(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0023986 A1
`(43) Pub. Date:
`Feb. 3, 2005
`Mizukoshi et al.
`
`US 20050023986A1
`
`(54) ORGANIC EL DISPLAY DEVICE WITH
`GAMMA CORRECTION
`
`(75) Inventors: Seiichi Mizukoshi, KanagaWa (JP);
`Nobuyuki Mori, Saitama (JP); Kouichi
`onomura’ Kanagawa (JP)
`Corres Ondence Address
`Thomgs H Close
`'
`Patent Legal Sta?.
`Eastman Kodak Company
`343 State Street
`Rochester, NY 14650-2201 (US)
`
`(73) Assignee; Eastman Kodak Company
`
`(21) APPL NO;
`
`10/629,488
`
`(22) Filed;
`
`Ju]_ 29, 2003
`
`Publication Classi?cation
`
`(51) Int. Cl.7 ..................................................... .. G09G 3/10
`
`(52) US. Cl. ........................................................ .. sis/169.3
`
`(57)
`
`ABSTRACT
`
`An organic EL display device Which displays by individu
`ally controlling an amount of current of organic EL ele
`ments, Which are arranged in a matrix, according to an input
`image signal, comprising:
`a lookup table for storing gamma compensation data
`for compensating an image signal;
`
`storage means for storing an equation for performing
`gamma compensation of the input image signal; and
`
`table data generation means for generating table lookup
`data and stormg such data in the lookup table on the
`basis of the equation stored in the storage means, and
`Wherein the table data generated by the table data
`generation means is stored in the lookup table by an
`initialization operation to perform gamma compen
`sation of the input image signal.
`
`5R
`
`,
`8
`_
`R SIgnaI +9 LUT
`——>
`
`8
`/
`/
`56 --> D A
`
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`
`PV
`dd
`
`7
`
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`
`Rin
`
`'
`6'"
`
`G Si nal
`g
`
`8/
`/
`
`B Signal
`
`/
`/
`
`,
`LUT
`
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`/
`
`5B
`N
`'
`8/
`/
`LUT
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`9
`
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`
`D/A
`
`0-—>
`
`6G
`
`68
`
`" '
`
`a
`In
`
`09 D/A
`
`<_Black level offset voltage
`
`1
`
`Inter Partes Review of RE 43,707
`IPR 2014-00778
`Exhibit 1021
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 1 0f 8
`
`US 2005/0023986 A1
`
`Data
`
`PVdd
`0
`
`Gate
`
`Vgs
`
`i.
`35 e MEN‘
`
`FEI'OK AK?
`
`2
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 2 of 8
`
`US 2005/0023986 A1
`
`hkqV3..wImNam
`
`_u_u>n_
`
`am
`
`_8m_mN.
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`
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`
`3
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 3 0f 8
`
`US 2005/0023986 A1
`
`OLED Display device
`
`.
`
`1 2
`/
`
`____ _ - -|
`
`9 Luminance
`meter outDut
`
`Fig. 3
`
`4
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 4 0f 8
`
`US 2005/0023986 A1
`
`Luminance
`
`White
`
`- - _ _ _ _ _ . . . . . _ _ _ _ _ _ _ _ _ - - - - - - - _ - - - -
`
`X Measurement point
`
`Black
`
`Signal Level
`
`Black Signal
`input level
`
`White Signal
`input level
`
`Fig. 4
`
`5
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 5 0f 8
`
`US 2005/0023986 A1
`
`Output
`
`256
`
`0
`
`256
`
`Fig. 5
`
`Input
`
`Luminance
`
`White
`
`X Measurement point
`
`L=f(V)
`
`Black
`
`Signal level
`
`Black signal
`input level
`
`White signal
`input level
`
`Fig. 6
`
`6
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 6 of 8
`
`US 2005/0023986 A1
`
`FE.7
`
`> 2 9
`
`O\
`
`13
`
`FLASHMEMORY
`
`
`
`Blackleveloffsetvoltage
`
`
`
`
`
`7
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 7 0f 8
`
`US 2005/0023986 A1
`
`Black Level offset voltage
`
`Black level
`adjustment
`voltage
`
`_>
`
`a
`;
`
`0
`
`lcv
`
`:
`'l‘
`lcv 1
`( Prescribed threshold value )
`of CV current detection
`circuit
`
`Fig. 8
`
`8
`
`

`
`Patent Application Publication Feb. 3, 2005 Sheet 8 0f 8
`
`US 2005/0023986 A1
`
`R Signal voltage
`
`Black voltage ........ _ _
`
`White Voltage L ---------- _ _
`
`-One Horizontal scanning period
`
`R Signal panel input waveform
`
`Fig. 9
`
`9
`
`

`
`US 2005/0023986 A1
`
`Feb. 3, 2005
`
`ORGANIC EL DISPLAY DEVICE WITH GAMMA
`CORRECTION
`
`FIELD OF THE INVENTION
`
`[0001] The present invention relates to an organic EL
`display device Which individually performs an initialization
`gamma adjustment for input signal Which controls the EL
`display device.
