c12) United States Patent
`Kondo et al.
`
`I 1111111111111111 11111 1111111111 1111111111 1111111111 111111111111111 11111111
`US006525704Bl
`US 6,525,704 Bl
`Feb.25,2003
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54)
`
`IMAGE DISPIAY DEVICE TO CONTROL
`CONDUCTION TO EXTEND THE LIFE OF
`ORGANIC EL ELEMENTS
`
`(75)
`
`Inventors: Yuji Kondo, Tokyo (JP); Atsushi Kota,
`Tokyo (JP)
`
`(73) Assignee: NEC Corporation, Tokyo (JP)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 273 days.
`
`(21) Appl. No.: 09/589,283
`
`(22) Filed:
`
`Jun.8,2000
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 9, 1999
`
`(JP)
`
`.................... ....................... 11-162422
`
`Int. Cl.7 .................. ........... G09G 3/30; G09G 3/ 10
`(51)
`(52) U.S. Cl. ....................................... 345/78; 315/169.3
`(58) Field of Search .............................. 345/36, 45, 76,
`345/77, 78, 79, 80, 211, 212, 214, 215,
`52-54; 315/ 169.3; 340/825.81
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,079,483 A * 1/1992 Sato ........................ 315/169.3
`5,576,726 A * 11/1996 Rhyne et al. ................. 345/76
`5,652,600 A * 7/1997 Khormaei et al.
`............ 345/76
`5,670,792 A * 9/1997 Utsugi et al. ................. 257/59
`5,714,968 A * 2/1998 Ikeda .......................... 345/77
`5,940,053 A * 8/1999 Ikeda .......................... 345/77
`6,011,529 A * 1/2000 Ikeda .......................... 345/77
`6,091,203 A * 7/2000 Kawashima et al. ..... 315/169.3
`6,175,345 Bl * 1/2001 Kuribayashi et al. ......... 345/76
`6,188,375 Bl * 2/2001 Kagey .. . .. . . .. . .. . .. . .. . .. . .. . 345/76
`
`6,246,384 Bl * 6/2001 Sano . .. . .. . .. . .. . .. . .. ... ... ... 345/76
`6,278,423 Bl * 8/2001 Wald et al. ................... 345/76
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`
`A 11-95723
`
`4/1999
`
`* cited by examiner
`
`Primary Examiner----Bipin Shalwala
`Assistant Examiner-Jeff_ Piziali
`(74) Attorney, Agent, or Firm-Young & Thompson
`
`(57)
`
`ABSTRACT
`
`An image display device applies (MxN) data voltages in
`order to M rows of data lines N voltages at a time, and in
`synchronization with these data voltages, applies scan volt(cid:173)
`age in order to the N columns of scan lines. This scan
`voltage causes M rows and N columns of switching ele(cid:173)
`ments to turn on one column at a time, and accordingly,
`(MxN) data voltages that are applied from the M rows of
`data lines are individually held by M rows and N columns
`of voltage holding means. In accordance with these held
`voltages, M rows and N columns of drive transistors apply
`a drive voltage that is constantly applied to power supply
`electrodes to (MxN) organic EL elements. The M rows and
`N columns of organic EL elements are accordingly actively
`driven and a multiple gray-scale dot matrix image is dis(cid:173)
`played. However, conduction control elements halt the
`application of the drive voltage to the M organic EL ele(cid:173)
`ments of the nth column immediately before the scan
`voltage is applied to the scan line of the nth column. As a
`result, conduction to the organic EL elements is halted
`instantaneously even when an image of the same luminance
`is continuously displayed, thereby extending the life of the
`organic EL elements.
`
`17 Claims, 13 Drawing Sheets
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`11
`I
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`m+ 1
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`14
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`12
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`15
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`13
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`18
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`m
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`n-1
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`16
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`19
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`20
`
`n
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`17
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`

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`U.S. Patent
`
`Feb.25,2003
`
`Sheet 1 of 13
`
`US 6,525,704 Bl
`
`Fig.l(Prior Art)
`
`8
`
`m
`
`1
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`
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`
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`
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`
`3
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`

