Image display apparatus controlling brightness of current-controlled light emitting element

• US 20040252089A1
• Filed: 05/13/2004
• Published: 12/16/2004
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: Kyocera Corporation
• Inventors: Ono, Shinya, Kobayashi, Yoshinao, Tsujimura, Takatoshi
• Granted Patent: US 7,259,737 B2
• Time in Patent Office: Days
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: 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
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a 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

An image display apparatus according to the present invention includes a data line that supplies a voltage determined based on emission brightness, a first switching unit that controls writing of the voltage supplied from the data line, a driver element that controls a current flowing through a current-controlled light emitting element, an organic electro-luminescence element that emits light of brightness corresponding to current applied, a reference-voltage writing unit that supplies a predetermined reference voltage, and a threshold-voltage detecting unit that detects a threshold voltage of the driver element.

Claims

1. An image display apparatus comprising a display pixel, wherein the display pixel includes

a current-controlled light emitting element that emits light of brightness corresponding to current applied;

a driver element that includes a thin film transistor, and controls the current flowing through the current-controlled light emitting element;

a data line that supplies a voltage determined based on emission brightness;

a first switching unit that controls writing of the voltage supplied from the data line;

a first capacitor having a first electrode electrically connected to a gate electrode of the driver element, to hold a gate voltage of the driver element;

a reference-voltage writing unit that includes

a supply source provided separately from the data line for supplying a predetermined reference voltage to a second electrode of the first capacitor; and

a second switching unit that controls electrical conduction between the supply source and the second electrode of the first capacitor; and

a threshold-voltage detecting unit that detects a threshold voltage of the driver element, including

a third switching unit that controls electrical conduction between the gate electrode and a drain electrode of the driver element; and

a capacitance for supplying charges to the drain electrode of the driver element.

2. The image display apparatus according to claim 1, wherein the threshold-voltage detecting unit detects the threshold voltage of the driver element based on a mechanism that

the third switching unit is set to ON while the reference voltage is supplied to the second electrode of the first capacitor,

the driver element is set to ON based on a gate-source voltage generated by electric charges accumulated in the capacitance,

the gate-source voltage is dropped to the threshold voltage due to a decrease in the electric charges in the capacitance resulting from current flowing between a drain and a source of the driver element, and

the driver element is set to OFF.

3. The image display apparatus according to claim 1, wherein the data line supplies the voltage determined based on emission brightness to the first capacitor, after the threshold-voltage detecting unit detects the threshold voltage.

4. The image display apparatus according to claim 1, further comprising a second capacitor having an electrode electrically connected to the first electrode of the first capacitor and the gate electrode of the driver element.

5. The image display apparatus according to claim 1, wherein the supply source has both functions of a current supply source for the current-controlled light emitting element and a charge supply source for the capacitance.

6. The image display apparatus according to claim 1, wherein the current-controlled light emitting element and the capacitance are formed by a single organic electro-luminescence element.

7. The image display apparatus according to claim 1, further comprising a scan line that controls driven states of the second switching unit and the third switching unit.

8. An image display apparatus of an interlace system comprising a display pixel, wherein the display pixel includes

a current-controlled light emitting element that emits light of brightness corresponding to current applied;

a driver element that includes a thin film transistor, and controls the current flowing through the current-controlled light emitting element;

a reference-voltage writing unit that writes the reference voltage in the first capacitor, including

a first capacitor that holds a gate-source voltage of the thin film transistor;

a data line that supplies a voltage determined based on emission brightness and a predetermined reference voltage alternately; and

a first switching unit that controls electrical conduction between the data line and the first capacitor; and

a threshold-voltage detecting unit that detects a threshold voltage of the driver element, including

a second switching unit that controls electrical conduction between a gate electrode and a drain electrode of the driver element; and

a capacitance that is formed by the current-controlled light emitting element, and supplies electric charges accumulated to the drain electrode of the driver element.

9. The image display apparatus according to claim 8, wherein the threshold-voltage detecting unit detects the threshold voltage of the driver element based on a mechanism that

the driver element is set to the ON state based on a gate-source voltage generated by the electric charges accumulated in the capacitance when the reference voltage is supplied from the data line to the first capacitor,

the gate-source voltage drops to the threshold voltage due to a decrease in the electric charges resulting from current flowing between a drain and a source of the driver element, and

the driver element is set to OFF.

10. The image display apparatus according to claim 8, further comprising a second capacitor arranged between the first capacitor and the driver element.

11. The image display apparatus according to claim 8, further comprising a power line that applies a voltage in a forward direction to the current-controlled light emitting element to supply the current, and applies a voltage in a reverse direction to the current-controlled light emitting element so that the electric charges are accumulated in the capacitance.

12. The image display apparatus according to claim 11, wherein the power line is electrically connected to the current-controlled light emitting element in an nth display pixel and the current-controlled light emitting element in an mth display pixel, where n and m are different positive integer, and supplies a voltage in same direction simultaneously to the nth current-controlled light emitting element and the mth current-controlled light emitting element.

13. The image display apparatus according to claim 8, further comprising:

a first scan line for controlling a driven state of the first switching unit; and

a second scan line for controlling a driven state of the second switching unit.

14. The image display apparatus according to claim 8, further comprising a third scan line for controlling driven states of the first switching unit in an nth stage and the second switching unit in an mth stage.

15. The image display apparatus according to claim 11, wherein the power line is electrically connected to the current-controlled light emitting element in an nth display pixel and the current-controlled light emitting element in an mth display pixel, where n and m are different positive integer, and supplies a voltage in a forward direction to one of the current-controlled light emitting element in an nth display pixel and the current-controlled light emitting element in an mth display pixel to emit the light, while supplying a voltage in a reverse direction to other current-controlled light emitting element so that the electric charges are accumulated in the other current-controlled light emitting element.