(12) United States Patent
`Sekiya et al.
`
`USOO6583775B1
`(10) Patent No.:
`US 6,583,775 B1
`(45) Date of Patent:
`Jun. 24, 2003
`
`(54) IMAGE DISPLAY APPARATUS
`
`(75) Inventors: Mitsunobu Sekiya, Tokyo (JP); Akira
`Yumoto, Kanagawa (JP)
`
`(73) Assignee: Sony Corporation, Tokyo (JP)
`
`12/1998
`7/1998
`
`JP
`1O-319908
`WO
`98/331.65
`sk -
`cited by examiner
`Primary Examiner Dennis-Doon Chow
`(57)
`ABSTRACT
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 212 days.
`
`The invention provides an image display apparatus which
`the degree of freedom in designing of an active
`Increases une aeg
`designing OI an
`element of a pixel to allow good designing and can adjust the
`display brightness freely and Simply. Each pixel includes a
`light emitting element (OLED) with a brightness value
`(21) Appl. No.: 09/594,087
`which varies depending upon an amount of current Supplied
`(22) Filed:
`Jun. 15, 2000
`thereto, a first TFT controlled by a scanning line for writing
`brightness information given thereto from a data line into the
`(30)
`Foreign Application Priority Data
`pixel, and a second TFT for controlling the amount of
`is
`Jun. 17, 1999
`(JP) ...........................................
`Jun. 2, 2000 (JP) ....................................... oilo current to be supplied to the OLED corresponding to the
`brightness information written. Writing of the brightness
`(51) Int. Cl. .................................................. G09G 3/30
`information into each pixel is performed by applying an
`(52) U.S. Cl. .............................. 345/76; 345/77; 345/82
`electric Signal corresponding to the brightness information
`(58) Field of Search .............................. 345/92, 87, 76,
`to the data line while the Scanning line is Selected. The
`345/77, 80, 82, 55; 315/169.4, 169.3, 169.1;
`brightness information written in each pixel is held by the
`340/815.45
`pixel also after the Scanning line is placed into a non
`Selected State So that the OLED can continue lighting with
`a brightness value corresponding to the brightness informa
`tion held by the pixel. A Stopping control line compulsorily
`extinguishes the OLEDs of the pixels connected to the same
`Scanning line at least in a unit of a Scanning line So that the
`OLEDs are placed into an extinguished State from a lit State
`within a period of one Scanning cycle after the brightness
`information is written into the pixels until new brightness
`information is written into the pixels Subsequently.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,198.803 A * 3/1993 Shie et al. .................. 340/782
`5,952,789 A
`9/1999 Stewart et al. ........... 315/169.4
`6,229,506 B1
`5/2001 Dawson et al. ............... 345/82
`6,229,508 B1
`5/2001 Kane ........................... 345/82
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`O 905 673
`
`3/1999
`
`26 Claims, 12 Drawing Sheets
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`U.S. Patent
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`Jun. 24, 2003
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`1
`IMAGE DISPLAY APPARATUS
`
`US 6,583,775 B1
`
`BACKGROUND OF THE INVENTION
`This invention relates to an image display apparatus
`which includes a pixel whose brightness is controlled with
`a signal, and more particularly to an image display apparatus
`which includes, for each pixel, a light emitting element for
`emitting light with brightness which is controlled with
`current Such as an organic electroluminescence (EL) ele
`ment. More specifically, the present invention relates to an
`image display apparatus of the active matrix type wherein
`the amount of current to be Supplied to a light emitting
`element is controlled by an active element Such as a field
`effect transistor of the insulated gate type provided in each
`pixel.
`Generally, in an image display apparatus of the active
`matrix type, a large number of pixels are arranged in a
`matrix, and the intensity of light is controlled for each of the
`pixels in response to brightness information given thereto to
`display an image. Where liquid crystal is used as an electro
`optical Substance, the transmission factor of each pixel
`varies in response to a Voltage written in the pixel. Even with
`an image display apparatus of the active matrix type which
`employs an organic electroluminescence material as an
`electro-optical Substance, basic operation is Similar to that
`where liquid crystal is employed. However, different from a
`liquid crystal display apparatus, an organic EL display
`apparatus is an apparatus of the Self light emission type
`wherein each pixel has a light emitting element. Thus, the
`organic EL display apparatus is advantageous in that it
`exhibits a higher degree of visibility than a liquid crystal
`display apparatus, that it does not require a back light and
`that it has a higher responding Speed. The brightness of each
`individual light emitting element is controlled with the
`amount of current. In other words, the organic EL display is
`Significantly different from the liquid crystal display appa
`ratus and So forth in that the light emitting elements are of
`the current driven type or the current controlled type.
