DISPLAY DEVICE AND METHOD OF DRIVING THE SAME

• US 20110096059A1
• Filed: 06/01/2009
• Published: 04/28/2011
• Est. Priority Date: 08/07/2008
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ohhashi, Seiji
• Granted Patent: US 8,674,914 B2
• Time in Patent Office: Days
• US Class Current: 345/212
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2310/0262 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 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• 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

Switching TFTs are controlled to a conducting state and a switching TFT to a non-conducting state, to provide a potential according to a threshold voltage to a gate terminal of a driving TFT. Then, in at least one embodiment, with the TFT maintaining the conducting state, a potential of a data line Sj is changed from a reference potential Vpc to a data potential Vdata to place the TFT in a conducting state. At this time, a current Ia flows and thus the gate terminal potential of the TFT rises. The higher the mobility of the TFT, the larger the amount of change in gate terminal potential and the smaller the current flowing through an organic EL element upon light emission. By this, a current that is not affected by variations in the threshold voltage of the TFT nor by variations in the mobility of the TFT flows through the organic EL element. Thus, in a current-driven type display device, variations in both the threshold voltage and mobility of a drive element are compensated for.

Claims

1. A current-driven type display device comprising:

a plurality of pixel circuits arranged at respective intersections of a plurality of scanning lines and a plurality of data lines; and

a drive circuit that selects a write-target pixel circuit using the corresponding scanning line, and provides a data potential according to display data to the corresponding data line, wherein

each of the pixel circuits includes;

an electro-optic element provided between a first power supply wiring line and a second power supply wiring line;

a drive element provided in series with the electro-optic element and between the first power supply wiring line and the second power supply wiring line;

a compensation capacitor having a first electrode connected to a control terminal of the drive element; and

a compensation switching element provided between the control terminal and one current input/output terminal of the drive element, and

for the write-target pixel circuit, the drive circuit controls the compensation switching element to a conducting state to provide a potential according to a threshold voltage to the control terminal of the drive element, and thereafter switches a potential provided to a second electrode of the compensation capacitor to another with the compensation switching element maintaining the conducting state, to provide a write potential according to the display data and the threshold voltage to the control terminal of the drive element.

2. The display device according to claim 1, wherein each of the pixel circuits further includes:

a writing switching element provided between the second electrode of the compensation capacitor and the corresponding data line;

an interruption switching element provided between the drive element and the electro-optic element; and

a holding capacitor provided between the control terminal and the other current input/output terminal of the drive element.

3. The display device according to claim 2, wherein for the write-target pixel circuit, the drive circuit controls the writing switching element and the compensation switching element to a conducting state and controls the interruption switching element to a non-conducting state while providing a predetermined reference potential to the data line, and thereafter switches a potential provided to the data line to the data potential with states of the respective switching elements being maintained.

4. The display device according to claim 1, wherein each of the pixel circuits further includes:

an interruption switching element provided between the one current input/output terminal of the drive element and the first power supply wiring line; and

a writing switching element provided between the other current input/output terminal of the drive element and the corresponding data line, wherein

the second electrode of the compensation capacitor is connected to a control wiring line to which the drive circuit provides a potential.

5. The display device according to claim 4, wherein for the write-target pixel circuit, the drive circuit controls the writing switching element and the compensation switching element to a conducting state and controls the interruption switching element to a non-conducting state while providing the data potential to the data line, and thereafter switches the potential provided to the control wiring line to another with states of the respective switching elements being maintained, to provide the write potential to the control terminal of the drive element.

6. The display device according to claim 5, wherein after the drive circuit switches the potential provided to the control wiring line to another to provide the write potential to the control terminal of the drive element, the drive circuit switches the potential provided to the data line to a reference potential which is closer to the potential at the control terminal of the drive element than the data potential.

7. The display device according to claim 5, wherein for the write-target pixel circuit, the drive circuit provides, to the data line, a potential determined by the display data and an amount of change in potential provided to the control wiring line, while the writing switching element is controlled to the conducting state.

8. The display device according to claim 5, wherein for the write-target pixel circuit, the drive circuit provides, to the data line, a potential at which a voltage applied to the electro-optic element is lower than or equal to a light-emission threshold voltage, while the writing switching element is controlled to the conducting state.