`Fig.2a
`(Prior
`Fig.2b
`(Prior
`Fig.2c
`(Prior
`Fig.2d
`(Prior
`Fig.2e
`(Prior
`Fig.2f
`(Prior
`
`n-1
`
`SCAN LINE
`Art)
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`Ar·t)
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`
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`SAMSUNG EX. 1016 - 3/22
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`

`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 3 of 13
`
`US 6,525,704 Bl
`
`Fig.3
`
`11
`I
`
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`
`14
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`12
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`Fig.4
`
`DATA DRIVE CIRCUIT
`
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`
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`

`Fig.5
`Fig.5
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`SAMSUNG EX. 1016 - 6/22
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`SAMSUNG EX. 1016 - 6/22
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`

`

`U.S. Patent
`
`Feb.25, 2003
`
`Sheet 6 of 13
`
`US 6,525,704 Bl
`
`' :
`Fig. 6a SCAN LINE n-1 _.____..._---!I__ ____ ,---------r------6v
`'
`
`I
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`EL ELEMENT
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`
`SAMSUNG EX. 1016 - 7/22
`
`

`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 7 of 13
`
`US 6,525,704 Bl
`
`Fig.7
`
`18
`
`m
`
`m + 1
`
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`
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`
`19
`
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`SAMSUNG EX. 1016 - 8/22
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`

`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 8 of 13
`
`US 6,525,704 Bl
`
`SCAN LINE n- 1 __. ___ ..._ _ __,p-----r----t--------
`_,,__ __ ...... __ -+---~H-----~---------
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`SAMSUNG EX. 1016 - 9/22
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`

`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 9 of 13
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`US 6,525,704 Bl
`
`Fig.9
`
`18
`
`rn
`
`/
`
`61
`
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`
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`
`19
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`20
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`n
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`SAMSUNG EX. 1016 - 10/22
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`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 10 of 13
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`US 6,525,704 Bl
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`Fig . 1 0 a SCAN LINE n-1
`
`Fi g . 1 Q b SCAN LINE n
`
`Fig . 1 0 c EL ELEMENT
`
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`72
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`m+ 1
`73
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`14
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`13
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`U.S. Patent
`
`Feb.25,2003
`
`Sheet 11 of 13
`
`US 6,525,704 Bl
`
`Fig.12a
`
`SCAN" LINE n-1
`
`Fig.12b
`
`SCAN" LINE n
`
`Fig.12c
`
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`
`SAMSUNG EX. 1016 - 12/22
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`

`U.S. Patent
`
`Feb.25,2003
`
`Sheet 12 of 13
`
`US 6,525,704 Bl
`
`Fig.13
`
`18
`
`m
`
`72
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`
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`
`13
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`U.S. Patent
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`Feb.25,2003
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`Sheet 13 of 13
`
`US 6,525,704 Bl
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`ORGANIC EL ELEMENT
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`SAMSUNG EX. 1016 - 14/22
`
`

