Methods and apparatus for obtaining accurate GNSS time in a GNSS receiver

• US 7,969,355 B2
• Filed: 10/15/2009
• Issued: 06/28/2011
• Est. Priority Date: 09/06/2007
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Li, Ming-Hung, Huang, Kung-Shuan
• Primary Examiner(s): LIU, HARRY K
• Application Number:
  US12/580,231
• Publication Number:
  US 20100033373A1
• Time in Patent Office: 621 Days
• Field of Search: 342/357.62
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/39 the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
• CPC Class Codes: G04R 20/04 Tuning or receiving; Circuits therefor

Abstract

A method for obtaining GNSS time in a GNSS receiver includes: deriving a relationship between a first clock signal and the received GNSS time; latching a second clock signal and the first clock signal at a first latching point to obtain a clock value A1 of the first clock signal and a clock value B1 of the second clock signal; calculating a GNSS time C1 corresponding to the clock value A1 according to the relationship; latching the first clock signal and the second clock signal at a second latching point to obtain a clock value A2 of the first clock signal and a clock value B2 of the second clock signal; and calculating a GNSS time C2 corresponding to the clock value A2 according to the GNSS time C1, the clock value B1, and the clock value B2.

Claims

1. A method for obtaining Global Navigation Satellite System (GNSS) time in a GNSS receiver, the method comprising:

deriving a relationship between a first clock signal and the received GNSS time;

latching a second clock signal and the first clock signal at a first latching point;

calculating a first GNSS time corresponding to the first latching point;

latching the first clock signal and the second clock signal at a second latching point; and

calculating a second GNSS time according to the first GNSS time, the first latching point, and the second latching point.

2. The method of claim 1, further comprising:

powering off the GNSS receiver during the time period between the first latching point and the second latching point.

3. The method of claim 1, further comprising:

calculating the second GNSS time by the following equation;

C2=C1+(B2−

B1)−

B_bias;

Wherein C1 is the first GNSS time, C2 is the second GNSS time, B1 is a clock value of the second clock signal in the first latching point, B2 is a clock value of the second clock signal in the second latching point, and the B_bias is the clock bias of the second clock signal between the clock values B1 and B2.

4. The method of claim 1, further comprising:

calculating a clock bias between the first latching point and the second latching point; and

calculating the second GNSS time according to the clock bias, the first GNSS time, the first latching point, and the second latching point.

5. The method of claim 1, further comprising:

storing at least the first latching point and the first GNSS time into a memory.

6. The method of claim 1, wherein the relationship between the first clock signal and the GNSS time represents value mapping between the clock value of the first clock signal and the GNSS time.

7. The method of claim 1, further comprising:

updating the relationship after each position fix is obtained.

8. The method of claim 1, wherein the first clock signal has higher resolution than the second clock signal.

9. The method of claim 1, wherein the first clock signal is generated from a temperature compensated crystal oscillator and the second clock signal is generated from a real time clock signal.

10. The method of claim 1, wherein the edge represents the end of a clock cycle of the specific signal.

11. An apparatus for obtaining Global Navigation Satellite System (GNSS) time in a GNSS receiver according to a first clock signal from a first clock source, the apparatus comprising:

a second clock source for generating a second clock signal;

a time-latching logic circuit, coupled to the second clock source, for performing a time-latching operation to latch the first clock signal and the second clock signal at a first latching point, and further latching the first clock signal and the second clock signal at a second latching point; and

a processing module, coupled to the second clock source and the time-latching logic circuit, for deriving a relationship between the first clock signal and the GNSS time, calculating a first GNSS time corresponding to the first latching point according to the relationship, and calculating a second GNSS time according to the first GNSS time, the first latching point and the second latching point.

12. The apparatus of claim 11, wherein the GNSS receiver is powered off during the time period between the first latching point and the second latching point.

13. The apparatus of claim 11, wherein the processing module calculates the second GNSS time by the following equation:

C2=C1+(B2−

B1)−

B_bias;

wherein C1 is the first GNSS time, C2 is the second GNSS time, B1 is a clock value of the second clock signal in the first latching point, B2 is a clock value of the second clock signal in the second latching point, and the B_bias is the clock bias of the second clock signal between the clock values B1 and B2.

14. The apparatus of claim 11, wherein the processing module calculates a clock bias between the first and second latching points of the second clock signal and calculates the second GNSS time according to the clock bias, the first GNSS time, the first latching point, and the second latching point.

15. The apparatus of claim 11, wherein the apparatus further comprises a memory;

and the processing module stores at least the first latching point and the first GNSS time into the memory.

16. The apparatus of claim 11, wherein the relationship between the first clock signal and the GNSS time represents value mapping between the clock value of the first clock signal and the GNSS time.

17. The apparatus of claim 11, wherein the processing module is capable of updating the relationship after each position fix is obtained.

18. The apparatus of claim 11, wherein the first clock signal has higher resolution than the second clock signal.

19. The apparatus of claim 11, wherein the first clock signal is generated from a temperature compensated crystal oscillator within the first clock source, and the second clock signal is generated from a real time clock signal of the second clock source.

20. The apparatus of claim 11, wherein the edge represents the end of a clock cycle of the specific signal.