Light emission drive circuit and its drive control method and display unit and its display drive method

• US 20060125740A1
• Filed: 12/12/2005
• Published: 06/15/2006
• Est. Priority Date: 12/13/2004
• Status: Active Grant

• Current Assignee: Solas OLED Limited (Atlantic IP Services Limited)
• Original Assignee: Casio Computer Company Limited
• Inventors: Shirasaki, Tomoyuki, Ogura, Jun
• Granted Patent: US 7,663,615 B2
• Time in Patent Office: Days
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• 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 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• 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 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 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/063 Waveforms for resetting the whole screen at once
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 3/3266 Details of drivers for scan electrodes

Abstract

A light emission drive circuit includes an electric charge accumulating section for accumulating electric charges on the basis of a gradation sequence signal designating a luminance gradation sequence. A light emission control section flows a light emission drive current having a current value in accordance with an amount of the electric charges accumulated in the electric charge accumulating section. A writing control section controls a supplying state of the electric charges based on the gradation sequence signal to the electric charge accumulating section on the basis of a first control signal. A voltage control section controls a drive voltage for operating the light emission controlling section on the basis of a second control signal.

Claims

1. A light emission drive circuit for supplying a light emission drive current to make a light emission element perform light emission, comprising:

an electric charge accumulating section for accumulating electric charges on the basis of a gradation sequence signal designating a luminance gradation sequence;

a light emission control section for flowing a light emission drive current having a current value in accordance with an amount of the electric charges accumulated in the electric charge accumulating section;

a writing control section for controlling a supplying state of the electric charges based on the gradation sequence signal to the electric charge accumulating section on the basis of a first control signal; and

a voltage control section for controlling a drive voltage for operating the light emission controlling section on the basis of a second control signal.

2. The light emission drive circuit according to claim 1, wherein the light emission control section has a drive transistor including a current path and a control terminal, in which a current value of the light emission drive current is set due to a potential difference between the control terminal and one end of the current path.

3. The light emission drive circuit according to claim 1, wherein the light emission control section has a drive transistor including a current path and a control terminal, the drive transistor flowing the light emission drive current of the current value, which is based on the current value of the writing current flowing through the current path in a light emission operation time period as the gradation sequence signal in a writing operation time period.

4. The light emission drive circuit according to claim 1, wherein the light emission control section has a drive transistor including a current path and a control terminal, the drive transistor applying a voltage that attains to a saturated range to one end and the other end of a current path in a light emission operation time period.

5. The light emission drive circuit according to claim 2, wherein a precharge voltage exceeding a threshold value of the drive transistor is applied to the electric charge accumulating section.

6. The light emission drive circuit according to claim 5, wherein the writing control section partially discharges the electric charges accumulated in the electric charge accumulating section on the basis of the precharge voltage and remains the electric charges equivalent to the threshold voltage of the drive transistor.

7. The light emission drive circuit according to claim 2, wherein a precharge voltage exceeding the minimum luminance value necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence is applied to the electric charge accumulating section.

8. The light emission drive circuit according to claim 7, wherein the writing control section partially discharges the electric charges accumulated in the electric charge accumulating section on the basis of the precharge voltage and remains the electric charges equivalent to the minimum luminance electric charges.

9. The light emission drive circuit according to claim 2, wherein the electric charge accumulating section is provided with a gradation sequence signal via the writing control section or the light emission control section.

10. The light emission drive circuit according to claim 1, wherein the gradation sequence signal is a gradation sequence current having a current value for making the light emission element perform the light emission operation at a desired gradation sequence.

11. The light emission drive circuit according to claim 1, wherein the gradation sequence signal is a gradation sequence current having a predetermined current value for making the light emission element perform the no-light emission operation.

12. The light emission drive circuit according to claim 5, wherein the precharge voltage and the gradation sequence signal are supplied to the electric charge accumulating section at different timing.

13. The light emission drive circuit according to claim 1, wherein the gradation sequence signal is a gradation sequence current having a current value for making the light emission element perform the light emission operation at a predetermined luminance gradation sequence or a gradation sequence voltage having a predetermined voltage value for making the light emission element perform the no-light emission operation, and one of the gradation sequence current and the gradation sequence is selectively applied to the electric charges accumulation section.

