is a block diagram illustrating a functional configuration of the image display apparatus 10.

  The main body unit 100 includes a transmission / reception unit 110, a battery 120, and an operation unit 130.

  The transmission / reception unit 110 transmits / receives various data such as audio data and image data (image data D0 relating to RGB three colors) to / from an external device via a wireless line. The battery 120 is configured to be detachable from the main body unit 100 and supplies power to each unit of the image display device 10. Examples of the battery 120 include a rechargeable storage battery such as a lithium ion battery. The operation unit 130 includes operation buttons for inputting various information indicating numbers, characters, selection instructions, and the like.

  The display unit 200 includes a control unit 210, an image signal line drive circuit 220, a scanning signal line drive circuit 230, and a power supply circuit 240.

  For example, the control unit 210 includes various circuits, a CPU, a ROM, a RAM, and the like, and the CPU executes a program stored in a storage medium such as a ROM, thereby realizing various functions and controls related to the operation of the display unit 200. To do. For example, the control unit 210 receives the image data D0 sent from the transmission / reception unit 110, and controls to display an image based on the image data D0 on the organic EL display.

  More specifically, the control unit 210 refers to gradations relating to the three colors RGB (hereinafter referred to as “R gradation”, “G gradation”, and “B gradation”, respectively) included in the image data D0. ”, That is, a combination of R, G, and B gradations, and based on a predetermined calculation rule, gradations relating to four colors of RGBW (hereinafter referred to as“ RGBW gradations ”) The combination of gradations is referred to as “W gradation”. An image is displayed on the organic EL display based on the RGBW gradation information. Note that the gradation conversion processing from the RGB gradation to the RGBW gradation is performed based on a predetermined rule for reducing power consumption, which will be described later.

  The image signal line driving circuit 220 controls the timing for supplying the pixel data signal to the image signal lines provided in the organic EL display. The scanning signal line driving circuit 230 controls the timing for supplying the scanning signal to the scanning signal lines arranged in the organic EL display. The operations of the image signal line driving circuit 220 and the scanning signal line driving circuit 230 are controlled by signals from the control unit 210.

  The power supply circuit 240 supplies power supplied from the battery 120 to each pixel of the organic EL display based on a control signal from the control unit 210.

<Schematic configuration of display unit>
FIG. 14 is a block diagram illustrating an outline of a functional configuration of the display unit 200. In FIG. 14, two orthogonal XY axes are attached to clarify the orientation relationship.

  The display unit 200 includes an organic EL display AA, a control unit 210, an image signal line drive circuit 220, a scanning signal line drive circuit 230, and a power supply circuit 240. The control unit 210 includes a timing generation circuit TC.

  In the organic EL display AA, a large number of pixel circuits 7 are arranged in a matrix (that is, a lattice) along the vertical direction (Y direction) and the horizontal direction (X direction). Since the configuration and operation of the pixel circuit 7 are the same as those of the pixel circuit 7 according to the basic technology described above, the same reference numerals are given here and description thereof is omitted. An image signal line Lis is provided for each column of pixel circuits 7 parallel to the Y direction, and each image signal line Lis is electrically connected to a plurality of pixel circuits 7 in common. A scanning signal line Lss is provided for each row of the pixel circuits 7 parallel to the X direction, and each scanning signal line Lss is electrically connected to the plurality of pixel circuits 7 in common. The pixel circuit 7 controls the luminance of the display unit 200 in which a plurality of pixels are arranged for each pixel.

  In the organic EL display AA, a plurality of picture elements are arranged in a matrix. The picture element is composed of four pixels R, G, B, and W pixels. The R, G, B, and W pixels include organic EL elements 1 that emit light of R, G, B, and W colors, respectively.

  Hereinafter, the characteristics of the four types of R, G, B, and W pixels will be described as having the characteristics shown in Table 1 above. In addition, a portion formed by the organic EL element 1 and the drive transistor 2 connected in series to the organic EL element 1 (a portion surrounded by an alternate long and short dash line in FIG. 1) is referred to as a light emitting element circuit 5. Note that the first light-emitting element circuit in the present invention is a circuit including a first light-emitting element and a first driving transistor connected in series to the first light-emitting element, and the second light-emitting element circuit is a second light-emitting element circuit. The third light-emitting element circuit is composed of a second light-emitting element and a second driving transistor connected in series to the second light-emitting element, and the third light-emitting element circuit is connected in series to the third light-emitting element and the third light-emitting element. The circuit composed of the driving transistor and the fourth light emitting element circuit refer to a circuit composed of the fourth light emitting element and the fourth driving transistor connected in series to the fourth light emitting element. In the present embodiment, the power supply voltage (that is, the potential VDD) applied to each light emitting element circuit 5 is assumed to be a predetermined value (for example, about 11.4 V).

  The timing generation circuit TC synchronizes with the image data D0 sent from the main body 100, and outputs a signal for controlling the supply timing of the pixel signal from the image signal line drive circuit 220 to each image signal line Lis. On the other hand, a signal for controlling the supply timing of the scanning signal to each scanning signal line Lss is sent from the scanning signal line driving circuit 230 to the scanning signal line driving circuit 230.

  The image signal line driving circuit 220 supplies a pixel signal to the image signal line Lis in response to a signal from the timing generation circuit TC. On the other hand, the scanning signal line driving circuit 230 supplies a scanning signal to the scanning signal line Lss in response to a signal from the timing generation circuit TC. By such control of the timing generation circuit TC, a pixel data signal is appropriately supplied to each pixel circuit 7 via the image signal line Lis.

  The power supply circuit 240 supplies power required for light emission to each pixel circuit 7 under the control of the control unit 210.

