I 1111111111111111 11111 111111111111111 1111111111 1111111111111111 IIII IIII IIII
`US007995047B2
`
`(12) United States Patent
`Mizuki et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,995,047 B2
`Aug. 9, 2011
`
`(54) CURRENT DRIVING DEVICE
`
`(75)
`
`Inventors: Makoto Mizuki, Kyoto (JP); Kazuyoshi
`Nishi, Kyoto (JP); Tetsuro Ohmori,
`Osaka (JP); Tomokazu Kojima, Osaka
`(JP); Hiroshi Kojima, Kyoto (JP)
`
`(73) Assignee: Panasonic Corporation, Osaka (JP)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 904 days.
`
`(21) Appl. No.: 11/954,659
`
`(22) Filed:
`
`Dec. 12, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2008/0143429 Al
`
`Jun. 19, 2008
`
`(30)
`
`Foreign Application Priority Data
`
`Dec. 13, 2006
`
`(JP) ................................. 2006-335850
`
`(51)
`
`Int. Cl.
`GOSF 1/10
`(2006.01)
`(52) U.S. Cl. ........................................ 345/204; 327/108
`( 58) Field of Classification Search . ... ... ... ... .. ... .. 345/7 6,
`345/204; 327 /108
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`7 /2003 Everitt
`6,594,606 B2
`6,628,274 Bl *
`........... 345/209
`9/2003 Morita
`6,765,560 Bl *
`........... 345/204
`7/2004 Ozawa
`6,777,885 B2 *
`8/2004 Koyama ..................... 315/169.1
`6,882,186 B2 *
`4/2005 Nishitoba
`........... 327/108
`7,012,597 B2 *
`3/2006 Kasai ............................ 345/204
`5/2006 LeChevalier
`7,050,024 B2
`7,064,969 B2 *
`6/2006 West ............................. 363/132
`
`7,221,349 B2 *
`7,466,166 B2 *
`7,864,167 B2 *
`2002/0135314 Al*
`2004/0108988 Al *
`2004/0239668 Al *
`2004/0251844 Al
`2005/0231241 Al
`2006/0158402 Al
`
`5/2007 Hashido et al. ................. 345/89
`12/2008 Date et al. ..................... 327/108
`........... 345/204
`1/2011 Morosawa et al.
`9/2002 Kitahara et al.
`........... 315/169.3
`6/2004 Choi ............................... 345/96
`12/2004 Morosawa et al.
`........... 345/212
`12/2004 Hashido et al.
`10/2005 Date et al.
`7/2006 Nathan et al.
`
`FOREIGN PATENT DOCUMENTS
`JP
`2004-219955
`8/2004
`2005-121843
`JP
`5/2005
`2005-311591
`JP
`11/2005
`* cited by examiner
`
`Primary Examiner - Bipin Shalwala
`Assistant Examiner - Afroza Chowdhury
`(74) Attorney, Agent, or Firm -McDermott Will & Emery
`LLP
`
`ABSTRACT
`(57)
`A current driving device comprises: a voltage supply part; a
`current supply part; and a plurality of current output parts,
`each comprising a current-voltage converting function, a
`voltage-current converting function, and a voltage holding
`capacitance element. The current output part takes three
`operation modes. Under a voltage supply mode, the current
`output part receives a voltage from the voltage supply part and
`holds the voltage in the voltage holding capacitance element.
`Under a current supply mode, the current output part receives
`the current from the current supply part, generates a second
`voltage by the current-voltage converting function and holds
`the voltage in the voltage holding capacitance element. Under
`a current output part, the current output part outputs an output
`current according to the voltage held in the voltage holding
`capacitance element by the voltage-current converting func(cid:173)
`tion. By charging the current output part with the reference
`voltage before the calibration performed by using the refer(cid:173)
`ence current, calibration of the current output part is per(cid:173)
`formed at a high speed.
`
`10 Claims, 9 Drawing Sheets
`
`OUT1
`
`OUT2
`
`OUTn
`
`A1
`
`A2
`
`An
`
`B
`
`Action control circuit
`
`SAMSUNG, EXH. 1001, P. 1
`
`