`Similarly to the liquid crystal display apparatus, the
`organic EL display apparatus can possibly use a simple
`matrix System or an active matrix System as a driving System
`therefor. Although the former is Simple in Structure, it is
`difficult to implement a display apparatus of a large Size and
`a high resolution. Therefore, much effort has been and is
`directed to development of organic EL display apparatus of
`the active matrix System. In the organic EL display apparatus
`of the active matrix System, current to flow to a light
`emitting element provided in each pixel is controlled by an
`active element usually in the form of a thin film transistor
`which is a kind of a field effect transistor of the insulated
`gate type and may be hereinafter referred to as TFT. An
`organic EL display apparatus of the active matrix System is
`disclosed, for example, in Japanese Patent Laid-open No.
`Hei 8-234683, and an equivalent circuit for one pixel in the
`organic EL display apparatus is shown in FIG. 10. Referring
`to FIG. 10, the pixel PXL shown includes a light emitting
`element OLED, a first thin film transistor TFT1, a second
`thin film transistor TFT2, and a holding capacitor Cs. The
`light emitting element OLED is an organic electrolumines
`cence (EL) element. Since an organic EL element in most
`cases has a rectification property, it is often called OLED
`(organic light emitting diode) and, in FIG. 10, the mark of
`a diode is used for the light emitting element OLED.
`However, the light emitting element is not limited to an
`OLED, but may be any element only if the brightness
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`thereof is controlled with the amount of current to flow
`therethrough. It is not always required for an OLED to have
`a rectification property. In the pixel shown in FIG. 10, a
`reference potential (ground potential) is applied to the
`Source S of the second thin film transistor TFT2, and the
`anode A (positive electrode) of the light emitting element
`OLED is connected to a power supply potential Vdd while
`the cathode K (negative electrode) is connected to the drain
`D of the second thin film transistor TFT2. Meanwhile, the
`gate G of the first thin film transistor TFT1 is connected to
`a scanning line X and the source S of the first thin film
`transistor TFT1 is connected to a data line Y. The drain D of
`the first thin film transistor TFT1 is connected to the holding
`capacitor CS and the gate G of the Second thin film transistor
`TFT2.
`In order to cause the pixel PXL to operate, the Scanning
`line X is placed into a Selected State first, and then a data
`potential Vdata representative of brightness information is
`applied to the data line Y. Consequently, the first thin film
`transistor TFT1 is rendered conducting, and the holding
`capacitor CS is charged or discharged and the gate potential
`of the second thin film transistor TFT2 becomes equal to the
`data potential Vdata. Then, if the Scanning line X is placed
`into a non-Selected State, then the first thin film transistor
`TFT1 is turned off, and the second thin film transistor TFT2
`is electrically disconnected from the data line Y. However,
`the gate potential of the second thin film transistor TFT2 is
`held stably by the holding capacitor Cs. The current flowing
`to the light emitting element OLED through the second thin
`film transistor TFT2 exhibits a value which depends upon a
`gate-Source Voltage Vgs of the Second thin film transistor
`TFT2, and the light emitting element OLED continues to
`emit light with a brightness value corresponding to the
`amount of current Supplied from the Second thin film tran
`Sistor TFT2.
`In the present Specification, the operation of Selecting a
`Scanning line X to transmit a potential of a data line Y to the
`inside of a pixel is hereinafter referred to as “write”. Where
`the current flowing between the drain and the source of the
`second thin film transistor TFT2 is represented by Ids, this
`is driving current flowing to the light emitting element
`OLED. If it is assumed that the second thin film transistor
`TFT2 operates in a Saturation region, then the current Ids is
`represented by the following expression:
`
`lds = (1/2) u. Cox. (W / L). (Vgs - Vth)?
`= (1/2) p. Cox. (W / L). (Vdata - Vth)?
