Method and system for programming, calibrating and driving a light emitting device display

• US 8,259,044 B2
• Filed: 10/01/2009
• Issued: 09/04/2012
• Est. Priority Date: 12/15/2004
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Chaji, Gholamreza Reza, Servati, Peyman
• Primary Examiner(s): ABDULSELAM, ABBAS I
• Application Number:
  US12/571,968
• Publication Number:
  US 20100033469A1
• Time in Patent Office: 1,069 Days
• Field of Search: 345/76, 345/82, 345/204, 345/83, 345/211, 345/690, 315/169.3
• US Class Current: 345/82
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• 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 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 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• 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 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• 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
• 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

A method and system for programming, calibrating and driving a light emitting device display is provided. The system may include extracting a time dependent parameter of a pixel for calibration.

Claims

1. A system for a display array having a pixel circuit, the pixel circuit being programmed through a data line, the system comprising:

a data source for providing a programming data into the pixel circuit;

a current-controlled voltage source associated with the data source for converting a current on the data line to a voltage associated with the current to extract a time dependent parameter of the pixel circuit; and

a current conveyor for extracting the current of the data line, the current conveyor including X, Y, and Z terminals, the data source applying a programming voltage to the Y terminal, the X terminal being connected to the data line and being forced by feedback to have the same voltage as that of the Y terminal, the current of the X terminal being duplicated to the Z terminal which is connected to the current-controlled voltage source.

2. The system according to claim 1, further comprising:

a controller for determining the time dependent parameter of the pixel circuit based on the voltage associated with the current.

3. The system according to claim 1, wherein the pixel circuit includes a current mirror.

4. The system according to claim 3, wherein the pixel circuit includes:

first and second mirror transistors, each having a gate terminal, a first terminal and a second terminal;

first and second switch transistors, each having a gate terminal, a first terminal and a second terminal;

a storage capacitor; and

a light emitting device,

wherein the first terminal of the first mirror transistor is connected to the data line through the first switch transistor and is connected to the storage capacitor through the second switch transistor, the second terminal of the first mirror transistor is connected to the storage capacitor and the light emitting device, the gate terminals of the first and second mirror transistors are connected to the storage capacitor and are connected to the data line through the first and second switch transistors, the first terminal of the second mirror transistor is connected to a voltage supply line, the second terminal of the second mirror transistor is connected to the storage capacitor and the light emitting device.

5. The system according to claim 3, wherein the pixel circuit includes:

first and second mirror transistors, each having a gate terminal, a first terminal and a second terminal;

first and second switch transistors, each having a gate terminal, a first terminal and a second terminal;

a storage capacitor; and

a light emitting device,

wherein the first terminal of the first mirror transistor is connected to the data line through the first switch transistor and is connected to the storage capacitor through the second switch transistor, the gate terminals of the first and second mirror transistors are connected to the storage capacitor and are connected to the data line through the first and second switch transistors, and the first terminal of the second mirror transistor is connected to the light emitting device.

6. The system according to claim 1, wherein the display array is an AMOLED array.

7. The system according to claim 1, wherein the pixel circuit includes a driving transistor connected in series with a light emitting device, and wherein the extracted time dependent parameter of the pixel circuit includes a threshold voltage of the driving transistor.

8. The system according to claim 7, wherein the extracted time dependent parameter of the pixel circuit also includes a turn on voltage of the light emitting device.

9. The system according to claim 7, wherein the programming data provided to the pixel circuit via the data source is modified according to the extracted time dependent parameter.

10. The system according to claim 1, wherein the pixel circuit is programmed via a voltage modified according to the extracted time dependent parameter.

11. The system according to claim 1, wherein the pixel circuit includes a driving transistor connected in series with a light emitting device, a storage capacitor connected to a gate terminal of the driving transistor, and wherein the pixel circuit is programmed by applying the programming voltage on the data line, via the current conveyor, the programming voltage corresponding to the programming data, and wherein the pixel circuit is configured such that the current on the data line, conveyed to the current-controlled voltage source via the current conveyor, is the current through the driving transistor while the programming voltage is applied.

12. The system according to claim 11, wherein the extracted time dependent parameter is a threshold voltage of the driving transistor and is determined according to a function including the voltage associated with the current provided by the current-controlled voltage source and the programming voltage.

13. The system according to claim 12, wherein the data source is operated to calibrate a subsequent programming voltage according to the extracted time dependent parameter.