`

`U.S. Patent
`
`Aug. 9, 2011
`
`Sheet 1 of 9
`
`US 7,995,047 B2
`
`F I G. 1 A
`
`11
`
`T1
`
`T2
`
`So1
`
`So2~
`
`V1
`
`Voltage
`supply
`source
`
`N1
`Sw2~
`s~
`
`<..
`<..
`G1 G2
`
`G3
`
`Gm
`
`;--7~
`i\ ·--~ i\
`
`i\
`QN2 QN3
`
`QNm
`
`A Current output part
`
`F I G. 1 B
`
`T1 T2
`
`V1
`
`Voltage t - - - - (cid:173)
`supply
`source
`
`VREFIREFIOUTA!OUTB
`
`CTL DATA
`
`A Current output part
`
`SAMSUNG, EXH. 1001, P. 2
`
`

`

`So1
`
`So2
`
`Sw1 .Sw2 ________ ,,___ ....
`
`Sw3
`
`G1-Gm
`
`DATA
`
`FIG. 2
`
`DATA
`
`Calibration
`according to
`present invention
`
`\J
`1 _ _ _ _ _ /!__
`
`_
`
`I
`
`I
`
`I
`
`I
`I
`t
`I
`I
`I
`I
`
`(cid:141)•
`
`I
`I
`
`I
`t
`
`Current output time
`
`V(N2)
`
`___________ ....._ __ __. .... ,... ~
`
`_._.._.
`
`Current output time
`
`Current
`supply mode
`M2
`
`Calibration mode
`Mc
`
`--L--~------------
`I
`... -
`I
`I
`I
`: Current calibration :
`:
`only
`:
`(cid:141) l
`.(cid:141)
`111:•
`: Voltage
`:
`:supply mode :
`M1
`
`SAMSUNG, EXH. 1001, P. 3
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`

`

`F I G. 3
`
`OUT1
`
`OUT2
`
`OUTn
`
`Nl 1
`
`11
`
`V1
`
`AO
`
`A1
`
`VREF IREF IOUTA IOUTB
`
`VREF IREF IOUTAIOUT
`
`CTL
`
`DATA
`
`CTL
`
`DATA
`
`A2
`
`•••••
`
`An
`
`CTL
`
`DATA Din
`
`Signal
`input
`circuit
`
`B
`
`Action control circuit
`
`r.,J =-('t)
`
`('t) -tH
`
`0 -.
`
`\0
`
`c
`
`r.,J_
`-.l
`'tc
`\0
`Ul
`
`0 .a;::...
`-.l
`t::c
`N
`
`SAMSUNG, EXH. 1001, P. 4
`
`

`

`F I G. 4
`
`V1
`
`QNx
`
`Ad
`
`QN21
`
`VREF IREFIOUTAIOUT __ VREF IREFIOUTAIOUT
`DATA
`DATA
`CTL
`CTL
`
`AO
`
`An
`
`SAMSUNG, EXH. 1001, P. 5
`
`

`

`F I G. 5
`
`OUT1
`
`OUT2
`
`OUTn
`
`N11
`
`I1
`
`)
`QNx
`
`AO
`
`A1
`
`A2
`
`An
`
`VREF IREROUTA
`
`lOUTB
`
`VREF
`
`lREF IOUT A IOUTB
`
`CTL
`
`DATA
`
`CTL
`
`DATA
`
`CTL
`
`DATA
`
`•••••
`
`VREF IREF JOUTA lOUTB
`
`CTL
`
`DATA Din
`
`Signal
`--+-----1 input
`circuit
`
`B
`
`Action control circuit
`
`SAMSUNG, EXH. 1001, P. 6
`
`

