US007227519B1
`
`(12) United States Patent
`Kawase et a].
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,227,519 B1
`Jun. 5, 2007
`
`(54)
`
`(75)
`
`METHOD OF DRIVING DISPLAY PANEL,
`LUMINANCE CORRECTION DEVICE FOR
`DISPLAY PANEL, AND DRIVING DEVICE
`FOR DISPLAY PANEL
`
`Inventors: Toru KaWase, Katano (JP); Hideo
`KurokaWa, Katano (JP); Koji
`Akiyama, NeyagaWa (JP); Tetsuya
`Shiratori, Osaka (JP)
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6/1987 Ando .................. .. 315/368.12
`4,672,275 A *
`4/1997 Doherty .......... ..
`345/693
`5,619,228 A *
`9/1997 Cappels et al.
`345/601
`5,670,985 A *
`8/1999 Wagner .......... ..
`345/690
`5,933,130 A *
`2/2000 Howard et al.
`345/76
`6,023,259 A *
`2/2000 Xie et al. ................ .. 345/75.1
`6,025,819 A *
`9/2003 Yamaguchi et al. ..... .. 345/74.1
`6,621,475 B1 *
`6,633,301 B1 * 10/2003 Dallas et al. ............. .. 345/597
`
`(73)
`
`Assignee: Matsushita Electric Industrial Co.,
`Ltd., Osaka (JP)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 145 days.
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`JP
`
`06-236161
`
`8/1994
`
`(21)
`
`(22)
`
`(86)
`
`Appl. No.:
`
`10/089,802
`
`PCT Filed:
`
`Oct. 4, 2000
`
`PCT No.:
`
`PCT/JP00/06893
`
`§ 371 (C)(1)s
`(2), (4) Date:
`
`Apr. 4, 2002
`
`(87)
`
`PCT Pub. No.: WO01/26085
`
`PCT Pub. Date: Apr. 12, 2001
`
`Foreign Application Priority Data
`(30)
`Oct. 4, 1999
`Nov. 19, 1999
`Apr. 4, 2000
`
`(JP)
`
`............................... .. 11-282765
`
`(JP)
`
`............................... .. 11-329492
`
`(JP)
`
`........................... .. 2000-101959
`
`(51)
`
`(52)
`(58)
`
`Int. Cl.
`(2006.01)
`G09G 3/30
`US. Cl. ...................................................... .. 345/77
`
`Field of Classi?cation Search ............. .. 345/74.1,
`345/75.1, 75.2, 76, 77, 78, 89, 82, 83, 904;
`348/l80il89; 324/121 R
`See application ?le for complete search history.
`
`(Continued)
`Primary ExamineriKevin M. Nguyen
`(74) Attorney, Agent, or F irmiSteptoe & Johnson LLP
`
`(57)
`
`ABSTRACT
`
`In conventional methods of correction luminance in dis
`plays, it has been necessary to interrupt video display during
`use in order to carry out correction. This is a problem in that
`interruptions are not good for workability from the perspec
`tive of the user of the image display device. In consideration
`of this, the present invention realiZes a display Without
`non-uniformity in illumination With respect to both initial
`characteristics and change over time by measuring anode
`current of an FED and creating a luminance correction
`memory. In addition, by illuminating arbitrary pixels during
`video idle periods, capturing the luminance information
`from the pixels, and renewing a correction memory based on
`this luminance information, correction for change over time
`is possible Without interrupting video display. Thus, a dis
`play device that can maintain high quality images is pro
`vided.
`
`66 Claims, 52 Drawing Sheets
`
`Luminance Correction Operation
`S 1
`S2
`/
`/
`
`S3
`/
`
`S4
`/
`
`Driving of Pixel
`(Illumination)
`
`Calculation of
`Capturing of
`\ Luminance % Correction
`Information
`Value
`
`Saving to
`’ Correction
`Memory
`
`Blanking Period
`
`

