Adaptive control boost current method and apparatus

• US 20030156101A1
• Filed: 10/17/2002
• Published: 08/21/2003
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Clare Micronix Integrated Systems, Inc.
• Original Assignee: Clare Micronix Integrated Systems, Inc.
• Inventors: LeChevalier, Robert
• Granted Patent: US 7,019,720 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• 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 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• 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 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

A method and apparatus for adapting and applying current boost levels to precharge current-driven elements in a matrix, and a method to make devices for this purpose. Elements are driven during successive scan cycles, each having a precharge period and an exposure period. One or more conduction voltages are sensed while an element conducts a selected exposure current, with early samples taken nearer the beginning of exposures and late samples taken nearer the end. Charge delivered during the precharge period is adjusted to reduce differences between early and late voltage samples.

Claims

1. A method of controlling a quantity of electrical charge provided to a matrix display connection during a precharge period, the method comprising:

driving a current through a matrix element connected to a first matrix connection during a conduction period;

deriving a control voltage from at least one voltage from a path of the current;

adjusting the quantity of electrical charge based at least in part upon the derived control voltage; and

providing the adjusted electrical charge quantity to a second matrix connection during the precharge period.

2. The method of claim 1, wherein the first and second matrix connections are the same connection.

3. The method of claim 1, further comprising changing the provided electrical charge quantity by changing a level of precharge current supplied during the precharge period.

4. The method of claim 1, further comprising changing the provided electrical charge quantity by applying precharge current for a selectively changed duration during the target precharge period.

5. The method of claim 1, further comprising changing the electrical charge quantity provided to a particular matrix connection during the precharge period by providing current to the particular matrix connection for an adjusted length of time within the precharge period.

6. The method of claim 1, further comprising basing the control voltage level on voltages of the matrix connection generated at a plurality of distinct periods during the conduction period

7. The method of claim 6, wherein:

a first period of the plurality of distinct periods is within four microseconds of a beginning of a conduction period; and

a second period of the plurality of different periods is closer to an end than to the beginning of the conduction period.

8. The method of claim 6, wherein a first period of the plurality of distinct periods is an early period located closer to a beginning than to an end of a corresponding conduction period.

9. The method of claim 8, wherein a second period of the plurality of distinct periods is a late period which ends a substantially greater time after a beginning of an associated conduction period than a time between the end of the early period and the beginning of the conduction period corresponding to the early period.

10. The method of claim 9, wherein the early period and the late period end during the same conduction period.

11. The method of claim 1, wherein the control voltage is responsive to a combination of voltages corresponding to a plurality of elements conducting concurrently.

12. The method of claim 1, wherein the control voltage is responsive to a combination of voltages derived from a plurality of elements conducting nonconcurrently.

13. The method of claim 1, wherein the matrix element comprises an organic light emitting diode (OLED).

14. The method of claim 1, wherein:

the control voltage is responsive to a difference between a first voltage and a second voltage;

the first voltage is derived from at least one voltage generated during an early portion of the conduction period; and

the second voltage is derived from at least one voltage generated after the early portion of the conduction period.

15. The method of claim 14, further comprising:

determining differences between the first voltage and the second voltage;

integrating the differences; and

adjusting a charge delivered during the target precharge period based on a result of the integration.

16. The method of claim 15, further comprising changing the quantity of charge delivered during the precharge period by adjusting a current level supplied during the precharge period.

17. The method of claim 14, further comprising providing at least a part of the charge quantity under control of a current reference.

18. The method of claim 17, wherein the current reference controls the current.

19. The method of claim 1, further comprising:

digitizing voltages present during conduction; and

manipulating resultant digitized voltage values to control adjustment of the charge quantity.

20. The method of claim 19, further comprising:

sampling voltages from selected matrix connections at early and late times relative to corresponding conduction period spans;

determining a difference between the voltages sampled at early times and the voltages sampled at late times; and

adjusting the charge quantity in accordance with a deviation of the determined difference from a desired value for the difference.

21. The method of claim 1, further comprising omitting provision of boost current to a particular matrix element connection during a precharge period preceding an exposure period for which a conduction period of zero is assigned to the particular matrix connection.

22. The method of claim 1, further comprising discharging a particular matrix connection to a lower voltage during an exposure period at a termination of a conduction period for the particular matrix connection.

23. The method of claim 1, further comprising providing a boost current to a matrix connection during a particular precharge period only When:

(i) the matrix connection has not conducted current since a most recent discharge of the connection; and

(ii) a non-zero conduction is assigned for the matrix connection during a conduction period immediately following the particular precharge period.

24. The method of claim 1, further comprising:

deriving the control voltage with respect to a first reference voltage; and

adjusting the charge quantity with respect to a second reference voltage.

25. A method of adapting a precharge current delivered to a matrix, the method comprising:

selecting the matrix element for sampling;

applying a predetermined precharge current to the matrix element during a precharge period of a scan cycle;

driving an exposure current into the selected matrix element during an exposure period of the scan cycle;

sampling a conduction voltage during the exposure period of the scan cycle; and

determining a subsequent precharge current level for the matrix element based at least in part on the sampled conduction voltage.