`

`U.S. Patent
`
`Aug. 9, 2011
`
`Sheet 6 of 9
`
`US 7,995,047 B2
`
`FIG. 6 A PriorArt
`
`11
`
`T1
`
`T2
`
`So1
`
`So2~
`
`N1
`Sw2___.
`
`'\
`"\
`G1 G2
`
`A
`
`F I G . 6 B Prior Art
`
`T1 T2
`
`!REF IOUT A IOUTB
`
`CTL DATA
`
`A
`
`SAMSUNG, EXH. 1001, P. 7
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`

`

`F I G . 7 Prior Art
`
`So1
`
`So2
`
`Sw1, Sw2
`
`G1-Gm
`
`DATA
`
`DATA
`
`V(N2)
`
`Current output time
`
`Calibration mode
`
`Current output time
`
`> = ~
`
`~
`N
`Q
`~
`~
`
`rJj =-~
`
`~ --l
`Q -\0
`
`SAMSUNG, EXH. 1001, P. 8
`
`

`

`F I G · 8 Prior Art
`
`11
`
`OUT1
`
`11
`
`OUT2
`
`1rv
`
`OUTn
`
`---------------
`----------+--------------.a---------~-------------.
`
`,,
`
`lREF JOUT A lOUTB
`
`CTL DATA
`,d,.
`H
`
`AO
`~ ., ,.
`
`A1
`~ ., r
`!REF IOUT A JOUTB
`lREF lOUT A lOUTB
`
`CTL DATA
`. a
`.j ..
`
`'-
`
`CTL DATA
`.a .
`. a
`'
`
`A2
`
`•••••
`
`---
`
`, ,
`
`An
`~
`IREF IOUT A IOUTB
`
`CTL DATA
`.H..
`,H
`
`'
`
`Din
`~
`
`Signal
`input
`circuit
`
`<
`Action control circuit
`B / - - - - - - - - - - - - - - - - - - - - -~
`
`SAMSUNG, EXH. 1001, P. 9
`
`

`

`F I G · 9 Prior Art
`
`... !------------
`
`___ _,, ___ ..,.... ____________ ~Value after
`calibration
`
`Target value
`
`,/
`
`V(N2)
`
`Current output time
`
`Calibration mode
`
`(cid:141),
`
`Current output time
`
`SAMSUNG, EXH. 1001, P. 10
`
`