14. The light emission drive circuit according to claim 2, wherein the writing control section has a selection transistor including a current path to which a precharge voltage of which absolute value is larger than the absolute value of the threshold voltage of the drive transistor or larger than the absolute value of the minimum luminance voltage necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence, and the gradation sequence signal are selectively supplied;

and a control terminal to which the first control signal is applied.

15. The light emission drive circuit according to claim 2, wherein the voltage control section has a hold transistor including a current path of which one end side is provided with the supplying voltage and of which other end side is connected to the control terminal of the drive transistor and one end side of the electric accumulating section;

and a control terminal to which the second control signal is applied.

16. A light emission circuit comprising:

a selection line;

a hold line;

is a data line;

a supplying voltage line;

a hold transistor having a gate electrically connected to the hold line, and a current path;

a drive transistor having a gate and a current path, the gate of the drive transistor being electrically connected to one end of the current path of the hold transistor and one end of the current path of the drive transistor being connected to the supplying voltage line; and

a selection transistor having a gate and a current path, the gate of the selection transistor being electrically connected to the selection line, one end of the current path of the selection transistor being connected to the other end of the current path of the drive transistor, and the other end of the current path of the selection transistor being connected to the data line.

17. The light emission drive circuit according to claim 16, wherein different control signals are outputted to the selection line and the hold line, respectively.

18. The light emission drive circuit according to claim 16, wherein the selection transistor is turned on by a first control signal from the selection line in a precharge time period, the hold transistor is turned on by a second control signal from the hold line, and a voltage of which absolute is larger than the absolute value of the threshold voltage of the drive transistor or a voltage exceeding the minimum luminance voltage necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence is provided to the drive transistor;

and

the selection transistor is turned off by the first control signal from the selection line in a correction operation time period, and the voltage between the gate of the drive transistor and the other end of the current path of the drive transistor is set so as to decrease to the threshold voltage of the drive transistor or the minimum luminance voltage.

19. A drive control method of a light emission drive circuit, which supplies a light emission drive current to a light emission element to make the light emission element perform the light emission, comprising:

setting a first potential difference equivalent to a threshold value of a transistor element, or a first potential difference equivalent to the minimum luminance voltage necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence between a gate and a source of a transistor element to supply the light emission drive current to the light emission element;

applying a gradation sequence signal to make the light emission element perform the light emission operation at a luminance gradation sequence to the transistor element and setting a second potential difference in accordance with the luminance gradation sequence between the gate and the source of the transistor element; and

turning on the transistor element at a predetermined conducting state on the basis of the second potential difference, generating the light emission drive current having a current value in accordance with the luminance gradation sequence, and supplying it to the light emission element.

20. The drive control method according to claim 19, wherein setting the first potential difference includes a step of setting a third potential difference on the basis of a precharge voltage of which absolute value is larger than that of the threshold voltage or a third potential difference on the basis of the precharge voltage of which absolute value is larger than that of the minimum luminance voltage between the gate and the source of the transistor element;

and a step of turning on the transistor element on the basis of the third potential difference and setting the potential difference between the gate and the source of the transistor element at the first potential difference.

21. The drive control method according to claim 19, wherein setting the second potential difference includes a step of adding electric charges of the first potential difference between the gate and the source of the transistor element to electric charges accumulated based on a gradation sequence current applied to the transistor element, the gradation sequence current as the gradation sequence signal having a current value for making the light emission element perform the light emission operation at a desired luminance gradation sequence.

22. The drive control method of the light emission drive circuit according to claim 19, wherein setting the second potential difference includes discharging electric charges based on the first potential difference held between the gate and the source of the transistor element by applying a gradation sequence voltage as the gradation sequence signal having a predetermined voltage for making the light emission element perform the no-light emission operation.

23. A display unit comprising:

a plurality of display pixels each of which includes a light emission element and a light emission drive circuit having an electric charge accumulating section for accumulating electric charges based on a gradation sequence signal to designate a luminance gradation sequence in accordance with display data, a light emission control section for generating a light emission drive current having a predetermined current value in accordance with the electric charges accumulated in the electric charge accumulating section and supplying the light emission drive current to the light emission element, a writing control section for controlling the supplying state of the electric charges based on the gradation sequence signal to the electric charge accumulating section, and a voltage control section for controlling a drive voltage for making the light emission control section perform the operation, respectively;

a selection line in which a writing control signal for controlling the operation state of the writing control section of the each display pixel is applied;

a hold line in which a voltage control signal for controlling the operation state of the voltage control section of the each display pixel is applied; and

a data line to which the gradation sequence is supplied.,

24. The display unit according to claim 23, which further comprising a selection driver which applies the writing control signal in the selection line;

a hold driver which applies the writing control signal in the hold line; and

a data driver which supplies the gradation sequence signal to the data line.

