# US 2003/0214522 A1 · Image display apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2003/0214522 A1 - Document ID: US20030214522A1 - Status: Published application - Kind: A1 - Application number: 10/438,037 - Filed: 2003-05-15 - Published: 2003-11-20 - Earliest claimed: 2002-05-17 - Assignees: Hitachi, Ltd. - Inventors: Hiroshi Kageyama; Hajime Akimoto - Web page: https://patentgrep.com/patent/US20030214522A1 ## CPC - G09G 3/3233: with pixel circuitry controlling the current through the light-emitting element - G09G 3/2011: {by amplitude modulation} - G09G 3/2014: {by modulation of the duration of a single pulse during which the logic level remains constant} - G09G 3/2022: {using sub-frames} - G09G 2300/0809: Several active elements per pixel in active matrix panels - G09G 2300/0819: used for counteracting undesired variations, e.g. feedback or autozeroing - G09G 2300/0828: forming a digital to analog [D/A] conversion circuit - G09G 2300/0852: being a dynamic memory with more than one capacitor - G09G 2300/0861: with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes - G09G 2310/0262: The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes - G09G 2310/066: Waveforms comprising a gently increasing or decreasing portion, e.g. ramp - G09G 2320/0252: Improving the response speed - G09G 2320/043: Preventing or counteracting the effects of ageing - G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00) ## Abstract There is provided an image display apparatus having light emitting elements in its pixels, and capable of producing a high-resolution, multi-gray-scale-level display. In an embodiment of the present invention, each of pixel circuits is provided with a current limiting circuit for generating a specified drive current and a time modulation circuit for modulating a duration of time supplying the specified drive current to the light emitting element. In another embodiment of the present invention, each of pixel circuits is provided with a current limiting circuit for generating a specified drive current and a current generator circuit for generating a plurality of values of currents on the basis of the specified drive current. ## Claims ### Claim 1 An image display apparatus comprising a plurality of pixels disposed on a substrate, a plurality of signal lines for inputting display signals into said plurality of pixels, and a plurality of signal lines for inputting control signals into said plurality of pixels, wherein said plurality of signal lines for inputting display signals into said plurality of pixels and said plurality of signal lines for inputting control signals into said plurality of pixels are arranged in a matrix configuration, each of said plurality of pixels is provided with a light emitting element with light intensity thereof varying with a current therethrough, and a pixel circuit for driving said light emitting element, and said pixel circuit is provided with current limiting means for generating a specified drive current, and a time modulator circuit for modulating a duration of time supplying said specified drive current to said light emitting element. ### Claim 2 (depends on 1) An image display apparatus according to claim 1, wherein said time modulator circuit modulates said duration of time based upon said display signals in a form of analog voltage signals. ### Claim 3 (depends on 1) An image display apparatus according to claim 1, wherein said time modulator circuit modulates said duration of time based upon said display signals in a form of digital signals. ### Claim 4 (depends on 1) An image display apparatus according to claim 1, wherein said specified drive current is a maximum current flowing through said light emitting element. ### Claim 5 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said specified drive current is capable of being varied based upon said reference current. ### Claim 6 (depends on 1) An image display apparatus according to claim 1, wherein said pixel circuit is formed of thin film transistors. ### Claim 7 (depends on 1) An image display apparatus according to claim 1, wherein said pixel circuit is formed of thin film transistors of only one of n-channel and p-channel types. ### Claim 8 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said current limiting means generates said specified drive current on a basis of said reference current. ### Claim 9 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said current limiting means is provided with storage means for storing information on a value of said reference current. ### Claim 10 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and a plurality of lines each for supplying said reference current to said current limiting means of a corresponding one of said plurality of pixels. ### Claim 11 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said reference-current source is formed of thin film transistors fabricated on said substrate. ### Claim 12 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said reference-current source is formed by using resistors formed of one of metal lines and silicon films fabricated on said substrate. ### Claim 13 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, said current limiting means is provided with storage means for storing information on a value of said reference current, and said storage means is reset by said time modulator circuit. ### Claim 