`

`US 6,525,704 Bl
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`1
`IMAGE DISPIAY DEVICE TO CONTROL
`CONDUCTION TO EXTEND THE LIFE OF
`ORGANIC EL ELEMENTS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to an image display device
`for displaying an image, and more particularly to an image
`display device that displays an image by actively driving a
`multiplicity of two-dimensionally arranged organic EL
`(Electro-Luminescent) elements.
`2. Description of the Related Art
`EL displays for displaying a dot matrix image in which a
`multiplicity of organic EL elements are two-dimensionally
`arranged have currently been developed as image display
`devices for displaying various images in locations subject to
`radical changes in illumination, such as the interior of an
`automobile. Organic EL elements are light-emitting ele- 20
`ments that spontaneously emit light and can be driven by a
`low-voltage direct current.
`Methods of driving organic EL clements include passive
`matrix drive methods and active matrix drive methods. An
`active matrix drive method can achieve high luminance with
`high efficiency because the organic EL elements are lit
`continuously until updating of the display image.
`As an example of an image display device of the prior art,
`explanation is presented with reference to FIG. 1 and FIG.
`2 regarding an EL display that actively drives organic EL 30
`elements.
`As shown in FIG. 1, EL display 1 that is presented as an
`example of the prior art includes organic EL element 2 as
`well as power supply line 3 and ground line 4 as a pair of
`power supply electrodes. A predetermined drive voltage is 35
`constantly applied to power supply line 3, and ground line
`4 is constantly maintained at O V, which is the reference
`voltage.
`Organic EL element 2 is directly connected to ground line
`4 but is connected to power supply line 3 by way of drive 40
`TFT (Thin-Film Transistor) 5. This drive TFT 5 includes a
`gate electrode, and the drive voltage that is applied to ground
`line 4 from power supply line 3 is supplied to organic EL
`element 2 according to a data voltage that is applied to this
`gate electrode.
`One end of capacitor 6 is connected to the gate electrode
`of drive TFT 5, and the other end of this capacitor 6 is
`connected to ground line 4.
`Data line 8 is connected to this capacitor 6 and the gate
`electrode of drive TFT 5 by way of switching TFT 7, which
`is a switching element, and scan line 9 is connected to the
`gate electrode of this switching TFT 7.
`A data voltage for driving the light emission intensity of
`organic EL element 2 is supplied to data line 8, and a scan
`voltage for controlling switching TFT 7 is applied to scan
`line 9. Capacitor 6 holds the data voltage and applies it to the
`gate electrode of drive TFT 5, and switching TFT 7 turns the
`connection between capacitor 6 and data line 8 ON and OFF.
`In EL display 1, (MxN, M and N are predetermined 60
`natural numbers) organic EL elements 2 are arranged two(cid:173)
`dimensionally in M rows and N columns (not shown in the
`figures), and M rows of data lines 8 and N columns of scan
`lines 9 are connected in a matrix to these M rows and N
`columns of organic EL elements 2. In the figures, the term 65
`" row" refers to the dimension parallel to the vertical direc(cid:173)
`tion and the term "column" refers to the dimension parallel
`
`2
`to the horizontal direction, but this is merely a matter of
`definition, and the reverse case is also possible.
`EL display 1 according to the above-described construc(cid:173)
