Display driver and semiconductor device

A display driver includes a gamma correction data transmission unit that transmits a plurality of gamma correction data pieces one by one in each predetermined period. A brightness level indicated by a video signal is converted into a gradation voltage with a gamma characteristic based on the gamma correction data piece transmitted from the gamma correction data transmission unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display driver for driving a display panel and a semiconductor device in which the display driver is provided.

2. Description of the Related Art

Display drivers for driving a display panel such as a liquid crystal display panel and an organic EL display panel generate gradation voltages corresponding to brightness levels of respective errors indicated by input video signals, and apply the gradation voltages to respective source lines of the display panels as pixel drive voltages. The display drivers perform gamma correction to correct the correspondence relation between brightness indicated by the input video signal and brightness actually displayed on the display panel, in each of red, green, and blue colors.

As such a display driver that performs the gamma correction, there is proposed one that includes three systems of gradation voltage conversion circuits. The three systems of gradation voltage conversion circuits include three systems of registers to store set values for the gamma correction on a color-by-color (red, green, and blue) basis, and convert display data into gradation voltages on a color-by-color (red, green, and blue) basis in accordance with characteristics based on the set values stored in the registers (for example, see Patent Document 1: Japanese Patent Application Laid-Open No. 2012-137783).

SUMMARY OF THE INVENTION

By the way, the gradation voltage conversion circuit includes, in addition to the aforementioned registers, a ladder resistor to generate a reference gradation voltage corresponding to each gradation in accordance with the set value stored in the register, and an amplifier to output the voltage.

Accordingly, the display driver needs to have the three systems of gradation voltage conversion circuits (including the registers, the ladder resistors, and the amplifiers) corresponding to respective colors, thus causing an increase in the area of the gradation voltage conversion circuit in a chip and hence an increase in the size of the display driver.

Therefore, an object of the present invention is to provide a display driver that can be reduced in size, and a semiconductor device in which the display driver is formed.

According to one aspect of the present invention, a display driver supplies a display device having a plurality of display cells with gradation voltages corresponding to the brightness levels of the respective display cells indicated by a video signal. The display driver includes a gamma correction data transmission unit for transmitting a plurality of gamma correction data pieces representing gamma correction values one by one in each predetermined period, and a gradation voltage conversion unit for converting the brightness levels into the gradation voltages with a gamma characteristic based on the gamma correction value indicated by the gamma correction data piece transmitted from the gamma correction data transmission unit.

According to another aspect of the present invention, a semiconductor device includes a display driver that is formed therein and supplies a display device having a plurality of display cells with gradation voltages corresponding to the brightness levels of the respective display cells indicated by a video signal. The display driver includes a gamma correction data transmission unit for transmitting a plurality of gamma correction data pieces representing gamma correction values one by one in each predetermined period, and a gradation voltage conversion unit for converting the brightness levels into the gradation voltages with a gamma characteristic based on the gamma correction value indicated by the gamma correction data piece transmitted from the gamma correction data transmission unit.

According to one aspect of the present invention, the display driver is provided with the gamma correction data transmission unit that transmits the plurality of gamma correction data pieces one by one in each predetermined period. The gradation voltage conversion unit converts the brightness levels indicated by the video signal into the gradation voltages with the gamma characteristic based on the gamma correction data piece transmitted from the gamma correction data transmission unit.

According to such a configuration, the display driver just has only one system of gradation voltage conversion unit, irrespective of the number of types of gamma characteristics. Therefore, it is possible to reduce the size of the circuit, as compared with a configuration in which, for example, three systems of gradation voltage conversion units for each of three types of gamma characteristics corresponding to red, green, and blue colors are provided to convert brightness levels into gradation voltages with the gamma characteristics.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a block diagram showing the schematic configuration of a display apparatus100including a display driver according to the present invention. InFIG. 1, a display device20is constituted by, for example, a liquid crystal display panel, and includes m (m is a natural number of 2 or more) horizontal display lines S1to Smextending in a horizontal direction of a two-dimensional screen and n (n is an even number of 2 or more) data lines D1to Dnextending in a vertical direction of the two-dimensional screen. At each of intersections between each horizontal display line and each data line, a display cell CRfor red display, a display cell CGfor green display, or a display cell CBfor blue display is formed.

In the display device20, as shown inFIG. 1, the display cell CRis formed at each of the intersections between the horizontal display line S1and the data lines D1to Dn. The display cell CGis formed at each of the intersections between the horizontal display line S2and the data lines D1to Dn. The display cell CBis formed at each of the intersections between the horizontal display line S3and the data lines D1to Dn. The display cell CRis formed at each of the intersections between the horizontal display line S4and the data lines D1to Dn. The display cell CGis formed at each of the intersections between the horizontal display line S5and the data lines D1to Dn. The display cell CBis formed at each of the intersections between the horizontal display line S6and the data lines D1to Dn.

In other words, the horizontal display lines S(3r−2)(r is natural numbers) are red display lines in each of which n display cells CRfor red display are arranged. The horizontal display lines S(3r−1)are green display lines in each of which n display cells CGfor green display are arranged. The horizontal display lines S(3r)are blue display lines in each of which n display cells CBfor blue display are arranged.

A drive control unit11generates an image data signal VDX in a format ofFIG. 2based on a video signal VD.

In other words, the drive control unit11first calculates display data PD that represents a brightness level of each display cell (CR, CG, CB) as, for example a 256-step brightness gradation of 8 bits, on the basis of the video signal VD. Next, the drive control unit11groups 3·n pieces of display data PD corresponding to three horizontal display lines of every three horizontal display lines S adjoining to each other on a color-by-color basis. In other words, the drive control unit11groups the 3·n pieces of display data PD into a display data series LDRincluding the display data PD1to PDncorresponding to the red display cells CR, a display data series LDGincluding the display data PD1to PDncorresponding to the green display cells CG, and a display data series LDBincluding the display data PD1to PDncorresponding to the blue display cells CB.

