Real time clock calibration system

• US 20080222440A1
• Filed: 03/07/2007
• Published: 09/11/2008
• Est. Priority Date: 03/07/2007
• Status: Abandoned Application

• Current Assignee: LSI Corporation (Broadcom, Inc.)
• Original Assignee: LSI Corporation (Broadcom, Inc.)
• Inventors: Jones, Stephen, Judge, Rupinder
• Application Number:
  US11/715,182
• Publication Number:
  US 20080222440A1
• Time in Patent Office: Days
• US Class Current: 713/400
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock

Abstract

A temperature-based real time clock calibration system and method for performing the same. The system in one embodiment includes a real time clock calibrated against a reference frequency, a temperature sensor being operative to measure a instantaneous temperature T1, and control circuitry operative to receive and sense the temperature T1. Control logic, preferably implemented in the control circuitry in one embodiment, determines when to recalibrate the real time clock against the reference frequency based on the measured temperature T1. In one embodiment, the reference frequency is generated by a main system clock. The system may be used during sleep mode or another reduced power operating mode of an electronic device.

Claims

1. A real time clock calibration system for an electronic device comprising:

a real time clock calibrated against a reference frequency;

a first temperature sensor operative to measure an instantaneous temperature T1;

control circuitry operative to sense the temperature T1; and

control logic implemented in the control circuitry and being operative to determine when to recalibrate the real time clock against the reference frequency based on the measured temperature T1.

2. The real time clock calibration system of claim 1, wherein an initial calibration temperature T_CT of the real time clock is measured and received by the control circuitry, the control logic being further operative to use the initial calibration temperature to determine when to recalibrate the real time clock.

3. The real time clock calibration system of claim 2, further comprising the control logic being operative to calculate a temperature differential Δ

T_A between the initial calibration temperature T_CT and the instantaneous temperature T1, wherein the real time clock is recalibrated if the difference Δ

T_A is greater than a predetermined differential temperature limit Δ

T_L that has been preprogrammed into the control logic.

4. The real time clock calibration system of claim 1, further comprising the control logic being operative to generate a signal to initiate recalibration of the real time clock.

5. The real time clock calibration system of claim 1, wherein the reference frequency is generated by a main system clock.

6. The real time clock calibration system of claim 5, wherein the real time clock is recalibrated against the main system clock.

7. The real time clock calibration system of claim 1, wherein the control circuit senses the temperature T1 during sleep mode operation of an electronic device.

8. The real time clock calibration system of claim 7, wherein the electronic device is a mobile handset.

9. The real time clock calibration system of claim 1, wherein the real time clock is disposed in an electronic device.

10. The real time clock calibration system of claim 9, wherein the electronic device is a mobile telecommunication handset.

11. The real time clock calibration system of claim 1, wherein the control logic is implemented in hardware, firmware, software, or a combination thereof.

12. The real time clock calibration system of claim 1, wherein the real time clock is a 32 kHz crystal oscillator.

13. An electronic device with a real time clock calibration system comprising:

a device housing;

a microprocessor including a main system clock;

a real time clock being operative to be calibrated against the main system clock, the real time clock having an initial calibration and associated initial calibration temperature T_CT;

at least one temperature sensor being operative to measure an instantaneous temperature T1 in the housing;

control circuitry being operative to receive a first temperature signal indicative of the initial calibration temperature T_CT and a second temperature signal indicative of instantaneous temperature T1, the control circuit including control logic implementing a routine using temperatures T_CT and T1 to determine when to recalibrate the real time clock.

14. The electronic device of claim 13, further comprising the control logic being operative to calculate a temperature differential Δ

T_A between the initial calibration temperature T_CT and the instantaneous temperature T1, wherein the real time clock is recalibrated if the difference Δ

T_A is greater than a predetermined differential temperature limit Δ

T_L that has been preprogrammed into the control logic.

