Radio communications devices with backlighting circuits having brownout detection circuits responsive to a current through a light emitting diode

• US 6,256,007 B1
• Filed: 05/11/2000
• Issued: 07/03/2001
• Est. Priority Date: 10/30/1997
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Northcutt, John W., Walukas, Joel J.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Bell, Paul A.
• Application Number:
  US09/569,492
• Time in Patent Office: 418 Days
• Field of Search: 315/66, 315/119, 315/121, 315/122, 315/123, 315/124, 315/127, 315/128, 315/224, 315/291, 315/307, 315/310, 315/311, 323/282, 324/426, 327/89, 327/108, 340/636, 340/825.82, 340/825.44, 345/82, 345/102, 345/211, 345/212, 349/61, 349/69, 363/89, 455/566, 455/572, 455/574
• US Class Current: 345/102
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs

Abstract

A backlighting circuit for user interface in an electronic device includes at least one light emitting diode optically coupled to the user interface wherein the at least one light emitting diode provides backlighting for the user interface. A current source is electrically coupled in series with the at least one light emitting diode wherein the current source controls a current through the at least one diode. In addition, a brownout detection circuit determines a brownout condition for the user interface responsive to the current through the diode. Related communications devices and methods are also discussed.

Claims

1. A radio communications device comprising:

a housing;

a transceiver in said housing for transmitting and receiving radio communications to and from a radio base station;

a user interface on said housing;

a backlighting circuit in said housing wherein said backlighting circuit includes,

at least one light emitting diode optically coupled to said user interface wherein said at least one diode provides backlighting for the user interface, and

a current source electrically coupled in series with said at least one light emitting diode wherein said current source controls a current through said at least one diode; and

a brownout detection circuit wherein said brownout detection circuit determines a brownout condition for the user interface responsive to said current through said at least one light emitting diode falling below a predetermined threshold wherein said brownout detection circuit determines a brownout condition using a comparison between a reference signal and a feedback signal from said current source; and

a control circuit wherein said control circuit is electrically coupled to said brownout detection circuit and wherein said control circuit turns said current source off in response to a determination that a brownout condition has occurred.

2. A radio communications device according to claim 1 wherein said brownout detection circuit comprises an analog-to-digital converter.

3. A radio communications device according to claim 1 wherein said brownout detection circuit comprises a comparator.

4. A radio communications device according to claim 1 wherein said user interface comprises one of a keypad and a liquid crystal display.

5. A radio communications device according to claim 1 wherein said at least one light emitting diode comprises a plurality of pairs of series coupled light emitting diodes and wherein each of said pairs of series coupled light emitting diodes is electrically coupled in parallel.

6. A radio communications device comprising:

a housing;

a transceiver in said housing for transmitting and receiving radio communications to and from a radio base station;

a user interface on said housing;

a backlighting circuit in said housing wherein said backlighting circuit includes,

at least one light emitting diode optically coupled to said user interface wherein said at least one diode provides backlighting for the user interface, and

a current source electrically coupled in series with said at least one light emitting diode wherein said current source controls a current through said at least one diode; and

a brownout detection circuit wherein said brownout detection circuit determines a brownout condition for the user interface responsive to said current;

wherein said current source controls said current through said at least one diode in response to a comparison between a reference signal and a feedback signal from said current source.

7. A radio communications device according to claim 6 further comprising:

a control circuit wherein said control circuit is electrically coupled to said brownout detection circuit and wherein said control circuit turns said current source off in response to a determination that a brownout condition has occurred.

8. A radio communications device according to claim 6 further comprising:

a control circuit wherein said control circuit is electrically coupled to said brownout detection circuit and wherein said control circuit turns the radio communications device off in response to a determination that a brownout condition has occurred.

9. A radio communications device according to claim 6 wherein said brownout detection circuit determines that said brownout condition has occurred when said current through said at least one diode falls below a predetermined threshold.

10. A radio communications device according to claim 6 wherein said current source comprises:

a transistor electrically coupled in series between said diode and a feedback node;

a program resistor electrically coupled in series between said feedback node and a ground voltage node; and

an operational amplifier including a first input electrically coupled to said reference signal, a second input electrically coupled to said feedback signal at said feedback node, and an output electrically coupled to a control electrode of said transistor wherein said operational amplifier drives said control node of said transistor in response to said comparison of said reference signal and said feedback signal.

11. A radio communications device according to claim 6 wherein said current source comprises:

a transistor electrically coupled in series between said at least one light emitting diode and a feedback node;

a program resistor electrically coupled in series between said feedback node and a ground voltage node; and

a comparison circuit including a first input electrically coupled to said reference signal, a second input electrically coupled to said feedback signal at said feedback node, and an output electrically coupled to a control electrode of said transistor wherein said comparison circuit drives said control node of said transistor in response to said comparison of said reference signal and said feedback signal.

12. A radio communications device comprising:

a housing;

a transceiver in said housing for transmitting and receiving radio communications to and from a radio base station;

a user interface on said housing;

a backlighting circuit in said housing wherein said backlighting circuit includes,

at least one light emitting diode optically coupled to said user interface wherein said at least one diode provides backlighting for the user interface, and

a constant current source electrically coupled in series with said at least one light emitting diode wherein said constant current source controls a current through said at least one diode in response to a comparison between a reference signal and a feedback signal from said constant current source.

13. A radio communications device according to claim 12 wherein said constant current source comprises:

a transistor electrically coupled in series between said diode and a feedback node;

a program resistor electrically coupled in series between said feedback node and a ground voltage node; and

an operational amplifier including a first input electrically coupled to said reference signal, a second input electrically coupled to said feedback signal at said feedback node, and an output electrically coupled to a control electrode of said transistor wherein said operational amplifier drives said control node of said transistor in response to said comparison of said reference signal and said feedback signal.

14. A radio communications device according to claim 13 wherein said operational amplifier is implemented as a portion of an Application Specific Integrated Circuit (ASIC).

15. A radio communications device according to claim 12 wherein said at least one light emitting diode comprises a plurality of pairs of series coupled light emitting diodes and wherein each of said pairs of series coupled light emitting diodes is electrically coupled in parallel.

16. A radio communications device according to claim 12 further comprising a brownout detection circuit wherein said brownout detection circuit determines a brownout condition for the user interface responsive to said feedback signal.

17. A radio communications device according to claim 16 further comprising a control circuit wherein said control circuit is electrically coupled to said brownout detection circuit and wherein said control circuit turns said constant current source off in response to a determination that a brownout condition has occurred.

18. A radio communications device according to claim 17 wherein said brownout detection circuit determines that said brownout condition has occurred when said current through said at least one diode falls below a predetermined threshold.

19. A radio communications device according to claim 16 further comprising a control circuit wherein said control circuit is electrically coupled to said brownout detection circuit and wherein said control circuit turns said radio communications device off in response to a determination that a brownout condition has occurred.

20. A radio communications device according to claim 16 wherein said brownout detection circuit determines that said brownout condition has occurred when said current through said at least one diode falls below a predetermined threshold.

21. A radio communications device according to claim 20 wherein said user interface comprises one of a keypad and a liquid crystal display.

22. A radio communications device according to claim 12 wherein said constant current source comprises:

a transistor electrically coupled in series between said at least one light emitting diode and a feedback node;

a program resistor electrically coupled in series between said feedback node and a ground voltage node; and

a comparison circuit including a first input electrically coupled to said reference signal, a second input electrically coupled to said feedback signal at said feedback node, and an output electrically coupled to a control electrode of said transistor wherein said comparison circuit drives said control node of said transistor in response to said comparison of said reference signal and said feedback signal.