The drive control unit11, as shown inFIG. 2, generates the image data signal VDX in which the display data series LDRcorresponding to red are arranged in (3r−2)th horizontal scan periods H, the display data series LDGcorresponding to green are arranged in (3r−1)th horizontal scan periods H, and the display data series LDBcorresponding to blue are arranged in (3r)th horizontal scan periods H. Furthermore, the drive control unit11arranges γ-correction data, which is used when displaying each display data series (LDR, LDG, LDB), for each horizontal scan period H of the image data signal VDX.

In other words, as shown inFIG. 2, positive γ-correction data PGRand negative γ-correction data NGReach representing γ-correction values for a red component are arranged in the horizontal scan period H having the display data series LDRin the image data signal VDX. Positive γ-correction data PGGand negative γ-correction data NGGeach representing γ-correction values for a green component are arranged in the horizontal scan period H having the display data series LDGin the image data signal VDX. Positive γ-correction data PGBand negative γ-correction data NGBeach representing γ-correction values for a blue component are arranged in the horizontal scan period H having the display data series LDBin the image data signal VDX. The γγ-correction data (PGR, NGR, PGG, NGG, PGB, NGB) represents information corresponding to γ-correction values that are used when converting the display data PD into gradation voltages. To be more specific, the γ-correction data represents information for designating, out of nodes (called output taps below) between resistors in ladder resistors (described later), a plurality of output taps, for example, five output taps to perform a conversion corresponding to the γ-correction values.

The drive control unit11supplies the image data signal VDX generated as described above to a data driver13. Furthermore, whenever the drive control unit11detects a horizontal synchronization signal from the video signal VD, the drive control unit11supplies a horizontal synchronization detection signal to a scan driver12.

The scan driver12sequentially applies scan pulses to each of the horizontal display lines S1to Smof the display device20in synchronous timing with the horizontal synchronization detection signal.

The data driver13is formed in a semiconductor IC (integrated circuit) chip.

FIG. 3is a block diagram showing the internal configuration of the data driver13. As shown inFIG. 3, the data driver13has a γ-correction data transmission unit130, a data capture unit131, a gradation voltage conversion unit132, and an output unit133.

The γ-correction data transmission unit130extracts the positive γ-correction data PGR, PGG, or PGBfrom the image data signal VDX, and supplies the extracted positive γ-correction data to the gradation voltage conversion unit132as γ-correction data SP. The γ-correction data transmission unit130also extracts the negative γ-correction data NGR, NGG, or NGBfrom the image data signal VDX, and supplies the extracted negative γ-correction data to the gradation voltage conversion unit132as γ-correction data SN.

The data capture unit131sequentially captures the display data PD1to PDnconstituting the display data series (LDR, LDG, LDB) from the image data signal VDX for each horizontal scan period H, and supplies the n pieces of display data PD1to PDnto the gradation voltage conversion unit132as display data Q1to Qn.

The output unit133selects one of each of the positive gradation voltages P1to Pnand each of the negative gradation voltages N1to Nnin an alternate manner at established intervals, and supplies the selected gradation voltages to the data lines D1to Dnof the display device20as gradation voltages G1to Gn.

FIG. 4is a block diagram showing an example of the internal configuration of the γ-correction data transmission unit130and the gradation voltage conversion unit132. As shown inFIG. 4, the γ-correction data transmission unit130includes a γ-correction data extraction circuit21, a γ register22, a γ-correction data extraction circuit23, and a γ register24.

The γ-correction data extraction circuit21extracts positive γ-correction data PGR, PGG, or PGBfrom an image data signal VDX, and supplies the extracted positive γ-correction data PGR, PGG, or PGBto the γ register22in each horizontal scan period H. The γ register22writes over previous data and holds the positive γ-correction data PGR, PGG, or PGBsupplied by the γ-correction data extraction circuit21. The γ register22transmits the one piece of γ-correction data, which is held as described above, of the γ-correction data PGR, PGG, and PGBto the gradation voltage conversion unit132over the one horizontal scan period H as positive γ-correction data SP.

The γ-correction data extraction circuit23extracts negative γ-correction data NGR, NGG, or NGBfrom the image data signal VDX, and supplies the extracted negative γ-correction data NGR, NGG, or NGBto the γ register24in each horizontal scan period H. The γ register24writes over previous data and holds the negative γ-correction data NGR, NGG, or NGBsupplied by the γ-correction data extraction circuit23. The γ register24transmits the one piece of γ-correction data, which is held as described above, of the γ-correction data NGR, NGG, and NGBto the gradation voltage conversion unit132over the one horizontal scan period H as negative γ-correction data SN.

According to the configuration as described above, the γ-correction data transmission unit130transmits the γ-correction data pieces PGR, PGG, and PGBto the gradation voltage conversion unit132one by one for each horizontal scan period H. The γ-correction data transmission unit130also transmits the γ-correction data pieces NGR, NGG, and NGBto the gradation voltage conversion unit132one by one for each horizontal scan period H.

The gradation voltage conversion unit132includes reference gradation voltage generation circuits32and33, and DA conversion circuits34and35.

Each of the reference gradation voltage generation circuits32and33has voltage setting terminals T1to T3and output terminals U1to U256to output reference gradation voltages of 256 steps.

The reference gradation voltage generation circuit32is supplied with set voltages VG1to VG3, which have the following magnitude relations of voltage values, through the voltage setting terminals T1to T3of itself.
VG1>VG2>VG3

The reference gradation voltage generation circuit32generates 256-step positive reference gradation voltages Y1to Y256having difference voltage values to each other on the basis of the set voltages VG1to VG3, and supplies the positive reference gradation voltages Y1to Y256to the DA conversion circuit34.