`tion is capable of driving organic EL elements 2 with
`5 variable light emission intensity. In such a case, a scan
`voltage is applied to scan line 9 and switching TFT 7 is
`controlled to an ON state as shown in FIG. 2b and FIG. 2c,
`and a data voltage from the data line that corresponds to the
`light emission intensity of organic EL element 2 in this state
`10 is supplied to and held in capacitor 6 as shown in FIG. 2e.
`The data voltage held by this capacitor 6 is applied to the
`gate electrode of drive TFT 5 as shown in FIG. 2d, and as
`a result, as shown in FIG. 2f, the drive voltage that is
`constantly generated at power supply line 3 and ground line
`15 4 is supplied to organic EL element 2 by drive TFT 5 in
`accordance with the gate voltage. As a result, organic EL
`element 2 emits light at an intensity that accords with the
`data voltage that was supplied to data line 8.
`In EL display 1, data voltage and scan voltage are applied
`in a matrix to M rows of data lines 8 and N columns of scan
`lines 9, and each of M rows and N columns of organic EL
`elements 2 are therefore lit at different intensities, thereby
`displaying a dot-matrix image with the gray scale expressed
`25 in pixel units.
`In such a case, the scan voltage is applied in order one
`column at a time to N columns of scan lines 9 in EL display
`1 as shown in FIG. 2a and FIG. 2b, and when this scan
`voltage is being applied, one column of M data voltages is
`therefore applied in order to M rows of data lines 8.
`The state in which the drive voltage is applied to organic
`EL element 2 in accordance with the data voltage that is held
`by capacitor 6 as described in the foregoing explanation
`continues even when switching TFT 7 is placed in the OFF
`state by the scan voltage of scan line 9. Organic EL element
`2 thus continues emission that is controlled to a predeter-
`mined luminance until the next instance of control, and EL
`display 1 therefore is capable of displaying a bright and
`high-contrast image.
`In EL display 1 in which organic EL elements 2 are
`actively driven as described above, however, organic EL
`elements 2 have a short life. Various explanations can be
`offered, but characteristically, it is clear that continuous
`application of the drive voltage of the same polarity to
`45 organic EL electrodes 2 results in a short life of the elements.
`In an EL display (not shown) that passively drives organic
`EL elements 2, for example, it has been confirmed that
`organic EL elements 2 have a longer life than in the case of
`active drive because the polarity of voltage applied to
`organic EL elements 2 reverses during the drive process. A
`passive-type EL display as described hereinabove, however,
`is incapable of driving organic EL elements 2 at both high
`luminance and high contrast, and such a display is therefore
`difficult to use in devices requiring high luminance.
`
`50
`
`55
`
`SUMMARY OF TIIE INVENTION
`
`It is an object of the present invention to provide an image
`display device capable of employing active drive to light
`organic EL elements at high luminance and high efficiency
`while enabling longer life of the elements.
`According to one aspect of the present invention, (MxN)
`organic EL elements are arranged two-dimensionally in M
`rows and N colunms, (MxN) data voltages that individually
`set the light-emission luminance of these (MxN) organic EL
`elements are applied in order N times for each of the M rows
`of data lines, and the scan voltage is applied in order to the
`
`SAMSUNG EX. 1016 - 15/22
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`