`
`BACKGROUND OF THE INVENTION
`[0002] Organic EL display devices have organic EL ele
`ments and are arranged in a matriX as piXels and individually
`controls the emission of the organic EL elements of the
`respective piXels to make display. Organic EL display
`devices include an active type and a passive type. The active
`type organic EL display device, has associated With each
`pixel, a piXel, a drive circuit for controlling current through
`the corresponding organic EL element. Active matriX types
`of drives are better for high de?nition display.
`
`[0003] FIG. 1 shoWs an eXample of the piXel circuit of an
`active type organic EL display device. A drive TFT 1 is a
`p-channel type and has a source connected to a poWer supply
`PVdd Which eXtends in a vertical direction and a drain
`connected to an anode of an organic EL element 2. Acathode
`of the organic EL element 2 is connected to a cathode poWer
`supply CV.
`
`[0004] A gate of the drive TFT 1 is connected to a source
`of an n-channel type selection TFT3. Adrain of the selection
`transistor is connected to a data line Data Which eXtends in
`a vertical direction, and a gate thereof is connected to a gate
`line Gate Which eXtends in a horiZontal direction. The gate
`of the drive TFT 1 is also connected to one end of a retention
`capacitor C, the other end of Which is connected to a
`capacitor poWer supply Vsc.
`[0005] Thus, the selection TFT 3 is turned on When the
`gate line Gate is set to a high level. At this time, When an
`image signal representing luminance of the piXel is applied
`to the data line Data, a voltage of the image signal is held in
`the retention capacitor C and applied to the gate of the drive
`TFT 1. Therefore, a gate voltage of the drive TFT 1 is
`controlled by the image signal, and the current flowing to the
`organic EL elements 2 is controlled. The gate voltage of the
`drive TFT 1 is held by virtue of the retention capacitor C
`even after the selection TFT 3 is turned off.
`
`[0006] A luminous volume of the organic EL elements 2 is
`substantially proportional to its drive current. Therefore, the
`organic EL elements 2 emit light according to the image
`signal.
`[0007] Here, the display device does not have a linear
`relationship (gamma) betWeen the input signal level and the
`display luminance. Therefore, gamma compensation is per
`formed in order to provide an appropriate relationship.
`
`[0008] To turn on the drive TFT 1 in the pixel circuit
`shoWn in FIG. 1, a gate-to-source voltage Vgs must be a
`prescribed threshold voltage (Vth) or more. The image
`signal is basically data corresponding to the luminance of
`emitted light, and the minimum level corresponds to the
`black level. Therefore, a data voltage to be supplied to the
`piXel circuit is required to carry out black level offset setting
`so to offset the image signal by a voltage corresponding to
`the threshold voltage Vth.
`
`[0009] FIG. 2 shoWs an eXample of a conventional struc
`ture to perform black level offset setting and gamma com
`pensation. Respective signals of RGB are gamma-compen
`sated by respective gamma compensation lookup tables
`(LUT) 5R, 5G, 5B, converted into analog signals by D/A
`converters 6R, 6G, 6B and input to a display panel 7.
`Contents of the LUTs 5R, 5G, 5B have the table data stored
`in the ?ash memory 9 Written therein by a CPU 8 before they
`are shoWn on the display panel 7.
`[0010] In this eXample, the black level offset is adjusted by
`the D/A converters 6R, 6G, 6B so that a black input voltage
`of the display panel 7 can be output for the black signal.