The reference gradation voltage generation circuit33is supplied with set voltages VG3to VG5, which have the following magnitude relations of voltage values, through the voltage setting terminals T1to T3of itself.
VG3>VG4>VG5

The reference gradation voltage generation circuit33generates 256-step negative reference gradation voltages X1to X256having difference voltage values to each other on the basis of the set voltages VG3to VG5, and supplies the negative reference gradation voltages X1to X256to the DA conversion circuit35.

The DA conversion circuit34selects a reference gradation voltage that corresponds to a brightness gradation represented by display data Q of each piece of the display data Q1to Qnsupplied by the data capture unit131, from the positive reference gradation voltages Y1to Y256. The DA conversion circuit34outputs each of the gradation voltages Y, which are selected for each piece of the display data Q1to Qnas described above, as positive gradation voltages P1to Pn.

The DA conversion circuit35selects a reference gradation voltage that corresponds to a brightness gradation represented by display data Q of each piece of the display data Q1to Qnsupplied by the data capture unit131, from the negative reference gradation voltages X1to X256. The DA conversion circuit35outputs each of the gradation voltages X, which are selected for each piece of the display data Q1to Qnas described above, as negative gradation voltages N1to Nn.

FIG. 5is a circuit diagram showing the internal configuration of each of the reference gradation voltage generation circuits32and33. Note that, the reference gradation voltage generation circuits32and33have the same circuit configuration. Each of the reference gradation voltage generation circuits32and33includes input amplifiers AMP1and AMP2, a first ladder resistor (RD0to RD160), a γ characteristic regulation circuit SX, output amplifiers AP0to AP6, and a second ladder resistor (R0to R254).

The first ladder resistor has resistors RD0to RD160connected in series. Output taps a1to a160, which are nodes of the resistors RD0to RD160, are connected to the γ characteristic regulation circuit SX. Note that, to the midpoint output tap a81of the output taps a1to a160, the voltage setting terminal T2is connected.

The input amplifier AMP1amplifies a voltage received at the voltage setting terminal T1with a gain of 1, and supplies the amplified voltage through a line L0to one end of the first resistor RD0of the first ladder resistor and the output amplifier AP0. The input amplifier AMP2amplifies a voltage received at the voltage setting terminal T3with a gain of 1, and supplies the amplified voltage through a line L6to one end of the last resistor RD160of the first ladder resistor and the output amplifier AP6.

The γ characteristic regulation circuit SX connects five output taps that correspond to a γ-correction value represented by γ-correction data SP (SN) supplied by the γ-correction data transmission unit130, in other words, five output taps of the output taps a1to a160of the first ladder resistor to lines L1to L5, respectively. Note that, the line L1is connected to an input terminal of the output amplifier AP1, and the line L2is connected to an input terminal of the output amplifier AP2. The line L3is connected to an input terminal of the output amplifier AP3, the line L4is connected to an input terminal of the output amplifier AP4, and the line L5is connected to an input terminal of the output amplifier AP5. For example, the γ characteristic regulation circuit SX connects, out of the five output taps that correspond to the γ-correction value represented by the γ-correction data SP (SN), the first output tap to the line L1, the second output tap to the line L2, and the third output tap to the line L3. Moreover, the γ characteristic regulation circuit SX connects the fourth output tap of the five output taps that correspond to the γ-correction value represented by the γ-correction data to the line L4, and connects the fifth output tap to the line L5.

The second ladder resistor has resistors R0to R254connected in series. The output terminal U1is connected to one end of the first resistor R0of the resistors R0to R254, and the output terminal U256is connected to one end of the last resistor R254. Furthermore, as shown inFIG. 5, the output terminals U2to U255are connected to nodes of the resistors R0to R254connected in series, respectively.

The output amplifier AP0amplifies a voltage of the line L0with a gain of 1, and supplies the amplified voltage to one end of the resistor R0and the output terminal U1. The output amplifier AP1amplifies a voltage of the line L1with a gain of 1, and supplies the amplified voltage to the node between the resistors R0and R1and the output terminal U2. The output amplifier AP2amplifies a voltage of the line L2with a gain of 1, and supplies the amplified voltage to the node between the resistors R30and R31and the output terminal U31. The output amplifier AP3amplifies a voltage of the line L3with a gain of 1, and supplies the amplified voltage to the node between the resistors R126and R127and the output terminal U127. The output amplifier AP4amplifies a voltage of the line L4with a gain of 1, and supplies the amplified voltage to the node between the resistors R214and R215and the output terminal U215. The output amplifier AP5amplifies a voltage of the line L5with a gain of 1, and supplies the amplified voltage to the node between the resistors R253and R254and the output terminal U255. The output amplifier AP6amplifies a voltage of the line L6with a gain of 1, and supplies the amplified voltage to one end of the resistor R254and the output terminal U256.

According to the configuration ofFIG. 5, the reference gradation voltage generation circuit32(33) generates the reference gradation voltages Y1to Y256(X1to X256) having a γ characteristic based on the γ-correction data SP (SN) supplied by the γ-correction data transmission unit130, and supplies the reference gradation voltages Y1to Y256(X1to X256) to the DA conversion circuit34(35) through the output terminals U1to U256.

The operation of the configuration shown inFIGS. 4 and 5will be described below with reference toFIG. 2.

First, in a horizontal scan period CY1of an image data signal VDX in which a display data series LDRis arranged, as shown inFIG. 2, the γ-correction data extraction circuit21of the γ-correction data transmission unit130extracts positive γ-correction data PGRarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGRto the γ register22. In the horizontal scan period CY1, the γ-correction data extraction circuit23of the γ-correction data transmission unit130extracts negative γ-correction data NGRarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGRto the γ register24. Thus, as shown inFIG. 2, the γ register22supplies the γ-correction data PGRto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while holding the γ-correction data PGR. Also, as shown inFIG. 2, the γ register24supplies the γ-correction data NGRto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while holding the γ-correction data NGR.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having a γ characteristic based on the γ-correction data PGR, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having a γ characteristic based on the γ-correction data NGR, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35. The DA conversion circuit34converts display data Q1to Qncorresponding to the aforementioned display data series LDRinto analog positive gradation voltages P1to Pn, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristic based on the γ-correction data PGR. The DA conversion circuit35converts display data Q1to Qncorresponding to the aforementioned display data series LDRinto analog negative gradation voltages N1to Nn, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristic based on the γ-correction data NGR.