`

`US 6,525,704 Bl
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`3
`N columns of scan lines in synchronization with the data
`voltages that are applied to these M rows of data lines. The
`scan voltage that is applied in order to these N columns of
`scan lines causes the M rows and N columns of switching
`elements to turn on one column at a time, and the (MxN)
`data voltages that are applied from the M rows of data lines
`in accordance with the ON state of these M rows and N
`columns of switching elements are individually held by M
`rows and N columns of data voltage holding means. The
`drive voltage that is constantly applied to the power supply
`electrode is applied to the (MxN) organic EL elements by
`the M rows and N columns of drive transistors in individual
`correspondence to the held voltage of the (MxN) voltage
`holding means. The M rows and N columns of organic EL
`elements are thus actively driven at individually differing
`luminances to display a multiple gray-scale dot matrix
`image.
`Immediately before the application of the scan voltage to
`the scan line of the nth column, however, a conduction
`control element halts the application of the drive voltage to
`the M organic EL elements of the nth column. As a result,
`conduction to the actively driven organic EL elements is
`halted an instant before performing display control of the
`image, even when an image is continuously displayed at the
`same luminance, thereby enabling a longer life of the
`organic EL elements.
`According to another aspect of the present invention, a
`conduction control element applies a reverse voltage, which
`has the opposite polarity of the drive voltage, to the M
`organic EL elements of the nth column immediately before
`the scan voltage is applied to the scan line of the nth column.
`As a result, the polarity of voltage that is applied to actively
`driven organic EL elements is reversed an instant before
`performing display control of the image, even when an
`image is continuously displayed at the same luminance,
`thereby enabling a longer life of organic EL elements.
`In an embodiment, when a scan voltage is applied to the
`scan line of the (n-a)th column, a conduction control
`element halts the application of the drive voltage to the
`organic EL elements of the nth column. As a result, the
`application of the drive voltage to the M organic EL ele(cid:173)
`ments of the nth column can be simply and reliably halted
`al a dtsirtd timing immtdialdy bdort lht scan vollagt is
`applied to the scan line of the nth column.
`In an embodiment, when the scan voltage is applied to the
`scan lines of the (n-a)th column, a conduction control
`element applies a reverse voltage to the organic EL elements
`of the nth column. As a result, application of a reverse
`voltage, which has the opposite polarity of the drive voltage,
`to the M organic EL elements of the nth column can be
`simply and reliably performed at a desired timing immedi(cid:173)
`ately before the scan voltage is applied to the scan lines of
`the nth column.
`In an embodiment, when the scan voltage is applied to the
`scan lines of the (n-a)th column, a conduction control
`element halts the application of the drive voltage to the
`organic EL elements of the nth column and applies a reverse
`voltage. As a result, the application of a reverse voltage,
`which has a polarity opposite that of the drive voltage, to the
`M organic EL elements of the nth column can be simply and
`reliably carried out at a desired timing immediately before
`the scan voltage is applied to the scan lines of the nth
`column.
`In an embodiment, when a scan voltage is applied to the
`scan lines of the (n-b)th column, a conduction control
`element halts the application of the drive voltage to the
`
`5
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`20
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`25
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`4
`organic EL elements of the nth column, and when a scan
`voltage is applied to the scan lines of the (n-a)th column, the
`conduction control element applies a reverse voltage to the
`organic EL elements of the nth column. Accordingly, a
`reverse voltage can be reliably conducted to the organic EL
`elements after the application of the drive voltage to the
`organic EL elements has been reliably halted.
`In an embodiment, when a scan voltage is applied to the
`scan lines of the (n-a)th column, a conduction control
`10 element discharges the voltage held by a voltage holding
`means of the nth column. As a result, application of the drive
`voltage to the organic EL elements can be simply and
`reliably halted by controlling the voltage holding means.
`In an embodiment, when a scan voltage is applied to the
`15 scan lines of the (n-a)th column, a conduction control
`element disconnects the connection between the power
`supply electrode and the organic EL elements of the nth
`column. As a result, the application of drive voltage to the
`organic EL elements can be reliably halted.
`In an embodiment, a conduction control element conducts
`the scan voltage that is applied to the scan lines of the
`(n-a)th column to the organic EL elements of the nth column
`as the reverse voltage. As a result, the scan voltage can be
`used as the reverse voltage that is conducted to the organic
`EL elements, and a proper reverse voltage can be reliably
`generated by means of a simple construction.
`In an embodiment, when a scan voltage is applied to the
`scan lines of the (n-b)th column, a conduction control
`30 element discharges the voltage that is held by the voltage
`holding means of the nth column and conducts the scan
`voltage that is applied to the scan lines of the (n-a)th column
`to the organic EL elements of the nth column as the reverse
`voltage. Accordingly, the application of drive voltage to the
`35 organic EL elements by the scan voltage of the scan lines of
`the (n-b)th column can be halted through control of the
`voltage holding means, the scan voltage of the scan lines of
`the (n-a)th column can be conducted as the reverse voltage
`to the organic EL elements for which this current conduction
`40 has been halted, and a reverse voltage can be applied to
`organic EL elements for which the drive voltage has been
`completely halted.
`In an embodiment, when a scan voltage is applied to the
`scan lines of the (n-b)th column, a conduction control
`45 element disconnects the connection between the power
`supply electrode and the organic EL elements of the nth
`column and conducts the scan voltage that is applied to the
`scan lines of the (n-a)th column to the organic EL elements
`of the nth column as a reverse voltage. Accordingly, the
`50 application of drive voltage to the organic EL elements by
`the scan voltage of the scan lines of the (n-b)th column can
`be halted by disconnecting the power supply electrodes, the
`scan voltage of the scan lines of the (n-a)th column can be
`conducted as the reverse voltage to the organic EL elements
`55 for which this current conduction has been halted, and a
`reverse voltage can be applied to the organic EL elements for
`which the drive voltage has been completely halted.
`In an embodiment, a is equal to 1. Accordingly, the
`conduction control element controls conduction to organic
`60 EL elements when the scan voltage is applied to the scan
`lines of the preceding column, but control of conduction to
`the organic EL elements of the first column is effected when
`the scan voltage is applied to the scan lines of the Nth
`column, which is the last column. Accordingly, the control
`65 of conduction to the organic EL elements of the first column
`at a proper timing and by a simple construction can be
`realized by a construction in which a conduction control
`
`SAMSUNG EX. 1016 - 16/22
`
`