`

`US 7,995,047 B2
`
`1
`CURRENT DRIVING DEVICE
`
`FIELD OF THE INVENTION
`
`The present invention relates to a current driving device
`used preferably as a driver for displays such as organic EL
`(Electro-luminescence) panels, LED panels, and the like.
`
`BACKGROUND OF THE INVENTION
`
`Recently, flat-panel displays have a larger screen and
`higher definition, while establishing reduction in thickness,
`weight, and cost. With such backgrounds, it is required for
`display drivers to improve the uniformity in the displayed
`image qualities through decreasing variations between output 15
`electric currents that are outputted from output terminals.
`Variations in the electric currents in static actions of current
`mirrors include variations caused due to fabrication processes
`of each transistor, variations of gate voltages caused due to
`resistances of power supply wirings, and the like. Further,
`variations due to dynamic actions of the current mirrors
`include variations caused due to injection of electric charges
`from a display panel or instantaneous fluctuations of power
`supply, for example. Furthermore, generally, a driver IC is
`formed in a multi-output structure with a stick-like slim 25
`shape, since it is mounted to a frame part of a flat panel.
`Because of restrictions in the LSI shape, characteristics of
`transistors disposed therein vary depending on positions of
`slim-layout elements. Therefore, even if a same gate voltage
`is applied in a current mirror structure, the output currents 30
`from each of current-summing DA converter circuits do not
`necessarily become the same.
`As a method for decreasing such variations, there is a
`current driving device having a current output part, such as
`the one shown in FIG. 6A and FIG. 6B, for example (see US 35
`2005/0231241Al , for example). This current output part has
`a calibration function and a current output function. "Calibra(cid:173)
`tion" means to have a reference current value by a reference
`current source stored in the current output part.
`Under a calibration mode, current output switches Sol and 40
`So2 are set to a nonconductive state, while a current input
`switch Swl, a calibration switch Sw2, and all signal response
`switches Gl-Gm are set to a conductive state. Current output
`terminals Tl and T2 are isolated from the outside. Nodes Nl
`and N2 are short-circuited, and drains and gates ofNch tran(cid:173)
`sistors QNl-QNm are short-circuited to receive electric cur(cid:173)
`rents from a reference current source 11. Through this, the
`Nch transistors QNl-QNm generate, at the node N2, a gate
`voltage that is necessary for allowing the electric current from
`the reference current source 11 to flow through the transistors
`themselves . A voltage holding capacitance element Cl is
`charged to the above-described gate voltage. A voltage V (N2)
`of the node N2 corresponds to a voltage that is capable of
`passing an electric current that is equal to the reference cur(cid:173)
`rent generated by the reference current source 11 through the
`Nch transistors QNl-QNm which are all in a conductive state.
`In conclusion, the current output part A comes to store the
`reference current generated by the reference current source
`11.
`Under a current output mode, the current input switch Swl 60
`and the calibration switch Sw2 are turned to a nonconductive
`state, and either one of the current output switch Sol or So2 is
`set to a conductive state while the other is remained in a
`nonconductive state. The conduction state of the signal
`response switches Gl-Gm is determined depending on an
`input signal supplied from the outside. The voltage holding
`capacitance element Cl holds the voltage charged by the
`
`2
`calibration action, and continues to supply the electric current
`to the gate terminals of the Nch transistors QNl-QNm. The
`Nch transistors QNl-QNm output an electric current in accor(cid:173)