Next, in a horizontal scan period CY2of the image data signal VDX in which a display data series LDGis arranged, as shown inFIG. 2, the γ-correction data extraction circuit21extracts positive γ-correction data PGGarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGGto the γ register22. In the horizontal scan period CY2, the γ-correction data extraction circuit23extracts negative γ-correction data NGGarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGGto the γ register24. Thus, as shown inFIG. 2, the γ register22supplies the γ-correction data PGGto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while writing over the previous data and holding the γ-correction data PGR. Also, as shown inFIG. 2, the γ register24supplies the γ-correction data NGGto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while writing over the previous data and holding the γ-correction data NGG.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having a γ characteristic based on the γ-correction data PGG, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having a γ characteristic based on the γ-correction data NGG, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35. The DA conversion circuit34converts display data Q1to Qncorresponding to the aforementioned display data series LDGinto analog positive gradation voltages P1to Pn, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristic based on the γ-correction data PGG. The DA conversion circuit35converts display data Q1to Qncorresponding to the aforementioned display data series LDGinto analog negative gradation voltages N1to Nn, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristic based on the γ-correction data NGG.

Next, in a horizontal scan period CY3of the image data signal VDX in which a display data series LDBis arranged, as shown inFIG. 2, the γ-correction data extraction circuit21extracts positive γ-correction data PGBarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGBto the γ register22. In the horizontal scan period CY3, the γ-correction data extraction circuit23extracts negative γ-correction data NGBarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGBto the γ register24. Thus, as shown inFIG. 2, the γ register22supplies the γ-correction data PGBto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while writing over the previous data and holding the γ-correction data PGB. Also, as shown inFIG. 2, the γ register24supplies the γ-correction data NGBto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while writing over the previous data and holding the γ-correction data NGB.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having a γ characteristic based on the γ-correction data PGB, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having a γ characteristic based on the γ-correction data NGB, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35. The DA conversion circuit34converts display data Q1to Qncorresponding to the aforementioned display data series LDBinto analog positive gradation voltages P1to Pn, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristic based on the γ-correction data PGB. The DA conversion circuit35converts display data Q1to Qncorresponding to the aforementioned display data series LDBinto analog negative gradation voltages N1to Nn, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristic based on the γ-correction data NGB.

As described above, in the display device100, as shown inFIG. 2, the drive control unit11supplies the data driver13with the image data signal VDX in which the γ-correction data PG and NG, which is used when converting the display data PD1to PDninto the positive and negative gradation voltages, are arranged together with the display data PD1to PDnof one horizontal display line in each horizontal scan period H. Therefore, in the γ-correction data transmission unit130of the data driver13, the γ registers22and24are overwritten with the γ-correction data PG and NG included in the image data signal VDX, respectively, in each horizontal scan period. The gradation voltage conversion unit132converts the display data PD1to PDnof one horizontal display line into the positive gradation voltages P1to Pnand the negative gradation voltages N1to Nnwith conversion characteristics based on the γ-correction data PG and NG that has been written in the γ registers22and24, respectively. The drive control unit11and the data driver13of the display device100repeatedly perform such a series of processes.

Accordingly, to generate the positive (negative) gradation voltages P1to Pn(N1to Nn) in the gradation voltage conversion unit132, as shown inFIG. 5, only one system of the reference gradation voltage generation circuit (33) that includes the amplifiers (AMP1, AMP2, and AP0to AP6), the ladder resistors (RD0to RD160and R0to R254), and the γ characteristic regulation circuit (SX) is required.

Therefore, according to the configuration as shown inFIGS. 3 to 5, it is possible to reduce the size of the circuit, as compared with the driver of Patent Document 1 in which gradation voltage generation circuits specific to each of red, green, and blue components (i.e. three systems of gradation voltage generation circuits) are provided.

In the aforementioned embodiments, PGRand NGRindicate γ-correction data for a red component, PGGand NGGindicate γ-correction data for a green component, and PGBand NGBindicate γ-correction data for a blue component. The drive control unit11may change the contents itself of each of PGR, NGR, PGG, NGG, PGB, and NGBon a horizontal display line basis. Thus, it is possible to change the setting of the γ characteristic on a horizontal display line (a horizontal scan period) basis.

In the example shown inFIG. 2, the γ-correction data PG and NG corresponding to one of red, green, and blue colors is arranged immediately before the display data series LD of one horizontal display line in each horizontal scan period H of the image data signal VDX, but the γ-correction data PG and NG is not necessarily arranged in every horizontal scan period H.

When there is no vacant time to arrange the γ-correction data PG and NG in each horizontal scan period H of the image data signal VDX, all the γ-correction data PG and NG may be arranged only in the head portion of one vertical scan period.

FIG. 6is a drawing showing another example of the format of the image data signal VDX generated in consideration of this point. In other words, as shown inFIG. 6, the drive control unit11supplies the data driver13with the image data signal VDX in which the display data series LD corresponding to one horizontal display line is arranged in each horizontal scan period H and all the γ-correction data PGR, PGG, PGB, NGR, NGG, and NGBare arranged only in the head portion of one vertical scan period V. In this case, the γ-correction data transmission unit130of the data driver13has the configuration ofFIG. 7, instead of the configuration ofFIG. 4.