<Gradation conversion processing to reduce power consumption>
<Concept of gradation conversion processing>
○ In the case of white display:
FIG. 15 shows the usage ratio of the W pixel and the R, G, R, G, and the like from the combination of RGBW pixels that do not use any W pixel to the combination of RGBW pixels that use the maximum W pixel when displaying white (Ws). It is the figure which showed the relationship with the required power supply voltage (Voled + Vgs-Vth) of B and W pixels. In FIG. 15, the horizontal axis indicates the usage ratio of the W pixel, and the vertical axis indicates the necessary power supply voltage for the R, G, B, and W pixels. Specifically, the relationship between the usage ratio of the W pixel and the required power supply voltage of the R pixel is a curve V1r (thin line), and the relationship between the usage ratio of the W pixel and the required power supply voltage of the G pixel is a curve V1g (thick broken line). The relationship between the W pixel usage ratio and the B pixel required power supply voltage is indicated by a curve V1b (thin broken line), and the relationship between the W pixel usage ratio and the W pixel required power supply voltage is indicated by a curve V1w (thick line).

  Here, the necessary power supply voltage for the organic EL display AA as a whole must satisfy the following conditions (I) and (II).

  (I) Since the R, G, and B pixels emit light corresponding to the maximum gradation in RGB single color display, the necessary power supply voltage for the organic EL display AA as a whole is required for each R, G, and B pixel. The maximum voltage is exceeded.

  (II) The necessary power supply voltage as a whole of the organic EL display AA is not less than the maximum value among the necessary power supply voltages of the R, G, B, and W pixels.

  In FIG. 15, the necessary power supply voltage for the entire organic EL display AA that satisfies the above conditions (I) and (II) is the maximum value of the necessary power supply voltage for the B pixel when the W pixel usage ratio is around 0 to 0.75. (Here, approximately 11.4 V) (a dashed line in the figure), and when the W pixel usage ratio is in the vicinity of 0.75 to 1, it is a value equivalent to the necessary power supply voltage of the W pixel.

  FIG. 16 is a diagram showing the relationship between the W pixel usage ratio and power consumption when displaying white (Ws). Here, regarding the usage ratio of each W pixel, the product of the required power supply voltage as the whole organic EL display AA shown in FIG. 15 and the current shown in FIG. 11 is used as the power consumption.

  Although the current shown in FIG. 11 is minimized when the W pixel usage ratio is 1, as shown in FIG. 16, the power consumption is minimized because the W pixel usage ratio is 0. 75. The minimum power consumption, that is, when the W pixel usage ratio is 0.75, the power consumption is 774 mW, when the W pixel usage ratio is 0, the power consumption is 886 mW, and the W pixel usage ratio is 1. The power consumption at this time is 809 mW.

  As described above, in consideration of the necessary power supply voltage, when the ratio of the emission luminance of the R, G, B, and W pixels that minimizes the product of the voltage and the current is adopted, the power consumption is reduced.

○ For chromatic display:
FIG. 17 is a diagram showing the relationship between the usage ratio of W pixels and the necessary power supply voltage (Voled + Vgs−Vth) of R, G, B, and W pixels when displaying a chromatic color that is not white. Note that the chromatic color here is composed of 150 gradations for the R color, 255 gradations for the G color, and 255 gradations for the B color. Xs ". In FIG. 17, as in FIG. 15, the horizontal axis indicates the W pixel usage ratio, and the vertical axis indicates the required power supply voltage for the R, G, B, and W pixels. Specifically, the relationship between the usage ratio of the W pixel and the required power supply voltage of the R pixel is a curve V2r (thin line), and the relationship between the usage ratio of the W pixel and the required power supply voltage of the G pixel is a curve V2g (thick broken line). The relationship between the usage ratio of the W pixel and the required power supply voltage of the B pixel is indicated by a curve V2b (thin broken line), and the relationship between the usage ratio of the W pixel and the required power supply voltage of the W pixel is indicated by a curve V2w (thick line).

  In FIG. 17, the necessary power supply voltage for the organic EL display AA as a whole satisfying the above conditions (I) and (II) is the necessary power supply voltage for the B pixel when the W pixel usage ratio is around 0 to 0.83. It becomes a value corresponding to the maximum value (dashed line in the figure), and becomes a value equivalent to the necessary power supply voltage of the W pixel when the W pixel usage ratio is near 0.83 to 1.

  FIG. 18 is a diagram showing the relationship between the W pixel usage ratio and power consumption when displaying chromatic colors (Xs). Here, regarding the usage ratio of each W pixel, the product of the required power supply voltage as the whole organic EL display AA shown in FIG. 17 and the current shown in FIG. 11 is used as the power consumption.

  Although the current shown in FIG. 11 is minimized when the W pixel use ratio is 1, as shown in FIG. 18, the power consumption is minimized because the W pixel use ratio is 0. 83. The minimum power consumption, that is, the power consumption when the W pixel usage ratio is 0.83 is 517 mW, the power consumption when the W pixel usage ratio is 0 is 611 mW, and the W pixel usage ratio is 1. Power consumption is 532 mW.

  In the case of displaying an arbitrary chromatic color, similarly to the case of displaying white, the ratio of emission luminance of R, G, B, and W pixels that minimizes the product of voltage and current in consideration of the necessary power supply voltage. It can be seen that the power consumption is reduced when is adopted.

