Active matrix display

• US 6,693,388 B2
• Filed: 07/22/2002
• Issued: 02/17/2004
• Est. Priority Date: 07/27/2001
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Oomura, Masanobu
• Primary Examiner(s): Nguyen, Hoang
• Application Number:
  US10/199,075
• Publication Number:
  US 20030020413A1
• Time in Patent Office: 575 Days
• Field of Search: 315/169.1, 315/169.3, 315/169.4, 315/224, 315/291, 345/76, 345/77, 345/82
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0895 having more than one selection line for a two-terminal active matrix LCD, e.g. Lechner and D2R circuits
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

An active matrix display is provided which eliminates variation of a threshold voltage of an active element inside a pixel and variation of a driving current due to the Early effect and supplies a desired driving current to a light emitting element of each pixel steadily and accurately. The active matrix display has a current-voltage converter arranged in series in a supply path through which a driving current is supplied to a light emitting element and has a voltage control current source that is controlled by an output voltage of the current-voltage converter, thereby generating a monitor current having correlation with the driving current at the time of setting the driving current, controlling a gate voltage of a driving current generating transistor based on the monitor current such that a desired luminance can be realized and holding the control voltage in a capacitor.

Claims

1. An active matrix display in which a plurality of pixels provided with a pixel circuit containing at least a light emitting element are arranged in a matrix shape and which has at least a scanning side drive circuit and a data side drive circuit for performing control of said pixel circuit,

wherein said light emitting element is a light emitting element of a current control type, luminance of which changes according to a driving current flowing to the light emitting element,

wherein said pixel circuit comprises at least said light emitting element, a first voltage control current source, a first switch circuit, a driving current-voltage converter, a second voltage control current source and a second switch circuit,

said first voltage control current source comprising at least an active element controlled by a control voltage and a memory circuit capable of storing said control voltage and having a function of generating said driving current based on said control voltage,

said first switch circuit having a function of switching said first voltage control current source to a voltage controllable state and a control voltage holding state,

said driving current-voltage converter being serially connected to a current path through which said driving current flows and having a function of converting said driving current into a voltage,

said second voltage control current source having a function of generating a monitor current correlating with said driving current based on an output voltage of said driving current-voltage converter, and

said second switch circuit having a function of switching said second voltage control current source to an output state and a non-output state,

wherein said scanning side drive circuit is at least connected to said first switch circuit and said second switch circuit and has a function of performing control for switching said first voltage control current source to the voltage controllable state or the control voltage holding state and control for switching said second voltage control current source to the output state or the non-output state, and

wherein said data side drive circuit is at least connected to said first voltage control current source via said first switch circuit and connected to said second voltage control current source via said second switch circuit and has a function of controlling a control voltage of said first voltage control current source based on said monitor current correlating with said driving current such that a current value of said driving current becomes a desired current value corresponding to luminance information when said first voltage control current source is in the voltage controllable state and said second voltage control current source is in the output state.

2. An active matrix display according to claim 1,

wherein said light emitting element, said first voltage control current source and said driving current-voltage converter are connected between a power supply potential and a ground potential in the order of said first voltage control current source, said light emitting element and said driving current-voltage converter or in the order of said driving current-voltage converter, said light emitting element and said first voltage control current source.

3. An active matrix display according to claim 1,

wherein said light emitting element, said first voltage control current source and said driving current-voltage converter are connected between a power supply potential and a ground potential in the order of said driving current-voltage converter, said first voltage control current source and said light emitting element or in the order of said light emitting element, said first voltage control current source and said driving current-voltage converter.

4. An active matrix display according to claim 1,

wherein said memory circuit of said first voltage control current source includes a capacitor, and said active element of said first voltage control current source, said second voltage control current source, said driving current-voltage converter, said first switch circuit and said second switch circuit are constructed by insulated-gate field-effect transistors.

5. An active matrix display according to claim 4,

wherein said insulated-gate field-effect transistor is a thin film transistor.

6. An active matrix display according to claim 1,

wherein said memory circuit of said first voltage control current source includes a capacitor, said active element of said first voltage control current source, said second voltage control current source, said driving current-voltage converter, said first switch circuit and said second switch circuit are constructed by insulated-gate field-effect transistors, and said insulated-gate field-effect transistor is a thin film transistor, and

wherein said active element constituting said first voltage control current source includes a capacitor for causing a contact layer on a power supply side and a gate electrode to overlap each other to store a voltage.

7. An active matrix display according to claim 1,

wherein said data side drive circuit includes at least a reference current source having luminance information, a reference voltage source and a voltage comparator for inputting an output end voltage of said reference current source having luminance information and a voltage of said reference voltage source, and has a function of inputting said monitor current in an output end of said reference current source having luminance information and controlling a control voltage of said first voltage control current source by said voltage comparator such that a current value of said monitor current and an output current value of said reference current source having luminance information become equal when said first voltage control current source is in the voltage controllable state and said second voltage control current source is in the output state.

8. An active matrix display according to claim 1,

wherein said data side drive circuit includes at least a reference voltage source having luminance information, a monitor current-voltage converter for converting said monitor current into a voltage and a voltage comparator with a voltage of said reference voltage source having luminance information and an output voltage of said monitor current-voltage converter as inputs, and has a function of controlling a control voltage of said first voltage control current source by said voltage comparator such that a voltage of said reference voltage source having luminance information and an output voltage of said monitor current-voltage converter become equal when said first voltage control current source is in the voltage controllable state and said second voltage control current source is in the output state.

9. An active matrix display according to claim 1,

wherein said data side drive circuit includes at least a reference voltage source, a monitor current-voltage converter for converting said monitor current into a voltage and a voltage comparator with a voltage of said reference voltage source and an output voltage of said monitor current-voltage converter as inputs, a conversion gain of said monitor current-voltage converter changing according to luminance information, and

wherein said data side drive circuit has a function of controlling a control voltage of said first voltage control current source by said voltage comparator such that a voltage of said reference voltage source and an output voltage of said monitor current-voltage converter become equal when said first voltage control current source is in the voltage controllable state and said second voltage control current source is in the output state.

10. An active matrix display according to claim 1,

wherein said data side drive circuit includes at least a monitor current-voltage converter for converting said monitor current into a voltage, a reference current source having luminance information, a reference current-voltage converter for converting an output current of said reference current source having luminance information into a voltage and a voltage comparator with an output voltage of said monitor current-voltage converter and an output voltage of said reference current-voltage converter as inputs, and has a function of controlling a control voltage of said first voltage control current source by said voltage comparator such that an output voltage of said monitor current-voltage converter and an output voltage of said reference current-voltage converter become equal when said first voltage control current source is in the voltage controllable state and said second voltage control current source is in the output state.

11. An active matrix display according to claim 1,

said driving current-voltage converter and said second voltage control current source have a current mirror structure.