Method and apparatus for adjusting reference oscillator frequency in a mobile wireless device

• US 20040142701A1
• Filed: 01/16/2003
• Published: 07/22/2004
• Est. Priority Date: 01/16/2003
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Charles Abraham To Global Locate Incorporated
• Inventors: Abraham, Charles
• Granted Patent: US 7,155,183 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H03J 2200/11 Cellular receiver, e.g. GSM, combined with a GPS receiver
• CPC Class Codes: H03J 7/04 where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
• CPC Class Codes: H04B 1/3805 with built-in auxiliary receivers
• CPC Class Codes: H04B 1/403 using the same oscillator for generating both the transmitter frequency and the receiver local oscillator frequency

Abstract

A method and apparatus for using a conventional oscillator in a cellular telephone transceiver as a source of a reference signal for a GPS receiver. In one embodiment, the method comprises using a voltage-controlled oscillator (“VCXO”) within a cellular telephone transceiver to generate a reference frequency signal for the GPS receiver. Circuitry within the telephone transceiver generates a frequency error signal. Both of these signals are coupled to GPS circuitry and used to control a carrier numerically controlled oscillator (“NCO”) and a code NCO. The NCOs produce a tuning signal and a timing signal, respectively. The GPS circuitry uses the NCO generated signals to process GPS signals.

Claims

1. Within a mobile device comprising cell phone circuitry and GPS circuitry, a method for producing a reference signal for a GPS receiver comprising:

producing a cellular oscillator signal and a frequency error signal within the cell phone circuitry, where the frequency error signal is for controlling an oscillator to operate the cell phone circuitry within cell phone network specifications;

coupling the oscillator signal to at least one numerically controlled oscillator within GPS circuitry;

processing the frequency error signal to produce a frequency control value that is coupled to the at least one numerically controlled oscillator; and

generating, within said at least one numerically controlled oscillator, a signal in response to said cellular oscillator signal and said frequency control value that is used for processing GPS signals.

2. The method of claim 1 wherein the frequency error signal is maintained by the cell phone circuitry within said cell phone transmission specifications.

3. The method of claim 1 wherein the frequency error signal represents the frequency difference between a cellular telephone signal carrier or pilot tone and a signal derived from the cellular oscillator signal.

4. The method of claim 1 wherein the frequency control value is a digital word.

5. The method of claim 1 wherein said at least one numerically controlled oscillator comprises:

a carrier numerically controlled oscillator for generating a carrier tuning signal; and

a code numerically controlled oscillator for generating a code timing signal.

6. The method of claim 5 wherein said carrier tuning signal substantially reduces frequency error caused by Doppler shift.

7. Apparatus within an integrated mobile device comprising:

cell phone circuitry for generating of an oscillator signal and a frequency error signal;

a controller, coupled to said cell phone circuitry, for processing the frequency error signal to produce a frequency control value;

a carrier numerically controlled oscillator, within GPS circuitry, for generating a carrier tuning oscillator signal in response to said oscillator signal and said frequency control value signal; and

a code numerically controlled oscillator, within GPS circuitry, for generating a code timing oscillator signal in response to said oscillator signal and said frequency control value.

8. The apparatus of claim 7 wherein the cell phone circuitry comprises a voltage controlled crystal oscillator (VCXO) for generating the oscillator signal.

9. The apparatus of claim 7 wherein said GPS circuitry comprises assisted GPS circuitry.

10. The apparatus of claim 7 wherein the frequency control value is a digital word.

11. A method for processing GPS signals in a mobile device during out-of-network coverage, where said mobile device comprises a GPS receiver and a wireless transceiver, comprising:

a) searching for a pilot tone or a carrier signal of a cellular telephone by tuning a frequency of an oscillatory signal generator;

b) fixing the frequency of said oscillatory signal generator when said pilot tone or said carrier signal are not found;

c) searching for said GPS satellite signals; and

d) returning to step (a) when said GPS satellite signals are not found.

12. The method of claim 11, wherein said searching step for said pilot tone and said carrier signal occurs for a first predetermined time;

said fixing step occurs when said first predetermined time lapses;

said searching step for said GPS satellite signals occurs for a second predetermined time; and

said returning step occurs after said second predetermined time lapses.

13. The method of claim 12, wherein said first predetermined time is in a range of about 20 to 30 seconds.

14. The method of claim 12, wherein said second predetermined time is in a range of about 20 to 30 seconds.