9. The display device according to claim 1, wherein each of the pixel circuits further includes:

a writing switching element provided between the second electrode of the compensation capacitor and the corresponding data line;

an interruption switching element provided between the drive element and the electro-optic element;

a first initialization switching element provided between the second electrode of the compensation capacitor and a third power supply wiring line; and

a second initialization switching element provided between the one current input/output terminal of the drive element and the third power supply wiring line.

10. The display device according to claim 9, wherein for the write-target pixel circuit, the drive circuit controls the writing switching element, the compensation switching element, and the second initialization switching element to a conducting state and controls the interruption switching element and the first initialization switching element to a non-conducting state while providing the data potential to the data line, and thereafter controls the writing switching element to a non-conducting state and controls the first initialization switching element to a conducting state with the compensation switching element maintaining the conducting state.

11. A method of driving a current-driven type display device including a plurality of pixel circuits arranged at respective intersections of a plurality of scanning lines and a plurality of data lines, the method comprising:

when each of the pixel circuits includes an electro-optic element provided between a first power supply wiring line and a second power supply wiring line;

a drive element provided in series with the electro-optic element and between the first power supply wiring line and the second power supply wiring line;

a compensation capacitor having a first electrode connected to a control terminal of the drive element; and

a compensation switching element provided between the control terminal and one current input/output terminal of the drive element,

a selecting step of selecting a write-target pixel circuit using the corresponding scanning line;

a threshold state setting step of controlling, for the write-target pixel circuit, the compensation switching element to a conducting state to provide a potential according to a threshold voltage to the control terminal of the drive element; and

a conducting state setting step of switching, for the write-target pixel circuit, after the threshold state setting step, a potential provided to a second electrode of the compensation capacitor to another with the compensation switching element maintaining the conducting state, to provide a write potential according to display data and the threshold voltage to the control terminal of the drive element.

12. The drive method according to claim 11, wherein when each of the pixel circuits further includes:

a writing switching element provided between the second electrode of the compensation capacitor and the corresponding data line;

an interruption switching element provided between the drive element and the electro-optic element; and

a holding capacitor provided between the control terminal and the other current input/output terminal of the drive element,

in the threshold state setting step, for the write-target pixel circuit, the writing switching element and the compensation switching element are controlled to a conducting state and the interruption switching element is controlled to a non-conducting state while a predetermined reference potential is provided to the corresponding data line, and

in the conducting state setting step, the potential provided to the data line is switched to a data potential according to the display data, with states of the respective switching elements being maintained.

13. The drive method according to claim 11, wherein when each of the pixel circuits further includes:

an interruption switching element provided between the one current input/output terminal of the drive element and the first power supply wiring line; and

a writing switching element provided between the other current input/output terminal of the drive element and the corresponding data line, and the second electrode of the compensation capacitor is connected to a control wiring line,

in the threshold state setting step, for the write-target pixel circuit, the writing switching element and the compensation switching element are controlled to a conducting state and the interruption switching element is controlled to a non-conducting state while a data potential according to the display data is provided to the corresponding data line, and

in the conducting state setting step, a potential provided to the control wiring line is switched to another with states of the respective switching elements being maintained, to provide the write potential to the control terminal of the drive element.

14. The drive method according to claim 11, wherein when each of the pixel circuits further includes:

a writing switching element provided between the second electrode of the compensation capacitor and the corresponding data line;

an interruption switching element provided between the drive element and the electro-optic element;

a first initialization switching element provided between the second electrode of the compensation capacitor and a third power supply wiring line; and

a second initialization switching element provided between the one current input/output terminal of the drive element and the third power supply wiring line,

in the threshold state setting step, for the write-target pixel circuit, the writing switching element, the compensation switching element, and the second initialization switching element are controlled to a conducting state and the interruption switching element and the first initialization switching element are controlled to a non-conducting state while a data potential according to the display data is provided to the corresponding data line, and

in the conducting state setting step, the writing switching element is controlled to a non-conducting state and the first initialization switching element is controlled to a conducting state, with the compensation switching element maintaining the conducting state.