InFIG. 7, a γ-correction data extraction circuit41extracts the positive γ-correction data PGR, PGG, and PGBarranged in the head portion of the one vertical scan period V in each vertical scan period V of the image data signal VDX. The γ-correction data extraction circuit41supplies the extracted γ-correction data PGRto a γ register42, supplies the extracted γ-correction data PGGto a γ register43, and supplies the extracted γ-correction data PGBto a γ register44. The γ register42captures the γ-correction data PGRsupplied by the γ-correction data extraction circuit41, and, as shown inFIG. 6, supplies the γ-correction data PGRto a selector45, while holding the γ-correction data PGRover the one vertical scan period V. The γ register43captures the γ-correction data PGGsupplied by the γ-correction data extraction circuit41, and, as shown inFIG. 6, supplies the γ-correction data PGGto the selector45, while holding the γ-correction data PGGover the one vertical scan period V. The γ register44captures the γ-correction data PGBsupplied by the γ-correction data extraction circuit41, and, as shown inFIG. 6, supplies the γ-correction data PGBto the selector45, while holding the γ-correction data PGBover the one vertical scan period V. The selector45sequentially selects the three pieces of γ-correction data PGR, PGG, and PGBone by one in each horizontal scan period H, and, as shown inFIG. 6, supplies the selected γ-correction data to the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP.

A γ-correction data extraction circuit51extracts the negative γ-correction data NGR, NGG, and NGBarranged in the head portion of the one vertical scan period V in each vertical scan period V of the image data signal VDX. The γ-correction data extraction circuit51supplies the extracted γ-correction data NGRto a γ register52, supplies the extracted γ-correction data NGGto a γ register53, and supplies the extracted γ-correction data NGBto a γ register54. The γ register52captures the γ-correction data NGRsupplied by the γ-correction data extraction circuit51, and, as shown inFIG. 6, supplies the γ-correction data NGRto a selector55, while holding the γ-correction data NGRover the one vertical scan period V. The γ register53captures the γ-correction data NGGsupplied by the γ-correction data extraction circuit51, and, as shown inFIG. 6, supplies the γ-correction data NGGto the selector55, while holding the γ-correction data NGGover the one vertical scan period V. The γ register54captures the γ-correction data NGBsupplied by the γ-correction data extraction circuit51, and, as shown inFIG. 6, supplies the γ-correction data NGBto the selector55, while holding the γ-correction data NGBover the one vertical scan period V. The selector55sequentially selects the three pieces of γ-correction data NGR, NGG, and NGBone by one in each horizontal scan period H, and, as shown inFIG. 6, supplies the selected γ-correction data to the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN.

Thus, when the γ-correction data transmission unit130has the configuration ofFIG. 7, to generate the positive (negative) gradation voltages P1to Pn(N1to Nn), the selector45(55) and the γ register specific to each of red, green, and blue components i.e. three systems of γ registers42to44(52to54) are required.

However, as to the reference gradation voltage generation circuit32(33), only one system is required for each polarity, so that it is possible to reduce the size of the circuit, as compared with the driver of Patent Document 1 in which independent three systems of circuits corresponding to three colors of red, green, and blue are required.

In the above-described embodiments, the reference gradation voltage generation circuit32(33) is provided with the input amplifiers AMP1and AMP2and the first ladder resistor (RD0to RD160), and a plurality of voltages having different voltage values from each other are supplied to the γ characteristic regulation circuit SX through the respective output taps (a1to a160) of the first ladder resistor. However, a circuit constituted by the first ladder resistor and the input amplifiers AMP1and AMP2may be eliminated, and a voltage group corresponding to the voltages outputted from the plurality of output taps of the circuit may be directly supplied from the outside to the γ characteristic regulation circuit SX.

In the above-described embodiments, the γ-correction data pieces (PGR, PGG, PGB, NGR, NGG, and NGB) are supplied to the data driver13in the form of the image data signal VDX, but the γ-correction data may not be included in the image data signal VDX, but may be directly supplied from the outside to the data driver13. Thus, even when there is insufficient vacant time to arrange the γ-correction data in each horizontal scan period H of the image data signal VDX, the γ-correction data can be rewritten in each horizontal scan period H.

The above-described embodiments describe the configuration and operation of the drive control unit11and the data driver13by taking a case where the display device20is a liquid crystal display panel as an example, but the display device20may be, for example, an organic EL (electroluminescence) panel. In this case, the drive control unit11supplies the data driver13with an image data signal VDX that includes only positive γ-correction data (PGR, PGG, and PGB) as γ-correction data. Furthermore, the organic EL panel eliminates the need for providing the γ-correction data extraction circuit23and the γ register24included in the γ-correction data transmission unit130, and eliminates the need for providing the reference gradation voltage generation circuit33and the DA conversion circuit35included in the gradation voltage conversion unit132.

In the last analysis, the display driver including the drive control unit11and the data driver13just needs to include the following gamma correction data transmission unit (130) and gradation voltage conversion unit (32,34). The gamma correction data transmission unit transmits a plurality of gamma correction data pieces (PGR, PGG, PGB) one by one in each predetermined period (H). The gradation voltage conversion unit converts brightness levels (Q1to Qn) indicated by a video signal into gradation voltages (P1to Pn), with a gamma characteristic based on the gamma correction data piece transmitted from the gamma correction data transmission unit. The gamma correction data transmission unit just needs to include the following control unit (11), gamma correction data extraction unit (21,41), and gamma register (22). The control unit generates an image data signal (VDX) in which a plurality of gamma correction data pieces (PGR, PGG, PGB) are arranged one by one in each horizontal scan period, as well as series of display data pieces (PD1to PDn) indicating the brightness levels of respective display cells (CR, CG, CB) indicated by a video signal (VD) are grouped and arranged on a horizontal scan period basis. The gamma correction data extraction unit sequentially extracts a gamma correction data piece from the image data signal in each horizontal scan period. The gamma register transmits the gamma correction data piece extracted by the gamma correction data extraction unit to the gradation voltage conversion unit, while holding the gamma correction data piece. A gamma correction data transmission unit just needs to include the following control unit (11), gamma correction data extraction unit (41), plurality of gamma registers (42to44), and selector (45). The control unit generates an image data signal (VDX) in which a plurality of gamma correction data pieces (PGR, PGG, PGB) are arranged in a head portion of each vertical scan period (V), as well as series of display data pieces (PD1to PDn) indicating the brightness levels of the respective display cells (CR, CG, CB) indicated by a video signal (VD) are grouped and arranged on a horizontal scan period basis. The gamma correction data extraction unit sequentially extracts a plurality of gamma correction data pieces from the image data signal in each vertical scan period. Then, the plurality of gamma registers each hold the plurality of gamma correction data pieces extracted by the gamma correction data extraction unit. The selector selects the gamma correction data pieces held in the respective gamma registers one by one in each horizontal scan period, and transmits the selected gamma correction data piece to the gradation voltage conversion unit.

