(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0156837 A1
`Kasai
`(43) Pub. Date:
`Jul. 21, 2005
`
`US 2005O156837A1
`
`(54) DRIVING CIRCUIT, ELECTRO-OPTICAL
`DEVICE, METHOD OF DRIVING THE
`SAME, AND ELECTRONIC APPARATUS
`(75) Inventor: Toshiyuki Kasai, Okaya-shi (JP)
`Correspondence Address:
`OLIFF & BERRIDGE, PLC
`P.O. BOX 19928
`ALEXANDRIA, VA 22320 (US)
`(73) Assignee: Seiko Epson Corporation, Tokyo (JP)
`
`11/006,713
`(21) Appl. No.:
`Dec. 8, 2004
`(22) Filed:
`9
`Foreign Application Priority Data
`(30)
`Jan. 21, 2004 (JP)...................................... 2004-01.32O1
`
`Publication Classification
`(51) Int. Cl. .......................................... G09G 3/30
`(52) U.S. Cl. ................................................................ 345/77
`
`(57)
`
`ABSTRACT
`
`When respective bits of grayscale data DX1 are '0' which
`represents black, upon detection, a NOR circuit of a voltage
`Supply circuit sets an output Signal active. Then, a transistor
`is turned on, and a black voltage VBr is supplied to a data
`line. By this embodiment, since all transistors of a current
`Supply circuit are turned off, a current is not outputted.
`Meanwhile, in the case in which a grayscale level to be
`displayed is other than black, a current Idata is outputted
`from the current supply circuit.
`
`1.
`
`600A
`POWER SUPPLY
`CIRCUIT
`
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`
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`Wodr
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`Vddg
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`
`700
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`
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`2.
`2
`H
`
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`rh
`EHEHigh
`
`IX
`
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`X
`X
`DATALINE DRIVING CIRCUIT
`GRAYSCALE SIGNAL SUPPLY CIRCUIT
`OX1
`GARYSCALE DATA GENERATING CIRCUITN-210
`
`220
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 001
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 1 of 11
`
`US 2005/0156837 A1
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Lino-IO 9NIAl-O3NIONINNVOS
`
`001
`
`008.
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 002
`
`

`

`Patent Application Publication Jul. 21
`2005 Sheet 2 of 11
`FG 2
`
`US 2005/0156837 A1
`
`
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 003
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 3 of 11
`
`US 2005/0156837 A1
`
`FIG. 3
`
`
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 004
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 4 of 11
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`US 2005/0156837 A1
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`
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 005
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 5 0f 11
`
`US 2005/0156837 A1
`
`FIG. 5
`
`U81
`
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`
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`
`[.
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 006
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 006
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 6 of 11
`F.G. 6
`
`US 2005/0156837 A1
`
`TS
`
`tge
`
`61O
`RVARIABLE
`VOLTAGE
`GENERATING CIRCUIT
`62O
`G VARIABLE
`VOLTAGE
`GENERATING CIRCUIT
`630
`-
`B VARIABLE
`VOLTAGE
`GENERATING CIRCUIT
`
`DC/DC
`611 - 66NVERTER
`
`Voddr
`VBr
`
`Voddg
`
`DC/DC
`621-33NeRTER - VBg
`-
`Voddb
`DC/DC
`631-35NeRTER - VBb
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 007
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 7 of 11
`FIG 7
`
`US 2005/0156837 A1
`
`
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 008
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 8 of 11
`FG. 8
`
`US 2005/0156837 A1
`
`H
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 009
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 9 of 11
`FIG 9
`
`US 2005/0156837 A1
`
`
`
`OX1
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 010
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 10 of 11
`
`US 2005/0156837 A1
`
`FIG 10
`
`
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 011
`
`

`

`Patent Application Publication Jul. 21, 2005 Sheet 11 of 11
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`US 2005/0156837 A1
`
`F.G. 12
`
`
`
`4002
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 012
`
`