`

`US 7,227,519 B1
`Page 2
`
`US. PATENT DOCUMENTS
`
`6 897 855 B1 *
`’
`’
`
`5/2005 Matthies et al
`' """"" "
`
`345/204
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`
`07-181911
`07-181916
`08-030231
`08-314412
`
`7/1995
`7/1995
`2/1996
`11/1996
`
`JP
`
`JP
`JP
`
`JP
`JP
`JP
`
`09-281925
`
`10031450
`11-015437
`
`“'085104
`11-015430
`11-344949
`
`10/1997
`
`2/1998
`1/1999
`
`3/1999
`11/1999
`12/1999
`
`* cited by examiner
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 1 of 52
`
`US 7,227,519 B1
`
`Video Signal
`
`1
`
`Video decoder
`
`Duminance Horizontal, Vertical signal
`Signal
`
`2
`
`Il
`
`-- ----------.
`
`5}
`
`lI I
`
`12
`Correction Circuit
`
`q D
`
`Signal Driver
`
`riving
`Current
`
`
`‘W:
`orrection Value
`C
`Correction
`Arithmetic Unit
`v
`I Value Memory
`_-__
`
`.-I
`
`1:
`
`1
`
`I l II II
`
`ScanDriver
`
`[1
`
`EEl DisplayPanel
`
`| 9
`
`10
`Anode Current
`Measuuring Means
`
`Luminnance
`Measuring Means
`
`

`

`U.S. Patent
`
`Jun. 5,2007
`
`Sheet 2 0f 52
`
`US 7,227,519 B1
`
`Fig.
`
`GND
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 5,2007
`Jun. 5, 2007
`
`Sheet 3 0f 52
`Sheet 3 of 52
`
`US 7,227,519 B1
`US 7,227,519 B1
`
`Fig. 3
`
`C2
`
`ii; my 0
`
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`
`i?
`
`32
`
`

`

`U.S. Patent
`
`Jun. 5,2007
`
`Sheet 4 0f 52
`
`US 7,227,519 B1
`
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`

`U.S. Patent
`
`Jun. 5,2007
`
`Sheet 5 0f 52
`
`US 7,227,519 B1
`
`Fig. 5
`
`Amphtude Value
`(Current / Voltage)
`
`A One Horizontal Period
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 6 0f 52
`
`US 7,227,519 B1
`
`Input Gray Scale Data
`
`In
`Decimal
`
`In Binary
`
`A
`
`B
`
`38
`
`1
`
`O
`
`0110
`
`

`

`U.S. Patent
`
`Jun. 5,2007
`
`Sheet 7 0f 52
`
`US 7,227,519 B1
`
`Output Waveform '
`
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`01 02 0304 05 06 0708 09 1101112 15 1141516
`
`

`

`U.S. Patent
`
`m.
`
`2
`
`US 7,227,519 B1
`
`Fig 8
`
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`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 9 0f 52
`
`US 7,227,519 B1
`
`Clock
`
`Start
`Data
`
`SR.
`
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`
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`
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`
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`
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`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 5, 2007
`Jun. 5, 2007
`
`Sheet 10 0f 52
`Sheet 10 of 52
`
`US 7,227,519 B1
`US 7,227,519 B1
`
`Fig. 10
`Fig. 10
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 5, 2007
`Jun. 5, 2007
`
`Sheet 11 0f 52
`Sheet 11 of 52
`
`US 7,227,519 B1
`US 7,227,519 B1
`
`Fig. 11
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 12 0f 52
`
`US 7,227,519 B1
`
`Fig. 12
`
`20
`J
`/
`
`21
`
`22
`
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`
`58
`
`- /
`Emlssion
`urrent Value 5 A/D 5
`
`55
`
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`
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`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 13 0f 52
`
`US 7,227,519 B1
`
`7
`
`Signal Driver
`
`WY
`53% ------- -
`
`Display Panel
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 5, 2007
`Jun. 5, 2007
`
`Sheet 14 0f 52
`Sheet 14 of 52
`
`US 7,227,519 B1
`US 7,227,519 B1
`
`(a)
`(a)
`
`(b)
`(b)
`
`(c)
`(c)
`
`(d)
`(d)
`
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`
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`MW H M
`
`(f)
`(f)
`
`
`
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`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 15 0f 52
`
`US 7,227,519 B1
`
`Fig.
`
`15
`
`Video Signal
`4
`
`Corrector
`
`V
`Signal Driver
`NW --------- -- t
`
`5
`/
`/
`Correction
`Value Table
`
`6
`/
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`Correction
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`//7
`Circuit
`Luminance Information
`9
`/57
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`Capturing
`Display Panel |/
`Means
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 16 0f 52
`
`US 7,227,519 B1
`
`A
`
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`