In the above-described embodiment, the display device20in which the n number of display cells C of the same color (either one of red, blue and green) are formed in each of the horizontal display lines S1to Sm, as shown inFIG. 1, is driven as a display device. However, instead of the display device20, a general display device in which three systems of display cells having different display colors (red, blue, or green) from each other are adjacently arranged in a periodic manner in each of the horizontal display lines S1to Smmay be driven.

Considering the aforementioned point,FIG. 8is a block diagram showing another configuration of the display apparatus100. In the configuration ofFIG. 8, the display apparatus100includes a drive control unit11A, a scan driver12A, and a data driver13A, which are formed in a semiconductor IC chip, and a display device20A.

Just as with the display device20shown inFIG. 1, the display device20A includes an m (m is an integer of 2 or more) number of horizontal display lines S1to Smextending in a horizontal direction of a two-dimensional screen and an n (n is an integer of 2 or more) number of data lines D1to Dnextending in a vertical direction of the two-dimensional screen. In the display device20A, a display cell CRfor red display, a display cell CGfor green display, or a display cell CBfor blue display is formed at each of intersections between each horizontal display line and each data line. However, in the display device20A, just as with general liquid crystal display panels, the display cells are adjacently arranged in a periodic manner in each horizontal display line in order of, for example, the display cells CR, CG, and CB. Therefore, an m number of display cells CRthat correspond to the horizontal display lines S1to Smare formed in each of the data lines D(3k-2)(k is an integer of 1 or more). An m number of display cells CGthat correspond to the horizontal display lines S1to Smare formed in each of the data lines D(3k-1). An m number of display cells CBthat correspond to the horizontal display lines S1to Smare formed in each of the data lines D(3k).

The drive control unit11A generates an image data signal VDX in a format illustrated inFIG. 9on the basis of a video signal VD.

Specifically, the drive control unit11A first calculates a display data piece PD that represents a brightness level of each display cell (CR, CG, CB) as, for example, a 256-step brightness gradation of 8 bits, on the basis of the video signal VD. The drive control unit11groups, in each frame of the video signal VD, an (n×m) number of display data pieces PD corresponding to the frame into first to n-th display data groups PX1to PXn, on the basis of each of the data lines D1to Dn. In other words, each of the display data groups PX1to PXn has a series of display data pieces PD1to PDmcorresponding to an m number of display cells C formed at intersections between the data line D corresponding to the display data group PX and each of the horizontal display lines S1to Sm. For example, the display data group PX1has a series of display data pieces PD1to PDmcorresponding to an m number of display cells CRformed at intersections between the data line D1and each of the horizontal display lines S1to Sm. The display data group PX2has a series of display data pieces PD1to PDmcorresponding to an m number of display cells CGformed at intersections between the data line D2and each of the horizontal display lines S1to Sm.

The drive control unit11A, as shown inFIG. 9, generates the image data signal VDX in which the first to n-th display data groups PX1to PXn are sequentially arranged in respective data scan periods Tv. Note that the data scan period Tv has such a length that, for example, one vertical scan period of the image data signal VDX is divided by the total number n of the data lines D1to Dn. Furthermore, the drive control unit11A arranges γ-correction data, which is used when displaying each display data group, in each data scan period Tv of the image data signal VDX.

The display data pieces PD1to PDmbelonging to the display data groups PX(3k-2)of the first to n-th display data groups PX1to PXn are all display data for red display. The display data pieces PD1to PDmbelonging to the display data groups PX(3k-1)are all display data for green display. The display data pieces PD1to PDmbelonging to the display data groups PX(3k)are all display data for blue display. Thus, the drive control unit11A arranges positive γ-correction data PGRand negative γ-correction data NGR, which represent γ correction values for red components, in the data scan periods Tv having the display data groups PX(3k-2). The drive control unit11A arranges positive γ-correction data PGGand negative γ-correction data NGG, which represent γ correction values for green components, in the data scan periods Tv having the display data groups PX(3k-1). The drive control unit11A arranges positive γ-correction data PGBand negative γ-correction data NGB, which represent γ correction values for blue components, in the data scan periods Tv having the display data groups PX(3k).

To be more specific, the γ-correction data (PGR, NGR, PGG, NGG, PGB, NGB) represents information for designating, out of output taps of ladder resistors shown inFIG. 5, a plurality (for example, five) of output taps to perform a conversion corresponding to the γ-correction values.

The drive control unit11A supplies the image data signal VDX generated as described above to the data driver13A, while supplying a data scan timing signal to the scan driver12A in synchronization with a vertical synchronization signal of the video signal VD.

As shown inFIG. 10, the scan driver12A sequentially and selectively supplies a scan pulse DSP having a voltage Vp to each of the data lines D1to Dnof the display device20A in accordance with the data scan timing signal at intervals of the data scan period Tv.

The data driver13A converts the m number of display data pieces PD1to PDmcontained in the image data signal VDX into gradation voltages G1to Gm, which each correspond to the brightness level of the display data piece, in each data scan period Tv, and supplies the gradation voltages G1to Gmto the horizontal display lines S1to Smof the display device20A in synchronization with the scan pulse DSP.