  As shown in FIGS. 15 to 18, when the use ratio of the W pixel is less than a predetermined value (for example, about 0.75 or about 0.83), the maximum power supply voltage required for the R, G, and B pixels is maximum. The value is larger than the required power supply voltage of the W pixel. On the other hand, when the use ratio of the W pixel is a predetermined value (for example, about 0.75 or about 0.83) or more, the required power supply voltage of the W pixel is the maximum value of the required power supply voltage of the R, G, and B pixels. It becomes the above value. When the W pixel usage ratio is at the predetermined value, power consumption is minimized.

  The inventor finds the above characteristics, and determines the power supply voltage necessary for causing the R, G, B pixels to emit light according to the maximum gradation, that is, the maximum value of the power supply voltage required for the R, G, B pixels, As a power supply voltage of the organic EL display AA, it has been devised to suppress power consumption by preventing the use ratio of W pixels from exceeding the predetermined value (for example, about 0.75 or about 0.83).

  However, if the power supply voltage necessary for causing the R, G, and B pixels to emit light according to the maximum gradation is the power supply voltage of the organic EL display AA, generally, the maximum value of the power supply voltage required for the W pixel is R, G , B is larger than the maximum value of the necessary power supply voltage of the B pixel, the W pixel cannot emit light according to the maximum gradation. That is, the W pixel can only emit light corresponding to a predetermined gradation or less that is smaller than the maximum gradation and corresponds to the power supply voltage of the organic EL display AA.

  For example, if the power supply voltage of the B pixel is the highest among the power supply voltages of the R, G, and B pixels, and the power supply voltage of the organic EL display AA is matched with the power supply voltage of the B pixel, the gradation is adjusted by 8 bits. In the case of representation, the W pixel can output only up to a predetermined gradation (here, 223 gradations). Note that even if light emission corresponding to a gray scale larger than 223 gray scales is performed, desired luminance does not appear, and the driving transistor is used in a linear region, so that the life of the pixel is shortened.

  FIG. 19 shows an achromatic color gradation (achromatic color gradation) and an R, G, B, and W gradation when the power supply voltage of the organic EL display AA is adjusted to the maximum required power supply voltage of the B pixel. It is a figure which shows a relationship. In FIG. 19, the horizontal axis represents an achromatic color gradation, and the vertical axis represents R, G, B, and W gradations. Specifically, the relationship between the achromatic color gradation and the R gradation is the curve Tr (thin line), the relationship between the achromatic color gradation and the G gradation is the curve Tg (thick broken line), the achromatic color gradation and the B gradation. Is represented by a curve Tb (thin broken line), and the relationship between the achromatic color gradation and the W gradation is represented by a curve Tw (thick line).

  As shown in FIG. 19, the W gradation increases in proportion to the achromatic gradation and reaches the 223 gradation, but when the achromatic gradation becomes 223 gradations or more, the achromatic gradation increases. However, the W gradation does not increase and becomes constant. On the other hand, when the achromatic color gradation is 223 gradations or more, the light emission of the G pixel is also used, and the G gradation increases as the achromatic color gradation increases.

  As described above, a configuration for realizing the gradation conversion processing that has been conceived by the present inventor will be described below. In this gradation conversion process, the maximum value of the required power supply voltage of the R, G, and B pixels is used as the power supply voltage of the organic EL display AA, and the use ratio of W pixels is larger than 0 and less than 1. This reduces power consumption.

<Functional configuration related to gradation conversion processing>
Here, it is assumed that the power supply voltage of the organic EL display AA is set to the maximum value (about 11.4 V) of the necessary power supply voltage of the B pixel due to the configuration of the power supply circuit 240 and the like. That is, the power supply voltage applied to the light emitting element circuits of the R, G, B, and W pixels is the power supply voltage necessary for causing the light emitting elements of the W pixel to emit light according to the maximum gradation, that is, the necessary power supply voltage of the W pixel Is set to a value relatively lower than the maximum value. For this reason, as shown in FIG. 19, the W gradation is always set to a predetermined gradation (223 gradations in FIG. 19) or less.

  FIG. 20 is a diagram illustrating a functional configuration related to the gradation conversion processing from the RGB gradation to the RGBW gradation executed in the control unit 210. For example, the control unit 210 implements the function of the conversion unit TP by reading and executing a program stored in a built-in ROM or the like with a built-in CPU.

  The line buffer LB is provided in the control unit 210, and temporarily stores pixel data for one line of each color regarding the image data D0 relating to the three colors RGB input from the main body unit 100. In FIG. 20, a line buffer related to 8-bit gradation is illustrated. Here, the image data D0 includes R, G, and B gradation information corresponding to the three colors RGB, and is received by the line buffer LB.

  The RGB-RGBW conversion table TB is a data table in which information indicating calculation rules for converting RGB gradations to RGBW gradations is stored. For example, the RGB-RGBW conversion table TB is prepared by storing in advance in a built-in ROM or the like. The

  This RGB-RGBW conversion table TB has a format in which a combination of R, G, B, and W gradations is associated with a number of combinations of R, G, and B gradations. More specifically, in the RGB-RGBW conversion table TB, a combination of R, G, B, and W gradations that minimizes power consumption is associated with each combination of R, G, and B gradations. It is a data table.

  For the RGB-RGBW conversion table TB, for all combinations of 8-bit R, G, B gradations, the same chromaticity as the chromaticity / luminance associated with each combination of R, G, B gradations. Of the combinations of R, G, B, and W gradations that achieve brightness, a range in which the required power supply voltage of the W pixel is less than or equal to the maximum required power supply voltage of the B pixel (here, 11.4 V) Thus, R, G, B, and W gradations that increase the usage ratio of the W pixel as much as possible can be calculated and associated with each other.