15. The electronic device of claim 13, further comprising the control logic being operative to generate a signal to initiate recalibration of the real time clock.

16. The electronic device of claim 13, wherein the control circuit senses the temperature T1 during a reduced power mode of operation of the electronic device.

17. The electronic device of claim 13, wherein the electronic device is a mobile telecommunication handset.

18. A real time clock calibration system for an electronic device comprising:

a real time clock calibrated against a reference frequency;

a temperature sensor located in, on or proximate to the device and operable to measure an instantaneous actual temperature T1 associated with the device; and

means for determining when to recalibrate the real time clock against the reference frequency based on the measured temperature T1.

19. The real time clock calibration system of claim 18, wherein the recalibration means includes control circuitry being operative to receive a temperature signal generated by the temperature sensor that is indicative of the actual temperature T1, the control circuit including control logic implementing a routine using temperature T1 to determine when to recalibrate the real time clock.

20. The real time clock calibration system of claim 19, wherein the control logic compares instantaneous temperature T1 to a historic calibration temperature T_CT measured and recorded for the real time clock.

21. The real time clock calibration system of claim 18, wherein the recalibration means includes control circuitry being operative to receive a temperature signal generated by the temperature sensor that is indicative of the instantaneous temperature T1, the control circuit including control logic implementing a routine to calculate a temperature differential Δ

T_A between instantaneous temperature T1 and an initial calibration temperature T_CT for the real time clock, the control logic further comparing calculated temperature differential Δ

T_A to a theoretical temperature differential limit Δ

T_L that is preprogrammed into the control logic for determining when to recalibrate the real time clock.

22. A method of recalibrating a real time clock comprising:

calibrating a real time clock in an electronic device having a housing;

measuring a first temperature associated with the housing;

comparing the first temperature to a second reference temperature, and

recalibrating the real time clock based on the comparison of the first temperature to the second reference temperature.

23. The method of claim 22, wherein the real time clock is recalibrated if the first temperature is greater than or less than the second temperature by a predetermined temperature differential limit programmed into the control logic.

24. The method of claim 22, wherein the second reference temperature is a housing temperature measured essentially concurrently with calibrating the real time clock.

25. The method of claim 23, wherein the second reference temperature is an initial calibration temperature measured at the start of a sleep mode operating condition of the electronic device.

26. The method of claim 22, wherein calibrating of the real time clock occurs at the start of a sleep mode operating condition of the electronic device.

27. The method of claim 22, further comprising a step of measuring a housing temperature at the time the calibration step is performed which represents the second reference temperature, the first temperature being measured after the calibration step is performed.

28. The method of claim 22, further comprising a step of generating an output signal to initiate the recalibrating step.

29. The method of claim 22, wherein the electronic device is a mobile telecommunication device.

30. The method of claim 22, wherein real time clock is a 32 kHz quartz oscillator.

31. A method of recalibrating a real time clock during a sleep mode operating condition of an electronic device having a microprocessor, the method comprising:

initiating sleep mode operation for the electronic device;

switching frequency control for the electronic device from a main system clock to a real time clock that consumes less power than the main system clock;

calibrating initially the real time clock against the main system clock;

measuring an initial calibration temperature essentially concurrently with calibrating the real time clock;

measuring a sleep mode operating temperature for the electronic device after measuring the initial calibration temperature of the real time clock;

comparing the sleep mode operating temperature to the initial calibration temperature; and

recalibrating the real time clock if the sleep mode operating temperature is greater than or less than the initial calibration temperature by a predetermined temperature differential limit.

32. The method of claim 31, wherein the steps of measuring the initial calibration and sleep mode operating temperatures both include using a temperature sensor disposed in a housing for the electronic device.

33. The method of claim 31, wherein the comparing step is performed by control logic implemented by a control circuit.

34. The method of claim 33, wherein the control logic is implemented in hardware, firmware, software, or a combination thereof associated with the electronic device.