14. The system according to claim 1, wherein the data source is operated to calibrate a subsequent programming voltage according to the extracted time dependent parameter.

15. The system according to claim 1, wherein the pixel circuit includes:

a driving transistor having a gate terminal, a first terminal, and a second terminal;

a storage capacitor connected to the gate terminal of the driving transistor;

a light emitting device to the first terminal of the driving transistor;

a first switch transistor connecting the first terminal of the driving transistor to the data line; and

a second switch transistor connecting the first terminal of the driving transistor to the gate terminal of the driving transistor.

16. The system according to claim 1, wherein the pixel circuit includes:

a driving transistor having a gate terminal, a first terminal, and a second terminal;

a storage capacitor connected to the second terminal of the driving transistor;

a light emitting device to the first terminal of the driving transistor;

a first switch transistor connecting the second terminal of the driving transistor to the data line; and

a second switch transistor connecting the second terminal of the driving transistor to the gate terminal of the driving transistor.

17. A system for a display array including a plurality of pixel circuits, each pixel circuit including a driving transistor, at least one switch transistor, a storage capacitor and a light emitting device, the system comprising:

a monitor for monitoring a current or voltage on at least one pixel circuit of the plurality of pixel circuits;

a driver for providing programming and calibration data to the at least one pixel circuit; and

a data process unit for controlling the driver to operate the display array, the data process unit extracting aging information of the at least one pixel circuit, based on the monitored current or voltage, and wherein the data process unit estimates an intermediate threshold voltage of the at least one pixel circuit according to a previous extracted threshold voltage, or a combination of the previous extracted threshold voltage and a resolution of the driver.

18. The system according to claim 17, wherein the data process unit determines a state of the at least one pixel circuit based on a comparison of the monitored current or voltage with a reference value, and wherein the data process unit estimates the intermediate threshold voltage based on the state of the at least one pixel circuit.

19. The system according to claim 17, wherein the driver provides a programming voltage determined based on the previous extracted threshold voltage and a programming data.

20. The system according to claim 17, wherein the driver provides a calibration voltage determined based on the intermediate threshold voltage and a bias voltage.

21. The system according to claim 17, wherein the monitor senses the current through a monitor line connected to the at least one pixel circuit.

22. The system according to claim 21, wherein the switch transistor includes first and second switch transistors,

each of the driving transistor, the first switch transistor and the second switch transistor including a gate terminal, a first terminal and a second terminal, and

the gate terminal of the driving transistor being connected to a signal line through the first switch transistor and being connected to the storage capacitor, the first terminal of the driving transistor being connected to the light emitting device and being connected to the monitor line through the second switch transistor.

23. The system according to claim 22, wherein the gate terminals of the first and second switch transistors are connected to a common select line.

24. The system according to claim 22, wherein the gate terminals of the first and second switch transistors are connected to first and second select lines.

25. The system according to claim 17, wherein the system implements, to pixel circuits in each row of the display array, one extraction operation for extracting the threshold voltages of the driving transistors in the pixel circuits during a frame time.

26. The system according to claim 17, wherein the at least one pixel circuit includes:

a first switch transistor connected to a data line conveying the programming and calibration data from the driver; and

a second switch transistor connected to a monitor line conveying the current or voltage to the monitor.

27. The system according to claim 26, wherein the storage capacitor is connected to a gate terminal of the driving transistor, the gate terminal of the driving transistor being connected to the data line through the first switch transistor, and wherein the light emitting device is connected to a first terminal of the driving transistor, the first terminal of the driving transistor being connected to the monitor line through the second switch transistor.

28. The system according to claim 27, wherein the first switch transistor is operated according to a first select line connected to a gate terminal of the first switch transistor, and the second switch transistor is operated according to a second select line connected to a gate terminal of the second switch transistor, and

wherein the data process unit is further configured to operate the first and second select lines to provide:

a first phase of an extraction cycle while both the first and second switch transistors are turned on by the first and second select lines and the gate terminal of the driving transistor is charged to a calibration voltage provided via the data line while the first terminal of the driving transistor is charged to a reference voltage provided via the monitor line, the reference voltage being sufficient to reverse bias the light emitting device;

a second phase of the extraction cycle while the first switch transistor is turned off by the first select line and a gate-source voltage of the driving transistors accounts for dynamic effects and the second switch transistor is turned on by the second select line to allow the monitor to detect current through the drive transistor;

a programming cycle while the first switch transistor is turned on by the first select line and a programming voltage is applied to the data line; and

a driving cycle while first switch transistor is turned off by the first select line and the driving transistor is driven according to the programming information such that a pixel current provided to the light emitting device is independent of the threshold voltage.