`U.S. Patent
`
`Jun. 5,2007
`
`Sheet 17 0f 52
`
`US 7,227,519 B1
`
`Fig. 17
`
`A
`Emission Current
`(Luminance)
`
`Id
`
`10
`
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`
`Driving Voltage
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 18 0f 52
`
`US 7,227,519 B1
`
`Fig. 18
`
`(a)
`Before Correction
`
`(b)
`After Correction
`
`Time
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 19 of 52
`
`US 7,227,519 B1
`
`Fig. 19
`
`IA ———————————————————
`
`Luminance
`(Emission Current)
`10 --------------------
`
`
`
`
`VAVO VB Driving Voltage
`
`

`

`U.S. Patent
`
`Jun.5,2007
`
`Sheet20 of52
`
`US 7,227,519 B1
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`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 21 of 52
`
`US 7,227,519 B1
`
`Fig. 21
`
`(a)
`
`(b)
`
`Applied Voltage
`Luminance
`
`Applied Voltage
`
`Luminance
`
`/
`/
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet22 of52
`
`US 7,227,519 B1
`
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`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 24 of 52
`
`US 7,227,519 B1
`
`Fig. 24
`
`Luminance
`
`System of
`Gray Scale
`Realization 2
`
`System of
`Gray Scale
`Realization l
`
`
`
`
`System of
`Gray Scale
`Realization 1
`
`——> Gray Scale Levels
`System of
`Gray Scale
`Realization 2
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 25 of 52
`
`US 7,227,519 B1
`
`Fig. 25
`
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`
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`
`
`