`

`US 2005/0156837 A1
`
`Jul. 21, 2005
`
`DRIVING CIRCUIT, ELECTRO-OPTICAL DEVICE,
`METHOD OF DRIVING THE SAME, AND
`ELECTRONIC APPARATUS
`
`BACKGROUND
`0001. The present invention relates to an electro-optical
`device using a Self-luminous element, a driving circuit and
`a driving method thereof, and an electronic apparatus using
`the electro-optical device.
`0002. As an image display device taking the place of
`liquid crystal display devices, a device comprising an
`organic light emitting diode element (hereinafter, referred to
`as OLED element) is being noticed. The OLED element is
`a current-driven Self-luminous element, unlike liquid crystal
`elements which change the amount of light to be transmitted.
`0003. In an electro-optical device having the OLED
`element implemented with an active matrix driving method,
`a pixel circuit for adjusting the light-emission grayScale
`level to the OLED element is provided. The setting of the
`light-emission grayScale level in each pixel circuit is per
`formed by Supplying a Voltage level or a current level
`depending on the light-emission grayScale level to the pixel
`circuit. The method in which the setting of the light
`emission grayScale level is performed by the Voltage level is
`called a current-program mode. The pixel circuit in the
`current-program mode operates to repeat alternately a writ
`ing period in which a current depending on the light
`emission grayScale level to be Supplied from a current
`generating circuit via a data line is Stored and a light emitting
`period in which the stored current is supplied to the OLED
`element. The storing of the current level is performed by
`providing a capacitive element between a gate and a Source
`of a transistor Serving as a current Source of the OLED
`element and by Storing charges in the capacitive element
`Such that a gate-Source Voltage of the transistor depends on
`the current.
`0004 Conventionally, as the current-generating circuit
`which generates the current to the pixel circuit, for example,
`a construction shown in FIG. 24 of Patent Document 1 may
`be exemplified. In this drawing, the current-generating cir
`cuit is a current-addition D/A converter in which by Switch
`ing respectively transistors 20a to 20f depending on each of
`6-bit digital data (D0 to D5), element currents i1 to i6 are
`Selected, and the Selected element current is Synthesized to
`obtain a current lout. Japanese Unexamined Patent Appli
`cation Publication No. 2003-233347.
`
`SUMMARY
`0005 Additionally, in the conventional current generat
`ing circuit, when the current lout depending on black data
`(grayScale level: 0) is Supplied to the data line, all the
`transistors 20a to 20f are turned off, and the data line
`becomes a high impedance State.
`0006. However, since the data line is accompanied by a
`parasitic capacitor, even though the data line is in a high
`impedance State in a present writing period, it is affected by
`a just before writing period. For this reason, in the pixel
`circuit, it is difficult to turn off thoroughly the transistor
`Serving as the current Source. As a result, there are problems
`in that phenomena Such as black floating which black
`display becomes Somewhat bright or 'tailing which black
`
`display after white display becomes gray is generated, which
`consequently deteriorates the display quality.
`0007. The present invention is made in consideration of
`the above-mentioned problems, and it is an object of the
`present invention to provide a driving circuit which can
`realize a black display exactly, an electro-optical device
`using the driving circuit, an electronic apparatus, and a
`driving method.
`0008. In order to solve the problems, there is provided a
`driving circuit according to the present invention to be used
`for an electro-optical device comprising a plurality of Scan
`ning lines, a plurality of data lines, and a plurality of pixel
`circuits each provided at interSections of the Scanning lines
`and the data lines, in which each of the pixel circuits
`includes a Self-luminous element, Stores a current Supplied
`via each of the data lines, and Supplies the Stored current to
`the Self-luminous element according to a signal Supplied via
`each of the Scanning lines. The driving circuit comprises
`Voltage Supply means, when a grayScale level to be dis
`played is a predetermined grayScale level, for Outputting a
`predetermined Voltage to each of the data lines, current
`Supply means, when the grayScale level to be displayed is
`not the predetermined grayScale level, for outputting a
`current according to the grayScale level to each of the data
`lines, and control means, when the grayScale level to be
`displayed is the predetermined grayScale level, for activating
`the Voltage Supply means and deactivating the current Sup
`ply means, and, when the grayScale level to be displayed is
`not the predetermined grayScale level, for deactivating the
`Voltage Supply means and activating the current Supply
`CS.
`0009. In a driving method in which a current is supplied
`to the data line, it is needed to Supply the same current as that
`flowing in an organic light emitting diode to the data line.
`For this reason, when black is displayed, a current does not
`flow. However, Since the data line is accompanied by the
`parasitic capacitor, due to influence by a previous State, a
`place which should display black may not be displayed on
`black. According to this invention, when a grayScale level to
`be displayed is a predetermined grayScale level, it is possible
`to write a predetermined Voltage to the data line. Further,
`when the grayScale level to be displayed is not the prede
`termined grayScale level, it is possible to output the current
`depending on grayScale level to the data line. Thus, it
`becomes possible to display the predetermined grayScale
`level irrespective of the previous State. Here, the predeter
`mined grayScale level may be a grayScale level in the
`vicinity of black, not being limited to black (grayScale level
`O). That is, a grayScale level less than previously determined
`reference grayScale level may be the predetermined gray
`Scale level.
`0010 Here, preferably, each of the pixel circuits com
`prises a driving transistor Serving as a current Source of the
`Self-luminous element, a capacitive element provided
`between a gate and a Source of the driving transistor, and
`means for Storing charges in the capacitive element Such that
`a gate-Source Voltage of the driving transistor depends on the
`current Supplied via each of the data lines, in which the
`Voltage Supply means generates, as the predetermined Volt
`age, a Voltage that turns off the driving transistor. In this
`case, Since the driving transistor is thoroughly turned off, a
`current does not flow in the Self-luminous element. AS a
`result, it is possible to display black exactly.
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 013
`
`