`dance with the voltage V (N2) of the node N2 from one (inan
`conductive state) of the current output terminals Tl and T2, in
`accordance with the conduction state of the signal response
`switches Gl-Gm.
`FIG. 7 shows a timing chart of a series of actions regarding
`calibration and output of the electric current performed in the
`10 current-summing DA converter circuit shown in FIG. 6A and
`FIG. 6B. The conductive state of the switches is shown with
`"H", and the nonconductive state thereof is shown with "L".
`"V (N2)" indicates the voltage V (N2) of the node N2 .
`Before calibration, the current output part A sets the current
`output witch Sol to be in a conductive state, and outputs, from
`the current output terminal Tl, the output current in accor(cid:173)
`dance with the state of the signal response switches Gl-Gm
`which are controlled by the voltage V (N2) of the node N2 and
`an input signal. The current output switch So2, the current
`20 input switch Swl, and the calibration switch Sw2 are set to be
`in a nonconductive state.
`During the calibration period, the current output switches
`Sol, So2 are set to a nonconductive state, the current input
`switch Swl and the calibration switch Sw2 are set to a con(cid:173)
`ductive state, and the signal response switches Gl-Gm for
`selecting the electric currents from the Nch transistors QNl(cid:173)
`QNm are all set to a conductive state. Through this, the Nch
`transistors QNl-QNm are set in a state where only the electric
`current of the reference current source 11 is supplied, and the
`voltage V (N2) of the node N2 is determined in accordance
`with the above-described actions.
`After completing the above-described calibration, the cur-
`rent input switch Swl and the calibration switch Sw2 are set
`to a nonconductive state, so that the voltage holding capaci(cid:173)
`tance element Cl holds the electric charge. That is, the volt(cid:173)
`age V (N2) of the node N2 is being maintained. Thereafter, the
`current output switch So2 is set to a conductive state, and the
`sum of the electric currents selected by the signal response
`switches Gl-Gm in accordance with the input signal is out(cid:173)
`putted from the current output terminal T2.
`FIG. 8 shows a structure of a current driving device that
`utilizes the current output part A shown in FIG. 6A and FIG.
`6B. (n+ 1 )-numbers of current output parts AO-An control the
`operation states under a calibration mode and a current output
`45 mode in accordance with control signals supplied from an
`action control circuit B. A signal input circuit Din supplies
`signals for controlling the signal response switches Gl-Gm
`within the internal structural elements (see FIG. 6A) of each
`of the current output parts AO-An. Calibration by the refer-
`50 ence current source 11 is performed on a single current output
`part among the (n+ 1 )-numbers of current output parts AO-Al
`by an internal operation of each of the current output parts
`AO-An. Calibration is performed in order from AO, to Al ,
`A2, - - - , and to An. The current output parts that are not under
`55 calibration are set to be in the current output mode, and output
`an electric current ton-numbers of output terminals OUTl(cid:173)
`OUTn. The electric currents are outputted in order from AO to
`Al,A2, - - - , and to An.
`The reference current, when there are a plurality of current(cid:173)
`sunnning DA converter circuits with the above-described
`current output parts, can be combined into the electric cur(cid:173)
`rents of the same current source. This makes it possible to
`achieve the uniformity in the display on a panel.
`Other related documents are: Japanese Unexamined Patent
`65 Publication 2004-219955, Japanese Unexamined Patent Pub(cid:173)
`lication 2005-121843, US2004/0251844Al , US7050024B2,
`US6594606B2, US2006/0 l 58402Al.
`
`SAMSUNG, EXH. 1001, P. 11
`
`

