System and method for achieving uniform screen brightness within a matrix display

• US 6,204,834 B1
• Filed: 08/17/1994
• Issued: 03/20/2001
• Est. Priority Date: 08/17/1994
• Status: Expired due to Fees

• Current Assignee: SI Diamond Technology, Inc. (Nano Magic, Inc.)
• Original Assignee: SI Diamond Technology, Inc. (Nano Magic, Inc.)
• Inventors: Baker, Robert C., Donoghue, William J., Kelley, Stephen H., Hilbert, Claude
• Primary Examiner(s): Liang, Regina
• Application Number:
  US08/292,135
• Time in Patent Office: 2,407 Days
• Field of Search: 345/63, 345/74, 345/75, 345/76, 345/77, 345/78, 345/89, 345/101, 345/147, 345/58, 345/148, 315/169.3, 315/169.1, 315/307, 315/308, 315/309, 315/297
• US Class Current: 345/75.2
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/0209 Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display
• 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 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/22 using controlled light sources

Abstract

A system and method for producing uniform energy dissipation in display pixels with widely varying electrical characteristics in order to equalize light output and improve yield within a matrix addressable display panel. The present invention is implemented within a driver circuit utilizing the concept of current integration. A reference voltage, which is proportional to the most efficient pixel within the display is compared to the energy dissipated within a particular pixel during illumination of that pixel. A current mirror circuit supplies a current equivalent to the current provided to the object pixel to an integrator circuit resulting in a rising voltage within the integrator circuit. The rising voltage is proportional to the energy being dissipated within the current pixel. Once the rising voltage is equal to or greater than the reference voltage, current is removed from the object pixel.

Claims

1. A method for increasing uniformity in screen brightness within a field emission matrix addressable display panel, said method comprising the steps of:

measuring energy dissipation in a first pixel within said display panel; and

compensating energy dissipation in a second pixel within said display panel as a function of said measured energy dissipation in said first pixel, wherein said compensating step further comprises the steps of;

integrating a first current signal in response to a received external voltage signal, wherein said first current signal is proportional to said measured energy dissipation;

supplying an energy signal to an electrode associated with said second pixel;

integrating a second current signal wherein said second current signal is proportional to said energy signal; and

removing said energy signal from said electrode in response to a comparison of said integrated first and second current signals.

2. The method as recited in claim 1 wherein said removing step removes said energy signal from said electrode when said integrated second current signal is equal to or greater than said integrated first current signal.

3. A system for displaying images on a matrix addressable display panel, said system comprising:

a plurality of pixels arranged within said display panel; and

driver means for selectively illuminating said pixels, wherein said driver means further comprises;

means for measuring current dissipation in a first pixel within said display panel; and

means for compensating current dissipation in a second pixel within said display panel as a function of said measured current dissipation in said first pixel, wherein said display panel is a diode cold cathode display and wherein said compensating means further comprises;

means for sensing a current supplied to said second pixel within said display;

means for integrating said sensed current;

means for comparing said integrated sensed current to a reference integrated current, wherein said reference integrated current is proportional to said current dissipation in said first pixel; and

means for removing said current from said second pixel when said integrated sensed and reference currents are equal.

4. The system as recited in claim 3 wherein said display panel is a diode cold cathode display, said system further comprising:

a microprocessor; and

a memory coupled to said microprocessor and to said display.

5. The system as recited in claim 3, wherein illumination of each of said pixels in said display panel is controlled on a pixel-by-pixel basis.

6. The system as recited in claim 3, further comprising:

means for compensating current dissipation in a third pixel within said display panel as a function of said measured current dissipation in said first pixel, wherein compensation of said current dissipation in said third pixel is performed independently of compensation of said current dissipation in said second pixel.

7. The system as recited in claim 3, wherein measuring of current dissipation in the first pixel and compensating of current dissipation in the second pixel are both performed in a dynamic manner.

8. A circuit adaptable for regulating energy supplied to a pixel within a matrix addressable display panel, said circuit comprising:

means for comparing a first voltage signal, which is proportional to a second voltage signal supplied to said pixel, to a reference voltage signal, wherein said second voltage signal supplied to said pixel has a substantially constant voltage level; and

means for removing said second voltage signal from said pixel in response to a comparison of said first and reference voltage signals, wherein said removing means turns off said pixel.

9. The circuit as recited in claim 8 wherein said pixel is of a diode configuration having an anode and a cathode.

10. The circuit as recited in claim 8 wherein said pixel is of a triode configuration.

11. The circuit as recited in claim 8, further comprising:

a current integrating means coupled to said comparing means.

12. The circuit as recited in claim 8 wherein said reference voltage signal is supplied by a current integrating means coupled to said comparing means.

