Calibrated real time clock for acquisition of GPS signals during low power operation

• US 20030083814A1
• Filed: 10/30/2001
• Published: 05/01/2003
• Est. Priority Date: 10/30/2001
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Gronemeyer, Steven A.
• Granted Patent: US 6,662,107 B2
• Time in Patent Office: Days
• US Class Current: 701/213
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/34 Power consumption
• CPC Class Codes: G04C 10/04 with means for indicating the condition of the power supply in general G01R31/36
• CPC Class Codes: G04F 5/00 Apparatus for producing preselected time intervals for use as timing standards generating clock signals for electric digital computers G06F1/04
• CPC Class Codes: G04G 19/12 Arrangements for reducing power consumption during storage
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Power is conserved in a Global Positioning System (GPS) receiver by shutting down selected components during periods when the GPS receiver is not actively calculating the GPS receiver location. A low power time keeping circuit accurately preserves GPS time when the selected components are deactivated. When the selected components are turned on in response to a wake-up command, time provided from the low power time keeping circuit, corrected for actual operating temperatures, and data from the GPS clock temperature/frequency table, are used to recalibrate time from a GPS oscillator. Positions of the GPS satellites are then estimated such that the real GPS time is quickly determined from the received satellite signals. Once real GPS time is determined from the detected satellite signals, the selected components are deactivated. The process described above is repeated such that accurate GPS time is maintained by the low power time keeping circuit.

Claims

1. A system for maintaining accurate Global Positioning System (GPS) time comprising:

a GPS oscillator configured to provide a signal corresponding to the GPS time, and further configured to be deactivated; and

a low power clock configured to provide a low power clock time such that when the GPS oscillator is activated, the GPS oscillator signal corresponding to the GPS time is updated using the low power clock time such that location associated with at least one GPS satellite is accurately estimated.

2. The system of claim 1, further comprising:

a temperature sensor coupled to the low power clock;

a first unit of memory configured to store data corresponding to a temperature and oscillation frequency of the low power clock; and

a processor coupled to the first unit of memory and the temperature sensor, and configured to compare a temperature sensed by the temperature sensor with the data corresponding to the temperature and oscillation frequency of the low power clock such that an error correction is determined, and further configured to correct the low power clock time provided by the low power clock.

3. The system of claim 2, further comprising:

a GPS oscillator temperature sensor coupled to the GPS oscillator; and

a second unit of memory coupled to the processor, the second unit of memory configured to store data corresponding to a temperature and oscillation frequency of the GPS oscillator, wherein the processor is further configured to compare a GPS oscillator temperature sensed by the GPS oscillator temperature sensor with the data corresponding to the temperature and oscillation frequency of the GPS oscillator such that a GPS oscillator error correction is determined, and further configured to correct the signal provided by the GPS oscillator.

4. The system of claim 1, further comprising:

a means for deactivating selected components residing in a GPS receiver unit; and

an alarm unit configured to activate the selected components and the GPS oscillator.

5. The system of claim 4, wherein the alarm unit activates the selected components periodically.

6. The system of claim 4, wherein the alarm unit activates the selected components in response to a position query.

7. A method for maintaining accurate Global Positioning System (GPS) time, the method comprising the steps of:

deactivating a plurality of selected components residing in a GPS receiver unit at the start of a predefined period of time;

deactivating a GPS oscillator configured to provide a GPS time signal at the start of the predefined period of time;

activating the GPS oscillator at the end of the predefined time period;

receiving information corresponding to time from a low power clock when the GPS oscillator is activated; and

updating the GPS time signal in response to receiving the low power clock time such that location of at least one GPS satellite is accurately estimated.

8. The method of claim 7, further comprising the steps of:

calibrating the GPS time signal with respect to a real GPS time from at least one satellite signal such that the calibrated GPS time signal accurately corresponds to the real GPS time; and

calibrating a low power clock based upon the calibrated GPS time signal such that the low power clock accurately corresponds to the real GPS time.

9. The method of claim 7, further comprising the steps of:

detecting temperature of the low power clock;

determining an error correction factor associated with the detected temperature of the low power clock; and

correcting the low power clock time according to the determined error correction factor.

10. The method of claim 9, further comprising the steps of:

sensing frequency of an oscillator residing in the low power clock; and

building a table of oscillator data, the oscillator data corresponding to the sensed frequency of the oscillator at each one of a plurality of detected temperatures; and

determining a frequency versus temperature correction factor based upon the oscillator data such that the error correction factor is determined.