  However, since the conversion from the R, G, B gradation to the R, G, B, W gradation is non-linear, the R, G, B gradation represented by a predetermined number of bits (here, 8 bits) is used. When converted to R, G, B, and W gradations represented by the same number of bits (here, 8 bits), color reproducibility, that is, image quality is deteriorated. Therefore, the RGB-RGBW conversion table TB is, for example, R, G, B gradation represented by 8 bits and R, G, B, represented by 10 bits capable of expressing gradations finer than 8 bits. It is assumed that the W gradation is associated.

  The conversion unit TP converts the R, G, B gradation of each picture element related to the image data D0 into the R, G, B, W gradation by referring to the RGB-RGBW conversion table TB. .

  Specifically, the conversion unit TP derives a combination of R, G, B, and W gradations that minimizes power consumption by the following (Procedure 1) to (Procedure 3).

  (Procedure 1) The line buffer LB receives image data D0 including R, G, and B gradation information relating to the three colors RGB.

  (Procedure 2) In accordance with the RGB-RGBW conversion table TB, a combination of R, G, B, and W gradations is derived from a combination of R, G, and B gradations associated with each picture element received by the line buffer LB. More specifically, from the combination of R, G, and B gradations represented by 8 bits related to each picture element received by the line buffer LB, it is represented by 10 bits associated with the RGB-RGBW conversion table TB. A combination of R, G, B, and W gradations is derived.

  (Procedure 3) Image data including R, G, B, and W gradation information expressed in 10 bits derived in Procedure 2 is output to the image signal line drive circuit (X driver) 220.

  Then, the image signal line driving circuit 220 applies a pixel data signal corresponding to the combination of R, G, B, and W gradations after conversion, that is, a potential Vdata to the image signal line Lis. The pixels emit light according to the R, G, B, and W gradations. That is, under the control of the control unit 210, the light emitting elements of the R, G, B, and W pixels associated with each picture element emit light based on each combination of R, G, B, and W gradations derived by the conversion unit TP. To do.

  As described above, in the image display device 10 according to the first embodiment of the present invention, conversion information in which a combination of R, G, B, and W gradations is associated with each combination of R, G, and B gradations. (Here, RGB-RGBW conversion table TB) is prepared in advance. Then, the image data D0 including R, G, B gradation information is received, and R, G, B derived from the R, G, B gradation information included in the image data according to the RGB-RGBW conversion table TB. Based on the combination of B and W gradations, the light emitting elements of R, G, B, and W pixels are caused to emit light. The power supply voltage applied to the light emitting element circuits of the R, G, B, and W pixels is set to be relatively lower than the voltage required when the light emitting element of the W pixel emits light according to the maximum gradation. . For this reason, when using W light emitting elements with excellent light emission efficiency to reduce power consumption, W pixels are used to the maximum in consideration of factors other than light emission efficiency (here, power supply voltage). The power consumption of the image display device can be further reduced as compared with the case where the above is performed.

  Further, since the power supply voltage is set to a value equal to or higher than the maximum value of the voltage required when the light emitting elements of the R, G, and B pixels are caused to emit light according to the maximum gradation, the R, G, and B gradations The power consumption can be reduced by suppressing the power supply voltage within a range where single color light emission of R, G, B colors corresponding to the maximum gradation is possible.

  In the combination of R, G, B, and W gradations according to the RGB-RGBW conversion table TB, the W gradation is set to be lower than the maximum gradation and equal to or less than a predetermined gradation corresponding to the power supply voltage. The For this reason, power consumption can be reduced by suppressing the power supply voltage.

  In particular, the RGB-RGBW conversion table TB is information in which a combination of R, G, B, and W gradations that minimizes power consumption is associated with each combination of R, G, and B gradations. As a result, the power consumption can be reduced more appropriately.

Second Embodiment
In the image display device 10 according to the first embodiment, a combination of R, G, B, and W gradations that minimizes power consumption is associated with each combination of R, G, and B gradations. An RGB-RGBW conversion table TB was prepared in advance, and the input R, G, B gradations were converted into R, G, B, W gradations according to the RGB-RGBW conversion table TB. On the other hand, in the image display apparatus 10A according to the second embodiment, for each of R, G, B, and W colors, a voltage table that stores the relationship between gradation and voltage (first to fourth of the present invention). Gradation voltage data) and a current table (corresponding to the first to fourth gradation current data of the present invention) storing the relationship between gradation and current are prepared in advance. By referring to the table, the input R, G, B gradations are converted into R, G, B, W gradations so that the power consumption is lowest.

  Compared with the image display apparatus 10 according to the first embodiment, the image display apparatus 10A according to the second embodiment includes the contents of the gradation conversion process, specifically, the contents of the data table used for the gradation conversion process. Although the tone conversion processing function is different, other configurations are the same. Therefore, in the image display device 10A according to the second embodiment, the same configurations as those of the image display device 10 according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. A configuration different from the image display apparatus 10 will be mainly described.

  FIG. 21 is a diagram illustrating a functional configuration related to a gradation conversion process from RGB gradations to RGBW gradations executed in the control unit 210A included in the display unit 200A in the image display apparatus 10A according to the second embodiment. It is. The control unit 210A implements the function of the power calculation conversion unit CP by reading and executing a program stored in a built-in ROM or the like with a built-in CPU.

  The line buffer LB is the same as that of the first embodiment, and functions as a receiving unit that receives image data D0 including R, G, and B gradation information relating to the three colors RGB.