25. The display unit according to claim 23, wherein the electric accumulating section includes a capacitance element, the light emission control section includes a drive transistor, wherein one end side of a current path through which the light emission drive current flows is connected to the light emission element and further, is connected to one end side of the capacitance element;

a supplying voltage for flowing the light emission drive current is applied to the other end side of the current path; and

a control terminal for controlling the supplying state of the light emission drive current is connected to the other end side of the capacitance element,

the writing control section includes a selection transistor, wherein one end side of a current path is connected to the data line, the other end side of the current path is connected to the one end side of the capacitance element; and

a control terminal is connected to the selection line, and

the voltage control section includes a hold transistor, wherein one end side of a current path is connected to the other end side of the capacitance element and a control terminal is connected to the hold line.

26. The display unit according to claim 25, wherein the light emission control section generates the light emission drive current having the predetermined current value, wherein the drive transistor is turned on at a predetermined conducting state in accordance with the potential difference based on the electric charges accumulated in the capacitance element.

27. The display unit according to claim 25, further comprising a supplying voltage driver for applying the supplying voltage to the other end side of the current path of the drive transistor.

28. The display unit according to claim 27, wherein the supplying voltage driver applies the supplying voltage to the control element of the drive transistor.

29. The display unit according to claim 24, wherein the data driver applies a precharge voltage exceeding the threshold value of the drive transistor to the data line, and the light emission drive circuit applies the precharge voltage applied to the data line to the electric charge accumulating section via the writing control section.

30. The display unit according to claim 29, wherein the light emission drive circuit partially discharges the electric charges accumulated in the electric charge accumulating section on the basis of the precharge voltage and remains the electric charges equivalent to the threshold voltage of the drive transistor.

31. The display unit according to claim 24, wherein the data driver applies a precharge voltage exceeding the minimum luminance value necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence to the data line;

the light emission drive circuit applies the precharge voltage applied to the data line to the electric charge accumulating section via the writing control section.

32. The display unit according to claim 31, wherein the light emission drive circuit partially discharges the electric charges accumulated in the electric charge accumulating section on the basis of the precharge voltage, remains the electric charges equivalent to the minimum luminance electric charge, and holds this electric charge.

33. The display unit according to claim 24, wherein the light emission drive circuit applies the gradation sequence signal applied from the data driver to the data line to the electric accumulating section via the writing control section.

34. The display unit according to claim 33, wherein the gradation sequence signal is a gradation sequence current having a predetermined current value for making the light emission element perform the light emission operation at a desired luminance gradation sequence on the basis of the display data;

and the electric charges in accordance with the gradation sequence current is accumulated in the electric accumulating section.

35. The display unit according to claim 33, wherein the gradation sequence signal is a gradation sequence voltage having a predetermined current value for making the light emission element perform the no-light emission operation on the basis of the display data;

and the electric charges accumulated in the electric accumulating section are discharged in accordance with the gradation sequence voltage.

36. The display unit according to claim 29, wherein the precharge voltage and the gradation sequence signal applied from the data driver to the data line are applied in the electric charge accumulating section via the writing control section at different timing respectively.

37. The display unit according to claim 35, wherein the data driver applies the gradation sequence current and the gradation sequence voltage to the data line selectively.

38. A display having:

a selection line;

a hold line;

a data line;

a supplying voltage line;

a hold transistor, in which a gate is connected to the hold line;

a drive transistor having a gate and a current path, the gate of the drive transistor being connected to one end of a current path of the hold transistor, and one end of the current path of the drive transistor being connected to the supplying voltage line;

a selection transistor having a gate and a current path, the gate of the selection transistor being connected to the selection line, one end of the current path of the selection transistor being connected to the other end of the current path of the drive transistor, and the other end of the current path of the selection transistor being connected to the data line;

a light emission element which is connected to the other end side of the current path of the drive transistor;

a selection driver which outputs a selection signal to the selection line;

a hold driver which outputs a hold signal to the hold line;

a data driver which supplies a gradation sequence signal to the data line; and

a supplying voltage driver which outputs a supplying voltage to the supplying voltage line.