29. The system according to claim 27, wherein the first switch transistor is operated according to a first select line connected to a gate terminal of the first switch transistor, and the second switch transistor is operated according to a second select line connected to a gate terminal of the second switch transistor, and

wherein the data process unit is further configured to operate the first and second select lines to provide:

a programming cycle while the first and second switch transistors are turned on by the first and second select lines and a programming voltage is applied to the data line;

an extraction cycle while the second switch transistor is turned on by the second select line to allow the monitor to detect current through the drive transistor; and

a driving cycle while the first switch transistor is turned off by the first select line and the driving transistor is driven according to the programming information such that a pixel current provided to the light emitting device is independent of the threshold voltage.

30. The system according to claim 27, wherein the first switch transistor is operated according to a first select line connected to a gate terminal of the first switch transistor, and the second switch transistor is operated according to a second select line connected to a gate terminal of the second switch transistor, and

wherein the data process unit is further configured to operate the first and second select lines to provide:

a first phase of an extraction cycle while the first and second switch transistors are turned on by the first and second select lines are turned on and the data line is set to turn off the driving transistor, and a current or voltage is applied to the light emitting device via the monitor line; and

a second phase of an extraction cycle while the second switch transistor is turned on by the second select line and the voltage or current of the light emitting device is measured to extract a shift in the operating voltage of the light emitting device.

31. The system according to claim 17, wherein the monitor includes at least one of a current sense amplifier or a current comparator.

32. The system according to claim 17, wherein the data process unit is further configured to:

extract aging information for each of the plurality of pixel circuits in the display array based on monitored current or voltage monitored from each of the plurality of pixel circuits, and

provide programming information to each of the plurality of pixel circuits, wherein the programming information provided to each of the plurality of pixel circuits is calibrated according to the extracted aging information.

33. The system according to claim 17, wherein the monitor detects a voltage of the light emitting device during an emission operation for the at least one pixel circuit and the extracted aging information includes an operating voltage of the light emitting device.

34. The system according to claim 17, wherein the monitor detects a current of the driving transistor during a calibration cycle separate from a driving cycle while the pixel current is driven to emit light.

35. The system according to claim 17, wherein the data process unit incrementally estimates the intermediate threshold voltage of the driver by:

comparing the monitored current or voltage with a reference value,

determining, based on the comparison, whether the threshold voltage of the at least one pixel circuit is greater than, equal to, or lesser than, a previous estimated threshold voltage, and

setting the intermediate threshold voltage to;

the previous estimated threshold voltage incremented by the resolution of the driver responsive to determining that the threshold voltage is greater than the previous estimated threshold voltage;

the previous estimated threshold voltage responsive to determining that the threshold voltage is equal to the previous estimated threshold voltage;

or

the previous estimated threshold voltage decremented by the resolution of the driver responsive to determining that the threshold voltage is lesser than the previous estimated threshold voltage.

36. The system according to claim 17, wherein the data process unit incrementally estimates the intermediate threshold voltage of the driver by comparing the monitored current or voltage with a reference value and determining, based on the comparison, an amount to add or subtract to a previous estimated threshold voltage to set the intermediate threshold voltage, and

wherein the amount to add or subtract is dynamically determined based on the rate of change of the threshold voltage.

37. The system according to claim 17, wherein the data process unit operates the monitor and the driver to:

program the display, via the data line, during a programming cycle;

drive the display to emit light, during an emission cycle; and

extract the aging information during an extraction cycle that is carried out on an extraction interval that is greater than a display refresh time such that multiple driving and programming operations are carried out between extraction cycles for each pixel circuit.

38. A system for a display array including a plurality of pixel circuits arranged in a plurality of rows, each pixel circuit including a driving transistor, at least one switch transistor, a storage capacitor and a light emitting device, the system comprising:

a monitor for monitoring a current or voltage on each of the plurality of pixel circuits;

a driver for providing programming and calibration data to each of the plurality of pixel circuits; and

a data process unit for controlling the driver to operate the display array, the data process unit extracting aging information for each of the plurality of pixel circuits, based on the monitored current or voltage, and

wherein the system consecutively implements, to pixel circuits in each row of the display array;

an extraction operation for extracting estimated threshold voltages of the driving transistors in the pixel circuits in a row,

a programming operation for programming the pixel circuits in the row, and

a driving operation for driving the pixel circuits in the row.