  The R voltage table TRe is a data table in which the R gradation and the necessary power supply voltage are associated with each other. The G voltage table TGe is a data table in which the G gradation and the necessary power supply voltage are associated with each other, and the B voltage table TBe. Is a data table in which the B gradation is associated with the necessary power supply voltage, and the W voltage table TWe is a data table in which the W gradation is associated with the necessary power supply voltage. The R current table TRi is a data table in which the R gradation and the current flowing through the R pixel are associated with each other, and the G current table TGi is a data table in which the G gradation and the current flowing through the G pixel are associated with each other. Yes, the B current table TBi is a data table in which the B gradation and the current flowing through the B pixel are associated with each other, and the W current table TWi is a data table in which the W gradation and the current flowing through the W pixel are associated with each other. is there.

  The R, G, B, and W voltage tables TRe, TGe, TBe, and TWe and the R, G, B, and W current tables TRi, TGi, TBi, and TWi are, for example, predetermined memories such as a ROM built in the control unit 210A. It is stored in a medium (storage means).

  FIG. 22A is a diagram illustrating the data content of the R voltage table TRe, and FIG. 22B is a diagram illustrating the data content of the R current table TRi.

  As shown in FIG. 22A, the R voltage table TRe has an 8-bit gradation expression for R pixels, that is, a necessary power supply voltage for each of the lowest gradation (0) to the maximum gradation (255 gradations). Is a data table associated with. Similarly, the G, B, and W voltage tables TGe, TBe, and TWe are data tables in which necessary power supply voltages are associated with the lowest gradation (0) to the maximum gradation (255 gradations), respectively. Yes. For the R, G, B, and W voltage tables TRe, TGe, TBe, and TWe, the relationship between the gradation of each color and the necessary power supply voltage as shown in FIG. Can be generated.

  Further, as shown in FIG. 22B, the R current table TRi is an 8-bit gradation expression for the R pixel, that is, for the lowest gradation (0) to the maximum gradation (255 gradations), respectively. This is a data table in which currents flowing in the light emitting elements of the R pixel are associated with light emission corresponding to each gradation. Similarly, in the G, B, W current tables TGi, TBi, TWi, the currents flowing in the light emitting elements of the respective color pixels are associated with the lowest gradation (0) to the maximum gradation (255 gradations). It is a data table. The R, G, B, and W current tables TRi, TGi, TBi, and TWi can be generated from the measurement values obtained by measuring the relationship between the gradation and the current flowing through the light emitting element in advance for each color pixel. is there.

  The RGB-RGBW calculation rule RT is stored in, for example, a predetermined storage medium such as a ROM built in the control unit 210A, and R for realizing the same chromaticity / luminance from a combination of R, G, B gradations. , G, B, and W are information indicating rules for calculating a combination of gradations. As described above, the same chromaticity / luminance can be realized by a plurality of R, G, B, and W gradations by changing the W pixel usage ratio, but this RGB-RGBW calculation rule RT Calculates a combination of a plurality of R, G, B, and W gradations that can realize the same chromaticity and luminance while changing the use ratio of the W pixel from the combination of the R, G, and B gradations. It is a rule for.

  Specific examples of the RGB-RGBW calculation rule RT include a data table in which a combination of R, G, B gradations and a combination of a plurality of R, G, B, W gradations are associated with each other, or a predetermined R, G , B gradation combinations are converted into one W gradation gradation, and a plurality of R, G, B, W gradation combinations are calculated from the R, G, B gradation combinations. Etc.

  Here, as described above, the RGB-RGBW calculation rule RT, the R, G, B, and W voltage tables TRe, TGe, TBe, and TWe, and the R, G, B, and W current tables TRi, TGi, TBi, and TWi Are stored in advance in a ROM or the like in the control unit 210A.

  The power calculation conversion unit CP functions as derivation means and recognition means of the present invention. The power calculation conversion unit CP uses the RGB-RGBW calculation rules RT, R, G, B, W voltage tables TRe, TGe, TBe, TWe, and R, G, B, W current tables TRi, TGi, TBi, TWi. While referring, the combination of R, G, B gradation of each picture element relating to the image data D0 is converted into a combination of R, G, B, W gradation so that the power consumption is minimized. .

  Specifically, the power calculation conversion unit CP performs the following (Procedure i) to (Procedure iv) for each picture element, so that R, G, B, and W gradations that minimize power consumption are obtained. Generate a combination.

  (Procedure i) The line buffer LB accepts image data D0 including R, G, B gradation information relating to the three colors RGB.

  (Procedure ii) In accordance with the RGB-RGBW calculation rule RT, a plurality of combinations of R, G, B, and W gradations are derived from combinations of R, G, and B gradations associated with each picture element received by the line buffer LB. .

  (Procedure iii) It is derived in Procedure ii by referring to the R, G, B, W voltage tables TRe, TGe, TBe, TWe and the R, G, B, W current tables TRi, TGi, TBi, TWi. Among the plurality of combinations of R, G, B, and W gradations, a combination of R, G, B, and W gradations that consumes the least amount of power is recognized. In the recognition process, for example, the sum of products of current and voltage corresponding to each color pixel is calculated as power consumption for all the combinations of R, G, B, and W gradations derived in step ii. This is realized by calculating a combination of R, G, B, and W gradations that minimizes power consumption. At this time, a power supply voltage (necessary power supply voltage) necessary for realizing light emission by the recognized R, G, B, and W gradations is also calculated.

  (Procedure iv) Image data including information indicating the combination of R, G, B, and W gradations recognized in the procedure iii is output to the image signal line drive circuit (X driver) 220, and in the procedure iii Information indicating the necessary power supply voltage calculated together is output to the power supply circuit 240.