FIG. 11is a block diagram showing the internal configuration of the data driver13A. As shown inFIG. 11, the data driver13A includes a γ-correction data transmission unit130A, a data capture unit131A, a gradation voltage conversion unit132A, and an output unit133A, instead of the γ-correction data transmission unit130, the data capture unit131, the gradation voltage conversion unit132, and the output unit133shown inFIG. 3.

The γ-correction data transmission unit130A extracts the positive γ-correction data PGR, PGG, or PGBfrom the image data signal VDX, and supplies the extracted positive γ-correction data to the gradation voltage conversion unit132A as γ-correction data SP. The γ-correction data transmission unit130A also extracts the negative γ-correction data NGR, NGG, or NGBfrom the image data signal VDX, and supplies the extracted negative γ-correction data to the gradation voltage conversion unit132A as γ-correction data SN.

The data capture unit131A captures the display data pieces PD1to PDmbelonging to the display data group PX from the image data signal VDX in each data scan period Tv, as shown inFIG. 9, and supplies the m number of display data pieces PD1to PDmto the gradation voltage conversion unit132A as display data pieces Q1to Qm.

The gradation voltage conversion unit132A converts the display data pieces Q1to Qminto analog positive gradation voltages P1to Pm, respectively, in each data scan period Tv with a conversion characteristic based on the positive γ-correction data (PGR, PGG, PGB) included in the image data signal VDX. Furthermore, the gradation voltage conversion unit132A converts the display data pieces Q1to Qminto analog negative gradation voltages N1to Nm, respectively, in each data scan period Tv with a conversion characteristic based on the negative γ-correction data (NGR, NGG, NGB) included in the image data signal VDX. The gradation voltage conversion unit132A supplies the gradation voltages P1to Pmand N1to Nmto the output unit133A.

The output unit133A alternately selects one of the positive gradation voltages P1to Pmand one of the negative gradation voltages N1to Nnat predetermined intervals, and supplies the selected gradation voltages to the horizontal display lines S1to Smof the display device20A as the above-described gradation voltages G1to Gm.

FIG. 12is a block diagram showing an example of the internal configuration of each of the γ-correction data transmission unit130A and the gradation voltage conversion unit132A. As shown inFIG. 12, the γ-correction data transmission unit130A includes a γ-correction data extraction circuit21A, a γ register22, a γ-correction data extraction circuit23A, and a γ register24.

The γ-correction data extraction circuit21A extracts the positive γ-correction data PGR, PGG, or PGBfrom the image data signal VDX, and supplies the extracted γ-correction data PGR, PGG, or PGBto the γ register22in each data scan period Tv, as shown inFIG. 9. The γ register22writes and holds the γ-correction data PGR, PGG, or PGBsupplied from the γ-correction data extraction circuit21A over previous data. The γ register22transmits the one piece of the γ-correction data PGR, PGG, or PGBheld as described above, out of the γ-correction data PGR, PGG, and PGB, to the gradation voltage conversion unit132A over the data scan period Tv, as positive γ-correction data SP.

The γ-correction data extraction circuit23A extracts negative γ-correction data NGR, NGG, or NGBfrom the image data signal VDX, and supplies the extracted negative γ-correction data NGR, NGG, or NGBto the γ register24in each data scan period Tv as shown inFIG. 9. The γ register24writes and holds the γ-correction data NGR, NGG, or NGBsupplied from the γ-correction data extraction circuit23A over previous data. The γ register24transmits the one piece of γ-correction data held as described above, out of the γ-correction data NGR, NGG, and NGB, to the gradation voltage conversion unit132A over the data scan period Tv, as negative γ-correction data SN.

The gradation voltage conversion unit132A includes reference gradation voltage generation circuits32and33and DA conversion circuits34A and35A.

The reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having γ characteristics based on the γ-correction data SP supplied from the γ-correction data transmission unit130A, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34A. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having γ characteristics based on the γ-correction data SN supplied from the γ-correction data transmission unit130A, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35A.

Note that, the internal configuration and the operation of each of the reference gradation voltage generation circuits32and33are the same as those ofFIG. 4, and thus a description thereof is omitted.

The DA conversion circuit34A selects a reference gradation voltage that corresponds to a brightness gradation represented by display data Q of each of the display data pieces Q1to Qmsupplied by the data capture unit131A, from the positive reference gradation voltages Y1to Y256. The DA conversion circuit34A outputs each of the gradation voltages Y, which have been selected for each of the display data pieces Q1to Qmas described above, as positive gradation voltages P1to Pm. The DA conversion circuit35A selects a reference gradation voltage that corresponds to a brightness gradation represented by display data Q of each of the display data pieces Q1to Qmsupplied by the data capture unit131A, from the negative reference gradation voltages X1to X256. The DA conversion circuit35A outputs each of the gradation voltages X, which have been selected for each of the display data pieces Q1to Qmas described above, as negative gradation voltages N1to Nm.

The operation of the configuration ofFIG. 12will be described below with reference toFIG. 9.

First, in a data scan period DS1of an image data signal VDX in which a display data group PX1is arranged, as shown inFIG. 9, the γ-correction data extraction circuit21A of the γ-correction data transmission unit130A extracts positive γ-correction data PGRarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGRto the γ register22. In the data scan period DS1, the γ-correction data extraction circuit23A of the γ-correction data transmission unit130A extracts negative γ-correction data NGRarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGRto the γ register24. Thus, as shown inFIG. 9, the γ register22supplies the γ-correction data PGRto a γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while holding the γ-correction data PGR. Also, as shown inFIG. 9, the γ register24supplies the γ-correction data NGRto a γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while holding the γ-correction data NGR.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having γ characteristics based on the γ-correction data PGR, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34A. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having γ characteristics based on the γ-correction data NGR, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35A. The DA conversion circuit34A converts each of the display data pieces Q1to Qmcorresponding to the above-described display data group PX1into analog positive gradation voltages P1to Pm, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristics based on the γ-correction data PGR. The DA conversion circuit35A converts each of the display data pieces Q1to Qmcorresponding to the above-described display data group PX1into analog negative gradation voltages N1to Nm, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristics based on the γ-correction data NGR.