`

`U.S. Patent
`
`Jun.5,2007
`
`Sheet26 of52
`
`US 7,227,519 B1
`
`11
`
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`
`
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`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 27 of 52
`
`US 7,227,519 B1
`
`
`
`VerticalBlankingPeriod
`
`
`Fig.27
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 28 of 52
`
`US 7,227,519 B1
`
`Fig. 28
`
`Luminance Correction Operation
`
`Si
`
`82
`
`83
`
`S4
`
` Driving of Pixel
`
`Saving to
`Correction
`Memory
`
`(Illumination)
`
`Capturing of
`" Luminance
`Information
`
`Calculation of
`' Correction
`Value
`
`
`
`Blanking Period
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 29 of 52
`
`US 7,227,519 B1
`
`Fig. 29
`
`Luminance Correction Operation
`
`81
`
`82
`
`83
`
`S4
`
`,
`.
`f
`.
`.
`Drwmg 0 pl“
`(Illummatlon)
`
`l
`
`Capturing of
`Luminance
`Information
`
`Calculation of
`Correction
`Value
`
`Saving to
`Correction
`Memory
`
`
`Blanking Period
`Arbitary Period
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 30 of 52
`
`US 7,227,519 B1
`
`Fig. 30
`
`
`
`Start of
`I
`Luminance Correction
`
`
`S 1 0
`
`Sll
`
`812
`
`813
`
`
`
`
`
`
`Driving of Pixel
`(Illumination)
`
`
`Capturing of
`Luminance
`Information
`
`
`Calculation of
`
`Correction
`v.1 -
`
`
`
`
`Saving to
`Correction
`
`
`
`Memory
`
`
`
`814
`
` Deviation
`
`Converged?
`
`
`
`
`815
`
`Advance to
`Next Pixel?
`
`$16
`
`
` All Pixels
`Completed?
`
`
`YES
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 31 of 52
`
`US 7,227,519 B1
`
`Fig. 31
`
`Start of
`
`Luminance Correction
`
`Driving of Pixel
`(Illumination)
`
`Capturing of
`Luminance
`
`
`Information
`
`
`Calculation of
`
`Correction
`
`Value
`
`
`Saving to
`
`Correction
`
`Memory
`
`
`"
`
`Advance to
`Next Pixel
`
`
`
`820
`
`82 1
`
`822
`
`823
`
`JSZ4
`
`All Pixels
`Completed?
`
`
`f/525
`
`
`
`.. YES
`
`826
`
`
`
`
`Examination of
`Convergence State
`
`
`
`
`.1; YES
`
`827
`
`Deviation Converge ‘
`for All Pixels
`
`Completion
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 32 of 52
`
`US 7,227,519 B1
`
`Fig. 32
`
`Id ------------------- .
`
`Luminance
`(Emission Current)
`
`
`
`
`IB """""""""
`
`
`V0 Driving Voltage
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 33 of 52
`
`US 7,227,519 B1
`
`Fig. 33
`
`Luminance
`(Emission Current)
`
`Vth(A) Vth(B)
`
`Driving Voltage
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 34 of 52
`
`US 7,227,519 B1
`
`Fig. 34
`
`Luminance
`
`400ccl/crn2
`
`(a)
`
`Elapsed Dr1v1ng T1me
`
`Luminance
`
`400cd/cm2
`
`(b)
`
`Elapsed Drivmg Time
`
`Luminance
`
`400Cd/Cm2
`
`80%
`
`20000
`
`(c)
`
`Elapsed Driving Time
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 35 of 52
`
`US 7,227,519 B1
`
`Fig. 35
`
`100
`
`Luminance
`Setting Value
`eneration Portio
`
`Video Signal
`
`
`
`
`Correction
`Value Arithmetic
`,
`
`-
`- Unit
`
`12 Correction Circuit
`
`Luminance Information
`Signal Driver
`
`
`Luminance
`Capturing
`Means
`
`Display Panel
`
`
`
`orrector
`
`orrection Value Tabl
`
`5'?
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 36 of 52
`
`US 7,227,519 B1
`
`Fig. 36
`
`Luminance
`
`Time
`Luminance Degradation Characteristics of Phosphors
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 37 of 52
`
`US 7,227,519 B1
`
`Fig. 37
`
`Luminance Correction Operation
`
`81
`84
`SB
`82
`
`
`
`Saving to
`Calculation of
`
`Capturing of
`
`
`Driving of Pixel
`
`
`Correction
`Correction
`~' Luminance
`
`
`(Illumination)
`Memory
`
`Value
`Information
`
`
`
`
`
`
`Degradation
`
`
`Characteristics of
`
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 38 of 52
`
`US 7,227,519 B1
`
`Fig. 38
`
`Video Signal
`
`190
`
`100
`
`
`Luminance
`Phosphor
`
`
`
`Setting Value
`Degradation
`
`
`Generation Portion
`Arithmetic Unit
`
`
`
`
`
` orrection
`
`
`alue Arithmetic
`
`- nit
`-
`
`F 12 Correction Circuit
`
`
`
` Luminance Information
`
`Correction Value Tabl
`
`
`
`Signal Driver
`
`57
`Luminance
`
`Means
`Capturing
`
`Display Panel
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 39 of 52
`
`US 7,227,519 B1
`
`Fig. 39
`
`00000000 ———-——>
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 40 of 52
`
`US 7,227,519 B1
`
`Fig. 40
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 41 of 52
`
`US 7,227,519 B1
`
`Fig. 41
`
`Luminance Correction
`Operation for Whole Screen
`
`Luminance Correction
`Operation for Whole Screen
`
`-----ss--—->‘———>‘--—-ss——--+———>}-~+-—->
`
`

`

`U.S. Patent
`
`Jun.5,2007
`
`Sheet42 of52
`
`US 7,227,519 B1
`
`Fig. 42
`
`Luminance
`
`Time
`
`
`

