WHITE POINT CONTROL IN BACKLIGHTS

• US 20100245227A1
• Filed: 03/24/2009
• Published: 09/30/2010
• Est. Priority Date: 03/24/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chen, Cheng, Chen, Wei, Zhong, John Z., Qi, Jun, Yin, Victor H.
• Granted Patent: US 8,378,958 B2
• Time in Patent Office: Days
• 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 2320/0633 by amplitude modulation of the brightness of the illumination source
• 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 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/28 using temperature feedback

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 backlight, comprising:

a first string of first light emitting diodes each selected from a first bin and configured to be driven at a first driving strength;

a second string of second light emitting diodes each selected from a second bin and configured to be driven at a second driving strength; and

a controller configured to dynamically adjust at least one of the first or second driving strengths to produce a white point substantially similar to a target white point.

2. The backlight of claim 1, wherein the first and second bins each define a different range of chromaticity values.

3. The backlight of claim 1, wherein the first and second light emitting diodes comprise phosphorous light emitting diodes.

4. The backlight of claim 1, comprising a driver with a first channel configured to drive the first string of first light emitting diodes and a second channel configured to drive the second string of second light emitting diodes.

5. The backlight of claim 1, wherein the first and second strings are mounted within an array tray of the backlight.

6. The backlight of claim 1, wherein the first and second strings are mounted within one or more light strips of the backlight.

7. A backlight, comprising:

a plurality of light emitting diode strings each comprising a group of light emitting diodes selected from a same bin of a plurality of bins and each arranged within the 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;

a memory configured to store values defining the target white point; and

a controller configured to detect a shift in the emitted white point and to adjust at least one of the respective driving strengths to compensate for the shift.

8. The backlight of claim 7, wherein at least one of the plurality of bins encompasses the target white point.

9. The backlight of claim 7, wherein the plurality of bins comprise complementary bins each bordering another bin encompassing the target white point.

10. The backlight of claim 7, wherein the one or more drivers are configured to receive control signals from the controller to adjust the respective driving strengths.

11. The backlight of claim 7, wherein the values comprise x and y chromaticity coordinates.

12. A backlight, comprising:

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

one or more drivers configured to drive the plurality of light emitting diode strings;

a color compensating string of color compensating light emitting diodes configured to be driven independently from the plurality of light emitting diode strings at a color compensating driving strength; and

a controller configured to detect a shift in the emitted white point and to vary the color compensating driving strength to counteract the shift in the emitted white point.

13. The backlight of claim 12, wherein the color compensating string is intermixed with the plurality of light emitting diode strings.

14. The backlight of claim 12, wherein the plurality of light emitting diode strings each comprise white light emitting diodes configured to emit light within a range of chromaticity values;

and wherein the color compensating light emitting diodes are configured to emit a color compensating light outside of the range.

15. The backlight of claim 12, wherein the plurality of light emitting diode strings are each configured to be driven at a constant rate.

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

driving a first string of first light emitting diodes selected from a first bin at a first driving strength;

driving a second string of second light emitting diodes selected from a second bin at a second driving strength, wherein the first and second driving strengths are configured to produce an emitted color that corresponds to a target white point;

receiving feedback indicating a shift in the emitted color; and

dynamically adjusting at least one of the first or second driving strengths to return the emitted color to the target white point.

17. The method of claim 16, wherein receiving feedback comprises receiving at least one of a user input, a sensed temperature, or a sensed light color.

18. The method of claim 16, wherein dynamically adjusting at least one of the first or second driving strengths comprises modulating a duty cycle of a current driven through at least one of the first or second strings using pulse width modulation.

19. The method of claim 16, wherein adjusting at least one of the first or second driving strengths comprises varying an amount of a current driven through at least one of the first or second strings using amplitude modulation.

20. The method of claim 16, wherein adjusting at least one of the first or second driving strengths comprises receiving at least one of a color or brightness value from a sensor and determining a driving strength adjustment based on the value.

21. A system comprising:

a backlight with a plurality of light emitting diode strings each comprising a group of light emitting diodes selected from a same bin of a plurality of bins and each arranged within the backlight to produce an emitted white point that substantially matches a target white point;

a controller configured to dynamically and independently adjust driving strengths of the plurality of light emitting diode strings to maintain the emitted white point; and

a liquid crystal display panel configured to be illuminated by the backlight.

22. The system of claim 21, comprising a processor configured to generate images to display on the liquid crystal display panel.

23. The system of claim 21, wherein the system comprises a laptop computer, a desktop computer, or a computer monitor.

24. The system of claim 21, comprising a user interface configured to receive a user input, wherein the controller is configured to adjust the driving strengths based on the user input.