`
`(1)
`
`where Cox is a gate capacitance per unit area and is given
`by the following expression:
`(2)
`Cox=eOerid
`In the expressions (1) and (2) above, Vth is a threshold
`voltage for the second thin film transistor TFT2, it is the
`mobility of carriers, Wis the channel width, L is the channel
`length, e 0 is the dielectric constant of vacuum, e r is the
`dielectric constant of the gate insulating film, and d is the
`thickness of the gate insulating film.
`According to the expression (1), the current Ids can be
`controlled with the data potential Vdata to be written into the
`pixel PXL, and as a result, the brightness of the light
`emitting element OLED can be controlled. Here, the reason
`why the second thin film transistor TFT2 operates in a
`Saturation region is Such as follows. In particular, the reason
`is that, Since, in a Saturation region, the current Ids is
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`controlled only with the gate-Source Voltage Vgs but does
`not rely upon the drain-Source Voltage Vds, even if the
`drain-Source Voltage Vds is fluctuated by a dispersion in
`characteristic of the light emitting element OLED, a prede
`termined amount of current Ids can be flowed to the light
`emitting element OLED.
`AS described hereinabove, with the circuit construction of
`the pixel PXL shown in FIG. 10, if writing of the data
`potential Vdata is performed once, then the light emitting
`element OLED continues to emit light with a fixed bright
`ness value for a period of one Scanning cycle (one frame)
`until it is rewritten. If a large number of such pixels PXL are
`arranged in a matrix as shown in FIG. 11, then an image
`display apparatus of the active matrix type can be con
`Structed. AS Seen from FIG. 11, a conventional image display
`apparatus includes a plurality of Scanning lines X1 to XN for
`Selecting pixels PXL in a predetermined Scanning cycle (for
`example, in a frame period complying with the NTSC
`Standards), and a plurality of data lines Y for providing
`brightness information (data potentials Vdata) for driving
`the pixels PXL. The scanning lines X1 to XN and the data
`lines Y extend perpendicularly to each other Such that the
`pixels PXL may be arranged in a matrix at interSecting
`points thereof. The scanning lines X1 to XN are connected
`to a Scanning line drive circuit 21, and the data lines Y are
`connected to a data line drive circuit 22. The Scanning lines
`X1 to XN are successively selected by the scanning line
`drive circuit 21 while writing of the data potentials Vdata is
`repeated Successively from the data lines Y by the data line
`drive circuit 22 thereby to display a desired image. While, in
`an image display apparatus of the simple matrix type, the
`light emitting element included in each pixel PXL emits
`light only at a Selected instant, the image display apparatus
`of the active matrix type shown in FIG. 11 is advantageous
`in that, Since the light emitting element of each pixel PXL
`35
`continues its light emission also after writing into it is
`completed, the peak brightness (peak current) of the light
`emitting elements can be decreased when compared with
`that of the image display apparatus of the Simple matrix
`type, particularly where the display device has a large size
`and a high resolution.
`FIG. 12 is an equivalent circuit diagram showing another
`conventional pixel Structure. In FIG. 12, elements corre
`sponding to those of the conventional pixel Structure shown
`in FIG. 10 are denoted by like reference characters to
`facilitate understanding. While the conventional pixel Struc
`ture of FIG. 10 uses a field effect transistor of the N-channel
`type for the thin film transistors TFT1 and TFT2, the
`conventional pixel structure of FIG. 12 uses a field effect
`transistor of the P-channel type. Accordingly, in the pixel
`structure of FIG. 12, the cathode K of the light emitting
`element OLED is connected to the negative power Supply
`potential Vdd and the anode A is connected to the drain D
`of the second thin film transistor TFT2 conversely to those
`in the pixel structure of FIG. 10.
`FIG. 13 is a cross sectional view schematically showing
`a sectional structure of the pixel PXL shown in FIG. 12.