`

`U.S. Patent
`
`Jun.5,2007
`
`Sheet43 of52
`
`US 7,227,519 B1
`
`Fig. 43
`
`Luminance
`
`Time
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 44 of 52
`
`US 7,227,519 B1
`
`Fig. 44
`
`1 8 0
`
`
`Recor rection
`Command
`Arithmetic Unit
`
`Video Signal
`‘1]
`
` Luminance
`Setting Value
`
`Generation Portion
` Correction
`.lICorrectionValueTable -EffieArithmetic
`
`
`
`
`
`100
`
`
`
`Luminance Information
`
`
`
`
`Luminance
`Capturing
`Means Display Panel
`
`
`,7
`
`12 Correction Circuit
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 45 of 52
`
`US 7,227,519 B1
`
`Fig. 45
`
`Luminance
`Luminance
`Correction
`Correction
`Operation
`Operation
`for Whole Screen for Whole Screen
`
`Luminance
`Correction
`Operation
`for Whole Screen
`
`Luminance
`Correction
`Operation
`for Whole Screen
`
`-----ss--—>+————>l———>}————>‘———>
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 46 of 52
`
`US 7,227,519 B1
`
`Fig. 46
`
`Controller
`
`Signal Driver
`
`502
`
`
`507
`
`509
`
`
`
`
`
`.-
`ScanDr1ver
`
`508
`
`
`
`
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 47 of 52
`
`US 7,227,519 B1
`
`Fig. 47
`
`Clock
`
`Start
`
`Date
`
`Current
`
`Source
`
`
`
`Panel Signal Line
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 48 of 52
`
`US 7,227,519 B1
`
`Fig. 48
`
`One Horizontal Period
`
`Scanning Period
`
`100%Illumination —L[—l__J—————l_l—
`
`50%Illumination __|_—|—J—__|._l—
`
`LSB IlluminationW
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 49 of 52
`
`US 7,227,519 B1
`
` 0
`
`Panel Signal Line Panel Signal Line
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 50 of 52
`
`US 7,227,519 B1
`
`Fig. 50
`
`Current
`(85:22:)
`
`LSB Output
`
`
`Time
`
`One Horizontal Period
`
`Blanking Period
`
`Scanning Period
`
`
`
`
`
`
`100%Output
`50%Output
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 51 of 52
`
`US 7,227,519 B1
`
`Fig. 51
`
`Video Signal
`
`LUT Creation Instruction
`
`
`
`SYNC
`Luminance (Synchronized
`in:-al
`Signal)
`
`60-2
`
`Singal
`
`If Monitor Signal
`
`612
`
`
`
`________‘
`—SITimingGeneration
`
`
`
`
`
`
`CorrectionDataCreation
`
`
`Monitor.--__-_
`
`ScanDriver
`
`
`
`
`
`
`
`. Multiple
`5 Electron Source
`
`
`
`611
`
`Luminance Monitor
`
`Luminance
`
`Measurin Device
`
`Signal
`
`

`

`U.S. Patent
`
`Jun. 5, 2007
`
`Sheet 52 of 52
`
`US 7,227,519 B1
`
`Fig. 52
`
`(a)
`
`(b)
`
`_|IIIII_IIIII_IIIII___WIIIIJlllllWIIII
`
`T||I|LIIIIIrlnll
`
`rIIIILIIIIIrIIII
`
`
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`
`lllll_lllll___WIIIII—lllll_|llll
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`
`rlIIIL
`
`lllll_llll|___.IIIIII.IIIIIfillll
`
`TIIIIJIIIIIwill!
`
`TIIIILIIIIITIIII
`
`_IIIIII_I|III.IIIII
`
`
`
` FIIIILIIIIIFllll444//////432
`
`1IIIIJIIIIITIIII
`
`IIIIIrIIII____IIIlII_IIIII_I|III
`r|I1IL
`
`FIIIiLlIIIIrIIIIIIIIIII___1III|JIIIII
`
`1I|II
`
`pD.A
`
`.m/
`
`d
`
`emeng.1amkuoLVl/
`
`