`

`US 2005/0156837 A1
`
`Jul. 21, 2005
`
`Further, preferably, the driving circuit further com
`0.011
`prises power Supply means for generating a power Supply
`Voltage and for Supplying the power Supply Voltage to a
`Source of the driving transistor of each of the pixel circuits,
`in which the Voltage Supply means comprises Voltage con
`trol means for controlling the predetermined Voltage
`depending on the power Supply Voltage and generates the
`predetermined Voltage Such that the driving transistor is
`turned off. Since on/off of the driving transistor is deter
`mined by a relationship of the power Supply Voltage and the
`gate Voltage, it is possible to Surely display black by
`generating the predetermined Voltage accompanied by the
`change in power Supply Voltage.
`0012 Further, preferably, when grayscale level to be
`displayed is the predetermined grayScale level, the current
`Supply means Sets an output terminal to a high impedance
`State. During a first period of a period in which the data lines
`are Selected, the control means connects the Voltage Supply
`means to the data line, and during a Second period, the
`control means connects the current Supply means to the data
`line. During the first period in which the data lines are
`Selected, the Voltage Supply means writes the predetermined
`Voltage into the data line, irrespective of the grayScale level
`to be displayed.
`0013 Further, preferably, when the grayscale level to be
`displayed is the predetermined grayScale level, the current
`Supply means Sets an output terminal to a high impedance
`State. During a first period of a period in which the data lines
`are Selected, the control means connects the voltage Supply
`means to the data line, and during a Second period, the
`control means connects the current Supply means to the data
`line. In addition, during the first period of the period in
`which the data lines are Selected, when the grayScale level
`to be displayed is the predetermined grayScale level, the
`Voltage Supply means writes the predetermined Voltage into
`the data line, and when grayScale level to be displayed is not
`the predetermined grayScale level, the Voltage Supply means
`writes a precharge Voltage into the data line. In this case,
`Since the writing of the predetermined Voltage and the
`Writing of the precharge Voltage are used together, it is
`possible to improve display quality with respect to other
`brightness display, as well as black display.
`0.014.
`In the above-mentioned driving circuit, the prede
`termined grayScale level is preferably black. In this case,
`when grayScale level to be displayed is black, the predeter
`mined Voltage is Supplied, and thus it becomes possible to
`Surely display black.
`0.015
`Next, there is provided an electro-optical device
`according to the present invention comprising a plurality of
`Scanning lines, a plurality of data lines, a plurality of pixel
`circuits respectively provided at interSections of the Scan
`ning lines and the data lines, each pixel circuit having a
`Self-luminous element, a driving transistor Serving as a
`current Source of the Self-luminous element, a capacitive
`element provided between a gate and a Source of the driving
`transistor, and means for Storing charges in the capacitive
`element Such that a gate-Source Voltage of the driving
`transistor depends on a current Supplied via the data lines,
`and a driving circuit as described above. Here, the Self
`luminous element is preferably an organic light emitting
`diode. In addition, an electronic apparatus according to the
`present invention comprises an electro-optical device as
`described above.
`
`0016. Next, there is provided a method of driving an
`electro-optical device according to the present invention
`which comprises a plurality of Scanning lines, a plurality of
`data lines, and a plurality of pixel circuits respectively
`provided at interSections of the Scanning lines and the data
`lines, in which each of the pixel circuits includes a Self
`luminous element, Stores a current Supplied via each of the
`data lines, and Supplies the Stored current to the Self
`luminous element according to a signal Supplied via each of
`the Scanning lines. When a grayScale level to be displayed is
`predetermined grayScale level, a predetermined Voltage is
`generated, and when grayScale level to be displayed is not
`the predetermined grayScale level, a current depending on
`grayScale level is generated. When the grayScale level to be
`displayed is the predetermined grayScale level, the prede
`termined Voltage is Supplied to each of the data lines, and
`when the grayScale level to be displayed is not the prede
`termined grayScale level, the current depending on the
`grayScale level to be displayed is Supplied to each of the data
`lines.
`0017. Here, preferably, each of the pixel circuits com
`prises a driving transistor Serving as a current Source of the
`Self-luminous element, a capacitive element provided
`between a gate and a Source of the driving transistor, and
`means for Storing charges in the capacitive element Such that
`a gate-Source Voltage of the driving transistor depends on the
`current Supplied via each of the data lines, in which the
`predetermined Voltage is a Voltage that turns off the driving
`transistor. In this case, since the driving transistor is thor
`oughly turned off, a current does not flow in the Self
`luminous element. As a result, it becomes possible to display
`black exactly.
`0018. In addition, preferably, a power supply voltage is
`generated and Supplied to a Source of the driving transistor
`of each of the pixel circuits, and the predetermined Voltage
`is controlled depending on the power Supply Voltage Such
`that the driving transistor is turned off.
`0019 Further, there is provided a method of driving an
`electro-optical device according to present invention com
`prising a plurality of Scanning lines, a plurality of data lines,
`and a plurality of pixel circuits respectively provided at
`interSections of the Scanning lines and the data lines, in
`which each of the pixel circuits includes a Self-luminous
`element and a driving transistor for driving the Self-lumi
`nous element, Stores a current Supplied via each of the data
`lines, and Supplies the Stored current to the Self-luminous
`element according to a signal Supplied via each of the
`Scanning lines. Preferably, during a first period of a period
`in which the data lines are Selected, a predetermined Voltage
`that turns off the driving transistor is written into each of the
`data lines, and during a Second period of the period in which
`the data lines are Selected, when grayScale level to be
`displayed is predetermined grayScale level, the data lines are
`Set to a high impedance State, and when the grayScale level
`to be displayed is not the predetermined grayScale level, a
`current depending on grayScale level to be displayed is
`Supplied to each of the data lines.
`0020) Further, there is provided a method of driving an
`electro-optical device according to the present invention
`comprising a plurality of Scanning lines, a plurality of data
`lines, and a plurality of pixel circuits respectively provided
`at interSections of the Scanning lines and the data lines, in
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 014
`
`