`However, in order to facilitate illustration, only the light
`emitting element OLED and the second thin film transistor
`TFT2 are shown in FIG. 13. The light emitting element
`60
`OLED includes a transparent electrode 10, an organic EL
`layer 11 and a metal electrode 12 placed one on another in
`this order. The transparent electrode 10 is provided sepa
`rately for each pixel and functions as the anode A of the light
`emitting element OLED, and is formed from a transparent
`conductive film of, for example, ITO. The metal electrode 12
`is connected commonly among the pixels and functions as
`
`4
`the cathode K of the light emitting element OLED. In
`particular, the metal electrodes 12 are connected commonly
`to a predetermined power Supply potential Vdd. The organic
`EL layer 11 is a composite film including, for example, a
`positive hole transporting layer and an electron transporting
`layer. For example, Diamyne is vapor deposited as the
`positive hole transporting layer on the transparent electrode
`10 which functions as the anode A (positive hole injecting
`electrode) and Alq3 is vapor deposited as the electron
`transporting layer on the positive hole transporting layer,
`and then the metal electrode 12 which functions as the
`cathode K (electron injecting electrode) is formed on the
`electron transporting layer. It is to be noted that Alq3
`represents 8-hydroxy quinoline aluminum. The light emit
`ting element OLED having Such a layered Structure as just
`described is a mere example at all. If a forward Voltage
`(approximately 10 V) is applied between the anode and the
`cathode of the light emitting element OLED having Such a
`Structure as described above, then injection of carrierS Such
`as electrons and positive holes occurs, and emission of light
`is observed. The operation of the light emitting element
`OLED is considered to be emission of light by excited
`elements formed from positive holes injected from the
`positive hole transporting layer and electrons injected from
`the electron transporting layer.
`Meanwhile, the second thin film transistor TFT2 includes
`a gate electrode 2 formed on a Substrate 1 made of glass or
`the like, a gate insulating film 3 placed on the upper face of
`the gate electrode 2, and a Semiconductor thin film 4 placed
`on the gate electrode 2 with the gate insulating film 3
`interposed therebetween. The semiconductor thin film 4 is
`formed from, for example, a polycrystalline Silicon thin film.
`The Second thin film transistor TFT2 includes a Source S, a
`channel Chand a drain D which form a path for current to
`be supplied to the light emitting element OLED. The chan
`nel Ch is positioned immediately above the gate electrode 2,
`and the second thin film transistor TFT2 of the bottom gate
`Structure is covered with an interlayer insulating film 5, and
`a Source electrode 6 and a drain electrode 7 are formed on
`the interlayer insulating film 5. The light emitting element
`OLED described above is formed on the elements men
`tioned above with another interlayer insulating film 9 inter
`posed therebetween.
`The first Subject to be solved when such an EL display
`apparatus of the active matrix type as described above is to
`be formed is that the degree of freedom in designing the
`Second thin film transistor TFT2 which is an active element
`for controlling the amount of current to flow through the
`light emitting element OLED is low and, under certain
`circumstances, practical designing Suitable for pixel dimen
`sions is difficult. The second subject to be solved is that it is
`difficult to freely adjust the display brightness of the entire
`Screen. The Subjects described are described giving specific
`design parameters with regard to the conventional apparatus
`described above with reference to FIGS. 10 to 13. In a
`typical design example, the Screen size is 20 cmx20 cm, the
`number of rows (scanning line number) 1,000, the number
`of columns (data line number) 1,000, the pixel size S=200
`umx200 um, the peak brightness Bp=200 cd/m’, the effi
`ciency of the light emitting element E=10 cd/A, the thick
`neSS of the gate insulating film of the Second thin film
`transistor TFT2 d=100 nm, the dielectric constant of the gate
`insulating film e r=3.9, the carrier mobility u=100 cm/VS,
`the peak current per pixel Ip=Bp/ExS=0.8 uA, the peak
`value of Vgs-Vth (driving voltage) Vp=5 V. In order to
`Supply the peak current Ip in the design example above, as
`a design example of the second thin film transistor TFT2, the
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`S
`channel width and the channel length are determined from
`the expressions (1) and (2) given hereinabove as follows:
`
`Channel width: W = 5 um
`
`(3)
`
`Channel length: L = {W f (2. Ip)}. u. Cox. Vp?
`= 270 um
`
`6
`display apparatus of the Simple matrix type, the Screen
`brightness can be adjusted comparatively simply by adjust
`ing the driving current upon addressing.
`However, with an organic display apparatus of the active
`matrix type, it is difficult to arbitrarily adjust the display
`brightness of the entire Screen. AS described above, the
`display brightness increases in proportion to the peak current
`Ip, and the peak current Ip increases in inverse proportion to
`the channel length L of the TFT2. Accordingly, in order to
`lower the display brightness, the channel length L should be
`increased. This, however, cannot be employed as a counter
`measure for Selecting the display brightness arbitrarily by a
`user. A method which seems possible to realize is to reduce
`the peak value Vp of the driving Voltage in order to reduce
`the brightness. However, if the peak value Vp is reduced,
`then deterioration of the picture quality is caused by noise or
`the like. On the contrary where it is desired to raise the
`brightness, even if it is tried to raise the peak value Vp of the
`driving Voltage, it is a matter of course that there is an upper
`limitation to it because of a Voltage withstanding property of
`the second thin film transistor TFT2 and so forth.
