Organic EL drive circuit and organic EL display device using the same organic EL drive circuit

• US 7,515,124 B2
• Filed: 05/23/2005
• Issued: 04/07/2009
• Est. Priority Date: 05/24/2004
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Kobayashi, Masato, Yaguma, Hiroshi
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): Nguyen; Jennifer T
• Application Number:
  US11/134,312
• Publication Number:
  US 20050270256A1
• Time in Patent Office: 1,415 Days
• Field of Search: 345/36, 345 44- 46, 345 76- 83, 345/105
• US Class Current: 345/76
• 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 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

An amplifier circuit for generating a predetermined constant voltage required for resetting organic EL elements or capacitors is provided and an operating current switching circuit switches the operating current of the amplifier circuit to an idling current in a display period and to a steady operation current required to performing a reset operation in a reset period, so that a shifting time of the amplifier circuit from the idling state to the steady operation state can be shortened and a constant control voltage for resetting the organic EL elements or the capacitors can be generated in an initial portion of the reset period.

Claims

1. An organic EL drive circuit for resetting organic EL elements or capacitors of pixel circuits of an organic EL display panel through terminal pins of said organic EL display panel in a reset period of a timing control signal having a predetermined frequency, for dividing a display period corresponding to a scan period of one horizontal line and the reset period corresponding to a retrace period of the horizontal scan, comprising:

an amplifier circuit for generating a predetermined constant voltage for resetting said organic EL elements or capacitors;

a reset switch provided between an output terminal of said amplifier circuit and one of said terminal pins and ON/OFF operated by one signal of the timing control signal, a reset control signal similar to the timing control signal, a reset pulse and another pulse generated in the reset period in synchronism with one of these signals or the reset pulse; and

an operating current switching circuit setting in response to the one signal an operating current of said amplifier circuit to an idling state current in the display period and a reset current required for a reset operation in the reset period or a period in which either the reset pulse or the another pulse is generated.

2. The organic EL drive circuit as claimed in claim 1, wherein said operating current switching circuit includes a constant current circuit for generating the operating current, the current of said constant current circuit being switched between the idling state and a steady operation state, according to the one signal.

3. The organic EL drive circuit as claimed in claim 2, wherein the one signal is changed in level from LOW through HIGH to LOW or from HIGH through LOW to HIGH, and said operating current switching circuit selects one of an idling state current and a steady operation state current with a timing of level change of the one signal from HIGH to LOW or a timing before the level change and the another state with a timing of level change from LOW to HIGH or before the level change.

4. The organic EL drive circuit as claimed in claim 3, wherein said organic EL display panel has a number of said terminal pins, said amplifier circuit is an operational amplifier having an operating current determined by the current of said constant current circuit, a plurality of said reset switches are provided correspondingly to at least a plurality of said terminal pins of the number of said terminal pins, respectively, and a plurality of said reset switches are turned ON simultaneously.

5. The organic EL drive circuit as claimed in claim 4, wherein each said reset switch is provided between said output terminal and each said terminal pin, said constant current circuit includes a current mirror circuit having a plurality of output side transistors as an operating current source of said operational amplifier and a switch circuit provided correspondingly to at least one of the plurality of said output side transistors, and the operating current of said operational amplifier is switched to one of the idling current and the steady operation state current correspondingly to an ON/OFF operation of said switch circuit according to the one signal.

6. The organic EL drive circuit as claimed in claim 5, wherein the one signal is a precharge pulse, one of the plurality of said output side transistors of said current mirror circuit has an operating current ratio 1:

N with respect to an input side transistor of said current mirror circuit, where N is 1 or larger, and said switch circuit is connected in series with said one output side transistor and turned ON together with said reset switch according to the precharge pulse.

7. The organic EL drive circuit as claimed in claim 6, further comprising a first D/A converter circuit and a second D/A converter circuit, wherein said first D/A converter circuit, said operational amplifier and said operating current switching circuit constitute a reset voltage generator circuit, said operational amplifier is supplied with a voltage converted by said first D/A converter circuit as an input voltage, said reset voltage generator circuit generates the predetermined constant voltage as a reset voltage for resetting said organic EL elements or said capacitors of said pixel circuits and said second D/A converter circuit is connected to said terminal pins and outputs drive currents to said organic EL elements or said capacitors of said pixel circuits by D/A converting a display data.

8. The organic EL drive circuit as claimed in claim 7, wherein said organic EL display panel is of the active matrix type and said reset voltage generator circuit resets voltages of said capacitors of said pixel circuits.

9. The organic EL drive circuit as claimed in claim 5, wherein the one signal is a precharge pulse, one of the plurality of said output side transistors of said current mirror circuit has an operating current ratio 1:

1/N with respect to an input side transistor of said current mirror circuit, where N is 1 or larger, another of said output side transistors has an operating current ratio 1;

1 with respect to said input side transistor, and said switch circuit is connected in series with said another output side transistor of said current mirror circuit and turned ON together with said reset switch according to the precharge pulse.

10. The organic EL drive circuit as claimed in claim 7, wherein said organic EL display panel is of the passive matrix type and said reset voltage generator circuit resets terminal voltages of said organic EL elements.

11. An organic EL display device including an organic EL drive circuit for resetting organic EL elements or capacitors of pixel circuits of an organic EL display panel through terminal pins of said organic EL display panel in a reset period of a timing control signal having a predetermined frequency, for dividing a display period corresponding to a scan period of one horizontal line and the rest period corresponding to a retrace period of the horizontal scan, said organic EL drive circuit comprising:

an amplifier circuit for generating a predetermined constant voltage for resetting said organic EL elements or capacitors;

a reset switch provided between an output terminal of said amplifier circuit and one of said terminal pins and ON/OFF operated by one signal of the timing control signal, a reset control signal similar to the timing control signal, a reset pulse and another pulse generated in the reset period in synchronism with one of these signals or the reset pulse; and

an operating current switching circuit setting in response to the one signal an operating current of said amplifier circuit to an idling state current in the display period and a reset current required for a reset operation in the reset period or a period in which either the reset pulse or the another pulse is generated.

12. The organic EL display device as claimed in claim 11, wherein said operating current switching circuit includes a constant current circuit for generating the operating current, the current of said constant current circuit being switched between the idling state and a steady operation state, according to the one signal.

13. The organic EL display device as claimed in claim 12, wherein the one signal is changed in level from LOW through HIGH to LOW or from HIGH through LOW to HIGH, and said operating current switching circuit selects one of an idling state current and a steady operation state current with a timing of level change of the one signal from HIGH to LOW or a timing before the level change and the another state with a timing of level change from LOW to HIGH or before the level change.

14. The organic EL drive circuit as claimed in claim 13, wherein said organic EL display panel has a number of said terminal pins, said amplifier circuit is an operational amplifier having an operating current determined by the current of said constant current circuit, a plurality of said reset switches are provided correspondingly to at least a plurality of said terminal pins of the number of said terminal pins, respectively, and a plurality of said reset switches are turned ON simultaneously.