ORGANIC EL DISPLAY APPARATUS AND DRIVING METHOD THEREFOR

• US 20070229428A1
• Filed: 03/30/2007
• Published: 10/04/2007
• Est. Priority Date: 03/31/2006
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kawasaki, Somei, Nakagawa, Katsumi, Iseki, Masami, Inaba, Yutaka
• Granted Patent: US 7,616,179 B2
• Time in Patent Office: Days
• US Class Current: 345/92
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• 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 2310/0262 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
• 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 organic EL display apparatus has a driving circuit. In the driving circuit, the source and drain of a driving transistor and the anode and cathode of an organic EL device are connected in series between voltage sources. A current passes between the source and drain of the driving transistor and between the anode and cathode of the organic EL device in accordance with a voltage between the gate and source of the driving transistor. Consequently, the organic EL device emits light. In order to store the voltage in the capacitor, a constant voltage source is connected to the gate of the driving transistor and the above-described series connection is disconnected at the source of the driving transistor and connected to a signal source. Then, a current signal output from the signal source passes between the source and drain of the driving transistor, and charges are stored in a capacitor in accordance with the current signal.

Claims

1. A driving method of an organic EL device in which, when the organic EL device emits light, a source and a drain of a driving transistor and an anode and a cathode of the organic EL device are connected in series between first and second constant voltage sources and a current flows between the anode and the cathode of the organic EL device in accordance with a gate-to-source voltage of the driving transistor, the gate-to-source voltage of the driving transistor being set in the following steps:

(1) disconnecting the series connection of the driving transistor and the organic EL device at the source of the driving transistor;

(2) connecting a third constant voltage source maintaining a potential different from a potential of each of the first and second constant voltage sources to a gate of the driving transistor;

(3) connecting the source of the driving transistor to a signal current source and passing a signal current between the source and the drain of the driving transistor to generate a voltage between the gate and the source of the driving transistor in a capacitor disposed between the gate and the source of the driving transistor;

(4) disconnecting the gate of the driving transistor from the third constant voltage source;

(5) disconnecting the source of the driving transistor from the signal current source; and

(6) reconnecting the source of the driving transistor to recover the series connection of the driving transistor and the organic EL device.

2. The driving method according to claim 1, wherein the series connection is established by connecting the drain of the driving transistor to the anode or cathode of the organic EL device.

3. The driving method according to claim 2,

wherein a potential of the third constant voltage source is set to a value closer to a potential of the second constant voltage source on the basis of a potential of the first constant voltage source, and

wherein, a voltage between the third and first constant voltage sources is equal to or larger than a sum of an anode-to-cathode voltage of the organic EL device and a gate-to-source voltage of the driving transistor, the voltages being obtained in the step (3) when the signal current is a signal current that minimizes luminance of an organic EL display apparatus, and is equal to or smaller than a sum of an anode-to-cathode voltage of the organic EL device and a gate-to-source voltage of the driving transistor, the voltages being obtained in the step (3) when the signal current is a signal current that maximizes luminance of the organic EL display apparatus.

4. The driving method according to claim 2, wherein a voltage between the first and second constant voltage sources is equal to or larger than a sum of a source-to-drain voltage of the driving transistor and an anode-to-cathode voltage of the organic EL device, the voltages being obtained in the step (3) when the signal current is a signal current that maximizes luminance of the organic EL display apparatus, and is smaller than a sum of a source-to-drain voltage of the driving transistor, an anode-to-cathode voltage of the organic EL device, and a threshold voltage of the driving transistor, the voltages being obtained in the step (3) when the signal current is a signal current that maximizes luminance of the organic EL display apparatus.

5. The driving method according to claim 1, wherein the series connection is established by connecting the source of the driving transistor to the anode or cathode of the organic EL device.

6. The driving method according to claim 5, wherein a potential of the third constant voltage source is equal to or larger than a sum of a gate-to-source voltage of the driving transistor and an anode-to-cathode voltage of the organic EL device, the voltages being obtained when the signal current is a signal current that minimizes luminance to be used at the time of display, and is equal to or smaller than a sum of a gate-to-source voltage of the driving transistor and an anode-to-cathode voltage of the organic EL device, the voltages being obtained when the signal current is a signal current that maximizes luminance to be used at the time of display.

7. The driving method according to claim 5, wherein a potential of the third constant voltage source is a sum of a gate-to-source voltage of the driving transistor and an anode-to-cathode voltage of the organic EL device, the voltages being obtained when the signal current is a signal current that sets luminance to be used at the time of display to average luminance.

8. The driving method according to claim 1, wherein the steps (4) and (5) are simultaneously performed.

9. The driving method according to claim 1, wherein the step (4) follows the step (5) after a predetermined time delay.

10. An organic EL display apparatus, comprising:

an organic EL device having two terminals, an anode and a cathode;

a driving transistor having three terminals, a gate, a source, and a drain;

a capacitor disposed between the gate and the source of the driving transistor;

first, second, and third constant voltage sources each maintaining a constant voltage;

a signal current source providing a signal current;

a first switch disposed between the gate of the driving transistor and the third constant voltage source;

a second switch disposed between the source of the driving transistor and the signal current source;

a third switch disposed between the source of the driving transistor and the second constant voltage source; and

opening and closing control means for controlling opening and closing of the first to third switches.

11. The organic EL display apparatus according to claim 10,

wherein the first to third switches are each configured with a respective TFT, channel conductivity types of the TFTs of the first and second switches being the same, and a channel conductivity type of the TFT of the third switch being different from that of the TFTs of the first and second switches, and

wherein the opening and closing control means is a control line connected to gates of the TFTs of the first to third switches.

12. The organic EL display apparatus according to claim 10,

wherein the first to third switches are each configured with a respective TFT, channel conductivity types of the TFTs of the second and third switches being different, and

wherein the opening and closing control means includes a first control line connected to gates of the TFTs of the second and third switches, and a second control line connected to a gate of the TFT of the first switch.

13. The organic EL display apparatus according to claim 11,

wherein the first to third switches are each configured with a TFT having the same channel conductivity types as a conductivity type of the driving transistor, and

wherein the opening and closing control means includes a first control line connected to gates of the TFTs of the first and second switches, and a second control line connected to a gate of the TFT of the third switch.

14. The organic EL display apparatus according to claim 11, wherein TFTs of the first to third switches and the driving transistor are made of amorphous silicon.

15. The organic EL display apparatus according to claim 11, wherein TFTs of the first to third switches and the driving transistor are made of metal oxide semiconductor.