`Since the contents of the LUT 5R, 5G, 5B are adjusted to
`values so that the black input voltage of the panel is output
`for the black signal, it is possible to omit adjustment by the
`D/A converters 6R, 6G, 6B.
`[0011] In any event, optimum gamma table values and
`black level values of each color must be measured for each
`panel before shipping from a factory. When the TFT char
`acteristics are substantially the same for the respective
`colors, the black level offset voltage value may be common
`to RGB.
`
`[0012] To measure the gamma and black level offset
`voltage of the display panel 7, data to provide a linear
`input/output characteristic is Written in the LUTs 5R, 5G,
`5B, and the input signal is changed in this state to measure
`the luminance characteristic of the panel for the respective
`colors RGB.
`
`[0013] A gamma compensation circuit for a display is
`proposed in Japanese Patent Laid-Open Publication No. Hei
`6-245222 (hereinafter referred to as the patent publication 1)
`or the like, but it does not propose What gamma compen
`sation is performed for the organic EL panel.
`
`SUMMARY OF THE INVENTION
`
`[0014] It is an object of the present invention to provide an
`organic EL display device Which can efficiently use a lookup
`table.
`[0015] This object is achieved by an organic EL display
`device Which displays by individually controlling an amount
`of current of organic EL elements, Which are arranged in a
`matriX, according to an input image signal, comprising:
`
`[0016] a lookup table for storing gamma compensa
`tion data for compensating an image signal;
`
`[0017] storage means for storing an equation for
`performing gamma compensation of the input image
`signal; and
`
`[0018] table data generation means for generating
`table lookup data and storing such data in the lookup
`table on the basis of the equation stored in the storage
`means, and Wherein the table data generated by the
`table data generation means is stored in the lookup
`table by an initialiZation operation to perform
`gamma compensation of the input image signal.
`
`[0019] According to the present invention described
`above, the table data generation means generates the table
`data according to data about the equation stored in the
`storage means and Writes the date into the lookup table.
`Therefore, it is not necessary to store all the table data, and
`
`10
`
`

`
`US 2005/0023986 Al
`
`Feb. 3, 2005
`
`the storage means does not need to have a large capacity.
`Measurement points required to determine the equation may
`be feWer than those When such an equation is not used, and
`it becomes easy to determine at a factory or the like.
`
`[0020] The table data generation means preferably
`includes a nonvolatile memory Which stores a coef?cient of
`the equation and processing means Which generates the
`equation using the coef?cient stored in the nonvolatile
`memory.
`[0021] The equation stored in the table data storage means
`is preferably obtained by making the organic EL panel emit
`light in a luminous amount according to input image signal
`levels of a plurality of stages, detecting the luminous
`amount, determining a relationship betWeen the input image
`signal level and the luminous amount, calculating an
`approximate expression indicating their relationship or only
`a prescribed coef?cient of the approximate expression, and
`determining based on the obtained approximate expression
`or the coef?cient.
`
`[0022] Alternatively, the equation stored in the table data
`storage means is preferably obtained by measuring a drive
`current passed to the organic EL elements When input image
`signals of a plurality of stages are supplied to make the
`organic EL elements emit light, determining a relationship
`betWeen the input image signal level and the luminous
`amount of the organic EL elements based on the luminous
`ef?ciency of the organic EL elements from the measured
`current value, calculating an approximate expression indi
`cating a relationship betWeen the input image signal and the
`luminous amount of the organic EL elements or a predeter
`mined coef?cient of the approximate expression according
`to the obtained result, and determining based on the obtained
`approximate expression or the coef?cient.
