Automatic brightness control using a variable time constant filter

• US 6,483,245 B1
• Filed: 09/08/2000
• Issued: 11/19/2002
• Est. Priority Date: 09/08/2000
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Visteon Corporation
• Inventors: Milne, Gregory J., Weindorf, Paul F. L.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Vu, Jimmy T.
• Application Number:
  US09/658,301
• Time in Patent Office: 802 Days
• Field of Search: 315/77, 315/80, 315/82, 315/149-159, 315/169.3, 345/7, 345/102
• US Class Current: 315/82
• CPC Class Codes: B60K 2360/33 Illumination features
• CPC Class Codes: B60K 2370/33 Illumination features
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/00 Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
• CPC Class Codes: G09G 3/06 using controlled light sources
• CPC Class Codes: G09G 3/22 using controlled light sources

Abstract

A method and apparatus is provided to control the brightness of an emissive display. Specifically, the brightness is incremented and decremented as the ambient environment becomes brighter and darker, respectively. A timing feature is also implemented to control the sensitivity of the system. Specifically, the time between adjustments of the display brightness is at least partially dependent on the magnitude of the difference between the desired brightness based on the ambient lighting environment and that of the actual display brightness.

Claims

1. A system for controlling brightness of an emissive display, comprising:

(A) an ambient light sensor configured to output an ambient signal corresponding to a sensed ambient illumination level;

(B) a display configured to receive an actual display brightness signal and to adjust an actual display brightness level based on said actual display brightness signal; and

(C) a processor executing a stored program to;

(1) receive said ambient light signals;

(2) determine a desired display brightness level corresponding to said ambient light signal; and

(3) output said actual display brightness signal to said display, wherein said actual display brightness level is adjusted at a rate of change, and wherein said rate of change increases as a magnitude of the difference between said desired display brightness level and said actual display brightness level decreases.

2. The system of claim 1, wherein said actual display brightness level is less than desired display brightness level, and wherein said actual display brightness level is is incremented based on said actual display brightness signal.

3. The system of claim 1, wherein said actual display brightness level is greater than said desired display brightness level, and wherein said actual display brightness level is decremented based on said actual display brightness signal.

4. The system of claim 1, wherein said processor determines an update interval based at least in part on said magnitude of the difference between said desired display brightness level and said actual display brightness level, and wherein said rate of change is no less than said update time interval.

31. The system of claim 1, wherein said processor determines said actual display brightness signal based on said desired display brightness level along with a previous actual display brightness level.

5. A method for controlling brightness of an emissive instrument display, comprising:

(A) receiving a first signal indicating an actual display brightness level;

(B) determining a second signal that is related to a desired display brightness level, wherein the desired display brightness level is at least partially dependent upon an ambient illumination level;

(C) determining a brightness difference magnitude between said first and second signals; and

(D) adjusting said actual display brightness level after expiration of an update time interval, wherein said update time interval is at least partially dependent upon said brightness difference magnitude.

6. The method as recited in claim 5, wherein said actual display brightness level is less than said desired display brightness level, step (D) further comprising incrementing said actual display brightness signal.

7. The method as recited in claim 5, wherein said actual display brightness level is greater than said desired display brightness level, step (D) further comprising decrementing said actual display brightness level.

8. The method as recited in claim 5, wherein said update time interval decreases as said brightness magnitude difference decreases.

9. The method as recited in claim 5, wherein said update time interval increases as said brightness magnitude difference increases.

10. The method as recited in claim 5, wherein said update time interval equals said brightness magnitude difference multiplied by a predetermined time constant.

11. The method as recited in claim 10, wherein said first signal is received at an initial time T, and wherein said second signal is received at a second time T1, wherein T1 is greater than T, and wherein step (D) further comprises:

subtracting T from T1 to determine a time difference variable; and

adjusting said actual brightness level when said time difference variable is greater than said update time interval.