`

`3
`With this method, however, the capacity for charging/dis(cid:173)
`charging the voltage holding capacitance element Cl
`becomes insufficient when the current value of the reference
`current source I1 is very small, so that it is difficult to charge
`the current of the Nch transistors QNl-QNm to accurately
`meet the value of the current from the reference current
`source I1 within the calibration period. FIG. 9 shows the state
`where the voltage holding capacitance element Cl is insuffi(cid:173)
`ciently charged because the reference current is very small.
`Further, when there is a change in the current value of the 10
`reference current source Il, the reference currents become
`varied depending on the output terminals with the successive
`calibration, until the reference currents of all the current
`output parts AO-An are updated.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention therefore is to provide a
`current driving device which can perform calibration at a high
`speed and improve the non-uniformity of the output currents
`even when a reference current is very small and when there is
`a change in the reference current.
`A current driving device of the present invention com(cid:173)
`prises:
`a first voltage supply part for supplying a first voltage;
`a first current supply part for supplying a first electric
`current;
`a plurality of output terminals; and
`a plurality of current output parts for outputting an electric
`current in accordance with the first electric current, each of 30
`the current output parts comprising a current-voltage convert(cid:173)
`ing fimction, a voltage-current converting fimction, a voltage
`holding part, and at least one current output terminal, wherein
`the current output part takes three operation modes, i.e. a
`voltage supply mode, a current supply mode, and a current 35
`output mode,
`under the voltage supply mode, the current output part
`receives the first voltage from the first voltage supply part and
`holds the voltage in the voltage holding part,
`under the current supply mode, the current output part 40
`receives the first current from the first current supply part, and
`generates a second voltage by the current-voltage converting
`function and holds the voltage in the voltage holding part, and
`under the current output mode, the current output part
`outputs an output current according to the voltage held in the 45
`voltage holding part by the voltage-current converting func(cid:173)
`tion. The voltage supply mode and the current supply mode
`correspond to the calibration mode.
`In the current driving device constituted in the manner
`described above, the current output part receives a supply of 50
`the first voltage from the first voltage supply part under the
`voltage supply mode, and holds the first voltage in the voltage
`holding part. Then, under the current supply mode, the cur(cid:173)
`rent output part receives a supply of the first electric current
`from the first current supply part, generates the second volt- 55
`age by the current-voltage converting function, and holds the
`second voltage in the voltage holding part. This makes it
`possible to charge the voltage holding part to a prescribed
`voltage at a higher speed. Then, under the current output
`mode, the current output part outputs an electric current 60
`according to the voltage held in the voltage holding part
`through the voltage-current converting function. For charging
`the voltage holding part, it is charged with the first voltage to
`a value close to the target voltage, and then charged further
`with a supply of the first electric current. Thus, even if the 65
`reference current supplied from the first current supply part is
`very small, it is possible to speed up the action for supplying
`
`US 7,995,047 B2
`
`25
`
`4
`the voltage to the voltage holding part until reaching the
`reference current and also to obtain the reference current
`accurately.
`In the current driving device with the above-described
`strncture, each of the output terminals is connected to the
`current output terminals provided to the plurality of the cur(cid:173)
`rent output parts, and each of the plurality of current output
`parts is connected in parallel to the first current supply part
`and the first voltage supply part used in common. With this
`strncture, the voltage holding parts provided to all the current
`output parts can be charged provisionally to the first voltage
`when it becomes necessary to perform extensive calibrations
`on all the current output parts, e.g. right after the startup or
`when there is a change in the first electric current. Therefore,
`15 it is possible to suppress unevenness in the display caused due
`to the change in the first electric current.
`Further, in the current driving device with the above-de(cid:173)
`scribed strncture, each of the current output parts actuates the
`current-voltage converting function under the voltage supply
`20 mode. With this strncture, for charging the voltage holding
`part, the voltage obtained by converting the first electric cur(cid:173)
`rent from the first current supply part can be combined with
`the supply of the first voltage from the first voltage supply
`part. Therefore, still higher speed charging can be achieved.
`Furthermore, in the current driving device with the above(cid:173)
`described strncture, each of the current output parts com(cid:173)
`prises a function of stopping the current-voltage converting
`function under the voltage supply mode. With this strncture,
`all the electric currents supplied from the first voltage supply
`part can be utilized for charging the voltage holding part.
`Thus, the power consumption can be reduced.
`Moreover, the current driving device with the above-de-
`scribed strncture further comprises a second current supply
`part for supplying a second electric current that is propor(cid:173)
`tional to the first electric current, and a current-voltage con(cid:173)
`verting part for generating the first voltage by receiving the
`second electric current, wherein the first voltage supply part
`controls supplies of the first voltage generated by the current(cid:173)
`voltage converting part to the current output parts. With this
`strncture, the first voltage supplied from the first voltage
`supply part to the current output part is generated from the
`second electric current by the current-voltage converting part.
`The second electric current from the second current supply
`part is proportional to the first electric current, so that the first
`voltage comes to have a value that corresponds to the first
`electric current. Therefore, it is possible to generate the first
`voltage having a value that almost equals to the final target
`value to be held in the voltage holding part.
`Further, in the current driving device with the above-de(cid:173)
`scribed strncture, the current-voltage converting part com(cid:173)
`prises a switching part for short-circuiting a node at which the
`first voltage emerges to a reference voltage node. When there
`is a change in the first electric current or the second electric
`current, it also takes time to change the second voltage gen-
`erated by the current-voltage converting part. With this strnc(cid:173)
`ture, however, the output voltage of the current-voltage con-
`verting part can be reset through actuating the switching part.
`Therefore, it is possible to speed up the change of the second
`voltage by the current-voltage converting part.
`Furthermore, the current driving device with the above(cid:173)
`described strncture further comprises a second voltage supply
`part with a larger voltage supply capacity than that of the first
`voltage supply part, wherein the use of the first voltage supply
`part and the use of the second voltage supply part are switched
`in accordance with the number of the current output parts that
`take the voltage supply mode among the plurality of current
`output parts. When there are a large number of current output
`
`SAMSUNG, EXH. 1001, P. 12
`
`

