Aging based white point control in backlights

• US 8,390,562 B2
• Filed: 03/24/2009
• Issued: 03/05/2013
• Est. Priority Date: 03/24/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chen, Cheng, Qi, Jun, Zhong, John Z., Yin, Victor H., Chen, Wei
• Primary Examiner(s): Cheng, Joe H
• Application Number:
  US12/410,204
• Publication Number:
  US 20100245228A1
• Time in Patent Office: 1,442 Days
• Field of Search: 345/102, 345/204, 345/609, 345/691, 345 87- 91, 345/690, 315/149, 315/224, 315/291, 315/307, 315/308, 315/312
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

Systems, methods, and devices are provided for maintaining a target white point on a light emitting diode based backlight. In one embodiment, the backlight may include two or more strings of light emitting diodes, each driven at a respective driving strength. Each string may include light emitting diodes from a different color bin, and the respective driving strengths may be adjusted, for example, through pulse width modulation or amplitude modulation, to maintain the target white point. In certain embodiments, the driving strengths may be adjusted to compensate for shifts in the white point that may occur due to temperature or aging. A controller may adjust the driving strengths based on feedback from a temperature sensor, from an optical sensor, from a user input, or from calibration data included within the backlight or system.

Claims

1. A display comprising:

a plurality of light emitting diodes arranged within a backlight to produce an emitted white point that corresponds to a target white point;

one or more drivers configured to drive groups of one or more light emitting diodes of the plurality of light emitting diodes at a respective driving strength;

one or more sensors disposed within the backlight with the plurality of light emitting diodes; and

a controller configured to detect aging within the display, to adjust at least one of the respective driving strengths to compensate for a shift in the emitted white point due to the aging, and to tune the respective driving strengths based on feedback received from the one or more sensors.

2. The display of claim 1, wherein the groups of one or more light emitting diodes comprise a first group of one or more light emitting diodes that comprises light emitting diodes from a first bin that defines a first range of color values, and wherein the groups of one or more light emitting diodes comprise a second group of one or more light emitting diodes that comprises light emitting diodes from a second bin that defines a second range of color values, and wherein the first range of color values is different from the second range of color values.

3. The display of claim 1, wherein the plurality of light emitting diodes are mounted within the backlight at spatially distributed positions for mixing their light outputs to produce the emitted white point.

4. The display of claim 1, wherein the plurality of light emitting diodes comprises at least one color compensating light emitting diode, and wherein the controller is configured to adjust the driving strength of the color compensating light emitting diode while maintaining the driving strength of the other light emitting diodes at a constant rate.

5. The display of claim 1, wherein the plurality of light emitting diodes each comprises a plurality of blue dies with yellow phosphor, and wherein the at least one respective driving strength drives light emitting diodes with a yellow tint when compared to the target white point.

6. The display of claim 1, comprising a liquid crystal display panel configured to be illuminated by the backlight.

7. A display comprising:

a plurality of light emitting diode strings each arranged within a backlight to produce an emitted white point that substantially matches a target white point;

one or more drivers configured to independently drive each of the plurality of light emitting diode strings at a respective driving strength;

one or more sensors disposed within the backlight, wherein the one or more sensors are intermixed with the plurality of light emitting diode strings; and

a controller configured to detect aging within the display based on feedback received from the one or more sensors and to adjust at least one of the respective driving strengths to compensate for a shift in the emitted white point due to the aging.

8. The display of claim 7, wherein the one or more sensors comprise optical sensors and wherein the feedback comprises a color or a brightness of light emitted by the backlight.

9. The display of claim 7, wherein the controller is configured to determine the shift in the emitted white point based on color values received from the one or more sensors.

10. The display of claim 9, wherein the controller is configured to adjust the at least one of the respective driving strengths based on the determined shift.

11. The display of claim 7, wherein the one or more sensors are configured to detect a brightness level of the backlight, and wherein the controller is configured to determine a magnitude of the driving strength adjustment based on the brightness level.

12. A display comprising:

a plurality of light emitting diode strings each arranged within a backlight to produce an emitted white point that substantially matches a target white point;

one or more drivers configured to independently drive each of the plurality of light emitting diode strings at a respective driving strength;

one or more optical sensors disposed within the backlight, wherein the one or more sensors are intermixed with the plurality of light emitting diode strings;

a memory configured to store compensation information correlating color feedback or brightness feedback, or both, from the one or more optical sensors of the backlight to a shift in the emitted white point; and

a controller configured to detect aging within the display based on the color feedback or the brightness feedback, or both, received from the one or more sensors, to adjust at least one of the respective driving strengths to compensate for the shift in the emitted white point, to receive a fine adjustment input from a user or a networked electronic device, and to adjust at least one of the respective driving strengths based at least in part on the fine adjustment input.

13. The display of claim 12, wherein the compensation information comprises at least one of a calibration curve, a table, or an algorithm.

14. The display of claim 12, wherein the controller is configured to determine a driving strength adjustment for the at least one respective driving strength based on a calibration curve defining driving strength increases based on the color feedback or the brightness feedback, or both.

15. The display of claim 12, wherein the controller is configured to continuously increase the at least one respective driving strength based at least in part on the detected aging at a rate defined by the compensation information.

16. A method of operating a backlight, the method comprising:

independently driving each of a plurality of light emitting diode strings at a respective driving strength to produce an emitted white point that substantially matches a target white point;

detecting aging within the backlight;

determining a shift in the emitted white point based on the detected aging;

adjusting at least one of the respective driving strengths to compensate for the shift;

receiving a fine adjustment input; and

adjusting the at least one of the respective driving strengths based at least in part on the fine adjustment input.

17. The method of claim 16, wherein detecting aging within the backlight comprises receiving backlight operational time from a clock.

18. The method of claim 17, wherein determining a shift in the emitted white point comprises comparing the operational time to a calibration curve correlating operational time to the shift in the emitted white point.

19. The method of claim 16, wherein determining a shift in the emitted white point comprises comparing color or brightness values received from an optical sensor to target white point values.

20. The method of claim 16, wherein adjusting the driving strength comprises comparing at least two of the respective driving strengths to determine whether the at least two respective driving strengths vary from each other by less than a specified amount.

21. The method of claim 16, wherein the fine adjustment input comprises color or brightness values received from an optical sensor.

22. The method of claim 16, wherein the fine adjustment input comprises a user input.

23. The method of claim 16, wherein the fine adjustment input is received through a network connection.