`
`SUMMARY OF THE INVENTION
`It is an object of the present invention to provide an image
`display apparatus which increases the degree of freedom in
`designing of an active element in the inside of a pixel to
`allow good designing and can adjust the Screen brightness
`freely and Simply.
`In order to attain the object described above, according to
`a first aspect of the present invention, there is provided an
`image display apparatus, comprising a plurality of pixels
`arranged in a matrix, a plurality of Scanning lines for
`Selecting the pixels in a predetermined Scanning cycle, a
`plurality of data lines extending perpendicularly to the
`Scanning lines for providing brightness information to drive
`the pixels, the pixels being disposed at interSecting points of
`the Scanning lines and the data lines, each of the pixels
`including a light emitting element for emitting light with a
`brightness value which varies depending upon an amount of
`current Supplied thereto, a first active element controlled by
`one of the Scanning lines for writing the brightness infor
`mation given thereto from one of the data lines into the pixel,
`and a Second active element for controlling the amount of
`current to be Supplied to the light emitting element in
`response to the brightness information written in the pixel,
`Writing of the brightness information into each of the pixels
`being performed by applying an electric Signal correspond
`ing to the brightness information to the data line connected
`to the pixel while the Scanning line connected to the pixel is
`Selected, the brightness information written in each of the
`pixels being held by the pixel also after the Scanning line
`connected to the pixel is placed into a non-Selected State So
`that the light emitting element of the pixel can continue
`lighting with a brightness value corresponding to the bright
`neSS information held by the pixel, and control means for
`compulsorily extinguishing the light emitting elements of
`those of the pixels which are connected to a Same one of the
`Scanning lines at least in a unit of a Scanning line So that the
`light emitting elements are placed into an extinguished State
`from a lit State within a period of one Scanning cycle after
`the brightness information is written into the pixels until
`new brightness information is written into the pixels Subse
`quently.
`Preferably, the control means is capable of adjusting a
`point of time at which each of the light emitting elements is
`changed over from a lit State to an extinguished State within
`a period of one Scanning cycle after the brightness informa
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`Here, it is the first problem that the channel length L given
`by the expression (3) above is equal to or greater than the
`pixel size (S=200 umx200 um). As seen from the expression
`(3), the peak current Ip increases in inverse proportion to the
`channel length L. In the example described above, in order
`to Suppress the peak current Ip to approximately 0.8 uA
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`which is Sufficient for operation, the channel length L. must
`be set long to 270 um. However, this is not preferable
`because it requires a large occupied area of the TFT2 in the
`pixel, resulting in reduction of the light emitting area.
`Besides, refinement of pixels becomes difficult. The essen
`tial problem resides in that, if a brightness value (peak
`current) required and parameters of a semiconductor process
`and So forth are given, then there is little degree of freedom
`in designing of the second thin film transistor TFT2. In
`particular, a possible idea for reducing the channel length L
`in the example described above is to reduce the channel
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`width was can be seen apparently from the expression (3).
`However, there is a limitation to refinement of the channel
`width W in terms of the process, and it is difficult to refine
`the channel width W significantly with respect to the degree
`described above in a thin film transistor process at present.
`It is another possible idea to reduce the peak value Vp of the
`driving Voltage. In this instance, however, in order to per
`form gradation control, it is necessary to control the intensity
`of light to be emitted from the light emitting element OLED
`with a very Small driving Voltage Step. For example, also in
`the case of the peak value Vp=5 V, if it is tried to control the
`intensity of light to be emitted with 64 gradations, then the
`Voltage Step per one gradation is approximately 5 V/64=80
`mV in average. If the Voltage Step is further reduced, then the
`display quality of the image display is influenced by fine
`noise or a dispersion of the TFT character. Accordingly,
`there is a limitation also to reduction of the peak value Vp
`of the driving Voltage. Another possible Solution is to Set
`process parameterS Such as the carrier mobility u appearing
`in the expression (3) to suitable values. However, it is
`generally difficult to control proceSS parameters to prefer
`able values with a high degree of accuracy, and
`economically, it is quite unrealistic to construct a production
`proceSS in accordance with Specifications of an image dis
`play apparatus to be designed at all. In this manner, in a
`conventional EL display apparatus of the active matrix type,
`the degree of freedom in designing of a pixel is So low that
`it is difficult to perform practical designing.