`
`[0023] According to the present invention, it is also desir
`able that the organic EL display device further comprises
`total current detection means for detecting a total current
`passing to all the organic EL elements arranged in a matrix,
`Wherein an offset voltage is generated to offset the input
`image signal according to the total current detected by the
`total current detection means so as to start to pass a current
`to the organic EL elements to cope With the black level of the
`input image signal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0024] FIG. 1 is a diagram shoWing a structure of a prior
`organic EL pixel circuit;
`[0025] FIG. 2 is a diagram shoWing the entire structure of
`an existing prior art organic EL display device;
`
`[0026] FIG. 3 is a diagram shoWing a luminance measur
`ing system of a display panel;
`[0027] FIG. 4 is a diagram shoWing a relationship
`betWeen a signal level and luminance;
`
`[0028] FIG. 5 is a diagram shoWing a relationship
`betWeen input and output of a lookup table;
`
`[0029] FIG. 6 is a diagram shoWing an equation Which
`represents a relationship betWeen a signal level and lumi
`nance;
`[0030] FIG. 7 is a diagram shoWing an embodiment of the
`organic EL display device according to an embodiment;
`
`[0031] FIG. 8 is a diagram shoWing a relationship
`betWeen a total current and a black level offset voltage; and
`
`[0032] FIG. 9 is a diagram shoWing an example of an
`input image signal to a display panel.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`[0033] FIG. 3 is a diagram schematically shoWing a
`measurement system. A prescribed input signal is supplied
`from a drive circuit 11 to the display panel 7 to emit light.
`A luminous amount of the display panel 7 is detected by a
`luminance meter 12. As described above, a relationship
`betWeen the input signal level and luminance of emitted
`light of each color is determined With the input signal varied
`in a prescribed range for the respective colors RGB. Thus,
`a relationship betWeen the signal level and the luminance as
`shoWn in, for example, FIG. 4 can be obtained.
`
`[0034] Thus, in the organic EL panel, a luminance increase
`rate becomes high as the input signal level becomes higher.
`Data for compensating this is Written in the lookup tables.
`For example, data to output 0 to 255 of the vertical axis With
`respect to the input of image signals 0 to 255 of the
`horiZontal axis shoWn in FIG. 5 is Written in the lookup
`tables. Thus, it becomes possible to carry out the gamma
`compensation.
`[0035] Here, the curve of FIG. 5 is a curve passing
`through the origin point and rising from input 0. Speci?cally,
`it is based on the premise that the black level offset is
`adjusted by the D/A converters 6R, 6G, 6B.
`[0036] FIG. 7 is a block diagram schematically shoWing
`the structure of an embodiment of this invention. An organic
`EL display panel 7 has the pixel circuits shoWn in FIG. 1
`arranged in a matrix in its inner display area. A vertical
`driver circuit and a horiZontal driver circuit are arranged in
`the periphery of the display area and serve to control the
`application of a voltage to the data line Data and the gate line
`Gate.
`
`[0037] The organic EL elements are divided for RGB (red,
`green, blue) respectively, and the same color pixels are
`arranged in a vertical direction. Speci?cally, a column of R,
`a column of G and a column of B are arranged sequentially
`in the perpendicular direction and repeatedly arranged
`sequentially in the horiZontal direction, and the image sig
`nals of RGB are respectively applied to the data line Data
`corresponding to the respective columns. The organic EL
`elements themselves may emit light in respective colors R,
`G and B or may emit White light, Which is changed into
`respective colors With respective color ?lters.
`[0038] The image signals for the respective RGB colors
`are separately input to the display panel 7. Input terminals
`for the image signals are indicated by Rin, Gin and Bin.
`Input image signals, R signal, G signal and B signal are input
`to the input terminals Rin, Gin, Bin via lookup tables (LUT)
`5R, 5G, 5B and D/A converters 6R, 6G, 6B. The display
`panel 7 is supplied from the poWer supply PVdd, Which is
`connected to the sources of the individual drive TFTs 1.
`MeanWhile, the cathode of the organic EL element 2 of each
`pixel is taken from the display panel and connected to a
`cathode poWer supply CV. Acurrent detection resistor R1 is
`disposed betWeen the cathode and the cathode poWer supply
`CV, and a voltage corresponding to a total value of current
`
`11
`
`

`
`US 2005/0023986 A1
`
`Feb. 3, 2005
`
`?owing to all organic EL elements 2 formed on the display
`panel 7 is obtained at either end of the current detection
`resistor R1.