  Then, the image signal line drive circuit 220 applies a pixel data signal corresponding to the combination of R, G, B, and W gradations after conversion, that is, the potential Vdata to the image signal line Lis and adjusts the power supply circuit 240. As a result, the high potential VDD corresponding to the necessary power supply voltage is applied to the VDD line Lvd, and the pixels corresponding to the converted R, G, B, and W gradations emit light in each picture element. That is, the control unit 210A controls each pixel based on each combination of R, G, B, and W gradations where the power consumption recognized by the power calculation conversion unit CP is lowest and the necessary power supply voltage. The light emitting elements of R, G, B, and W pixels emit light.

  As described above, according to the image display device 10A according to the second embodiment of the present invention, first, a plurality of combinations of R, G, B, and W gradations are calculated from combinations of R, G, and B gradations. Data (in this case, R, G, B, W voltage) storing a predetermined rule (here, RGB-RGBW calculation rule RT) and the relationship between gradation and voltage for each of R, G, B, W pixels Tables TRe, TGe, TBe, and TWe) and data (here, R, G, B, and W current tables TRi, TGi, TBi, and TWi) that store the relationship between gradation and current are prepared. Then, the image data D0 including R, G, B gradation information is received, and R, G, B, W is calculated from the R, G, B gradation information included in the image data D0 according to a predetermined calculation rule. A plurality of combinations of gradations are derived. Next, R, G, B, W voltage tables TRe, TGe, TBe, TWe and R, G, B, W current tables TRi, TGi, TBi, TWi are derived with reference to R, G, B, Among a plurality of combinations of W gradations, a combination of R, G, B, and W gradations that minimizes power consumption is recognized. Then, based on the recognized combination of R, G, B, and W gradations, the light emitting elements of R, G, B, and W pixels respectively emit light. By adopting such a configuration, power consumption can be reduced in consideration of the influence of the power supply voltage in addition to the light emission efficiency. Therefore, when reducing the power consumption by using a light emitting element having a color with excellent light emission efficiency, it is possible to appropriately reduce the power consumption in consideration of other factors besides the light emission efficiency.

  Further, based on the recognized combination of R, G, B, and W gradations and the R, G, B, and W voltage tables TRe, TGe, TBe, and TWe, light emitting elements for R, G, B, and W pixels The power supply voltage applied to each is adjusted. For this reason, it is possible to finely reduce the power consumption by suppressing the power supply voltage.

  As shown in FIG. 21, in the present embodiment, the R, G, B gradation relating to the 8-bit gradation expression is converted into the R, G, B, W gradation relating to the 8-bit gradation expression. Although it has been described that the tone conversion processing is performed, for example, when the conversion from the R, G, B gradation to the R, G, B, W gradation is a non-linear conversion, it has been described in the first embodiment. As described above, the color reproducibility, that is, the image quality is deteriorated. Therefore, from the viewpoint of suppressing the deterioration of the image quality, R, G, and B expressed by 10 bits from the combination of R, G, and B gradations expressed by 8 bits related to each picture element received by the line buffer LB. You may convert into the combination of B and W gradation. When such a configuration is adopted, the RGB-RGBW calculation rule RT is changed from R, G, B gradation relating to 8-bit gradation expression to R, G, B relating to 10-bit gradation expression. R, G, B, W voltage tables TRe, TGe, TBe, TWe, and R, G, B, W current tables TRi, TGi, TBi, TWi are 10-bit gradations. It only has to correspond to the expression.

  In general, the luminance and current are proportional to each color, and the luminance is proportional to the gray scale of the second power. Therefore, even if the R, G, B, and W current tables TRi, TGi, TBi, and TWi are not prepared, the steps are performed. The current may be calculated from the tone. That is, instead of the R, G, B, and W current tables TRi, TGi, TBi, and TWi, for each color, the current value is calculated by multiplying the gradation by the power of 2.2 and multiplying by a predetermined coefficient. Data defining the relationship between gradation and current may be stored in a predetermined storage medium such as a ROM in the control unit 210A.

<Modification>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the thing of the content demonstrated above.

  For example, in the first embodiment, the RGB-RGBW conversion table TB has R, G, B, and W gradations that minimize power consumption for each combination of R, G, and B gradations. Although the description has been made on the assumption that the combinations are associated with each other, the RGB-RGBW conversion table TB is not limited to this. Even when a combination of G, B, and W gradations is associated, power consumption can be reduced by suppressing the power supply voltage. That is, as described above, the combination of the R, G, B, and W gradations related to the RGB-RGBW conversion table TB is such that the W gradation is less than the maximum gradation and equal to or less than a predetermined gradation according to the power supply voltage. By setting within such a range, it is possible to reduce the power consumption by suppressing the power supply voltage as compared with the conventional technique that uses the W pixel to the maximum.

  In the second embodiment, the power supply voltage can be changed for each pixel. However, the present invention is not limited to this. For example, the power supply voltage may be changed for each line. It may be changed for each pixel, or the power supply voltage may be changed for each set of a plurality of other pixels.

  In the second embodiment, the power supply voltage is assumed to be changeable. However, as in the first embodiment, R, G, and B pixels are added to all the pixels of the organic EL display AA. A constant voltage equivalent to the maximum value of the power supply voltage (necessary power supply voltage) required for light emission according to the maximum gradation may be applied as the power supply voltage. That is, the power supply voltage applied to the light emitting elements of the R, G, B, and W pixels is the voltage necessary for causing the light emitting elements of the W pixel to emit light according to the maximum gradation, that is, the necessary power supply of the W pixel. It may be set relatively lower than the maximum value of the voltage. Even if such a configuration is adopted, similarly to the second embodiment, the power consumption can be reduced by suppressing the power supply voltage.