`In relation to the first problem described above, it is a
`Second problem that, in an EL display apparatus of the active
`matrix type, it is difficult to arbitrarily control the display
`brightness of the entire Screen. Generally, in an image
`display apparatus of a television Set or the like, it is an
`essential requirement for practical use that the display
`brightness of the entire Screen can be adjusted freely. For
`example, it is natural to Set the Screen brightness high when
`the image display apparatus is used in a light situation, but
`SuppreSS the Screen brightness low conversely when the
`image display apparatus is used in a dark Situation. Such
`adjustment of the Screen brightness can be realized readily
`by, for example, with a liquid crystal display, varying the
`power of the backlight. On the other hand, with an EL
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`tion is written into the pixels until new brightness informa
`tion is written into the pixels Subsequently.
`The image display apparatus may be constructed Such that
`the control means includes a third active element connected
`to a gate of the Second active element, which is in the form
`of a field effect transistor of the insulated gate type, of each
`of the pixels and is capable of providing a control Signal to
`the third active element to control a gate potential of the
`Second active element thereby to extinguish the light emit
`ting element of the pixel, the control Signal being applied to
`the third active elements included in those of the pixels
`which are on a Same one of the Scanning lines over a
`Stopping control line provided for and in parallel to each of
`the Scanning lines.
`AS an alternative, the image display apparatus may be
`constructed Such that the control means includes a third
`active element connected in Series to the light emitting
`element of each of the pixels and is capable of providing a
`control Signal to the third active element to cut off current to
`flow to the light emitting element, the control signal being
`applied to the third active elements included in those of the
`pixels which are on a Same one of the Scanning lines over a
`Stopping control line provided for and in parallel to each of
`the Scanning lines.
`Otherwise, the image display apparatus may be con
`Structed Such that the light emitting element of each of the
`pixels includes a two-terminal element having a rectification
`function and having a first terminal connected to the Second
`active element and a Second terminal connected to the
`Second terminals of those of the pixels which are connected
`to a Same one of the Scanning lines to which the pixel is
`connected but electrically isolated from the Second terminals
`of those of the pixels which are connected to any other one
`of the Scanning lines, and the control means controls a
`potential of the Second terminals of the two-terminal ele
`ments which are connected commonly to the same Scanning
`line to extinguish the two-terminal elements.
`The control means may Select, within a period of one
`Scanning cycle after the brightness information is written
`into the pixels until new brightness information is written
`into the pixels Subsequently, the Scanning lines again to
`write information representative of brightness of Zero into
`the pixels from the data lines to extinguish the light emitting
`elements of the pixels.
`The image display apparatus may be constructed other
`wise Such that each of the pixels further includes a capacitive
`element having an end connected to a gate of a field effect
`transistor of the insulated gate type which forms the Second
`active element for controlling the amount of current to flow
`to the light emitting element, and the control means controls
`a potential of the other end of the capacitive element to
`control a potential of the gate of the field effect transistor of
`the insulated gate type which forms the Second active
`element to extinguish the light emitting element.
`The control means may otherwise control a lighting point
`of time and an extinguishing point of time of the light
`emitting element included in each of the pixels at least in a
`unit of a Scanning line within one Scanning cycle after the
`brightness information is written into the pixel.
`The image display apparatus may be constructed other
`wise Such that pixels for red, green and blue are connected
`commonly to each of the Scanning lines, and the control
`means extinguishes the light emitting elements included in
`the pixels for red, green and blue at different points of time
`from one another.
`Preferably, the light emitting element is an organic elec
`troluminescence element.
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`8
`According to a Second aspect of the present invention,
`there is provided an image display apparatus wherein a
`plurality of pixels are lit in response to brightness informa
`tion within a period of one Scanning cycle after first bright
`neSS information is written into the pixels until new Second
`brightness information is written into the pixels, comprising
`a plurality of Scanning lines for individually Selecting the
`pixels in a predetermined Scanning cycle, a plurality of data
`lines formed perpendicularly to the Scanning lines for pro
`Viding brightness information for lighting the pixels,