Oscillating circuit and method for calibrating same

• US 6,472,943 B1
• Filed: 04/13/2001
• Issued: 10/29/2002
• Est. Priority Date: 12/21/2000
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonktiebolaget L.M. Ericsson
• Inventors: Purdy, David, Soong, Anthony Chak Keung, Lainson, Kate Jennings, Schwartz, Bruce S.
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/834,406
• Publication Number:
  US 20020158693A1
• Time in Patent Office: 564 Days
• Field of Search: 331/18, 331/44, 331/74, 327/105-107, 327/113, 327/117, 327/119, 327/141, 327/291, 327/513
• US Class Current: 331/44
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: H03L 1/027 by using frequency conversion means which is variable with temperature, e.g. mixer, frequency divider, pulse add/substract logic circuit H03L1/023, H03L1/026 take precedence
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

An oscillating circuit (10) includes a quartz crystal oscillator (12) for generating a clock signal (20). The clock signal is synchronized to a master signal (19) during the lock-in periods when the oscillating circuit (10) has access to the master signal (19). During the holdover periods when the oscillating circuit (10) loses access to the master signal (19), an oscillation frequency function predicts the crystal oscillation frequency in terms the physical parameters, e.g., time and temperature, that may affect the crystal oscillation frequency. The predicted frequency is compared with a standard frequency to generate an error signal. In response to the error signal, a fraction handler block (28) determines whether adding cycles to or deleting cycles from the clock signal, thereby calibrating the oscillation signal (13) of the oscillating circuit (10).

Claims

1. An oscillating clock circuit, comprising:

a crystal oscillator generating a crystal oscillation signal;

a controller coupled for receiving the crystal oscillation signal, the controller generating a modified frequency signal from the crystal oscillation signal,

the controller further coupled for receiving a synchronization signal, the controller generating a first calibration signal based on comparing the modified frequency signal to the synchronization signal,

the controller further generating a second calibration signal based on predicting a frequency of the crystal oscillation signal in response to a physical parameter of the crystal oscillator; and

a synthesizer coupled for receiving the modified frequency signal and calibration signals from the controller, the synthesizer generating a clock signal in response to the modified frequency signal and adjusting the clock signal in response to the calibration signals.

2. The oscillating clock circuit of claim 1, the controller generating the second calibration signal in response to the losing access to the synchronization signal.

3. The oscillating clock circuit of claim 1, wherein the physical parameter of the crystal oscillator is age.

4. The oscillating clock circuit of claim 1, wherein the physical parameter of the crystal oscillator is temperature.

5. The oscillating clock circuit of claim 1, the controller comprising a comparator coupled for receiving the modified frequency signal and the synchronization signal, the comparator generating an error signal by comparing the modified frequency signal and the synchronization signal, wherein the first calibration signal is based on the error signal.

6. The oscillating clock circuit of claim 1, the controller comprising a frequency signal generator for generating the modified frequency signal.

7. The oscillating clock circuit of claim 6, wherein the frequency signal generator comprises a frequency multiplier.

8. The oscillating clock circuit of claim 1, the controller configured for predicting the frequency of the crystal oscillation signal as a function of temperature of the crystal oscillator.

9. The oscillating clock circuit of claim 1, the controller configured for predicting the frequency of the crystal oscillation signal as a function of age of the crystal oscillator.

10. The oscillating clock circuit of claim 1, the controller configured for predicting the frequency of the crystal oscillation signal as a function of both temperature and age of the crystal oscillator.

11. An oscillating clock circuit, comprising:

a crystal oscillator generating a crystal oscillation signal;

a controller coupled for receiving the crystal oscillation signal and for predicting a frequency of the crystal oscillation signal in response to a physical parameter of the crystal oscillator.

12. The oscillating clock circuit of claim 11, the controller further coupled for receiving a synchronization signal, the controller generating a first calibration signal based on comparing the crystal oscillation signal to the synchronization signal, and a second calibration signal based on the predicted crystal oscillation frequency, the clock circuit further comprising:

a synthesizer coupled for receiving the crystal oscillation signal and calibration signals from the controller, the synthesizer generating a clock signal in response to the crystal oscillation signal and adjusting the clock signal in response to the calibration signals.

13. The oscillating clock circuit of claim 11, wherein the physical parameter of the crystal oscillator is age.

14. The oscillating clock circuit of claim 11, wherein the physical parameter of the crystal oscillator is temperature.

15. The oscillating clock circuit of claim 12, the controller comprising a comparator coupled for receiving the crystal oscillation signal and the synchronization signal, the comparator generating an error signal by comparing the crystal oscillation signal and the synchronization signal, wherein the first calibration signal is based on the error signal.

16. The oscillating clock circuit of claim 11, the controller configured for predicting the frequency of the crystal oscillation signal as a function of both temperature and age of the crystal oscillator.

17. A method for calibrating an oscillation signal generated by a crystal oscillator, comprising:

predicting a frequency of the oscillation signal based on a physical parameter of the crystal oscillator.

18. The method of claim 17, wherein the frequency of the oscillation signal is predicted as a function of temperature of the crystal oscillator.

19. The method of claim 17, wherein the frequency of the oscillation signal is predicted as a function of aging of the crystal oscillator.

20. The method of claim 17, wherein the frequency of the oscillation signal is predicted as a function of both temperature and aging of the crystal oscillator.

21. A method for calibrating a clock signal in a base station of a wireless communication network, comprising:

generating a oscillation signal using a crystal oscillator in the base station;

generating a modified frequency signal by multiplying a frequency of the oscillation signal by a predetermined factor;

receiving a master synchronization signal from a global positioning system satellite;

generating the clock signal by synchronizing the modified frequency signal to the master synchronization signal;

generating a predicted oscillation frequency of the crystal oscillator in terms of a physical parameter of the crystal oscillator during a holdover period in which the base station loses access to the master synchronization signal;

generating a calibration signal by comparing the predicted oscillation frequency with a standard frequency during the holdover period; and

generating the clock signal during the holdover period by adjusting the modified frequency signal in response to the calibration signal.

22. The method of claim 21, wherein the step of generating a predicted oscillation frequency of the crystal oscillator includes:

generating a temperature function;

sensing a temperature of the crystal oscillator; and

generating the predicted oscillation frequency in terms of the temperature in accordance to the temperature function.

23. The method of claim 22, wherein the step of generating a temperature function includes the steps of:

providing a plurality of temperature coefficients; and

generating a polynomial of the temperature in terms of the plurality of temperature coefficients.

24. The method of claim 23,

the step of providing a plurality of temperature coefficients including providing a first set of temperature coefficients and a second set of temperature coefficients;

and

the step of generating a polynomial of the temperature including generating the polynomial of the temperature using the first set of temperature coefficients in response to an increasing temperature and using the second set of temperature coefficients in response to a decreasing temperature.

25. The method of claim 23, the step of providing a plurality of temperature coefficients including:

storing a plurality of initial values for the plurality of temperature coefficients in a memory unit; and

reevaluating the plurality of temperature coefficients over a twenty four hour period in response to the base stating having access to the master synchronization signal.

26. The method of claim 23, the step of generating the predicted oscillation frequency of the crystal oscillator further including:

generating a drift function in terms of a time; and

generating the predicted oscillation frequency in terms of the temperature and the time in accordance to a sum the temperature function and the drift function.

27. The method as claimed in claim 21, the step of generating the clock signal including performing an action selected from a group of actions including:

adding at least one cycle to the modified frequency signal to generate the clock signal;

deleting at least one cycle from the modified frequency signal to generate the clock signal; and

passing the modified frequency signal as the clock signal.