`
`[0039] The voltage at each end of the resistor R1 is input
`to an A/D converter 13, converted into digital data and
`supplied to a CPU 8. A ?ash memory 9 is connected to the
`CPU 8. The ?ash memory 9 stores a black level adjustment
`voltage Which is a basic black level offset voltage and also
`stores data concerning gamma curves of respective colors
`Which are the basis for generating gamma compensation
`data concerning respective RGB colors to be Written into the
`lookup table 5. It may be con?gured to store only a coeffi
`cient of the gamma curves or gamma compensation curves
`into the ?ash memory 9 so to produce an equation by a
`program executed by the CPU 8 or to store the equation
`itself into the ?ash memory 9.
`
`[0040] When the system is activated, the CPU 8 reads data
`relating to the gamma curves or gamma compensation
`curves from the ?ash memory 9, generates data for the
`lookup tables relating to the gamma compensation curves,
`and Writes into the lookup tables 5R, 5G, 5B. The CPU 8
`also reads data about a black level adjustment voltage from
`the ?ash memory 9 and supplies it as the black level offset
`voltage to the D/A converters 6R, 6G; 6B. Thus, the RGB
`signals being input are gamma-compensated by the lookup
`tables 5R, 5G, 5B and converted into analog signals by the
`D/A converters 6R, 6G, 6B, and supplied to the display
`panel 7 With the black level adjusted.
`[0041] The CPU 8 changes the black level offset voltage
`according to an amount of current Icv Which is supplied
`from the A/D converter 13 and ?oWs to the organic EL
`elements of the display panel 7. Thus, When the Vth of the
`drive TFT 1 becomes loW because of an increase in tem
`perature, the black level offset voltage can be decreased so
`as to prevent the drive current of the organic EL elements
`from becoming excessively large.
`“Factory Setting”
`[0042]
`[0043] Here, setting before shipping from a factory Will be
`described. In a factory, the black level offset voltages and
`coe?icients of an approximate expression of a compensating
`gamma are previously prepared by the procedure given
`beloW.
`
`[0044] i) A table providing a linear relationship betWeen
`input and output is Written into the respective LUTs 5R, 5G,
`5B by the CPU 8.
`[0045] ii) A loW black level offset voltage is set by the
`CPU 8 so as to enable output of adequately loW voltages
`from the D/A converters 6R, 6G, 6B.
`[0046] iii) The RGB input signals are determined to have
`a value 0.
`[0047] iv) The G input signal is gradually increased While
`monitoring output data from the A/D converter 13, namely
`a total amount of current Icv ?oWing to the organic EL
`elements of the display panel 7, by the CPU 8. As the G input
`signal increases, the amount of current ?oWing to the
`organic EL elements increases so to increase output data
`(Dout) from the A/D converter 13, and When the output data
`Dout falls in a predetermined range (0<D out<D black), a
`value of output from the D/A converter 6G for G is deter
`mined as a black signal input level of the display panel 7.
`
`Here, the drive current Icv to the organic EL elements is
`substantially proportional to the luminance. Therefore, When
`the proportional coe?icient of the element (luminous effi
`ciency) is determined, the luminance can be knoWn from the
`results obtained by measuring the amount of current Icv
`?oWing to the organic EL elements Without actually mea
`suring it. In this embodiment, When the black signal input
`level is determined as described above, a value (output data
`Dout) of the current (Icv) ?oWing to the organic EL elements
`is monitored so that an optimum black level can be obtained
`depending on a state of emission by the organic EL elements
`according to the input image signal, and When the monitored
`value meets the above conditions, the input signal (D/A
`output) is determined as a black signal input level.
`
`[0048] The organic EL elements 2 often have a luminous
`amount of G larger than others because of the luminescent
`material used. Therefore, a signal for G may be used to
`measure the black level as described above. HoWever, the
`measurement may be carried out separately for colors R, G,
`B, so as to set the black signal input voltage for the
`respective colors.
`
`[0049] v) The black level offset voltage of each color is set
`by the CPU 8 so that the black signal input voltage deter
`mined in iv) is output When 0 is input to the D/A converter.
`[0050] vi) L-V (luminance-input voltage) characteristics
`of several points are measured for RGB respectively by the
`measuring system of FIG. 3. Thus, there is obtained a
`relationship shoWn in, for example, FIG. 6.
`
`[0051] vii) An expression, L=f(V), of the curve passing
`through the obtained points and the origin point (black level)
`is created as shoWn in FIG. 6. An expression, V=g(L), of the
`reverse characteristic of gamma is obtained from the former
`to determine coe?icients a, b, c, d. .