`

`US 7,227,519 B1
`
`1
`METHOD OF DRIVING DISPLAY PANEL,
`LUMINANCE CORRECTION DEVICE FOR
`DISPLAY PANEL, AND DRIVING DEVICE
`FOR DISPLAY PANEL
`
`TECHNICAL FIELD
`
`The present invention relates to light-emitting elements
`such as electron-emitting elements and organic EL elements,
`as well as to display elements that are made up of a plurality
`of these light-emitting elements. In particular, the present
`invention relates to a method of driving where luminance
`variation that arises as a result of change over time is
`corrected, to a luminance correction device thereof, and to a
`driving device that utilizes thereof.
`
`BACKGROUND ART
`
`First Background Art
`
`The configuration of a display device that utilizes con-
`ventional electron-emitting elements is shown in FIG. 46. In
`FIG. 46, reference numeral 509 denotes a matrix display
`panel with a plurality of signal lines and a plurality of scan
`lines, reference numeral 507 denotes a signal driver for
`driving the signal lines, reference numeral 508 denotes a
`scan driver for driving the scan lines, and reference numeral
`502 denotes a controller for controlling the signal driver 507
`and the scan driver 508. In cases of gray scale driving, data
`according to the video signals are supplied to the signal
`driver 507 and a gray scale control function is provided in
`the signal driver 507.
`In the past, two methods have been employed for this
`system of gray scale control. First, pulse width modulation
`(hereinafter referred to as PWM) will be explained as one of
`these methods. An example of the configuration of a signal
`driver according to this system is shown in FIG. 47 and is
`described with reference to the figures. In FIG. 47, reference
`numeral 540 denotes a shift register (abbreviated as S.R.) for
`determining the timing of the sampling of data signals
`according to clock and start signals from the controller.
`Reference numeral 541 denotes a latch that has the function
`
`of latching a plurality of signal data lines for indicating gray
`scale in accordance with the output timing of the SR. and
`temporarily storing this data. Reference numeral 542
`denotes a decoder for determining the output timing of a
`PWM based on the data stored in latch 541, and finally, at
`a PWM circuit 560, pulse width modulated outputs are
`supplied to the signal lines of the display panel. An example
`output is shown in FIG. 48. In synchronization with the
`driving of the scan lines, the pulse width of a constant output
`is controlled in one horizontal period at a time, outputs
`ranging from an output of 100% to an output of one LSB,
`which is the smallest unit, in accordance with the gray scale
`to be displayed, and gray scale display is thereby carried out.
`An example of a configuration of a signal driver for
`another method, a system of output amplitude modulation, is
`shown in FIG. 49 and is described with reference to the
`
`10
`
`15
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`20
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`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`figure. Parts having the same function as those of FIG. 47 are
`accorded the same reference numerals, and description is
`omitted. Reference numeral 543 denotes a D/A circuit for
`
`60
`
`converting data stored in the latch 541 to analog voltages,
`and these outputs are inputted to an amplifier. Voltages
`corresponding to output voltages of the D/A 543 are applied
`to the signal lines of the panel, whereby gray scale display
`by voltage amplitude modulation in accordance with the
`data signals is carried out. An example output is shown in
`
`65
`
`2
`
`FIG. 50. Throughout the effective scanning period of one
`horizontal period, a constant current ranging from an output
`of 100% to an output of one LSB, the smallest unit, is driven,
`whereby gray scale is displayed.
`Among the conventional examples described above,
`PWM is disadvantageous in that the LSB, the smallest unit,
`is reduced as the number of gray scale levels increases,
`making what is high-speed operation for a signal driver
`necessary. For example, in the case of 8-bit 256-level gray
`scale that is necessary for a nature video on a 640x480
`computer display panel, supposing video is displayed at 60
`frames/second, an LSB width of 0.12 us results, thereby
`necessitating what
`is extremely challenging high speed
`operation for a signal driver. Moreover, as the move toward
`higher
`resolution progresses,
`increasingly high speed
`response will be demanded. Furthermore, the capacitance
`component that is caused by the wiring, increases, and even
`if the signal driver does carry out high speed operation,
`current is lost to parallel capacitance, whereby the phenom-
`enon arises such that light is no longer emitted by the unit
`of an LSB and precision in gray scale expression is
`adversely affected.
`The other method, the system of output amplitude modu-
`lation, is not problematic in terms of high speed operation,
`but when there are numerous gray scale levels, deviations in
`the outputs of the signal driver become a problem. For
`example, in the case of a signal driver having a 100% output
`of 5 V, the LSB output is 20 mV during 8-bit 256-level gray
`scale, and it is difficult in terms of both cost and production
`to ensure this level of accuracy uniformly across all the
`lines.
`
`In addition, in a display panel in which a plurality of
`electron-emitting elements is arranged, there is variation in
`the actual electron-emitting characteristics of each element.
`This is because it is extremely difficult to make the con-
`figuration and process of all the electron-emitting elements
`exactly the same and because the electron-emitting surfaces
`are not uniform. As a result, even if the same driving voltage
`is applied to each of the elements, varying amounts of
`current are emitted, resulting in the problem of non-unifor-
`mity in luminance.
`Furthermore, in the case of displaying the same informa-
`tion over a long period (for example, a total illumination
`time of 3000 hours),
`the degradation of the elements
`progresses more in the elements that have been emitting
`light than in the elements that have not been emitting light.
`This given display of information is then terminated and
`subsequently, all of the pixels are illuminated by a same
`luminance command (for example, a same current value).
`While all of the pixels should emit
`light at
`the same
`luminance, pixels that had displayed the given display of
`information have a lower luminance than the other pixels
`because the degradation of these pixels has progressed
`further. Thus, differences in luminance arise, resulting in the
`problem of the appearance of the given information that had
`been displayed in the form of a phenomenon similar to
`sticking.
`Japanese Unexamined Patent Application 11-15430 is
`another example from prior art. This application realizes
`gray scale by combining pulse width control and amplitude
`control. It has a configuration such that an adder is employed
`to add the value for pulse width control and the value for
`amplitude width control. In this configuration, in accordance
`with the characteristics of the electron-emitting elements, a
`log amplifier is connected to the output of a PAM circuit, but
`if a log amplifier is not also connected to the output of a
`pulse width controller, a problem arises where the log
`
`