14 (depends on 1) An image display apparatus according to claim 1, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, said current limiting means is provided with storage means for storing information on a value of said reference current, said current limiting means is formed of at least one thin film transistor, said storage means is formed of a capacitor, and said capacitor stores a gate voltage of said at least one thin film transistor when said reference current flows through said at least one thin film transistor. ### Claim 15 (depends on 14) An image display apparatus according to claim 14, wherein said gate voltage stored in said capacitor is reset by said time modulator circuit, and thereby drain and source electrodes of said at least one thin film transistor are electrically disconnected from each other. ### Claim 16 (depends on 14) An image display apparatus according to claim 14, wherein said time modulator circuit is supplied with a triangular sweep voltage, and is configured to reset said gate voltage stored in said capacitor when said triangular sweep voltage becomes equal to an analog voltage signal stored in advance which is said display signal. ### Claim 17 (depends on 1) An image display apparatus according to claim 1, wherein said time modulator circuit is supplied with a triangular sweep voltage, and is formed of an inverter circuit configured to switch between supply and cutoff of a current when said triangular sweep voltage becomes equal to an analog voltage signal stored in advance which is said display signal. ### Claim 18 An image display apparatus comprising a plurality of pixels disposed on a substrate, a plurality of signal lines for inputting display signals into said plurality of pixels, and a plurality of signal lines for inputting control signals into said plurality of pixels, wherein said plurality of signal lines for inputting display signals into said plurality of pixels and said plurality of signal lines for inputting control signals into said plurality of pixels are arranged in a matrix configuration, each of said plurality of pixels is provided with a light emitting element with light intensity thereof varying with a current therethrough, and a pixel circuit for driving said light emitting element, and said pixel circuit is provided with current limiting means for generating a specified drive current, and a current generator circuit for a plurality of currents having different values on a basis of said specified drive current. ### Claim 19 (depends on 18) An image display apparatus according to claim 18, wherein values of said plurality of currents are controlled based upon said display signals in a form of analog voltage signals. ### Claim 20 (depends on 18) An image display apparatus according to claim 18, wherein values of said plurality of currents are controlled based upon said display signals in a form of digital signals. ### Claim 21 (depends on 18) An image display apparatus according to claim 18, wherein said specified drive current is a maximum current flowing through said light emitting element. ### Claim 22 (depends on 18) An image display apparatus according to claim 18, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said specified drive current is capable of being varied based upon said reference current. ### Claim 23 (depends on 18) An image display apparatus according to claim 18, wherein said pixel circuit is formed of thin film transistors. ### Claim 24 (depends on 18) An image display apparatus according to claim 18, wherein said pixel circuit is formed of thin film transistors of only one of n-channel and p-channel types. ### Claim 25 (depends on 18) An image display apparatus according to claim 18, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said current limiting means generates said specified drive current on a basis of said reference current. ### Claim 26 (depends on 18) An image display apparatus according to claim 18, wherein said image display apparatus further comprises a reference-current source disposed outside of said pixel circuit for generating a reference current, and said current limiting means is provided with storage means for storing information on a value of said reference current. ### Claim 27 (depends on 18) An image display apparatus according to claim 18, wherein said current generator circuit is formed of at least two thin film transistors, one of said at least two thin film transistors supplies a current to said light emitting element, another of said at least two thin film transistors passes a current by by-passing said light emitting element, and a ratio of a resistance between drain and source electrodes of said one of said at least two thin film transistors to that of said another of said at least two thin film transistors is varied by said display signals in a form of analog voltage signals. ### Claim 28 (depends on 18) An image display apparatus according to claim 18, wherein said current generator circuit is formed of a current mirror circuit composed of a plurality of thin film transistors having channel widths different from each other. ### Claim 29 (depends on 18) An image display apparatus according to claim 18, wherein said current generator circuit is formed of a current mirror circuit composed of a plurality of thin film transistors having different channel widths each proportional to the nth power of 2.