  In such a configuration, for the W gradation, only light emission corresponding to a predetermined gradation or less is possible. Therefore, the power calculation conversion unit CP needs a voltage exceeding a preset power supply voltage. It is necessary to set so that the W gradation is not derived. That is, since it is only necessary not to make power calculation and gradation conversion target for W gradation larger than the predetermined gradation, the processing related to power calculation and evaluation in the power calculation conversion unit CP is reduced, and The load is reduced. For example, with respect to the W voltage table TWe and the W current table TWi, since it is not necessary to store data related to the W gradation larger than the predetermined gradation, the amount of data prepared in advance is reduced. The data capacity of a storage medium such as a ROM can be used effectively. That is, it is possible to easily reduce power consumption by suppressing the power supply voltage.

  In the second embodiment, among the plurality of combinations of the R, G, B, and W gradations derived from the combination of the R, G, and B gradations, the R, G, B that consumes the lowest power is obtained. , W gradation combinations are recognized and adopted, and the light emitting elements of R, G, B, and W pixels emit light. However, the present invention is not limited to this, for example, a plurality of combinations of R, G, B, and W gradations Among them, a combination of R, G, B, and W gradations that is a predetermined one (for example, the second) from the lowest power consumption is recognized and adopted, and light emitting elements of R, G, B, and W pixels emit light. Variations can be considered. That is, among a plurality of combinations of R, G, B, and W gradations, a combination of R, G, B, and W gradations that consume relatively little power is recognized and adopted, and R, G, The light emitting elements of B and W pixels may emit light.

  Of the plurality of combinations of R, G, B, and W gradations, a combination of R, G, B, and W gradations that is a predetermined number from the lowest power consumption is adopted, and R, G, B, Even when the light emitting element of the W pixel is caused to emit light, the power consumption can be easily and appropriately reduced. However, among the plurality of combinations of R, G, B, and W gradations, the combination of the R, G, B, and W gradations that consumes the lowest power is adopted to emit light from the R, G, B, and W pixels. The power consumption can be more appropriately reduced by adopting a configuration in which each element emits light.

  In the first embodiment, the power supply voltage applied to all the pixels of the organic EL display AA is assumed to be constant. However, the present invention is not limited to this. For example, R, G, B, W after conversion A configuration in which the power supply voltage can be changed, for example, a power supply voltage corresponding to the gradation may be adopted.

  In the above embodiment, the case where four types of pixels in which one color of W is added to three colors of RGB is used for each picture element has been described. However, the present invention is not limited to this. For example, three colors of RGB In addition, four types of pixels may be used in which a color realized by appropriately mixing three colors of RGB other than W (hereinafter referred to as “X color”) is added. Further, the pixel to be added is not limited to a pixel of one color, and pixels of two or more colors may be added as appropriate. Furthermore, the original three colors are not limited to the three RGB colors, and may be three different colors such as yellow (Y), magenta (M), and cyan (C). As described above, the mixing ratio of the three colors for realizing the X color may be changed in accordance with the change of the types of the four or more pixels constituting each picture element. However, the luminous efficiency of the X color is better than the luminous efficiency when the other three colors are used to achieve the same chromaticity and luminance as the X color, and the maximum required power supply voltage of the other three colors is , X is required to be smaller than the maximum value of the necessary power supply voltage.

It is a figure which illustrates the pixel circuit of the image display apparatus which concerns on basic technology. It is a figure which shows typically the parasitic capacitance which generate | occur | produces in a pixel circuit. It is a timing chart which shows the drive waveform of the image display apparatus which concerns on basic technology. It is a figure which illustrates the flow of the electric current in the pixel circuit in a Cs initialization period. It is a figure which illustrates the flow of the electric current in the pixel circuit in a preparation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in a Vth compensation period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the writing period. It is a figure which illustrates the flow of the electric current in the pixel circuit in the light emission period. It is a figure which shows the relationship between the required power supply voltage of a RGBW pixel, and the gradation of RGBW. It is the figure which showed the relationship between the usage rate of W pixel in the case of displaying white, and the light-emitting luminance of each color pixel. It is the figure which showed the relationship between the usage ratio of W pixel in the time of displaying white, and the total value of the electric current which flows in all the pixels of an organic electroluminescent display. It is a figure which illustrates schematic structure of the image display apparatus which concerns on embodiment of this invention. It is a block diagram which illustrates the functional composition of an image display device. It is a block diagram which shows the outline of a function structure of a display part. It is the figure which showed the relationship between the usage rate of W pixel in the case of displaying white, and the required power supply voltage of each color pixel. It is the figure which showed the relationship between the usage-amount of W pixel at the time of displaying white, and power consumption. It is the figure which showed the relationship between the usage rate of W pixel at the time of displaying a chromatic color, and the required power supply voltage of each color pixel. It is the figure which showed the relationship between the usage-amount of W pixel at the time of displaying a chromatic color, and power consumption. It is a figure which shows the relationship between an achromatic color gradation and R, G, B, and W gradation. It is a figure which shows the function structure which concerns on a gradation conversion process. It is a figure which shows the function structure which concerns on the gradation conversion process which concerns on 2nd Embodiment. It is a figure which illustrates the voltage and electric current table concerning R color.