39. The system according to claim 38, wherein each pixel circuit includes:

a first switch transistor connected to a data line conveying the programming and calibration data from the driver; and

a second switch transistor connected to a monitor line conveying the current or voltage to the monitor.

40. The system according to claim 39, wherein the storage capacitor is connected to a gate terminal of the driving transistor, the gate terminal of the driving transistor being connected to the data line through the first switch transistor, and wherein the light emitting device is connected to a first terminal of the driving transistor, the first terminal of the driving transistor being connected to the monitor line through the second switch transistor.

41. The system according to claim 38, wherein the data process unit is operated to calibrate programming voltages for each pixel circuit based on the extracted aging information.

42. The system according to claim 38, wherein the extraction operation includes a one-bit extraction technique.

43. The system according to claim 38, wherein the extraction operation includes comparing the monitored current or voltage of each pixel circuit in the row to a reference value and adjusting a previously estimated threshold voltage of pixels in the row, based on the comparison.

44. The system according to claim 38, wherein each pixel circuit includes:

a first switch transistor connecting a first terminal of the driving transistor to a shared monitor and data line connected to both the driver and the monitor; and

a second switch transistor connected between a gate terminal of the driving transistor and the first terminal of the driving transistor, and

wherein the light emitting device is connected to the first terminal of the driving transistor, and the storage capacitor is connected to a gate terminal of the driving transistor.

45. The system according to claim 38, wherein each pixel circuit includes:

a first switch transistor connecting a first terminal of the driving transistor to a shared monitor and data line connected to both the driver and the monitor; and

a second switch transistor connected between a gate terminal of the driving transistor and a second terminal of the driving transistor, and

wherein the light emitting device is connected to the first terminal of the driving transistor, and the storage capacitor is connected between the gate terminal of the driving transistor and the first terminal of the driving transistor.

46. A method of driving a display array, the display array including a plurality of pixel circuits, each of the plurality of pixel circuits including a driving transistor, at least one switch transistor, a storage capacitor and a light emitting device, the method comprising:

applying a current or voltage to at least one pixel circuit of the plurality of pixel circuits;

monitoring a current or voltage flowing through the pixel circuit;

extracting aging information of the at least one pixel circuit, based on the monitored current or voltage, by estimating an intermediate threshold voltage of the at least one pixel circuit according to a previous extracted threshold voltage, or a combination of the previous extracted threshold voltage and a resolution of a driver for programming the at least one pixel circuit;

providing an operation voltage to the at least one pixel circuit according to programming and calibration data for the at least one pixel circuit, the calibration data being based on the extracted aging information of the at least one pixel circuit.

47. The method according to claim 46, wherein the extracting includes determining a state of the at least one pixel circuit by comparing the monitored current or voltage with a reference value and estimating the intermediate threshold voltage based on the state of the at least one pixel circuit.

48. The method according to claim 46, further comprising determining a programming voltage for the programming based on the previous extracted threshold voltage and a programming data.

49. The method according to claim 46, further comprising determining a calibration voltage for the calibration based on the intermediate threshold voltage and a bias voltage.

50. The method according to claim 46, wherein the extracting includes:

comparing the monitored current or voltage with a reference value,

determining, based on the comparison, whether the threshold voltage of the at least one pixel circuit is greater than, equal to, or lesser than, a previous estimated threshold voltage, and

setting the intermediate threshold voltage to;

the previous estimated threshold voltage incremented by the resolution of the driver responsive to determining that the threshold voltage is greater than the previous estimated threshold voltage;

the previous estimated threshold voltage responsive to determining that the threshold voltage is equal to the previous estimated threshold voltage;

or

the previous estimated threshold voltage decremented by the resolution of the driver responsive to determining that the threshold voltage is lesser than the previous estimated threshold voltage.

51. The method according to claim 46, wherein the extracting includes:

comparing the monitored current or voltage with a reference value and determining, based on the comparison, an amount to add or subtract to a previous estimated threshold voltage to set the intermediate threshold voltage, wherein the amount to add or subtract is dynamically determined based on the rate of change of the threshold voltage.