13. The circuit as recited in claim 8, further comprising:

means for supplying said reference voltage signal to said comparing means for a period of time proportional to a pulse width modulated signal.

14. The circuit as recited in claim 8 wherein said pixel comprises a field emission device.

15. The circuit as recited in claim 8 wherein said second voltage signal is removed from said pixel when said first voltage signal is equal to or greater than said reference voltage signal.

16. A circuit adaptable for regulating energy supplied to a pixel within a matrix addressable display panel, said circuit comprising:

means for comparing a first voltage signal, which is proportional to a second voltage signal supplied to said pixel, to a reference voltage signal;

means for removing said second voltage signal from said pixel in response to a comparison of said first and reference voltage signals, wherein said removing means turns off said pixel;

a current integrating means coupled to said comparing means; and

a current mirror means coupled to said pixel and to said current integrating means.

17. A circuit adaptable for regulating energy supplied to a pixel within a matrix addressable display panel, said circuit comprising:

means for comparing a first voltage signal, which is proportional to a second voltage signal supplied to said pixel, to a reference voltage signal;

means for removing said second voltage signal from said pixel in response to a comparison of said first and reference voltage signals, wherein said removing means turns off said pixel, wherein said reference voltage signal is supplied by a current integrating means coupled to said comparing means; and

a current source coupled to said current integrating means, said current source supplying a current proportional to energy required by a “

hottest”

pixel within said display panel.

18. A driver circuit adaptable for substantially equalizing light emitted from each of a plurality of pixels within a display, said circuit comprising:

means for mirroring a first current supplied to a particular pixel within said display, wherein said mirroring means produces a second current proportional to said first current;

means for integrating said second current;

means for comparing said integrated second current to an integrated reference current; and

means for removing said first current from said particular pixel when said integrated second and reference currents are at a predetermined ratio relative to each other.

19. The driver circuit as recited in claim 18 wherein said plurality of pixels are cold cathode field emission devices.

20. The driver circuit as recited in claim 19 wherein said field emission devices include a thin film of diamond as an emissive material.

21. The driver circuit as recited in claim 18 wherein said reference integrated current is switched “

on”

or “

off”

by a varying voltage signal.

22. The driver circuit as recited in claim 21 wherein said varying voltage signal is a pulse width modulated signal.

23. The driver circuit as recited in claim 18 wherein said reference integrated current is proportional to a voltage applied to a highest current/constant voltage pixel within said display.

24. The driver circuit as recited in claim 18, further comprising:

means for discharging said integrating means.

25. The driver circuit as recited in claim 18, further comprising:

means for deactivating said integrating means.

26. The driver circuit as recited in claim 18, further comprising:

means for precharging said particular pixel with a potential lower than required for activation of said particular pixel.

27. The driver circuit as recited in claim 18 wherein said display comprises:

a plurality of anode strips,

wherein said driver circuit is adaptable for selectively activating any one of said plurality of anode strips;

a plurality of cathode strips arranged in orthogonal relationship with said anode strips;

a phosphor coupled to said anode strips,

wherein each of said plurality of pixels is located at an intersection of one of said plurality of anode strips and one of said plurality of cathode strips; and

a cathode driver circuit adaptable for selectively activating any of said plurality of cathode strips.

28. A method for activating an electrode within a display panel, said method comprising the steps of:

comparing a first voltage, which is proportional to a second voltage supplied to said electrode, to a reference voltage;

removing said second voltage from said electrode in response to said comparing step so that there is no voltage being supplied to said electrode; and

precharging said electrode to a predetermined voltage level prior to supplying said second voltage to said electrode.

29. The method as recited in claim 28, further comprising the step of:

supplying said second voltage to said electrode in response to a selected signal.

30. The method as recited in claim 28, further comprising the step of:

modulating said reference voltage in response to an externally supplied variable signal.

31. The method as recited in claim 28 wherein said second voltage is removed from said electrode when said first voltage is equal or greater than said reference voltage.

32. A method for driving a pixel within a matrix addressable display panel, said method comprising the steps of:

integrating a first current signal in response to a received external voltage signal;

supplying an energy signal to an electrode associated with said pixel;

integrating a second current signal, wherein said second current signal is proportional to said energy signal;

comparing said integrated first and second current signals; and

removing said energy signal from said electrode in response to said comparing step.

33. The method as recited in claim 32 wherein said removing step removes said energy signal when said integrated second current signal is equal to or greater than said integrated first current signal.

34. The method as recited in claim 32 wherein said integrating step further comprises the step of:

mirroring a current signal provided to said electrode in order to produce said second current signal.

35. The method as recited in claim 32 wherein said first current signal is proportional to current drawn by a most efficient pixel within said display panel.