`

`US 7,227,519 B1
`
`3
`amplifier does not match with the characteristics. In addi-
`tion, while the characteristics of the electron-emitting ele-
`ments are taken to be the log characteristics,
`the actual
`characteristics of the elements do not precisely align with
`the straight line defining the log characteristics, and thus
`variation results. For these reasons, with only a simple log
`amplifier, it is difficult to output gray scale with accuracy.
`The configuration of this prior art example is also problem-
`atic in that it cannot counter variation in luminance and
`
`change over time in the creation of images.
`
`Second Background Art
`
`In the past, image display devices in which, for example,
`numerous electron-emitting elements are arranged have
`been subject to variation in luminance as a result of variation
`in the characteristics of elements. For various image forma-
`tion devices, high resolution and high quality images have
`been in demand, and in response to this, various driving
`methods for suppressing variation in luminance have been
`proposed.
`For example, Japanese Unexamined Patent Publication
`7-181911 is a prior art example. In FIG. 51, a representative
`figure is shown and operation will now be described.
`First, the procedure for creating a LUT for correction
`value data after production and the like of an image forma-
`tion device is described. At a timing generation circuit 602,
`various timing signals that correspond to the data creation
`procedure are generated when LUT creation instruction
`signals are received. In accordance with these signals, a
`correction data creation circuit 613 sends a signal so that a
`PWM/driver circuit 609 generates a drive signal having a
`specific driving voltage and a specific pulse width for the
`SCE element of a specific pixel. The element current If
`flowing to the SCE element selected by the drive signal and
`a signal from a scan driver 612 is detected by a current
`monitor circuit 610 using monitor resistance, this output is
`converted to a digital signal by an AD converter, and this
`signal is sent to a correction data creation circuit 613. This
`is carried out for all of the SCE elements. The resulting
`element current data for each of the SCE elements is stored
`in a current distribution table in a LUT as current distribu-
`
`tion data. Focusing on the strong correlation between the
`electron beam output of the SCE elements and the element
`current If flowing to the elements, the correction method as
`described below is executed.
`
`Specifically, a monitored element current and element
`current data stored in the correction data creation unit 613
`
`corresponding to the given element are compared such that
`if the difference is within a specified range, a value is
`designated as an acceptable value and if not, it is judged that
`correction is necessary. When correction is necessary, If
`correction data for the monitored pixel is created and written
`to a LUT 606. Note that, in the initial state, Ifcorrection data
`is set so that none of the pixels require correction. Element
`current data also is set to a same value in all of the pixels.
`In this manner, when Ifcorrection data is written to the LUT
`606, a video signal is corrected using this data, and the
`monitoring and evaluating of this same pixel, i.e., the pixel
`reset by the Ifcorrection data, is repeated until an acceptable
`value is reached.
`
`When it is determined that the element current If has
`reached an acceptable value, the element current data is
`renewed with this element current. This process is carried
`out on all of the elements, after which the process is
`terminated. In this manner, input video signals are corrected,
`making correction of variation in luminance possible.
`
`10
`
`15
`
`20
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`25
`
`30
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`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`By repeating the measurement of the current distribution
`data as described above according to necessity, it is possible
`to effectively carry out the correction of not only variation
`in the initial characteristics of the SCE elements but also of
`
`changes in characteristics over time. Carrying out driving as
`described above using correction values stored in the dis-