52. A system for a display array including a plurality of pixel circuits, each of the plurality of pixel circuits having a driving transistor, at least one switch transistor, a storage capacitor and a light emitting device, the light emitting device being located at a programming path for programming the pixel circuit, the system comprising:

a controller for controlling the operation of the display array;

a driver for providing an operation voltage to at least one pixel circuit of the plurality of pixel circuits based on the control of the controller; and

the driver providing the operation voltage to the at least one pixel circuit during a programming cycle such that the light emitting device is removed from the programming path.

53. The system according to claim 52, wherein the driver provides the operation voltage to the at least one pixel circuit during the programming cycle such that the light emitting device is reversely biased.

54. The system according to claim 52, wherein the at least one pixel circuit comprises a programming transistor, the at least one switch transistor comprises a first switch transistor and a second switch transistor,

gate terminals of the first switch transistor and the second switch transistor being connected to a select line, the first switch transistor and the second switch transistor being connected in series between a data line and a gate terminal of the driving transistor,

a gate terminal of the programming transistor being connected to the gate terminal of the driving transistor, the programming transistor being connected between the light emitting device and a connection point between the first switch transistor and the second switch transistor,

the storage capacitor being connected between the gate terminal of the driving transistor and the light emitting device,

the driving transistor being connected between a supply line and the light emitting device.

55. The system according to claim 52, further comprising an adjustable power supply line for applying a reference voltage sufficient to reverse bias the light emitting device.

56. A method of driving a display array including a pixel circuit programmed through a data line and a current conveyor for extracting a current of the data line, the current conveyor including X, Y, and Z terminals, the X terminal connected to the data line and being forced by feedback to have the same voltage as that of the Y terminal, the current of the X terminal being duplicated to the Z terminal, the method comprising:

providing programming data to the pixel circuit via a data source applying a programming voltage to the Y terminal of the current conveyor;

converting a current on the data line to a voltage associated with the current to extract a time dependent parameter of the pixel circuit via a current-controlled voltage source associated with the data source; and

extracting the current of the data line via the current-controlled voltage source connected to the Z terminal of the current conveyor.

57. The method according to claim 56, further comprising:

calibrating a subsequent programming voltage according to the extracted time dependent parameter; and

providing subsequent programming data to the pixel circuit via the data source applying the calibrated programming voltage to the Y terminal of the current conveyor.

58. A method of driving a display array including a plurality of pixel circuits arranged in a plurality of rows, each of the plurality of pixel circuits including a driving transistor, at least one switch transistor, a storage capacitor, and a light emitting device, the method comprising:

consecutively implementing, to pixel circuits in each row of the display array;

monitoring a current or voltage on pixel circuits in a row;

extracting aging information for the pixel circuits in the row, based on the monitored current or voltage during an extraction operation;

programming the pixel circuits in the row according to programming and calibration data during a programming operation; and

driving the pixel circuits in the row during a driving operation.

59. The method according to claim 58, wherein the extracting includes:

comparing the monitored current or voltage with a reference value,

determining, based on the comparison, whether the threshold voltage of the at least one pixel circuit is greater than, equal to, or lesser than, a previous estimated threshold voltage, and

setting the intermediate threshold voltage to;

the previous estimated threshold voltage incremented by the resolution of the driver responsive to determining that the threshold voltage is greater than the previous estimated threshold voltage;

the previous estimated threshold voltage responsive to determining that the threshold voltage is equal to the previous estimated threshold voltage;

or

the previous estimated threshold voltage decremented by the resolution of the driver responsive to determining that the threshold voltage is lesser than the previous estimated threshold voltage.

60. The method according to claim 58, wherein the extracting includes:

comparing the monitored current or voltage with a reference value and determining, based on the comparison, an amount to add or subtract to a previous estimated threshold voltage to set the intermediate threshold voltage, wherein the amount to add or subtract is dynamically determined based on the rate of change of the threshold voltage.

61. A method of driving a display array including a plurality of pixel circuits each having a driving transistor, at least one switch transistor, a storage capacitor, and a light emitting device, the light emitting device being located at a programming path for programming the pixel circuit, the method comprising:

providing an operation voltage to each of the plurality of pixel circuits via a driver operated based on the control of a controller, during a programming cycle; and

removing the light emitting device from the programming path during the programming cycle by setting a voltage supply line to a reference voltage.