`

`US 2005/0156837 A1
`
`Jul. 21, 2005
`
`which each of the pixel circuits includes a Self-luminous
`element and a driving transistor for driving the Self-lumi
`nous element, Stores a current Supplied via each of the data
`lines, and Supplies the Stored current to the Self-luminous
`element according to a signal Supplied via each of the
`Scanning lines. During a first period of a period in which the
`data lines are Selected, when a grayScale level to be dis
`played is a predetermined grayScale level, a predetermined
`Voltage that turns off the driving transistor is written into
`each of the data lines, and when the grayScale level to be
`displayed is not the predetermined grayScale level, a pre
`charge Voltage is Supplied to each of the data lines. And,
`during a Second period of the period in which the data lines
`are Selected, when the grayScale level to be displayed is the
`predetermined grayScale level, the data lines are Set to a high
`impedance State, and when the grayScale level to be dis
`played is not the predetermined grayScale level, a current
`depending on the grayScale level to be displayed is Supplied
`to each of the data lines.
`0021
`Further, in the method of driving an electro-optical
`device, the predetermined grayScale level is preferably
`black. In addition, the Self-luminous element is preferably an
`organic light emitting diode.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0022 FIG. 1 is a block diagram showing a construction
`of an electro-optical device according to a first embodiment
`of the present invention;
`0023 FIG. 2 is a timing chart of a scanning line driving
`circuit in the electro-optical device;
`0024 FIG. 3 is a circuit diagram showing a construction
`of a pixel circuit in the electro-optical device;
`0.025
`FIG. 4 is a circuit diagram showing a construction
`of a data line driving circuit in the electro-optical device;
`0.026
`FIG. 5 is a circuit diagram showing an example of
`a construction of a signal Supply unit in the data line driving
`circuit;
`FIG. 6 is a block diagram of a power supply circuit
`0.027
`which is used for an electro-optical device according to a
`Second embodiment of the present invention;
`0028 FIG. 7 is a circuit diagram of a voltage supply
`circuit and its peripheral constructions which are used for an
`electro-optical device according to a third embodiment of
`the present invention;
`0029 FIG. 8 is a timing chart of the voltage supply
`circuit and its peripheral constructions,
`0030 FIG. 9 is a circuit diagram showing an example of
`a construction of a Voltage Supply circuit according to a
`modified example of the third embodiment;
`0.031
`FIG. 10 is a perspective view showing a construc
`tion of a mobile type personal computer to which the
`electro-optical device is applied;
`0.032
`FIG. 11 is a perspective view showing a construc
`tion of a cellular phone to which the electro-optical device
`is applied; and
`0.033
`FIG. 12 is a perspective view showing a construc
`tion of a personal digital assistant to which the electro
`optical device is applied.
`
`DETAILED DESCRIPTION OF EMBODIMENTS
`
`1. First Embodiment
`0034 FIG. 1 is a block diagram showing a schematic
`construction of an electro-optical device according to a first
`embodiment of the present invention. An electro-optical