`

`US 7,995,047 B2
`
`6
`voltage holding part is raised at a high speed by using the
`voltage supply part under the voltage supply mode that is the
`first half part of the calibration mode, and the reference cur(cid:173)
`rent value by the current supply part is stored accurately in the
`latter half stage of the calibration mode. Therefore, even when
`the current value of the reference current source is very small,
`it becomes possible with the voltage supply part to compen(cid:173)
`sate for the capacity for supplying the voltage to the voltage
`holding part till reaching the reference current and to com-
`plete the calibration at a high speed for allowing the current
`flowing the voltage-current converting element to meet accu(cid:173)
`rately with the current value of the reference current source.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`10
`
`5
`parts, the load of the voltage supply part changes largely
`depending on how many current output parts are under the
`voltage supply mode. With this structure, however, it is pos(cid:173)
`sible to reduce EMI ( electromagnetic interference) and the
`power consumption by changing the output voltages
`smoothly through adding the second voltage supply part and
`switching between the use of the first voltage supply part and
`the use of the second voltage supply part in accordance with
`the load.
`Alternatively, in the current driving device with the above(cid:173)
`described structure, the first voltage supply part is constituted
`to be capable of changing its voltage supply capacity in accor(cid:173)
`dance with the number of the current output parts that take the
`voltage supply mode among the plurality of current output
`parts. With this structure, it is possible to reduce EMI (elec- 15
`tromagnetic interference) and the required area because the
`first voltage supply part is provided with the function of
`optimizing the voltage supply capacity in accordance with the
`load.
`A display device according to the present invention related 20
`to the current driving device described above comprises one
`of the above-described current driving devices mounted
`thereon so as to be driven by the current driving device.
`Displays on the screen can be made uniform with this display
`device.
`A current driving device according to the present invention
`comprises:
`a current input switch for controlling connection/discon(cid:173)
`nection states with respect to a current supply part;
`a voltage holding part for holding a reference voltage,
`which is charged by a flown current;
`a calibration switch interposed between the current input
`switch and the voltage holding part;
`a plurality of voltage-current converting elements for gen(cid:173)
`erating an electric current in accordance with the refer(cid:173)
`ence voltage held in the voltage holding part;
`a plurality of signal response switches that are on/off con(cid:173)
`trolled in accordance with inputted signals, the response
`switches being connected in series to each of the volt(cid:173)
`age-current converting elements, and each of which 40
`being connected in parallel to the calibration switch;
`a plurality of current output switches, each being inter(cid:173)
`posed between a connection node, which is provided
`between the current input switch and the calibration
`switch, and the plurality of current output terminals; and 45
`a high-speeding switch for controlling connection/discon(cid:173)
`nection states of the voltage supply part with respect to
`the voltage holding part.
`The calibration mode comprises two stages, i.e. the voltage
`supply mode and the current supply mode. In the voltage 50
`supply mode, the high-speeding switch is set to be in a con(cid:173)
`ductive state to connect the voltage supply part to the voltage
`holding part in order to boost up the potential level of the
`voltage holding part at a high speed. At that time, the current
`output switches are all set to be in a nonconductive state, and 55
`the calibration switch and all the signal response switches are
`set to be in a conductive state. Then, in the current supply
`mode, the high-speeding switch is turned to a nonconductive
`state. The current input switch and the calibration switch are
`set to be in a conductive state, so that the sum of the current 60
`values flown in the voltage-current converting element
`becomes equal to the reference current value that is supplied
`from the current supply part. Thus, the voltage holding part
`comes to hold the voltage that corresponds to passing the
`current ( equivalent to the reference current value) through the 65
`voltage-current converting element. That is, the reference
`current value is stored. As described, the potential of the
`
`The present invention is illustrated be way of example and
`not limitation in the figures of the accompanying drawings, in
`which like references indicate similar elements and in which:
`FIG. IA is a circuit diagram for showing a structure of a
`current output part according to a preferred embodiment of
`the present invention;
`FIG. lB is a block circuit diagram for showing the structure
`of the current output part according to the preferred embodi-
`25 ment of the present invention;
`FIG. 2 is a timing chart for showing actions of the current
`output part shown in FIG. IA and FIG. lB;
`FIG. 3 is a block circuit diagram for showing an overall
`structure of a current driving device according to the pre-
`30 ferred embodiment of the present invention;
`FIG. 4 is a circuit diagram for showing a specific structure
`of a voltage supply source according to the preferred embodi(cid:173)
`ment of the present invention;
`FIG. 5 is a block circuit diagram for showing an overall
`35 structure of a current driving device according to a modifica(cid:173)
`tion example of the preferred embodiment of the present
`invention;
`FIG. 6A is a circuit diagram for showing a structure of a
`current output part according to a conventional technique;
`FIG. 6B is a block circuit diagram for showing the structure
`of the current output part according to the conventional tech(cid:173)
`nique;
`FIG. 7 is a timing chart for showing actions of the current
`output part shown in FIG. 6A and FIG. 6B;
`FIG. 8 is a block circuit diagram for showing an overall
`structure of a current driving device according to the conven(cid:173)
`tional technique; and
`FIG. 9 is a timing chart for showing actions of the current
`output part shown in FIG. 6A and FIG. 6B, when a reference
`current is very small.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Hereinafter, an embodiment of a current driving device
`according to the present invention will be described in detail
`by referring to the accompanying drawings. Same reference
`numerals are applied to the same or corresponding compo(cid:173)
`nents within the drawings.
`FIG. IA is a circuit diagram for showing a structure of a
`current output part A that is mounted to a current driving
`device according to a preferred embodiment of the present
`invention, FIG. lB is a block circuit diagram for showing the
`structure of the current output part A, FIG. 2 is a timing chart
`for describing actions of the current output part A, FIG. 3 is a
`block circuit diagram for showing the overall structure of the
`current driving device, and FIG. 4 is a circuit diagram for
`showing an embodiment of a voltage supply source Vl.
`
`SAMSUNG, EXH. 1001, P. 13
`
`