26. The method of claim 25, further comprising:

sampling the conduction voltage relative to a first reference voltage; and

controlling the subsequent precharge current level with a signal relative a second reference voltage.

27. A method of manufacturing a circuit for controlling current drive to display elements, comprising:

configuring a plurality of exposure current sources to provide exposure currents to a plurality of display elements during an exposure period;

connecting a voltage sampling circuit, configured to obtain a plurality of sample voltages, to at least one conduction path of the exposure currents;

configuring combiner circuitry to combine the plurality of sample voltages;

connecting a precharge current source to at least one of the plurality of display elements to supply a precharge current thereto during a precharge period; and

providing a control, responsive to a combination of the plurality of sample voltages, of the precharge current delivery.

28. The method of claim 27, wherein:

the precharge current delivery control comprises a current control signal that

is responsive to the plurality of sample.

29. The method of claim 27, further comprising configuring the precharge current delivery control to adjust level of the precharge current during the precharge period.

30. The method of claim 27, further comprising configuring the control to adjust duration of current delivery during precharge.

31. The method of claim 27, further comprising:

incorporating an early sample combiner configured to combine voltages sampled during early portions of exposure period;

configuring a late sample combiner to combine voltages sampled during later portions of the exposure period; and

controlling the precharge current control circuit based at least in part on differences between combined early voltages and combined late voltages.

32. A method of controlling conduction of electrical charge to a matrix display during a precharge period, the method comprising:

supplying a current to a matrix element during a conduction period;

deriving a control voltage from at least one voltage from a path of the conduction period current;

adjusting a charge quantity based at least in part upon the derived control voltage; and

providing the adjusted charge quantity to at least one matrix element during a subsequent precharge period.

33. The method of claim 32, wherein:

deriving a control voltage comprises relating the control voltage to a first reference voltage; and

adjusting the charge quantity comprises providing a current control signal with respect to a different second reference voltage.

34. The method of claim 32, further comprising obtaining early conduction voltages at an early time preceding midway through the conduction period.

35. The method of claim 33, further comprising obtaining late conduction voltages at a late time which is later than are early time and within the conduction period.

36. The method of claim 34, wherein obtaining the early and late conduction voltages occurs within a single conduction period.

37. The method of claim 35, further comprising determining the derived control voltage based at least in part on a comparison of early and late conduction voltages.

38. The method of claim 36, further comprising integrating differences between early and late voltages.

39. An apparatus for driving current in devices of a matrix, comprising:

a first driver circuit connectable to a first terminal of a matrix element to provide a current thereto;

a sink circuit connectable to a second terminal of the matrix element to accept current conducted by the matrix element;

a sensing circuit configured to store a voltage developed when the matrix element conducts part of the current; and

a second driver circuit configured to output a quantity of charge which varies in response to the stored voltage.

40. The apparatus of claim 39, wherein the second driver circuit drives a current at a level which varies in response to the stored conduction voltage.

41. The apparatus of claim 39, wherein the second driver circuit comprises a precharge circuit having a conduction time control configured to conduct for a selectably variable portion of a precharge period.

42. The apparatus of claim 39, wherein the sensing circuit is configured to sense voltages developed at a plurality of different times relative to a conduction period span.

43. The apparatus of claim 42, wherein:

the sensing circuit is further configured to sense early voltages at times less than half of the conduction period span from a beginning of the span; and

the sensing circuit is further configured to sense late voltages at conduction period times substantially later than early voltage sensing times.

44. The apparatus of claim 43, wherein the second driver circuit is configured to adjust the output charge quantity based upon a difference between the early voltages and the late voltages.

45. The apparatus of claim 44, wherein the second driver circuit is configured to adjust the output charge quantity by varying a precharge current drive level based upon the difference between the early voltages and the late voltages.

46. The apparatus of claim 39, further comprising switches selectably coupling the sensing circuit to one of a plurality of matrix element voltages.

47. The apparatus of claim 39, further comprising a plurality of switches configured to selectably couple a plurality of voltage sensing circuits to a pre-exposure charge adjusting circuit.

48. The apparatus of claim 47, wherein the voltage sensing circuits comprise sample and hold circuits.

49. The apparatus of claim 48, wherein the pre-exposure charge adjusting circuit comprises a digital processor.

50. The apparatus of claim 39, wherein the matrix element comprises an organic light emitting diode (OLED).

51. The apparatus of claim 39, wherein the sensing circuit further comprises a combining circuit for combining voltages sensed at different times.

52. The apparatus of claim 51, wherein the combining circuit is configured to combine sensed voltages which correspond to different scan cycles.

53. The apparatus of claim 52, wherein the combining circuit comprises a first combining circuit configured to combine a plurality of voltages each sensed during an early portion of a corresponding conduction period to form a combined early voltage.

54. The apparatus of claim 53, further comprising a second combining circuit configured to combine a plurality of voltages each sensed during a late portion of a conduction period to form a combined late voltage.