`device 1 comprises an electro-optical panel AA and an
`exterior circuit. In the electro-optical panel AA, a display
`region A, a Scanning line driving circuit 100 and a data line
`driving circuit 200 are formed. Among them, in the display
`region A, m Scanning lines 101 and m light emission control
`lines 102 are formed in parallel in an X direction. Further, n
`data lines 103 are formed in parallel to a Y direction which
`is orthogonal to the X direction. And then, corresponding to
`interSections of the Scanning lines 101 and the data lines
`103, pixel circuits 400A are respectively provided. The
`respective pixel circuits 400A comprise an OLED element.
`The marks 'R', 'G' and 'B' shown in FIG. 1 mean red,
`green and blue respectively and represent light emission
`colors of the OLED elements. In this example, the pixel
`circuits 400A of the respective colors are arranged along the
`respective data lines 103.
`0035) Further, among the pixel circuits 400A, the pixel
`circuits 400A corresponding to R color are connected to a
`power Supply line LR, the pixel circuits 400A corresponding
`to G color are connected to a power Supply line LG, and the
`pixel circuits 400A corresponding to B color are connected
`to a power Supply line LB. A power Supply circuit 600A
`generates power Supply Voltages Vddr, Vddg and Vddb and
`black voltages VBr, VBg and VBb. The power supply
`voltages Vddr, Vddg and Vddb are supplied to the pixel
`circuits 400A corresponding to the respective RGB colors
`via the power supply lines LR, LG and LB, and the black
`voltages VBr, VBg and VBb are supplied to the data line
`driving circuit 200.
`0036) The scanning line driving circuit 100 generates
`Scanning Signals Y1, Y2, Y3, . . . and Ym for Sequentially
`Selecting the plurality of Scanning lines 101 and light
`emission control Signals Vgl, Vg2, Vg3, . . . and Vgm. The
`light emission control Signals Vg1, Vg2, Vg3, ... and Vgm
`are respectively supplied to the pixel circuits 400A via the
`respective light emission control lines 102. FIG. 2 shows an
`example of a timing chart of the Scanning Signals Y1 to Ym
`and the light emission control Signals Vg1 to Vgm. The
`Scanning Signal Y1 is a pulse having a width equivalent to
`one horizontal scanning period (1H) beginning with an
`initial timing of one vertical Scanning period (IF) and is
`supplied to the scanning line 101 of a first row. Subse
`quently, this pulse is Sequentially shifted and then the shifted
`pulses are respectively Supplied to the Scanning lines 101 of
`Second, third, ... and m-th rows as the Scanning Signals Y2,
`Y3, ... and Ym. Generally, if the scanning signal Yi which
`is to be supplied to the scanning line 101 of an i-th row (i is
`an integer Satisfying an expression of 1 sism) becomes H
`level, it means that the corresponding Scanning line 101 is
`Selected. Further, as the light emission control Signals Vg1,
`Vg2, Vg3, . . . and Vgm, Signals of which logic levels are
`inverted with respect to the logic levels of the Scanning
`signals Y1, Y2, Y3, . . . and Ym are used.
`0037. The data line driving circuit 200 supplies the
`respective pixel circuits 400A arranged in the selected
`Scanning line 101 with Supply grayScale Signals X1, X2, X3,
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 015
`
`

