Method and apparatus for self-calibration and adaptive temperature compensation in GPS receivers

• US 20060267703A1
• Filed: 05/26/2005
• Published: 11/30/2006
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Original Assignee: SiRF Technology Holdings Incorporated (Qualcomm, Inc.)
• Inventors: Wang, Chi-Shin, Han, Shaowei, Wang, Hansheng, Mo, Jun, Shridhara, Kudrethaya A.
• Granted Patent: US 7,459,984 B2
• Time in Patent Office: Days
• US Class Current: 331/176
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence

Abstract

The invention provides a method and apparatus to optimally estimate and adaptively compensate the temperature-induced frequency drift of a crystal oscillator in a navigational signal receiver. A Read-Write memory encodes two tables, one for looking up frequency drift values versus temperature readings and another one for valid data confirmation on the first table. The initially empty look-up table is gradually populated with frequency drift values while the receiver computes the frequency drift along with its position. During initial start of the receiver or re-acquisition of satellite signals, the stored frequency drift value corresponding to the current temperature is used. If no valid frequency drift value is available, the frequency drift value is computed based on the existing frequency drift values in the table. This invention reduces the Time-To-First-Fix (TTFF) of the receiver and enables the receiver to self-calibrate, thus no additional factory calibration would be necessary.

Claims

1. A method of compensating an oscillator frequency drift, comprising:

encoding a memory device with a first look-up table;

determining a frequency drift value associated with a temperature reading of said oscillator;

incrementally populating said first look-up table with said frequency drift values as said oscillator is exposed to temperature changes; and

adaptively compensating said temperature changes utilizing said first look-up table.

2. The method according to claim 1, further comprising:

initializing said first look-up table to all zeros once, at its very first use.

3. The method according to claim 1, further comprising:

averaging frequency drift values associated with same temperature reading.

4. The method according to claim 1, further comprising:

positioning a temperature sensor in proximity of or within said oscillator.

5. The method according to claim 1, further comprising:

retrieving from said first look-up table a frequency drift value that correspond to a temperature reading.

6. The method according to claim 1, further comprising:

discarding one or more frequency drift values that are higher or lower than predefined threshold values.

7. The method according to claim 1, further comprising:

validating said frequency drift values before storing in said first look-up table.

8. The method according to claim 1, further comprising:

encoding said memory device with a second look-up table for confirming that valid frequency drift values are stored in said first look-up table.

9. The method according to claim 1, wherein said first look-up table contains at least two valid frequency drift values, comprising:

determining whether said at least two valid frequency drift values include a first one that is at a higher temperature than a current temperature reading and a second one that is at a lower temperature than said current temperature reading.

10. The method according to claim 1, wherein said first look-up table contains at least two valid frequency drift values, comprising:

interpolating or extrapolating said at least two valid frequency drift values.

11. The method according to claim 10, further comprising:

utilizing a linear or non-linear approximation technique with minimum error criteria.

12. The method according to claim 1, wherein said first look-up table contains a single valid frequency drift value, further comprising:

utilizing zero, said single valid frequency drift value, or a previously stored value in said compensating step.

13. The method according to claim 1, wherein said first look-up table contains no valid frequency drift values, further comprising:

utilizing zero or a previously stored value in said compensating step.

14. A navigational satellite signal receiver implementing the method steps of claim 1,

said oscillator residing in said navigational satellite signal receiver.

15. A computer-readable medium storing computer-executable program instructions implementing the method steps of claim 1.

16. A navigational satellite signal receiver, comprising:

a local reference oscillator;

a temperature sensor in proximity or within said oscillator for obtaining temperature readings on said oscillator;

a processor coupled to said temperature sensor, said processor capable of processing navigational satellite signals; and

a memory device coupled to said processor and encoded with a first look-up table for storing frequency drift values associated with said temperature readings of said oscillator;

wherein

said first look-up table is initialized to all zeros and incrementally populated with said frequency drift values as said oscillator is exposed to temperature changes; and

wherein

said processor utilizes said first look-up table to adaptively compensate said temperature changes.

17. The navigational satellite signal receiver of claim 16, wherein

said memory device is encoded with a second look-up table for confirming that valid frequency drift values are stored in said first look-up table.

18. The navigational satellite signal receiver of claim 16, wherein

said oscillator embodying temperature uncompensated crystals.

19. The navigational satellite signal receiver of claim 16, wherein

said oscillator embodying temperature compensated crystals.

20. A computer-readable medium storing computer-executable program instructions, comprising:

code for encoding a memory device with a first look-up table;

code for determining a frequency drift value associated with a temperature reading of said oscillator;

code for incrementally populating said first look-up table with said frequency drift values as said oscillator is exposed to temperature changes;

code for adaptively compensating said temperature changes utilizing said first look-up table;

code for initializing said first look-up table to all zeros;

code for averaging frequency drift values associated with same temperature reading;

code for retrieving from said first look-up table a frequency drift value that correspond to a temperature reading;

code for discarding one or more frequency drift values that are higher or lower than predefined threshold values;

code for validating said frequency drift values before storing in said first look-up table;

code for encoding said memory device with a second look-up table for confirming that valid frequency drift values are stored in said first look-up table; and

code for determining whether there are at least two valid frequency drift values and correspondingly interpolating or extrapolating said at least two valid frequency drift values.