`tribution correction table makes it possible to realize a high
`quality video display without luminance variation.
`In the prior art example described above, a correction
`operation that adjusts for change over time is carried out as
`follows. In order to detect the change in the characteristics
`of the elements over time, after a suitable amount of time has
`passed,
`the element current If of each of the pixels is
`measured and this value is compared to the initial value for
`element current stored in the current distribution table in the
`LUT. In cases where the difference between the measured
`
`value and the initial value is equal to or greater than a
`specified value, it is judged that there has been a change in
`the characteristics of the element over time, and test driving
`is carried out in the same manner as was done initially to
`correct the correction values in the correction table.
`
`Because this correction is carried out sequentially on all
`of the pixels, a certain amount of time is required and the
`problem of having to interrupt video display during the
`correction operation arises.
`For example, suppose that resolution is VGA (640x480),
`frame rate 60 Hz, and video display carried out by line-
`sequential scanning. In this case, if measurement of the
`luminance of each pixel is carried out in the same cycle as
`display operation,
`the time required for measurement is
`640x480x1/5ox1/480:10.7 (sec). Because convergence to a
`given deviation or less is not realized with one correction, it
`is necessary to repeat correction. For example, if conver-
`gence to the value for deviation or less is realized by
`carrying out the correction 5 times, 54 seconds are required
`in total. In order to carry out the correction, it is necessary
`to interrupt video display during use, and this time cannot be
`ignored or permitted.
`Ideally, a display device that does not require correction
`operation is desired, because having to perform correction
`operations is not good for workability from the perspective
`of the user of the image display device and because it
`contributes to lower quality display.
`
`Third Background Art
`
`There is also a prior art example that adopts, as a system
`of gray scale realization, a system of gray scale control
`where output amplitude control and output pulse width
`control are carried out
`simultaneously. This prior art
`example describes a system for realizing high gray scale
`resolution without requiring high speed and high accuracy.
`However, problems sometimes arise in display at low lumi-
`nance levels.
`
`This method is described using FIG. 52. FIG. 52(a) shows
`an example where pulse width is divided into 16 and
`amplitude value divided into 4 to realize a total of 64 levels
`of grays scale. In this case, the elements of the display panel
`are made of organic EL or the like, and when tending toward
`low luminance, i.e., when the value for gray scale is small
`and the pulse width value small, the response speed some-
`times slows down drastically (FIG. 52(b)). In, for example,
`an organic EL element, it has been confirmed that response
`speed slows when a near threshold voltage is applied to
`realize low luminance. For this reason, even if the number
`of divisions of pulse width is reduced and constrain on
`response speed alleviated, because the amplitude value
`
`

`

`(3) In a device having phosphors, the degradation char-
`acteristics of the phosphors is considered in the carrying out
`of the luminance correction.
`
`25
`
`5
`the problem arises where
`small,
`is
`(applied voltage)
`response speed slows down to an even greater degree.
`
`DISCLOSURE OF THE INVENTION
`
`It is an object of the present invention to overcome the
`foregoing problems by providing a driving method for a
`display panel, a luminance correction device for a display
`panel, and a driving device for a display panel, each of
`which are primarily intended for the realization of a display
`in which non-uniformity in illumination does not arise with
`change over time.
`In order to achieve the above objects, the present inven-
`tion adopts the following driving method for luminance
`correction.
`
`(l) A luminance setting reference value is changed with
`the elapsing of time. Strain on elements is thereby alleviated
`and operating life extend