`

`US 2005/0156837 A1
`
`Jul. 21, 2005
`
`... and Xn. In this example, the Supply grayScale Signals X1,
`X2, X3, . . . Xn may be given as current signals which
`indicate grayScale brightness. The details of the data line
`driving circuit 200 will be described later.
`0.038 A timing generating circuit 700 generates various
`control Signals and outputs them to the Scanning line driving
`circuit 100 and the data line driving circuit 200. Further, an
`image processing circuit generates grayScale data D on
`which an image processing Such as a gamma correction is
`performed and outputs it to the data line driving circuit 200.
`Moreover, in this example, the power supply circuit 600A,
`the timing generating circuit 700 and the image processing
`circuit 800 are provided outside the electro-optical panel
`AA, but a part or all of these elements may be incorporated
`into the electro-optical panel AA. In addition, a part of
`elements provided in the electro-optical panel AA may be
`provided as an exterior circuit.
`0039) Next, the pixel circuit 400A will be described. In
`FIG. 3, a circuit diagram of the pixel circuit 400A is shown.
`The pixel circuit 400A shown in FIG. 3 corresponds to R
`color of the i-th row, to which the power Supply Voltage
`Vddr is supplied. The pixel circuits 400A corresponding to
`other colors are constructed Similarly, except that the power
`Supply Voltage Vddg (G color) or the power Supply Voltage
`Vddb (B color) is supplied, instead of the power supply
`voltage Vddr. The pixel circuit 400A comprises four thin
`film transistors (hereinafter, referred to as TFT) 401 to 404,
`a capacitive element 410, and an OLED element 420.
`Among them, a Source electrode of the p-channel type TFT
`401 is connected to the power supply line LR and a drain
`electrode thereof is connected to a drain electrode of the
`n-channel type TFT 403, a drain electrode of the n-channel
`type TFT 404 and a source electrode of the n-channel type
`TFT 4.02.
`0040. One end of the capacitive element 410 is connected
`to the Source electrode of the TFT 403 and other end thereof
`is connected to a gate electrode of the TFT 4.03 and a drain
`electrode of the TFT 402. A gate electrode of the TFT 403
`is connected to the Scanning line 101 and a Source electrode
`thereof is connected to the data line 103. Further, a gate
`electrode of the TFT 402 is connected to the scanning line
`101. Meanwhile, a gate electrode of the TFT 404 is con
`nected to the light emission control line 102 and a Source
`electrode thereof is connected to an anode of the OLED
`element 420. Here, the light emission control signal Vgi is
`supplied via the light emission control line 102. Further, as
`regards the OLED element 420, a light emitting layer is
`interposed between the anode and a cathode and light-emits
`with brightness depending on a forward current. Moreover,
`the cathode of the OLED element 420 is a common electrode
`over all the pixel circuits 400A and is set to low level
`(reference) potential in a power Supply.
`0041. In such a construction, if the scanning signal Yi
`becomes H level, the n-channel type TFT 402 is turned on,
`and then the TFT 401 functions as a diode in which the gate
`electrode and the drain electrode are connected to each other.
`If the Scanning Signal Yi becomes H level, the n-channel
`type TFT 4.03 also is turned on, similarly to the TFT 402. As
`a result, a current Idata of the data line driving circuit 200
`flows in a path passing through the power Supply line LR,
`the TFT 401, the TFT 4.03 and the data line 103. In this
`
`Situation, charges depending on a potential of the gate
`electrode of the TFT 401 are stored in the capacitive element
`410.
`0042. If the scanning signal Yi becomes Llevel, the TFTs
`403 and 402 are turned off. In this situation, since input
`impedance in the gate electrode of the TFT 401 is extremely