39. A display drive method of a display unit which comprises a display panel made by a plurality of display pixels and makes the each display pixel perform the light emission operation at a predetermined luminance gradation sequence by supplying a gradation sequence signal designating a luminance gradation sequence in accordance with the display data to the each display pixel, and displays desired image information on the display panel, the method comprising

setting at least part of the plural display pixels at a selection state, and setting a first potential difference equivalent to a threshold voltage of a transistor element or a first potential difference equivalent to the minimum luminance voltage necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence between one end of a gate and one end of a current path of a transistor element for supplying a light emission drive current to a current-controlled type of a light emission element provided in the each display pixel;

sequentially setting the display pixel for each row of the display panel at a selection state, sequentially applying a gradation sequence signal for making the light emission element of the each display pixel perform the light emission operation at a predetermined luminance gradation sequence in accordance with the display data, and setting a second potential difference in accordance with the luminance gradation sequence between a gate and one end of a current path of the transistor element; and

setting at least part of the plural display elements arranged on the display panel at a no-selection state, turning on the transistor element of the each display element on the basis of the second potential difference, and individually generating the light emission drive current having a current value in accordance with the luminance gradation sequence for the each light emission element and supplying the light emission current to the each light emission element.

40. The display drive method according to claim 39, wherein setting the first potential difference in the each display pixel includes:

a step of setting at least part of the plural display elements at a selection state and setting a third potential difference based on a precharge voltage of which absolute value is larger than the absolute value of the threshold voltage or a third potential difference based on the precharge voltage of which absolute value is larger than the absolute value of the minimum luminance voltage between one end of a gate and one end of a current path of the transistor element of the each display pixel; and

a step of setting at least part of the plural display elements at a no-selection state, turning on the transistor element based on the third potential difference set in the each display pixel, and setting the first potential difference between one end of the gate and one end of the current path of the transistor element.

41. The drive control method of the display unit ccording to claim 39, wherein the step of setting the econd potential difference includes a step of adding electric charges of the first potential difference between the gate and the source of the transistor element to electric charges accumulated based on a gradation sequence current applied to the transistor element, the gradation sequence current as the gradation sequence signal has a current value for making the light emission element perform the light emission operation at a desired luminance gradation sequence.

42. The display drive method of the display unit according to claim 39, wherein the step of setting the second potential difference includes a step of discharging electric charges based on the first potential difference held between the gate and the source of the transistor element by applying a gradation sequence voltage as the gradation sequence signal having a predetermined voltage for making the light emission element perform the no-light emission operation.

43. A light emission drive circuit for flowing a light emission drive current to make a light emission element perform light emission, comprising:

electric charge accumulating section for accumulating electric charges on the basis of a gradation sequence signal designating a luminance gradation sequence;

light emission control section for flowing a light emission drive current having a current value in accordance with the electric charges amount accumulated in the electric charge accumulating section; and

voltage setting section for partially discharging the electric charges accumulated in the electric charge accumulating section in order for the light emission control section to set the light emission drive current at the current value.

44. A drive control method of a light emission drive circuit for flowing a light emission drive current to make a light emission element perform light emission, comprising:

a first potential difference step of setting a first potential difference on the basis of a precharge voltage that is larger than the minimum luminance gradation sequence necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence or a threshold potential difference between the control terminal and one end of a current path of a drive transistor in which a current value of the light emission drive current is set by a potential difference between a control terminal and one end of the current path of the drive transistor;

a second potential difference step of setting a second potential difference equivalent to the minimum luminance potential difference or the threshold potential difference between the control terminal and one end of the current path of the drive transistor after turning on the drive transistor on the basis of the first potential difference; and

a third potential difference step of setting a third potential difference equivalent to the luminance gradation sequence between the control terminal and said one end of the current path of the drive transistor by applying a gradation sequence signal for making the light emission element to perform the light emission operation at a desired luminance gradation sequence and flowing the gradation sequence signal to the current path of the drive transistor.

45. A display unit comprising:

a plurality of display pixels including a light emission element; and

a light emission drive circuit having an electric charge accumulating section to accumulateelectric charges based on a gradation sequence signal to designate a luminance gradation sequence in accordance with the display data, a light emission control section to generate a light emission drive current having a current value in accordance with the electric charges accumulated in the electric charge accumulating section and supplying the light emission drive current to the light emission element, and a voltage setting section to discharge the electric charges accumulated in the electric charge accumulating section in order for the light emission control section to set the light emission drive current at the current value, respectively.