Next, in a data scan period DS2of the image data signal VDX in which a display data group PX2is arranged, as shown inFIG. 9, the γ-correction data extraction circuit21A extracts positive γ-correction data PGGarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGGto the γ register22. In the data scan period DS2, the γ-correction data extraction circuit23A extracts negative γ-correction data NGGarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGGto the γ register24. Thus, as shown inFIG. 9, the γ register22supplies the γ-correction data PGGto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while overwriting and holding the γ-correction data PGG. Also, as shown inFIG. 9, the γ register24supplies the γ-correction data NGGto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while overwriting and holding the γ-correction data NGG.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having γ characteristics based on the γ-correction data PGG, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34A. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having γ characteristics based on the γ-correction data NGG, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35A. The DA conversion circuit34A converts each of display data pieces Q1to Qmcorresponding to the above-described display data group PX2into analog positive gradation voltages P1to Pm, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristics based on the γ-correction data PGG. The DA conversion circuit35A converts each of the display data pieces Q1to Qmcorresponding to the above-described display data group PX2into analog negative gradation voltages N1to Nm, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristics based on the γ-correction data NGG.

Next, in a data scan period DS3of the image data signal VDX in which a display data group PX3is arranged, as shown inFIG. 9, the γ-correction data extraction circuit21A extracts positive γ-correction data PGBarranged in the head portion thereof from the image data signal VDX, and supplies the positive γ-correction data PGBto the γ register22. In the data scan period DS3, the γ-correction data extraction circuit23A extracts negative γ-correction data NGBarranged in the head portion thereof from the image data signal VDX, and supplies the negative γ-correction data NGBto the γ register24. Thus, as shown inFIG. 9, the γ register22supplies the γ-correction data PGBto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit32as γ-correction data SP, while overwriting and holding the γ-correction data PGB. Also, as shown inFIG. 9, the γ register24supplies the γ-correction data NGBto the γ characteristic regulation circuit SX of the reference gradation voltage generation circuit33as γ-correction data SN, while overwriting and holding the γ-correction data NGB.

Thus, the reference gradation voltage generation circuit32generates reference gradation voltages Y1to Y256having γ characteristics based on the γ-correction data PGB, and supplies the reference gradation voltages Y1to Y256to the DA conversion circuit34A. The reference gradation voltage generation circuit33generates reference gradation voltages X1to X256having γ characteristics based on the γ-correction data NGB, and supplies the reference gradation voltages X1to X256to the DA conversion circuit35A. The DA conversion circuit34A converts each of the display data pieces Q1to Qmcorresponding to the above-described display data group PX3into analog positive gradation voltages P1to Pm, respectively, on the basis of the reference gradation voltages Y1to Y256having the γ characteristics based on the γ-correction data PGB. The DA conversion circuit35A converts each of the display data pieces Q1to Qmcorresponding to the above-described display data group PX3into analog negative gradation voltages N1to Nm, respectively, on the basis of the reference gradation voltages X1to X256having the γ characteristics based on the γ-correction data NGB.

As described above, in the display device100, as shown inFIG. 8, the drive control unit11A supplies the data driver13A with the image data signal VDX, in which the display data PD1to PDmcorresponding to one data line D and the γ-correction data PG and NG used for converting the display data PD1to PDminto the positive and negative gradation voltages are arranged in each data scan period Tv as shown inFIG. 9. Therefore, in the γ-correction data transmission unit130A of the data driver13A, the γ registers22and24are overwritten with the γ-correction data PG and NG contained in the image data signal VDX, respectively, in each data scan period Tv. The gradation voltage conversion unit132A converts the display data PD1to PDmof one data line into the positive gradation voltages P1to Pmand the negative gradation voltages N1to Nmwith conversion characteristics based on the γ-correction data PG and NG that has been written in the γ registers22and24, respectively. The drive control unit11and the data driver13A of the display device100perform a series of processes as described above in a repeated manner.

Accordingly, to generate the positive (negative) gradation voltages P1to Pm(N1to Nm) in the gradation voltage conversion unit132A, as shown inFIG. 5, only one system of the reference gradation voltage generation circuit32(33) that includes amplifiers (AMP1, AMP2, and AP0to AP6), ladder resistors (RD0to RD160and R0to R254), and a γ characteristic regulation circuit (SX) is required.

As described above, the configuration ofFIG. 8adopts a drive method in which the data driver13A supplies the gradation voltages G1to Gmto the horizontal display lines S1to Smof the display device20A, and the scan driver12A sequentially supplies the scan pulses DSP to the data lines D1to Dn. Therefore, even when driving the normal display device in which three systems of display cells having different display colors (red, blue, or green) from each other are adjacently arranged in a periodic manner in each horizontal display line, only one system of the reference gradation voltage generation circuit32(33) that is shared among the colors (red, blue, and green) is required, thus allowing a reduction in the size of the circuit, as compared to conventional drivers.

Furthermore, since the configuration ofFIG. 8uses the general display device as the display device20A, ClearType (trademark) can be used for displaying words, though ClearType is difficult to use when driving the display device20, as shown inFIG. 1, in which the display cells (CR, CG, or CB) of the same color are arranged in each horizontal display line. ClearType (trademark) is one of anti-aliasing technologies developed by Microsoft Corporation to display fonts as font data. In the ClearType (trademark) technology, for example, the edge of a diagonal line of a letter is represented in units of display cell, instead of in units of pixel constituted of the three display cells (CR, CG, and CB) adjacent to each other.

This application is based on a Japanese Patent Application No. 2016-219527 which is hereby incorporated by reference.