`high, the charge Storing State in the capacitive element 410
`is not changed. A gate-source voltage of the TFT 401 is held
`to a voltage when the current Idata flows. Further, if the
`Scanning Signal Yi becomes L level, the light emission
`control signal Vgi becomes H level. For this reason, the
`n-channel type TFT 404 is turned on, and then between the
`Source and the drain of the TFT 401, a current Ioled
`depending on a gate Voltage thereof flows. More details, the
`current flows in a path passing through the power Supply line
`LR, the TFT 401, the TFT 404 and the OLED element 420.
`0043. Here, the current Ioled flowing in the OLED ele
`ment 420 is determined by a gate-source voltage of the TFT
`401, but, this voltage is the voltage held by the capacitive
`element 410 when the current Idata flow in the data line 103
`by the scanning signal Yi of H level. For this reason, when
`the light emission control Signal Vgi became H level, the
`current Ioled flowing in the OLED element 420 approxi
`mately accords with the current Idata flowed just before. In
`Such a manner, the pixel circuit 400A is a current program
`mode circuit Since light emission brightness is defined by the
`current Idata.
`0044) The TFT 401 functions as a driving transistor
`which supplies the OLED element 420 with the current
`Ioled. When the threshold voltage of the TFT 401 is Vth and
`the gate-source voltage thereof is Vgs, and the TFT 401
`operates in a Saturation region, the current Ioled is given by
`the following equation.
`
`0045 And then, if the gate-source voltage Vgs falls short
`of the threshold voltage Vith, the TFT 401 is turned off. In
`this case, Since the current Ioled is not Supplied, the OLED
`element 420 does not emit, such that black is displayed.
`Therefore, in order to display black, it is necessary to Set the
`gate Voltage Vgate So as to Satisfy the following equation.
`
`0046 For this reason, the above-mentioned black voltage
`VBr is set to satisfy the following equation.
`
`0047. Here, the equations regarding R color are
`described, but the same is applied to the black Voltages VBg
`and VBb of G color and B color. Further, the power supply
`voltage Vddr may be used as the black voltage VBr. In this
`case, Since there is no need for generating the black Voltage
`VBr specially, it is possible to simply the construction of the
`power supply circuit 600A.
`0048 Next, the detailed construction of the data line
`driving circuit 200 is shown in FIG. 4. The data line driving
`circuit 200 comprises a grayScale data generating circuit 210
`and a grayScale Signal Supply circuit 220. The grayScale data
`generating circuit 210 generates grayScale data DX1 to Dxn
`in a linear Sequence based on dot Sequential grayScale data
`D. FIG. 4 shows an example in which grayscale data DX1
`to DXn consists of four-bit data. The grayScale Signal Supply
`circuit 220 comprises in Signal Supply units US1, Us2, ... and
`
`LG Display Co., Ltd.
`Exhibit 1007
`Page 016
`
`

`

`US 2005/0156837 A1
`
`Jul. 21, 2005
`
`Usin. Here, the black voltage VBr is supplied to the signal
`Supply units US1, US4, . . . and USn-2 corresponding to R
`color, the black Voltage VBg is Supplied to the Signal Supply
`units US2, US5, ... and USn-1 corresponding to G color, and
`the black Voltage VBb is Supplied to the Signal Supply units
`Us3, Usó, .
`.
`. and USn corresponding to B color. The
`respective Signal Supply units US 1 to USn have the same
`construction, and thus, here, only the Signal Supply unit US 1
`will be described and the descriptions regarding other signal
`supply units Us2 to USn will be omitted.
`0049 FIG. 5 shows a construction of the signal supply
`unit US 1. The Signal Supply unit US 1 comprises a current
`supply circuit 230 and a voltage supply circuit 240. In the
`current Supply circuit 230, a reference Voltage Source VG
`generates a reference Voltage Vref a