55. The apparatus of claim 54, further comprising:

an integrator configured to integrate a value derived from a difference between the combined early voltage and the combined late voltage and producing an integrated difference value; and

a precharge current level control circuit responsive to the integrated difference value.

56. The apparatus of claim 55, wherein the integrator and precharge current level control circuit operate on digital value representations.

57. The apparatus of claim 55, wherein the integrator and precharge current level control circuit do not require digital representation of values.

58. The apparatus of claim 39, wherein the sensing circuit further comprises a combining circuit for combining voltages sensed at concurrent times.

59. The apparatus of claim 39, wherein:

the sensing circuit is further configured to sense the voltage relative to a first reference voltage; and

the second driver circuit is further configured to control a current source with respect to a different second reference supply of voltage.

60. An apparatus for controlling the supply of a current to a plurality of display elements, comprising:

an exposure current source configured to provide a current to at least one of the display elements during exposure periods;

a voltage sampling circuit configured to obtain a plurality of sample voltages from a conduction path of the exposure current;

a sample voltage combiner configured to combine the plurality of sample voltages; and

a precharge circuit configured to change a precharge current level based at least in part upon the combined sample voltages.

61. The apparatus of claim 60, wherein:

the plurality of sample voltages are obtained relative to a first reference voltage; and

the precharge circuit comprises a precharge current source controlled by a signal with respect to a different second reference voltage.

62. The apparatus of claim 60, further comprising:

a first sample combiner configured to combine voltages sampled during a first portion of an exposure period; and

a second sample combiner configured to combine voltages sampled during a second portion of the exposure period, wherein the first portion occurs before the second portion; and

wherein the precharge circuit is further configured to adjust the precharge current level based upon differences between combined early voltages and combined late voltages.

63. An apparatus for driving current in devices of a matrix, comprising:

means for driving current to a matrix element during a conduction period;

means for receiving current from the matrix element;

means for sensing a voltage developed when the matrix element conducts at least part of the conduction current; and

means for outputting, during a precharge period, a quantity of charge which varies in response to a signal derived from the means for sensing the voltage.

64. The apparatus of claim 63, wherein:

the voltage sensing means senses the voltage relative to a first reference voltage.

65. The apparatus of claim 63, wherein the means for outputting a charge quantity during precharge comprises a means for adjusting a precharge drive current in response to a signal derived from the means for sensing the voltage.

66. The apparatus of claim 63, wherein the means for outputting a charge quantity during precharge comprises means for conducting current for a selectably variable portion of a precharge period.

67. The apparatus of claim 63, wherein the means for sensing the voltage comprises means for sensing voltages developed at a plurality of different times relative to a conduction period span.

68. The apparatus of claim 67, wherein the means for sensing the voltage comprises:

means for sensing early voltages at early voltage sensing times which are less than half of a conduction period span from a beginning of the span; and

means for sensing late voltages at conduction period times which are substantially later than early voltage sensing times.

69. The apparatus of claim 68, wherein the means for outputting a charge quantity during precharge comprises means for adjusting the output charge quantity based upon a difference between the early voltages and the late voltages.

70. The apparatus of claim 69, wherein the means for outputting a charge quantity during precharge comprises means for adjusting the output charge quantity by varying a precharge current drive level based upon the difference between the early voltages and the late voltages.

71. The apparatus of claim 63, further comprising means for selectably coupling the voltage sensing means to one of a plurality of matrix elements.

72. The apparatus of claim 63, further comprising means for selectably coupling a plurality of voltage sensing circuits to a pre-exposure charge adjusting circuit.

73. The apparatus of claim 72, wherein the means for sensing the voltage comprises at least one sample and hold circuit.

74. The apparatus of claim 73, wherein the pre-exposure charge adjusting circuit comprises a digital processor.

75. The apparatus of claim 73, wherein the pre-exposure charge adjusting circuit comprises an integrated circuit.

76. The apparatus of claim 63, wherein the means for sensing the voltage comprises means for combining voltages sensed at different times.

77. The apparatus of claim 76, wherein the means for sensing the voltage comprises means for combining sensed voltages which correspond to different scan cycles.

78. The apparatus of claim 77, wherein the means for sensing the voltage comprises means for combining a plurality of voltages, each sensed during an early portion of a corresponding conduction period, to form a combined early voltage.

79. The apparatus of claim 78, wherein the means for sensing the voltage further comprises means for combining a plurality of voltages, each sensed during a late portion of a conduction period, to form a combined late voltage.

80. The apparatus of claim 79, wherein:

the means for sensing the voltage further comprises means for obtaining differences between the combined early voltage and the combined late voltage;

the means for sensing the voltage further comprises means for integrating the obtained differences; and

wherein voltage derived from the means for sensing the voltage is derived from the integrated differences.

81. The apparatus of claim 80, wherein the obtained differences are represented digitally.

82. The apparatus of claim 80, wherein the obtained differences are represented by circuit voltages.