TEMPERATURE BASED WHITE POINT CONTROL IN BACKLIGHTS

• US 20100244701A1
• 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, Zhong, John Z., Qi, Jun, Chen, Wei, Yin, Victor H.
• Granted Patent: US 8,575,865 B2
• Time in Patent Office: Days
• US Class Current: 315/117
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• 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; and

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

2. The display of claim 1, wherein the plurality of light emitting diodes are selected from neighboring bins surrounding a bin encompassing the target white point.

3. The display of claim 1, wherein the controller is configured to detect the temperature change based on an operational state of the backlight.

4. The display of claim 1, comprising a memory configured to store a calibration curve defining driving strength adjustments based on the detected temperature change.

5. The display of claim 1, comprising one or more sensors disposed in the backlight and configured to detect the temperature change.

6. The display of claim 5, wherein the sensors comprise optical sensors configured to sense a color of the emitted white point, and wherein the controller is configured to detect the temperature change based on the sensed color.

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;

a dedicated light emitting diode string disposed in an electronics region of the backlight;

a driver configured to independently drive the plurality of light emitting diodes at specified driving strengths and to drive the dedicated light emitting diode string at a dedicated driving strength; and

a controller configured to detect a temperature change within the display and to adjust the dedicated driving strength to compensate for a shift in the emitted white point due to the temperature change.

8. The display of claim 7, wherein the electronics region is adjacent to circuit boards.

9. The display of claim 7, wherein the plurality of light emitting diode strings comprise are configured to emit a first range of chromaticity values, and the dedicated light emitting diode string is configured to emit a second range of chromaticity values outside of the first range.

10. The display of claim 7, wherein the plurality of light emitting diode strings comprises a first string disposed in the electronics region and a second string disposed outside of the electronics region.

11. The display of claim 7, wherein the plurality of light emitting diode strings are disposed in a light strip and the dedicated light emitting diode string is disposed in another light strip.

12. The display of claim 7, comprising one or more sensors configured to measure temperatures within the backlight, and wherein the controller is configured to detect the temperature change based on the measured temperatures.

13. The display of claim 12, wherein the one or more sensors are configured to detect a temperature gradient within the backlight, and wherein the controller is configured to adjust the specified driving strengths and the dedicated driving strength to compensate for the temperature gradient.

14. 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 a temperature change within the backlight;

determining a shift in the emitted white point based on the detected temperature change; and

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

15. The method of claim 14, wherein detecting a temperature change comprises sensing a color of light output by the light emitting diode strings and correlating the sensed color to the temperature change.

16. The method of claim 14, wherein detecting a temperature change comprises receiving a temperature of the backlight from a temperature sensor disposed within the backlight.

17. The method of claim 14, wherein detecting a temperature change comprises detecting an operating period of the backlight, and wherein adjusting at least one of the respective driving strengths comprises adjusting the respective driving strength at a rate determined by a calibration curve for the detected operating period.

18. The method of claim 14, wherein adjusting at least one of the respective driving strengths comprises varying the respective driving strength at a constant rate until a temperature stabilization period is detected.

19. The method of claim 14, wherein dynamically adjusting at least one of the respective driving strengths comprises:

determining a temperature gradient within the backlight through feedback received from one or more temperature sensors; and

adjusting the respective driving strengths to balance the white point across the temperature gradient.

20. The method of claim 14, comprising determining a temperature profile within the backlight based on the detected temperature change.