`. of this expression.
`
`[0052] For example, the coe?icients a and b Which meet
`the expression beloW are determined for RGB respectively.
`
`[0053] viii) From the above expression, the reverse char
`acteristic of gamma of the panel is determined as indicated
`beloW.
`
`[0054] Values A and B are stored in the ?ash memory 9
`Which is a nonvolatile memory. Here, A=(1/a)(1/b), and
`
`[0055] Thus, necessary data is Written into the ?ash
`memory 9.
`
`[0056] The expression for the characteristics is not limited
`to that described above but may be another expression.
`
`[0057] “Initialization”
`
`[0058] When the system is activated, the black level offset
`voltage is set by the CPU 8 into the D/A converters 6R, 6G,
`6B according to the black level adjustment voltage stored in
`the ?ash memory 9 as described above. The CPU 8 uses the
`coe?icients A, B in the ?ash memory 9 to create table data
`from the expression V=AxLB and Writes the table data into
`the LUTs 5R, 5G, 5B.
`
`12
`
`

`
`US 2005/0023986 A1
`
`Feb. 3, 2005
`
`“Adjustment of Black Level in Use”
`
`[0059]
`[0060] In this embodiment, the black level offset voltage
`is adjusted at the time of use according to the total current
`of the organic EL elements detected by the current detection
`resistor R1 as described above. This procedure Will be
`described beloW.
`
`[0061] The voltages at both ends of the current detection
`resistor R1 are supplied as digital data to the CPU 8 by the
`A/D converter 12. The CPU 8 determines Whether or not the
`current Icv (total current ?oWing to the organic EL elements
`of the organic EL panel 7) ?oWing to the current detection
`resistor R1 has reached a prescribed threshold value Icv1,
`and When it is equal to or beloW the threshold value as shoWn
`in FIG. 8, outputs the black level offset voltage as it is.
`When the current Icv exceeds the threshold value Icv1, a
`signal Which increases according to the current Icv is
`supplied as a black level offset voltage to the D/A converters
`6R, 6G, 6B. Thus, the black level of the image signal is
`shifted as shoWn in FIG. 9
`[0062] A gate application voltage of the p-channel type
`drive TFT 1 is shifted upWard as Icv becomes larger.
`Therefore, even When the threshold voltage Vth of the drive
`TFT 1 becomes small due to the effect of temperature or the
`like, it can be compensated by changing the black level
`offset voltage. Speci?cally, the predetermined value of the
`black level is changed to make black more black With the
`increase in current Icv. As a result, current consumption (Cv
`current) of the organic EL display panel 7 does not exceed
`the predetermined value, and the prominence of black due to
`a change in temperature is limited.
`[0063] “Another Embodiment”
`[0064] The black level is determined commonly among
`colors RGB in the above-described embodiment, but a
`different value can be determined for each color individual
`measurement.
`
`[0065] As described above, the drive current Icv of the
`organic EL element and the luminance are substantially
`proportional to each other. Therefore, When the proportional
`coef?cient (luminous ef?ciency) is knoWn, a current can be
`measured instead of measuring the luminance With a lumi
`nance meter, and the luminance can be calculated. The drive
`current Icv of the organic EL elements can be measured by
`using the current detection resistor R1 shoWn in FIG. 7 as
`described above. Speci?cally, the luminance can be calcu
`lated from the voltages at both ends of R1 according to the
`structure shoWn in FIG. 7, and a gamma compensation
`curve can be created according to the drive current Icv of the
`organic EL elements Without using a luminance meter.
`[0066] Speci?cally, before shipping from the factory, the
`drive current Icv passed to the organic EL elements When
`plural levels of input image signals are supplied for each of
`R, Q B is measured, and the luminance (luminous amount)
`of the organic EL element according to the plural input
`image signal levels is calculated from the measured current
`value according to the knoWn (previously checked) lumi
`nous ef?ciency of organic EL elements. Thus, the relation
`ship shoWn in FIG. 6 is determined from the drive current
`value Without actually measuring the luminance. The
`obtained relationship, namely the approximate expression
`(or a coef?cient of a predetermined approximate expression)
`indicating the relationship betWeen the luminance deter
`
`mined from the drive current and the input signal voltage, is
`stored in the ?ash memory 9 or the like. It may be used at
`the time of initialiZation or When actually used.
