Image display apparatus using current-controlled light emitting element

• US 20040239596A1
• Filed: 02/18/2004
• Published: 12/02/2004
• Est. Priority Date: 02/19/2003
• Status: Active Grant

• Current Assignee: InnoLux Corporation
• Original Assignee: Chi Mei Optoelectronics (InnoLux Corporation), Kyocera Corporation
• Inventors: Ono, Shinya, Kobayashi, Yoshinao
• Granted Patent: US 7,358,941 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A pixel circuit includes a driver element that is supplied with a potential from a data line. The driver element controls a value of current passing through an electric light emitting element. Upon obtaining a threshold voltage, a conductive member connected to the electric light emitting element is made to be a floating state to cause the driver element to become on-state, variations in the potential of the conductive member caused by charges passing through the driver element to flow into the conductive member are detected by a threshold voltage detector to obtain the threshold voltage of the driver element.

Claims

1. An image display apparatus comprising:

a current-controlled light emitting element that emits light with a brightness corresponding to a current flowing in the current-controlled light emitting element;

a current source that supplies the current to the current-controlled light emitting element;

a driver element that includes at least first and second terminals and controls the current flowing into the electric light emitting element from the current source based on a potential difference applied between the terminals;

a data line that supplies a potential to the first terminal;

a conductive member that is electrically connected to the second terminal; and

a threshold voltage obtaining unit that obtains a threshold voltage of the driver element based on the potential of the conductive member corresponding to an amount of charges supplied from the current source to the second terminal.

2. The image display apparatus according to claim 1, wherein

the driver element becomes on-state by applying a potential higher than an estimated threshold voltage, between the first terminal and the second terminal upon starting to obtain the threshold voltage, and

the conductive member whose potential rises by accumulating charges supplied from the current source through the driver element and the current-controlled light emitting element after the driver element becomes on-state.

3. The image display apparatus according to claim 1, wherein

the driver element becomes off-state caused by rising of the potential of the conductive member up to a predetermined potential after the driver element becomes on-state, and

the threshold voltage obtaining unit obtains a threshold voltage based on the potential of the conductive member after the driver element becomes off-state.

4. The image display apparatus according to claim 1, wherein

the threshold voltage obtaining unit obtains a threshold voltage based on potentials of the conductive member at two or more different times after the driver element becomes on-state and before the driver element becomes off-state caused by rising of the potential of the conductive member up to a predetermined potential.

5. The image display apparatus according to claim 4, wherein

the threshold voltage obtaining unit obtains a threshold voltage using a total sum of a capacitance of the second terminal and a capacitance of a capacitor connected to the conductive member and a potential applied to the first terminal, as parameters.

6. The image display apparatus according to claim 4, wherein

the threshold voltage obtaining unit obtains the threshold voltage, and obtains a mobility in a current passage portion of the driver element and a coefficient according to a shape of the current passage portion.

7. The image display apparatus according to claim 1, further comprising:

a database in which potentials of the conductive member and threshold voltages of the driver element are associated with each other, wherein the threshold voltage obtaining unit obtains a threshold voltage by referring to the database based on the potentials of the conductive member at one or more times after the driver element becomes on-state.

8. The image display apparatus according to claim 1, wherein a potential is supplied to the first terminal upon displaying an image so that a voltage between the first terminal and the second terminal becomes a sum of the threshold voltage obtained by the threshold voltage obtaining unit and a data voltage corresponding to a display image.

9. The image display apparatus according to claim 6, wherein

the data line supplies a potential to the first terminal so that a voltage between the first terminal and the second terminal becomes a potential obtained by multiplying a sum of the threshold voltage obtained by the threshold voltage obtaining unit and a data voltage corresponding to a display image, by a value determined based on the mobility in the current passage portion of the driver element and the coefficient according to the shape of the current passage portion.

10. The image display apparatus according to claim 1, further comprising:

a constant potential supply unit that supplies a substantially constant potential upon displaying an image; and

a switching unit that establishes a connection between the constant potential supply unit and the conductive member upon displaying the image, and isolates the constant potential supply unit from the conductive member upon obtaining the threshold voltage.

11. The image display apparatus according to claim 1, wherein

the driver element is a thin film transistor which includes a gate electrode, a source electrode, and a drain electrode,

the first terminal corresponds to the gate electrode, and the second terminal corresponds to the source electrode.

12. The image display apparatus according to claim 1, wherein the current-controlled light emitting element is an organic electro-luminescence element.