12. The method as recited in claim 10, wherein said time constant is a first time constant if said actual display brightness level is greater than said desired display brightness level, and wherein said time constant is a second time constant if said actual display brightness level is less than said desired display brightness level, and wherein said first time constant is greater than said second time constant.

13. The method as recited in claim 5, further comprising manually adjusting said actual brightness level.

14. The method as recited in claim 5, wherein said desired brightness level is related to an ambient illumination condition.

15. The method as recited in claim 5, wherein actual brightness level is adjusted by one of increasing said actual brightness level and decreasing said actual brightness level, and wherein said actual brightness level is increased at a faster rate than it is decreased.

16. The method as recited in claim 5, wherein said actual brightness level is adjusted in small increments so as to be unnoticeable to the human eye.

17. The method as recited in claim 5, wherein said first signal is predetermined.

18. A method for controlling brightness of an emissive display, comprising:

(A) determining a first signal indicating an actual display brightness level at a first time T1;

(B) determining a second signal substantially related to a desired display brightness level at a second time T2;

(C) determining a difference magnitude between said first and second signals;

(D) determining a predetermined update time interval, wherein said update time interval is the product of said difference magnitude and a predetermined time constant;

(E) adjusting said actual display brightness level when the difference between T2 and T1 is greater than said update time interval.

19. The method as recited in claim 18, wherein step (E) further comprises incrementing said actual brightness level if said desired brightness level is greater than said actual brightness level.

20. The method as recited in claim 18, wherein step (E) further comprises decrementing said actual brightness level if said desired brightness level is less than said actual brightness level.

21. The method as recited in claim 18, wherein step (E) comprises one of incrementing and decrementing said actual brightness level, wherein said update time interval when said actual brightness level is incremented is less than said update time interval when said actual brightness level is decremented.

22. A system for controlling brightness of an illuminated instrument panel, comprising:

(A) means for receiving a first signal generally related to an actual brightness level;

(B) means for receiving a second signal that is related to a desired brightness level, wherein the desired display brightness level is at least partially dependent upon an ambient illumination level;

(C) means for determining a brightness difference magnitude between said first and second signals; and

(D) means for adjusting said actual brightness level after expiration of a predetermined update time interval, wherein said update time interval is at least partially dependent upon said difference magnitude.

23. The system as recited in claim 22, further comprising means for incrementing said actual brightness level if said desired brightness level is greater than said actual brightness level.

24. The system as recited in claim 22, further comprising means for decrementing said actual brightness level if said desired brightness level is less than said actual brightness level.

25. The system as recited in claim 22, wherein said update time interval increases as said brightness difference magnitude increases, and wherein said update time interval decreases as said brightness difference magnitude decreases.

26. A system for controlling brightness of an emissive display, comprising:

(A) an ambient light sensor configured to output an ambient signal corresponding to a sensed ambient illumination level;

(B) a display configured to receive an actual display brightness signal and to adjust an actual display brightness level based on said actual display brightness signal; and

(C) a processor executing a stored program to;

(1) receive said ambient light signals;

(2) determine a desired display brightness level corresponding to said ambient light signal; and

(3) output said actual display brightness signal to said display, wherein said actual display brightness level is adjusted at a rate of change, and wherein said rate of change decreases as a magnitude of the difference between said desired display brightness level and said actual display brightness level increases.

27. The system of claim 26, wherein said actual display brightness level is less than said desired display brightness level, and wherein said actual display brightness level is incremented based on said actual display brightness signal.

28. The system of claim 26, wherein said actual display brightness level is greater than said desired display brightness level, and wherein said actual display brightness level is decremented based on said actual display brightness signal.

29. The system of claim 26, wherein said processor determines an update interval based at least in part on said magnitude of the difference between said desired display brightness level and said actual display brightness level, and wherein said rate of change is no less than said update time interval.

30. The system of claim 26, wherein said processor determines said actual display brightness signal based on said desired display brightness level along with a previous actual display brightness level.