`

`US 7,995,047 B2
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`7
`
`<Current Output Part>
`First, the current output part A will be described by refer(cid:173)
`ring to FIG. lA and FIG. 18. One end of a voltage holding
`capacitance element Cl is connected to a ground terminal,
`and the other end is connected in common to gate terminals of
`m-numbers ofNch transistors QNl-QNm. Each source of the
`Nch transistors QNl-QNm is connected to a ground terminal,
`and each drain thereof is connected in series to signal
`response switches Gl-Gm which are ON/OFF controlled in
`accordance with input signals. The other ends of the signal
`response switches G 1-Gm are connected in common, and are
`also connected, via a current input switch Swl, to a reference
`current source 11 that supplies a constant current value (first
`electric current) to the current output part A, while being 15
`connected to the voltage holding capacitance element Cl via
`a calibration switch Sw2. A node Nl for connecting the
`current input switch Swl, the calibration switch Sw2, and the
`signal response switches Gl-Gm is connected to current out(cid:173)
`put tenninals Tl and T2 via current output switches Sol and 20
`So2, respectively. The circuit structure that has been
`described heretofore is the same as the circuit structure of a
`conventional technique shown in FIG. 6A and FIG. 6B.
`In this embodiment, further, a voltage supply source Vl for
`supplying a constant voltage (first voltage) to the current 25
`output part A is connected, via a high-speeding switch Sw3, to
`a node N2 that is a connection between the voltage holding
`capacitance element Cl and the calibration switch Sw2. The
`voltage supply source Vl corresponds to a first voltage supply
`part. The reference current source 11 corresponds to a first 30
`current supply part. The voltage holding capacitance element
`Cl corresponds to a voltage holding part. As the voltage
`holding capacitance element Cl, a parasitic capacitance pro(cid:173)
`vided originally to the gate terminals of the Nch transistors
`QNl-QNm may be used instead.
`This current output part A takes three operation states such
`as a voltage supply mode Ml, a current supply mode M2, and
`a current output mode M3. Among those, the voltage supply
`mode Ml and the current supply mode M2 constitute a cali(cid:173)
`bration mode Mc.
`<<Voltage Supply Mode Ml>>
`Now, the voltage supply mode Ml of the current output
`part A will be described first.
`First, each of the current output switches Sol and So2 is set
`to a nonconductive state, so that the current output terminals 45
`Tl and T2 are isolated from the node Nl. Further, the high(cid:173)
`speeding switch Sw3 is set to a conductive state, so that the
`voltage supply source Vl and the node N2 are connected. At
`this time, the voltage holding capacitance element Cl is
`charged to a constant voltage (this corresponds to the first 50
`voltage, and will be referred to as a reference voltage herein(cid:173)
`after) that is supplied from the voltage supply sourc