DISPLAY DEVICE AND DRIVING METHOD FOR DISPLAY DEVICE

• US 20080180365A1
• Filed: 03/26/2008
• Published: 07/31/2008
• Est. Priority Date: 09/27/2005
• Status: Abandoned Application

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: OZAKI, Tsuyoshi
• Application Number:
  US12/056,161
• Publication Number:
  US 20080180365A1
• 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 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2320/0295 by monitoring each display 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 display driving device includes a gradation voltage generating section which generates gradation voltage corresponding to display data, a constant current circuit section which supplies a predetermined constant current to a display pixel, a voltage detecting section which detects a voltage of a data line at the time of supplying the constant current as a detected voltage, and a voltage adding section which adds and subtracts the gradation voltage, a reference voltage corresponding to the detected voltage and an intrinsic voltage determined based on a design parameter of a driving transistor provided to the display pixel (driving circuit) so as to generate a pixel data voltage Vpix (=Vref−Vref0+Vdata), and supplies the pixel data voltage as a gradation signal to the data line.

Claims

1. A display device which displays image information corresponding to display data, comprising:

a display panel where a plurality of display pixels, each having a current-controlled light emitting element and a driving circuit for supplying a driving current to the light emitting element are arranged at intersecting points between a plurality of selection lines and data lines disposed in a column direction and a row direction, respectively;

a selection driving section which applies a selection signal to the display pixels on the lines on the display panel so as to set the display pixels into a selected state; and

a data driving section which generates a gradation signal corresponding to the display data so as to apply the gradation signal to the display pixels on the selection lines set into the selected state,

wherein the data driving section includes at least;

a constant current supplying section which supplies a constant current to the data lines; and

a voltage detecting section which detects voltages of the data lines at the time when the constant current is supplied to the driving circuits of the display pixels set into the selected state via the data lines.

2. The display device according to claim 1, wherein the data driving section further includes a gradation signal generating section which corrects a gradation voltage having a value corresponding to the display data based on the voltages of the data lines detected by the voltage detecting section so as to generate the gradation signal.

3. The display device according to claim 2, wherein the driving circuits have a driving element which includes a control terminal and an electric current path to which an electric current corresponding to a voltage value of the control terminal is applied and whose one terminal is electrically connected to the data lines and the light emitting elements so that the driving current is supplied to the light emitting elements,

the data driving section further includes a gradation voltage generating section which generates a gradation voltage having a value corresponding to the display data, and

the gradation signal generating section generates a pixel data voltage based on the voltages of the data lines detected by the voltage detecting section, the gradation voltage generated by the gradation voltage generation section and voltages intrinsic to the driving elements of the display pixels so as to apply the pixel data voltage as the gradation signals to the display pixels via the data lines, respectively.

4. The display device according to claim 3, wherein the voltages intrinsic to the driving elements are voltages between both ends of the electric current paths when the threshold voltages of the driving elements are 0V and the constant currents are applied to the electric current paths of the driving elements.

5. The display device according to claim 1, wherein the driving circuits have a driving element which includes a control terminal and an electric current path to which an electric current corresponding to a voltage of the control terminal is applied and whose one end is electrically connected to the data lines and the light emitting elements so that the driving currents are supplied to the light emitting elements, and

the voltages of the data lines detected by the voltage detecting section have a value corresponding to the voltages of the control terminals at the time when the constant currents is applied to the electric current paths of the driving elements via the data lines.

6. The display device according to claim 5, wherein the driving elements are electric field effect type thin film transistors, the electric current paths are formed between source and drain terminals of the thin film transistors, the control terminals are gate terminals, and the source terminals are electrically connected to the data lines and to one ends of the light emitting elements.

7. The display device according to claim 1, wherein an operation for supplying the constant current to the data lines by means of the constant current supplying section so as to detect the voltages of the data lines by means of the voltage detecting section is performed prior to an operation for applying the gradation signal to the display pixels by means of the selection driving section and the data driving section so as to allow the light emitting elements provided to the display pixels to emit light with a luminance gradation corresponding to the display data.

8. the display device according to claim 1, wherein the driving circuit has a control terminal and an electric current path to which an electric current corresponding to a voltage of the control terminal is applied and whose one end is electrically connected to the data line and the light emitting element so that the driving current is supplied to the light emitting element, and

the constant current is set to a value to a voltage value such that the voltage of the control terminal becomes higher than the threshold voltage of the driving element when the constant current is applied to the electric current path of the driving element.

9. The display device according to claim 8, wherein the constant current is set to a value such that the voltage of the control terminal becomes higher than a voltage obtained by adding the threshold voltage of the driving element and the gradation voltage corresponding to the display data when the constant current is applied to the electric current path of the driving element.

10. The display device according to claim 1, wherein the voltage detecting section has a voltage retaining section which temporarily retains voltage components corresponding to the voltages of the data lines.

11. The display device according to claim 1, wherein the voltage detecting section has a memory section which stores detected data corresponding to the detected voltages of the data lines individually according to each corresponding display pixel.