46. A display drive method of a display unit for making light emission elements of a plurality of display pixels to perform the light emission arranged in a row direction and a column direction, comprising:

a first potential difference step of setting the display pixel at a selection state and setting a first potential difference on the basis of a precharge voltage that is larger than the minimum luminance gradation sequence necessary for generating the light emission drive current required for making the light emission element perform the light emission operation at the minimum luminance gradation sequence or a threshold potential difference between the control terminal and one end of a current path of a drive transistor which can supply a light emission drive current to the light emission element;

a second potential difference step of setting a second potential difference equivalent to the minimum luminance potential difference or the threshold potential difference between the control terminal and one end of the current path of the drive transistor element in a state of turning on the drive transistor on the basis of the first potential difference;

a third potential difference step of setting a third potential difference equivalent to the luminance gradation sequence between the control terminal and said one end of the current path of the drive transistor by applying a gradation sequence signal for making the light emission element to perform the light emission operation at a desired luminance gradation sequence and flowing the gradation sequence signal to the current path of the drive transistor; and

a light emission step that the drive transistor flows the light emission drive current on the basis of the gradation sequence signal to the light emission element by applying a voltage so that a potential difference between said one end and the other end of the current path of the drive transistor is saturated.

47. A light emission drive circuit, comprising:

a light emission control section having a current path of flowing a light emission drive current from the current path;

an electric charge accumulating section to accumulate electric charges in accordance with a current value of a current flowing through the light emission control section;

a voltage setting section to supply a current of a current value that allows the light emission element to perform the light emission operation at a luminance other than the no-light luminance gradation sequence and accumulating the electric charges equivalent to the luminance gradation sequence in the electric charge accumulating section; and

a gradation sequence setting section to discharge the electric charges in the electric charge accumulating section such that the light emission element is made into the no-light emission state or the electric charges such that the light emission drive current does not flow.

48. A drive control method of a light emission drive circuit for flowing a light emission drive current to make a light emission element perform light emission, comprising:

a first potential difference step of generating a first potential difference between the control terminal and one end of the current path of a drive transistor before a luminance gradation sequence signal is applied to a drive transistor, the first potential difference being irrelevant to the current value the luminance gradation sequence signal and allows the light emission element to perform the light emission operation at a luminance gradation sequence other than a no-light emission luminance gradation sequence; and

a second potential difference step of generating a second potential difference between the control terminal and the one end of the current path of the drive transistor so that the light emission element performs the no-light emission state on the basis of a no-light emission luminance gradation sequence signal applied to the drive transistor when the luminance gradation sequence signal is the no-light emission luminance gradation sequence signal.

49. A display unit comprising:

a plurality of display pixels comprising;

a light emission element; and

a light emission drive circuit having a light emission control section to apply a light emission drive current from the current path to the light emission element, an electric charge accumulating section to accumulate electric charges in accordance with the current value of the current flowing the light emission control section, and a voltage setting section to accumulate the electric charges equivalent to the luminance gradation sequence in the electric charge accumulating section, respectively; and

a gradation sequence setting section to discharge the electric charges accumulated in the electric charge accumulating section so that a state of the electric charges allowing the light emission element to perform the light emission operation at a luminance gradation sequence other than a no-light emission luminance gradation sequence is changed into a state of the electric charges allowing the light emission element to perform the no-light emission state or the light emission drive current not to flow.

50. A display drive method of a display unit for making light emission elements of a plurality of display pixels to perform the light emission arranged in a row direction and a column direction, comprising:

a first potential difference step of generating a first potential difference between the control terminal and one end of the current path of a drive transistor before a luminance gradation sequence signal applied to a drive transistor, the first potential difference is irrelevant to the current value the luminance gradation sequence signal and allows the light emission element to perform the light emission operation at a luminance gradation sequence other than a no-light emission luminance gradation sequence; and

a second potential difference step of generating a second potential difference between the control terminal and the one end of the current path of the drive transistor so that the light emission element performs the no-light emission state on the basis of a no-light emission luminance gradation sequence signal applied to the drive transistor when the luminance gradation sequence signal is the no-light emission luminance gradation sequence signal.