11. The method of claim 9, further comprising the steps of:

detecting temperature of the GPS oscillator;

determining a GPS error correction factor associated with the detected temperature of the GPS oscillator; and

correcting the GPS time signal according to the determined GPS error correction factor.

12. The method of claim 11, further comprising the steps of:

sensing frequency of the GPS oscillator; and

building a table of GPS oscillator data, the GPS oscillator data corresponding to the sensed frequency of the GPS oscillator at each one of a plurality of detected temperatures; and

determining a frequency versus temperature correction factor based upon the GPS oscillator data such that the GPS error correction factor is determined.

13. The method of claim 7, further comprising the steps of:

generating an alarm signal at the end of the predefined period of time;

activating selected components of the GPS receiver unit such that the GPS time signal is updated; and

deactivating the selected components after the GPS time signal is updated.

14. The method of claim 13, further comprising the step of varying the predefined period of time in accordance with a detected temperature.

15. A system for maintaining accurate Global Positioning System (GPS) time, comprising:

means for deactivating a plurality of selected components residing in a GPS receiver unit at the start of a predefined period of time;

means for deactivating a GPS oscillator configured to provide a GPS time signal at the start of the predefined period of time;

means for activating the GPS oscillator at the end of the predefined time period;

means for receiving time from a low power clock when the GPS oscillator is activated; and

means for updating the GPS time signal in response to receiving the low power clock time such that location of at least one GPS satellite is accurately estimated.

16. The system of claim 15, further comprising:

means for detecting temperature of the low power clock;

means for determining an error correction factor associated with the detected temperature of the low power clock; and

means for correcting the low power clock time according to the determined error correction factor.

17. The system of claim 16, further comprising:

means for sensing frequency of an oscillator residing in the low power clock; and

means for building a table of oscillator data, the oscillator data corresponding to the sensed frequency of the oscillator at each one of a plurality of detected temperatures; and

means for determining a frequency versus temperature correction factor based upon the table of oscillator data such that the error correction factor is determined.

18. The system of claim 16, further comprising:

means for detecting temperature of the GPS oscillator;

means for determining a GPS error correction factor associated with the detected temperature of the GPS oscillator; and

means for correcting the GPS time signal according to the determined GPS error correction factor.

19. The method of claim 18, further comprising:

means for sensing frequency of the GPS oscillator; and

means for building a table of GPS oscillator data, the GPS oscillator data corresponding to the sensed frequency of the GPS oscillator at each one of a plurality of detected temperatures; and

means for determining a frequency versus temperature correction factor based upon the table of GPS oscillator data such that the GPS error correction factor is determined.

20. The system of claim 15, further comprising:

means for generating an alarm signal at the end of the predefined time period;

means for activating selected components of the GPS receiver unit such that the GPS oscillator signal is updated; and

means for deactivating the selected components after the GPS time signal is updated.

21. The system of claim 20, further comprising means for varying the predefined period of time time in accordance with a detected temperature.

22. A computer readable medium having a program for maintaining accurate Global Positioning System (GPS) time, the program comprising logic configured to perform the steps of:

receiving information corresponding to time from a low power clock when a GPS oscillator is activated;

receiving GPS time from the GPS oscillator when the GPS oscillator is activated; and

updating the GPS time based upon the received low power clock time such that a location of at least one GPS satellite is accurately estimated.

23. The computer readable medium of claim 22, further comprising logic configured to perform the steps of:

determining an error correction factor associated with a detected temperature of the low power clock;

correcting the low power clock time according to the determined error correction factor;

detecting temperature of the GPS oscillator;

determining a GPS error correction factor associated with the detected temperature of the GPS oscillator; and

correcting the GPS time according to the determined GPS error correction factor.

24. The computer readable medium of claim 23, further comprising logic configured to perform the steps of:

receiving frequency data corresponding to an oscillator frequency residing in the low power clock;

building a table of oscillator data, the oscillator data corresponding to the received frequency data at each one of a plurality of temperatures associated with the low power clock;

determining a frequency versus temperature correction factor based upon the table of oscillator data such that the error correction factor is determined;

receiving frequency data corresponding to a GPS oscillator frequency residing in the GPS oscillator;

building a table of GPS oscillator data, the GPS oscillator data corresponding to the received frequency data of the GPS oscillator at each one of a plurality of detected GPS oscillator temperatures; and

determining a frequency versus temperature correction factor based upon the GPS oscillator data such that the GPS error correction factor is determined.