`

`US 6,525,704 Bl
`
`5
`element controls conduction to organic EL elements when
`the scan voltage is applied to the scan lines of the preceding
`column.
`In an embodiment, a is equal to 1. Accordingly, a con(cid:173)
`duction control element controls conduction to organic EL 5
`elements when the scan voltage is applied to the scan lines
`of the preceding column, but a dummy scan voltage is
`applied to a dummy line that is provided parallel to the scan
`line of the first column immediately before application of the
`first-column scan voltage. Accordingly, control of conduc- 10
`tion to the organic EL elements of the first column is
`performed when the dummy scan voltage is applied to the
`dummy line. As a result, the control of conduction to the
`organic EL elements of the first column at a proper timing
`and by a simple construction can be realized by a construe- 15
`tion in which the conduction control element controls con(cid:173)
`duction to organic EL elements when the scan voltage is
`applied to the preceding scan line.
`In an embodiment, a is equal to 1 and b is equal to 2.
`Accordingly, a conduction control element halts the drive 20
`voltage that is applied to organic EL elements when the scan
`voltage is applied to the scan line of the second preceding
`column, and the conduction control element applies a
`reverse voltage to organic EL elements when the scan
`voltage is applied to the scan lines of the preceding column. 25
`However, the drive voltage to the organic EL elements of the
`first column is halted when the scan voltage is applied to the
`scan line of the (N-l)th column, and a reverse voltage is
`conducted to the organic EL elements of the first column
`when the scan voltage is applied to scan line of the Nth 30
`column. The drive voltage to the organic EL elements of the
`second column is halted when the scan voltage is applied to
`the scan lines of the Nth column. Accordingly, conduction to
`the organic EL elements of the first column and second
`column can be controlled at a proper timing and by a simple 35
`construction by a construction in which the conduction
`control element halts the drive voltage that is applied to the
`organic EL elements when the scan voltage is applied to the
`second preceding scan line and applies a reverse voltage to
`organic EL elements when the scan voltage is applied to the 40
`scan line of the preceding column.
`In an embodiment, a is equal to 1 and b is equal to 2.
`Accordingly, a conduction control element halts the drive
`voltage that is applied to organic EL elements when the scan
`voltage is applied to the scan line of the second preceding 45
`column, and the conduction control element applies a
`reverse voltage to organic EL elements when the scan
`voltage is applied to the scan lines of the preceding column.
`However, first and second dummy scan voltages are applied
`to first and second dummy lines that are provided parallel to 50
`the scan line of the first column immediately before appli(cid:173)
`cation of the first-column scan voltage. As a result, the drive
`voltage to the organic EL elements of the first column is
`halted when the scan voltage is applied to the first dummy
`line, and a reverse voltage is conducted when the scan 55
`voltage is applied to the second dummy line. The drive
`voltage to the organic EL elements of the second column is
`halted when the scan voltage is applied to the second dummy
`line. Accordingly, conduction to the organic EL elements of
`a first column and second column at a proper timing and by 60
`a simple construction can be realized by a construction in
`which a conduction control element halts the drive voltage
`that is applied to organic EL elements when the scan voltage
`is applied to the scan line of the second preceding column
`and applies a reverse voltage to organic EL elements when 65
`the scan voltage is applied to the scan line of the preceding
`column.
`
`6
`The above and other objects, features, and advantages of
`the present invention will become apparent from the fol(cid:173)
`lowing description with reference to the accompanying
`drawings which illustrate examples of the present invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a circuit diagram showing the principal features
`of an EL display of the prior art;
`FIG. 2 is a timing chart showing the signal waveform of
`each part;
`FIG. 3 is a circuit diagram showing the circuit configu(cid:173)
`ration of the principal components of the EL display, which
`is the image display device of the first embodiment of the
`present invention;
`FIG. 4 is a block diagram showing the overall construc(cid:173)
`tion of the EL display;
`FIG. 5 is a sectional diagram showing the thin-film
`structure of an organic EL element;
`FIG. 6 is a timing chart showing the signal waveform of
`each component of the EL display;
`FIG. 7 is a circuit diagram showing the circuit structure of
`the principal components of the EL display of the second
`embodiment;
`FIG. 8 is a timing chart showing the signal waveform of
`each component;
`FIG. 9 is a circuit diagram showing the circuit structure of
`the principal components of the EL display of the third
`embodiment;
`FIG. 10 is a timing chart showing the signal waveforms
`of each component;
`FIG. 11 is a circuit diagram showing the circuit structure
`of the principal components of the EL display of the fourth
`embodiment;
`FIG. 12 is a timing chart showing the signal waveform of
`each component;
`FIG. 13 is a circuit diagram showing the circuit structure
`of the principal components of a variant EL display;
`FIG. 14 is a circuit diagram showing the circuit structure
`of the principal components of the EL display of the fifth
`embodiment; and
`FIG. 15 is a timing chart showing the signal waveform of
`each component.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`For the sake of convenience in the explanations of the
`embodiments hereinbelow, " rows" refers to the dimension
`that is parallel to the vertical direction in the figures, and
`"columns" refers to the dimension