12. The display device according to claim 1, wherein the driving circuit has a driving element which has a control terminal and an electric current path to which an electric current corresponding to a voltage of the control terminal is applied and whose one end is electrically connected to the data line and the light emitting element so that the driving current is supplied to the light emitting element, and

the voltage detecting section has a memory section which stores the detected voltages of the data lines and threshold data generated based on voltages intrinsic to the corresponding driving elements on the display pixels individually according to corresponding respective display pixels.

13. The display device according to claim 12, wherein the voltage intrinsic to the driving element is a voltage between both terminals of the electric current path at the time when the threshold voltage of the driving element is 0V and the constant current is applied to the electric current path of the driving element.

14. The display device according to claim 1, wherein the data driving section has a constant voltage supplying section which applies a constant current to the data lines, and

an operation for applying the constant voltage to the data lines by means of the constant voltage supplying section is performed prior to an operation for supplying the constant current to the data lines by means of the electric current supplying section.

15. The display device according to claim 14, wherein the constant voltage applied by the constant voltage supplying section is set to a value which is higher than the voltages of the data lines at the time when the constant current is supplied to the data lines by the constant current supplying section.

16. The display device according to claim 1, wherein the driving circuit includes at least:

a first switch section whose contact with the light emitting element is connected to one end of an electric current path so that a predetermined supply voltage is applied to the other end of the electric current path;

a second switch section where the selection signal is applied to a control terminal, the supply voltage is applied to one end of the electric current path, and the control terminal of the first switch section is connected to the other end of the electric current path; and

a third switch section where the selection signal is applied to a control terminal, the data line is connected to one end of the electric current path and the connection contact point is connected to the other end of the electric current path,

the driving element is the first switch section, and

the voltage detecting section detects a voltage corresponding to an electric potential of the connection contact point of the first switch section.

17. The display device according to claim 1, wherein the light emitting element is an organic electroluminescence element.

18. A driving method for controlling a display device so that image information corresponding to display data is displayed, the display device including a display panel, where a plurality of display pixels, each having a current-controlled light emitting element and a driving circuit for supplying a driving current to the light emitting element are arranged at intersecting points between a plurality of selection lines and data lines disposed in a column direction and a row direction, respectively, and a constitution such that a selection signal is sequentially applied to the display pixels in respective selection lines on the display panel so that the display pixels are set into a selected state, and a gradation signal corresponding to display data for displaying desired image information is applied to the display pixels in the rows set into the selected state in synchronization with the selection timing so that the display pixels are allowed to emit light with predetermined luminance gradation and the desired image information is displayed on the display panel, the driving method comprising at least:

an operation for supplying a constant current to the data lines prior to an operation for applying the gradation signal to the display pixels; and

an operation for detecting voltages of the data lines at the time when the constant current is supplied to the display pixels set into the selected state via the data lines.

19. The driving method according to claim 18, wherein the driving circuit has a control terminal and an electric current path to which an electric current corresponding to a voltage of the control terminal is applied and whose one end is electrically connected to the data line and the light emitting element so that the driving current is supplied to the light emitting element, and

the driving method further comprises an operation for generating a pixel data voltage based on the detected voltages of the data lines, a gradation voltage generated according to the display data and voltages intrinsic to the driving elements on the display pixels so as to apply the pixel data voltage as the gradation signal to the display pixels via the data line.

20. The driving method according to claim 19, wherein the voltages intrinsic to the driving elements are a voltage between both ends of the electric current path at the time when threshold voltages of the driving elements are 0V and the constant current is applied to the electric currents of the driving elements.

21. The driving method according to claim 18, wherein the constant current is set to a value such that the voltage of the control terminal becomes higher than threshold voltages of the driving elements when the constant current is applied to the electric current paths of the driving elements.

22. The driving method according to claim 21, wherein the constant current is set to a value such that the voltage of the control terminal becomes higher than a voltage obtained by adding the threshold voltage of the driving element and the gradation voltage corresponding to the display data when the constant current is applied to the electric current paths of the driving elements.

23. The driving method according to claim 18, further comprising an operation for applying a constant current to the data lines prior to the operation for supplying the constant current to the data lines.

24. The driving method according to claim 23, wherein the constant voltage is set to a value higher than the voltages of the data lines at the time when the constant current is supplied to the data lines.

25. The driving method according to claim 18, wherein the operation for detecting the voltages of the data lines at the time of supplying the constant current to the display pixels set into the selected state via the data lines is performed in every display driving period at which the display pixels emit light with a luminance gradation corresponding to the display data.

26. The driving method according to claim 18, wherein the operation for detecting the voltages of the data lines at the time of supplying the constant current to the display pixels set into the selected state via the data lines is performed intermittently in an arbitrary processing cycle period in the case where a display driving period for allowing the display pixels to emit light with a luminance gradation corresponding to the display data is determined as one processing cycle period.