`
`[0067] As described above, according to the present
`invention, the table data generation means generates table
`data on the basis of data relating to the equation Which is
`stored in the storage means and Writes the data in the lookup
`table. Therefore, it is not necessary to store all the table data,
`and the storage means is not required to have a large
`capacity. By virtue of the equation, the gamma compensa
`tion curves can be created With a feW measuring points, and
`it becomes easy to perform setting at a factory or the like.
`
`[0068] In general, While there have been described that
`What are at present considered to be preferred embodiments
`of the invention, it is to be understood that various modi?
`cations may be made thereto, and it is intended that the
`appended claims cover all such modi?cations as fall Within
`the true spirit and scope of the invention.
`
`Parts List
`
`[0069] 1 drive TFT
`[0070] 2 EL element
`[0071] 3 channel type selection
`[0072] 7 display panel
`[0073] 8 CPU
`
`[0074] 9 ?ash memory
`
`[0075] 11 drive circuit
`
`[0076] 12 luminance meter
`
`[0077] 13 A/D converter
`[0078] C retention capacitor
`[0079] CV cathode poWer supply
`[0080] Dout output data
`
`[0081] Icv current
`[0082] PVdd poWer supply
`[0083] R1 current detection resistor
`[0084] SR, 5G, 5B lookup tables (LUT)
`[0085] 6R, 6G, 6B D/A converters
`[0086]
`Rin, Gin, Bin input terminals
`[0087]
`Vsc capacitor poWer supply
`Vgs gate-to-source voltage
`[0088]
`[0089]
`Vth threshold voltage
`
`What is claimed is:
`1. An organic EL display device Which displays by
`individually controlling an amount of current of organic EL
`elements, Which are arranged in a matrix, according to an
`input image signal, comprising:
`a lookup table for storing gamma compensation data for
`compensating an image signal;
`storage means for storing an equation for performing
`gamma compensation of the input image signal; and
`
`13
`
`

`
`US 2005/0023986 A1
`
`Feb. 3, 2005
`
`table data generation means for generating table lookup
`data and storing such data in the lookup table on the
`basis of the equation stored in the storage means, and
`Wherein the table data generated by the table data
`generation means is stored in the lookup table by an
`initialization operation to perform gamma compensa
`tion of the input image signal.
`2. The organic EL display device according to claim 1,
`Wherein the table data generation means comprises:
`
`a nonvolatile memory for storing a coefficient of the
`equation; and
`processing means for generating the equation by using a
`coef?cient stored in the nonvolatile memory.
`3. The organic EL display device according to claim 1
`Wherein the equation stored in the table data storage means
`is obtained by making the organic EL panel emit light in an
`amount according to input image signal levels of a plurality
`of stages, detecting the amount of emitted light to determine
`a relationship betWeen the input image signal level and the
`amount of emitted light, and calculating an approximate
`expression indicating the determined relationship or only a
`prescribed coefficient of the approximate expression accord
`ing to the determined result.
`4. The organic EL display device according to claim 1
`Wherein the equation stored in the table data storage means
`
`is obtained by supplying input image signals of plural stages
`to make the organic EL elements emit light so to measure a
`drive current passing to the elements; determining, from the
`measured current value, a relationship betWeen the input
`image signal level and the amount of emitted light of the
`organic EL elements according to a luminous ef?ciency of
`the organic EL elements; calculating, according to the deter
`mined relationship, an approximate expression indicating
`the relationship betWeen the input image signal and the
`amount of emitted light of the organic EL elements or a
`coef?cient of the prescribed approximate expression; and
`determining from the obtained approximate expression or
`coef?cient.
`5. The organic EL display device according to claim 1
`further comprising total current detection means for detect
`ing total current ?oWing to all the organic EL elements
`arranged in a matrix, Wherein:
`
`an offset voltage Which offsets the input image signal is
`determined according to the total current detected by
`the total current detection means so as to provide a
`voltage to make a current start passing to the organic
`EL elements according to a black level of the input
`image signal.
`
`14