Explanation of symbols

10, 10A Image display device 100 Main unit 200, 200A Display unit 210, 210A Control unit 220 Image signal line drive circuit (X driver)
230 Scanning signal line drive circuit (Y driver)
240 Power supply circuit CP Power calculation conversion unit D0 Image data signal LB Line buffer RT RGB-RGBW calculation rule TB RGB-RGBW conversion table TP conversion unit TRe R voltage table TGe G voltage table TBe B voltage table TWe W voltage table TRi R current table TGi G current table TBi B current table TWi W current table

Claims (15)

An image display device,
Converting first to third gradation information corresponding to first to third colors constituting image data into first to fourth gradation information corresponding to first to fourth colors Storage means for storing conversion information;
First to fourth light emitting elements emitting light of the first to fourth colors and first to fourth driving transistors connected in series to the first to fourth light emitting elements are provided. 1 to 4 light emitting element circuits;
With
A power supply voltage applied to the first to fourth light emitting element circuits is set to a value relatively lower than a voltage required for causing the fourth light emitting element to emit light according to the maximum gradation. An image display device characterized by the above. The image display device according to claim 1,
The image display apparatus, wherein the power supply voltage is set to a value equal to or greater than a maximum value of a voltage necessary for causing the first to third light emitting elements to emit light according to a maximum gradation. The image display device according to claim 1 or 2,
In the combination of the first to fourth gradations related to the conversion information, the fourth gradation is set to be smaller than the maximum gradation and equal to or less than a predetermined gradation corresponding to the power supply voltage. An image display device characterized by that. The image display device according to any one of claims 1 to 3,
The conversion information includes first to second power consumption that is lower than that in the case where the fourth light emitting element emits light according to the maximum gradation for each combination of the first to third gradations. 4. An image display device characterized by being information associated with a combination of four gradations. The image display device according to any one of claims 1 to 4,
The conversion information is information in which a combination of first to fourth gradations that minimizes power consumption is associated with each combination of the first to third gradations. An image display device. The image display device according to any one of claims 1 to 5,
An image display device, wherein the light emitting element is an organic EL element. An image display device,
First to fourth light-emitting elements that are included in each picture element and emit light of first to fourth colors different from each other;
A predetermined number for calculating a plurality of combinations of first to fourth gradations corresponding to the first to fourth colors from combinations of first to third gradations corresponding to the first to third colors. The first to fourth gradation voltage data storing the relationship between the gradation and the voltage for the first to fourth colors, and the gradation for the first to fourth colors, respectively. Storage means for storing first to fourth gradation current data storing a relationship with current;
Receiving means for receiving image data including information on first to third gradations relating to the first to third colors;
Derivation means for deriving a plurality of combinations of first to fourth gradations from information of first to third gradations included in the image data in accordance with the predetermined calculation rule;
With reference to the first to fourth gradation voltage data and the first to fourth gradation current data, among a plurality of combinations of the first to fourth gradations derived by the deriving means, Recognizing means for recognizing a combination of the first to fourth gradations having a relatively low power consumption;
An image display device comprising: The image display device according to claim 7,
The recognition means is
With reference to the first to fourth gradation voltage data and the first to fourth gradation current data, among a plurality of combinations of the first to fourth gradations derived by the deriving means, An image display device that recognizes a combination of first to fourth gradations that is a predetermined number from the lowest power consumption. The image display device according to claim 8,
The image display apparatus according to claim 1, wherein the predetermined number is first. The image display device according to any one of claims 7 to 9,
First to fourth light emitting element circuits including the first to fourth light emitting elements and first to fourth driving transistors connected in series to the first to fourth light emitting elements. The power supply voltage applied to the first to fourth light emitting element circuits is set to be relatively lower than the voltage required for causing the fourth light emitting element to emit light according to the maximum gradation. An image display device characterized by that. The image display device according to claim 10,
The power supply voltage is set to a value equal to or higher than the first to third required voltages necessary for causing the first to third light emitting elements to emit light according to the maximum gradation, respectively;
The image display apparatus, wherein the predetermined calculation rule is set so that the derivation unit does not derive a fourth gradation that requires a voltage exceeding the power supply voltage. The image display device according to any one of claims 7 to 11,
Power supplies applied to the first to fourth light-emitting elements based on the combination of the first to fourth gradations recognized by the recognition means and the first to fourth gradation voltage data, respectively. Adjusting means for adjusting the voltage,
An image display device further comprising: The image display device according to any one of claims 7 to 12,
An image display device, wherein the light emitting element is an organic EL element. First to fourth light emitting elements that emit light of first to fourth colors and first to fourth driving transistors connected in series to the first to fourth light emitting elements. To a fourth light emitting element circuit;
Conversion information for converting the first to third gradation information corresponding to the first to third colors into the first to fourth gradation information corresponding to the first to fourth colors; ,
A method of driving an image display device having
Accepting image data including the first to third gradation information;
Deriving a combination of first to fourth gradations from first to third gradation information included in the image data according to the conversion information;
With
A power supply voltage applied to the first to fourth light emitting element circuits is set to a value relatively lower than a voltage required for causing the fourth light emitting element to emit light according to the maximum gradation. A driving method of an image display device characterized by the above. A picture element configured to include first to fourth light emitting elements that emit light of first to fourth colors;
A predetermined number for calculating a plurality of combinations of first to fourth gradations corresponding to the first to fourth colors from combinations of first to third gradations corresponding to the first to third colors. The calculation rule of
First to fourth gradation voltage data storing the relationship between gradation and voltage for each of the first to fourth colors;
A driving method of an image display device comprising first to fourth gradation current data storing a relationship between gradation and current for each of the first to fourth colors,
Receiving image data including information of first to third gradations corresponding to the first to third colors;
Deriving a plurality of combinations of the first to fourth gradations from the first to third gradation information included in the image data in accordance with the predetermined calculation rule;
With reference to the first to fourth gradation voltage data and the first to fourth gradation current data, among the plurality of combinations of the first to fourth gradations derived in the step b, Recognizing a set of first to fourth gradation combinations of relatively low power consumption;
A method for driving an image display device comprising:

Images