36. The method as recited in claims 32, further comprising the step of:

precharging said electrode with a voltage below a threshold level required to activate said pixel.

37. The method as recited in claim 32, further comprising the steps of:

monitoring said energy signal; and

temporarily suspending said integrating step in response to said monitoring step.

38. The method as recited in claim 37, wherein said step of monitoring said energy signal further comprises monitoring said electrode associated with said pixel for a noise-related signal.

39. The method as recited in claim 38, wherein said noise-related signal is due to crosstalk between said electrode associated with said pixel and another electrode associated with a second pixel within said matrix addressable display panel.

40. A circuit adaptable for activating a pixel within a matrix addressable display panel, said circuit comprising:

first circuitry for selectively coupling a first voltage signal to an electrode associated with said pixel;

second circuitry for integrating a first current signal proportional to said first voltage signal, wherein said second circuitry further comprises;

a current mirror circuit coupled to said electrode;

a first switching device coupled to said current mirror circuit; and

a first capacitor coupled to said first switching device;

third circuitry for comparing said integrated first current signal to a reference voltage signal, said reference voltage signal dependent upon a received modulating signal; and

fourth circuitry, coupled to said third circuitry, for modulating said first voltage signal.

41. The circuit as recited in claim 40 wherein said first circuitry further comprises:

a second switching device coupled to said current mirror circuit, wherein said second switching device is responsive to said third circuitry.

42. The circuit as recited in claim 41, further comprising:

a second capacitor for storing said reference voltage signal;

a third switching device coupled to said second capacitor, wherein said third switching device is responsive to said received modulating signal; and

a second voltage signal coupled to said third switching device.

43. The circuit as recited in claim 42 wherein said third circuitry further comprises:

a comparator coupled to said first and second capacitors, and

wherein said fourth circuitry is coupled to said first switching device.

44. The circuit as recited in claim 40 wherein said second circuitry includes a capacitor for storing said reference voltage signal and for integrating said first current signal.

45. The circuit as recited in claim 40 wherein said second, third, and fourth circuitry are implemented on a low-voltage chip.

46. A circuit adaptable for activating a pixel within a matrix addressable display panel, said circuit comprising:

first circuitry for selectively coupling a first voltage signal to an electrode associated with said pixel;

second circuitry for integrating a first current signal proportional to said first voltage signal;

third circuitry for comparing said integrated first current signal to a reference voltage signal, said reference voltage signal dependent upon a received modulating signal;

fourth circuitry, coupled to said third circuitry, for modulating said first voltage signal; and

fifth circuitry for precharging said electrode.

47. The circuit as recited in claim 46 wherein said fifth circuitry further comprises:

a switching device for selectively coupling a second voltage signal to said electrode.

48. A circuit adaptable for driving an electrode within a display panel, said circuit comprising:

means for switching current to said electrode;

means for sampling said current supplied to said electrode;

means adaptable for providing said sampled current to an external circuit; and

means, coupled to said switching means, for removing said current from said electrode in response to a signal from said external circuit so that no current is supplied to said electrode, wherein said switching means comprises a FET, said monitoring means comprises a current mirror circuit, and said removing means comprises a FET.

49. The circuit as recited in claim 48 wherein said electrode is part of a field emission device.

50. A circuit adaptable for providing a switching signal operable for switching an energy source to an electrode within a display panel, said circuit comprising:

means adaptable for receiving a first energy signal proportional to an amount of energy supplied from said energy source to said electrode;

first means, coupled to said receiving means, for integrating said first energy signal;

second means for integrating a second energy signal proportional to a received modulating signal;

means for comparing said first and second integrated energy signals; and

means for outputting said switching signal in response to said comparison of said first and second integrated energy signals.

51. The circuit as recited in claim 50 wherein said modulating signal is a pulse width modulated signal.

52. The circuit as recited in claim 50 wherein said second energy signal is proportional to an energy signal supplied to a highest current/constant voltage pixel within said display panel.

53. The circuit as recited in claim 50, further comprising:

means for initializing said first and second integrating means.

54. The circuit as recited in claim 50 wherein said first and second integrating means are a capacitor.

55. A circuit comprising:

means for monitoring an energy signal applied to a pixel in a display device; and

means for modifying said energy signal applied to said pixel in response to detection of a noise-related signal in said energy signal by said monitoring means.

56. The circuit as recited in claim 55, wherein said monitoring means further comprises a switching means for detecting said noise-related signal, wherein said modifying means further comprises a logical device coupled to said switching means, wherein upon said detection of said noise-related signal, said switching means causes said logical device to output a signal that causes said modification of said energy signal.

57. The circuit as recited in claim 55, wherein said display device is an FED matrix addressable flat panel display, and said noise-related signal is caused by crosstalk between electrodes of said pixel and another pixel within said display.