DEVICES AND METHODS FOR CONTROLLING BRIGHTNESS OF A DISPLAY BACKLIGHT

• US 20140097765A1
• Filed: 11/16/2012
• Published: 04/10/2014
• Est. Priority Date: 10/05/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hussain, Asif, Pandya, Manisha P., Chen, Jingdong
• Granted Patent: US 9,826,596 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation

Abstract

Devices and methods for controlling brightness of a display backlight are provided. A display backlight controller may control the brightness of the display backlight by changing a duty cycle of a PWM signal that drives the LED current. However, because of LED efficacy and response time, the final output brightness (NITS) may not be linear between 0% to 100%. The disclosed methods may be used to correct the brightness using a predetermined correction factor. Further, the minimum and maximum duty cycle of the output dimming duty cycle may be limited or corrected. In one example, a backlight controller receives an input duty cycle and determines a product of the input duty cycle and a maximum duty cycle to produce a reduced duty cycle. Moreover, the backlight driver may determine a corrected duty cycle using the correction factor. The final output duty cycle and LED current may then be determined.

Claims

1. A backlight driver chip for an electronic device comprising:

an input configured to receive data corresponding to a duty cycle;

correction circuitry configured to determine a brightness correction factor based at least partially on the duty cycle and to determine a corrected duty cycle based at least partially on the brightness correction factor; and

an output configured to provide a current signal for driving a backlight device, wherein the current signal is based at least partially on the corrected duty cycle.

2. The backlight driver chip of claim 1, wherein the correction circuitry is configured to determine the brightness correction factor using a lookup table.

3. The backlight driver chip of claim 1, wherein the correction circuitry is configured to determine the brightness correction factor using linear interpolation of a plurality of brightness correction factors.

4. The backlight driver chip of claim 1, wherein determining the brightness correction factor using linear interpolation comprises performing linear interpolation using a first duty cycle and a corresponding first correction factor, and a second duty cycle and a corresponding second correction factor.

5. The backlight driver chip of claim 4, wherein the correction circuitry comprises zone selection circuitry configured to receive the duty cycle, select a linearity factor zone based on the duty cycle, and determine the brightness correction factor based on the linearity factor zone.

6. The backlight driver chip of claim 5, wherein the zone selection circuitry comprises a plurality of logic gates configured to select a zone based on the duty cycle.

7. The backlight driver chip of claim 1, comprising a storage device configured to store a plurality of brightness correction factors, wherein the plurality of brightness correction factors comprises the brightness correction factor.

8. The backlight driver chip of claim 1, wherein the current signal provided by the output is controlled by a pulse width modulated signal.

9. The backlight driver chip of claim 1, wherein the correction circuitry comprises a multiplier configured to determine the corrected duty cycle by multiplying the brightness correction factor by the duty cycle.

10. The backlight driver chip of claim 1, comprising a multiplier configured to multiply a maximum duty cycle by the duty cycle and to provide an adjusted duty cycle.

11. A method comprising:

receiving an input duty cycle at a backlight driver chip;

determining a correction factor using the backlight driver chip and based at least partially on the input duty cycle;

determining a corrected duty cycle using the backlight driver chip and based at least partially on the correction factor; and

providing a current signal for driving a backlight device, wherein the current signal is based at least partially on the corrected duty cycle.

12. The method of claim 11, comprising determining an adjusted duty cycle using a multiplier of the backlight driver chip to multiply the input duty cycle by a maximum duty cycle.

13. The method of claim 11, wherein determining the correction factor comprises using linear interpolation of a plurality of brightness correction factors.

14. The method of claim 11, wherein determining the correction factor comprises retrieving data from a lookup table using the input duty cycle.

15. The method of claim 11, comprising comparing the corrected duty cycle to a minimum duty cycle, wherein the current signal is based on the minimum duty cycle if the minimum duty cycle is greater than or equal to the corrected duty cycle.

16. An electronic display for an electronic device comprising:

a display panel configured to display an image;

a backlight device configured to provide a backlight to the display panel; and

a backlight driver chip configured to receive data corresponding to a duty cycle, to determine a brightness correction factor to apply to the duty cycle, and to provide a current signal to the backlight device based at least partially on the brightness correction factor.

17. The electronic display of claim 16, wherein the backlight driver chip is configured to determine the brightness correction factor without receiving data other than the duty cycle from a device external to the backlight driver chip.

18. The electronic display of claim 16, wherein the backlight driver chip comprises a storage device configured to store a plurality of brightness correction factors.

19. The electronic display of claim 16, wherein the backlight driver chip is configured to limit the duty cycle based on a maximum duty cycle and a minimum duty cycle.

20. A method comprising:

receiving an input duty cycle at a backlight driver chip;

determining a reduced duty cycle using the backlight driver chip, wherein the reduced duty cycle is a product of the input duty cycle and a maximum duty cycle;

determining a correction factor using the backlight driver chip, wherein the correction factor is based on the reduced duty cycle;

determining a corrected duty cycle using the backlight driver chip, wherein the corrected duty cycle is a product of the reduced duty cycle and the correction factor;

determining an output duty cycle using the backlight driver chip, wherein the output duty cycle is based on a comparison between a minimum duty cycle and the corrected duty cycle; and

providing a current output from the backlight driver chip, wherein the current output is based on the output duty cycle.

21. The method of claim 20, wherein the output duty cycle is the minimum duty cycle when the minimum duty cycle is greater than or equal to the corrected duty cycle.

22. The method of claim 20, wherein the output duty cycle is the corrected duty cycle when the corrected duty cycle is greater than the minimum duty cycle.

23. A backlight driver chip for an electronic device comprising:

an input configured to receive an input duty cycle;

a storage device configured to store a maximum duty cycle, a minimum duty cycle, and a plurality of brightness correction factors;

a first circuitry configured to determine an adjusted duty cycle comprising a product of the maximum duty cycle and the input duty cycle;

a second circuitry configured to determine a selected brightness correction factor of the plurality of brightness correction factors based at least partially on the adjusted duty cycle;

a third circuitry configured to determine a corrected duty cycle comprising a product of the selected brightness correction factor and the adjusted duty cycle;

a fourth circuitry configured to compare the minimum duty cycle to the corrected duty cycle, to provide an output duty cycle comprising the minimum duty cycle if the minimum duty cycle is greater than or equal to the corrected duty cycle, and to provide the output duty cycle comprising the corrected duty cycle if the corrected duty cycle is greater than the minimum duty cycle; and

pulse width modulation circuitry configured to provide a pulse width modulation signal for producing an output current to drive a backlight device, wherein the pulse width modulation signal is based on the output duty cycle.

24. The method of claim 23, wherein the second circuitry is configured to determine a zone of operation based on the adjusted duty cycle.

25. The method of claim 24, wherein the zone of operation is determined using a plurality of logic gates configured to receive the adjusted duty cycle.