SYSTEM AND METHOD FOR REDUCING HOLDOVER DURATION

• US 20120200361A1
• Filed: 02/06/2012
• Published: 08/09/2012
• Est. Priority Date: 06/19/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Rockstar Bidco LP (Rockstar Consortium Inc.)
• Inventors: SMILEY, Russell
• Granted Patent: US 8,598,956 B2
• Time in Patent Office: Days
• US Class Current: 331/18
• CPC Class Codes: G06F 1/04 Generating or distributing clock signals or signals derived directly therefrom
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H03L 7/087 using at least two phase detectors or a frequency and phase detector in the loop
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master

Abstract

A device is provided having a local oscillator (LO) configured to generate a first signal comprising at least one of timing information, frequency information, phase information and combinations thereof. The device also has a LO error corrector comprising an input, the input configured to receive a second signal comprising at least one of timing information, frequency information, phase information and combinations thereof. The second signal is used for disciplining the LO. The LO error corrector is capable of disciplining the LO using a source that is less accurate than a preferred second signal, if the preferred second signal is unavailable to discipline the LO.

Claims

1. A system comprising:

a local oscillator; and

a discipline signal provider configured to receive a primary reference signal and operable to;

determine an offset error of the local oscillator relative to the reference signal;

discipline the local oscillator based on the primary reference signal when the primary reference signal is available; and

when the primary reference signal is at least temporarily unavailable before the local oscillator is disciplined based on the primary reference signal, to correct the offset error of the local oscillator relative to the primary reference signal.

2. The system of claim 1, wherein the discipline signal provider is operable to:

compare the primary reference signal to an output of the local oscillator to derive a correction signal when the primary reference signal is available; and

provide the correction signal to the local oscillator to discipline the local oscillator when the primary reference signal is available.

3. The system of claim 2, wherein the discipline signal provider is operable to:

determine a relationship between the output of the local oscillator and the primary reference signal when the primary reference signal is available; and

discipline the local oscillator based on the determined relationship when the primary reference signal is at least temporarily unavailable.

4. The system of claim 3, wherein the determined relationship is linear over time.

5. The system of claim 1, wherein the discipline signal provider is operable to determine availability of the primary reference signal.

6. The system of claim 5, wherein the discipline signal provider is operable to determine availability of the primary reference signal by receiving information from at least one source external to the discipline signal provider, the information pertaining to the availability of the primary reference signal.

7. The system of claim 1, wherein:

the discipline signal provider is configured to receive an alternative reference signal; and

the discipline signal provider is operable to discipline the local oscillator based on the alternative reference signal while the primary reference signal is unavailable after correction of the offset error of the local oscillator relative to the primary reference signal.

8. The system of claim 7, wherein the discipline signal provider is operable to:

compare the received alternative reference signal to an output of the local oscillator to derive a correction signal associated with the alternative reference signal; and

provide the correction signal to the local oscillator to discipline the local oscillator.

9. The system of claim 1, wherein:

the local oscillator generates a signal comprising at least one of;

timing information;

frequency information; and

phase information; and

the discipline signal provider receives at least one reference signals comprising at least one of;

timing information;

frequency information; and

phase information.

10. The system of claim 1, wherein the discipline signal provider is configured to receive at least one reference signal selected from a group comprising:

a GPS timing signal;

a network timing signal;

a network frequency signal;

a signal generated by a mathematical model of the local oscillator;

a signal comprising synchronization information; and

a signal derived from a period during which the local oscillator was disciplined by a primary reference signal.

11. A method of operating a local oscillator comprising:

receiving a primary reference signal;

determining an offset error of the local oscillator relative to the reference signal;

disciplining the local oscillator based on the primary reference signal when the primary reference signal is available; and

when the primary reference signal is at least temporarily unavailable before the local oscillator is disciplined based on the primary reference signal, correcting the offset error of the local oscillator relative to the primary reference signal.

12. The method of claim 11 further comprising:

comparing the primary reference signal to an output of the local oscillator to derive a correction signal when the primary reference signal is available; and

providing the correction signal to the local oscillator to discipline the local oscillator when the primary reference signal is available.

13. The method of claim 11 further comprising:

determining a relationship between the output of the local oscillator and the primary reference signal when the primary reference signal is available; and

disciplining the local oscillator based on the determined relationship when the primary reference signal is at least temporarily unavailable.

14. The method of claim 13, wherein the determined relationship is linear over time.

15. The method of claim 11 further comprising determining availability of the primary reference signal.

16. The method of claim 15 further comprising determining availability of the primary reference signal by receiving information from at least one source external to the discipline signal provider, the information pertaining to the availability of the primary reference signal.

17. The method of claim 11 further comprising:

receiving an alternative reference signal; and

disciplining the local oscillator based on the alternative reference signal while the primary reference signal is unavailable after correction of the offset error of the local oscillator relative to the primary reference signal.

18. The method of claim 17 further comprising:

comparing the received alternative reference signal to an output of the local oscillator to derive a correction signal associated with the alternative reference signal; and

providing the correction signal to the local oscillator to discipline the local oscillator.

19. The method of claim 11, wherein:

the local oscillator generates a signal comprising at least one of;

timing information;

frequency information; and

phase information; and

the primary reference signals comprises at least one of;

timing information;

frequency information; and

phase information.

20. The method of claim 11, wherein the primary reference signal is selected from a group comprising:

a GPS timing signal;

a network timing signal;

a network frequency signal;

a signal generated by a mathematical model of the local oscillator;

a signal comprising synchronization information; and

a signal derived from a period during which the local oscillator was disciplined by a primary reference signal.