Reference timing signal oscillator with frequency stability

• US 6,711,230 B1
• Filed: 09/27/2002
• Issued: 03/23/2004
• Est. Priority Date: 09/27/2002
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Nicholls, Charles, Carleton, Gregory, Wu, Philippe, Yang, Yu, Gagnon, Eric
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Chang, Joseph
• Application Number:
  US10/255,835
• Time in Patent Office: 543 Days
• Field of Search: 331/18, 331/16, 331/17, 331/25, 331/176, 327/147, 327/156, 375/376
• US Class Current: 375/376
• CPC Class Codes: G04G 3/00 Producing timing pulses driving circuits for stepping motors G04C3/14; producing preselected time intervals for use as timing standards G04F5/00; pulse technique in general H03K; control, synchronisation, or stabilisation of generators in general H03L
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: G04G 7/02 by radio
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H03L 7/148 said digital means comprising a counter or a divider
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

An input reference timing signal oscillator of a phase-locked loop has a computer algorithm which adaptively models the multiple frequencies of an oscillator following a training period. The oscillator is part of a phase-locked loop and the oscillation frequency thereof is controlled in response to the phase detector output. The computer algorithm processes the control signal applied to the oscillator. The computer algorithm updates the characteristics of the model relating to the aging and temperature of the oscillator, using for example, a Kalman filter as an adaptive filter. By the algorithm, the subsequent model predicts the future frequency state of the oscillator on which it was trained. The predicted frequency of the model functions as a reference to correct the frequency of the oscillator in the event that no input reference timing signal is available. With the model updating algorithm, oscillators of low stability performance may be used as cellular base station reference oscillator.

Claims

1. A phase-locked loop (PLL) for providing a timing output signal, the PLL comprising:

an oscillator for generating an oscillation output signal in response to a control component of an input control signal;

a difference detector for detecting a difference between the oscillation output signal and an input reference timing signal when the input reference timing signal is available, thereby providing a difference signal; and

a processor for varying the control component of the input control signal applied to the oscillator in accordance with the difference detected by the difference detector and a frequency dependent element relating to the oscillator, the frequency dependent element being provided in accordance with a characteristic model that is updateable in accordance with the difference signal provided by the difference detector when the input reference timing signal is available, a frequency of the oscillation output signal generated by the oscillator being controlled in accordance with the varied control component of the input control signal.

2. The PLL of claim 1, wherein the processor comprises:

a processing unit for updating a parameter of the characteristic model, the parameter being changed in accordance with the e difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively, and for providing a characteristic signal in accordance with the updated parameter of the characteristic model, the control component of the input control signal being varied in accordance with the characteristic signal.

3. The PLL of claim 2, wherein the processing unit comprises:

a first processing unit for providing a first characteristic signal included in the characteristic signal in accordance with a first parameter of a first model included in the characteristic model, the first parameter being relating to an aging characteristic of the oscillator, the first processing unit updating the first parameter in accordance with the difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively.

4. The PLL of claim 3, the first processing unit further comprising:

a first update determinater for determining whether the first parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period,

wherein the first processing unit updates the first parameter in accordance with a past parameter.

5. The PLL of claim 3, the processing unit further comprising:

a second processing unit for providing a second characteristic signal included in the characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter in accordance with the difference signal and a temperature in relation to the oscillator when the input reference timing signal is available, the second processing unit updating the second parameter in accordance with a past parameter when the input reference timing signal is unavailable,

wherein the first and second characteristic signals are combined to produce the characteristic signal, so as to vary the control component of the input control signal.

6. The PLL of claim 5, the second processing unit further comprising:

a second update determinater for determining whether the second parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period,

wherein the second processing unit updates the second parameter in accordance with a past parameter.

7. The PLL of claim 5, the second processing unit comprising:

an update distinction detector for detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, the second parameter being positively or negatively updated in accordance with the detected distinction.

8. The PLL of claim 3, the processing unit further comprising:

a second processing unit for providing a second characteristic signal included in the characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter in accordance with the first characteristic signal provided by the first processing unit and a temperature in relation to the oscillator when the input reference timing signal is available, the second processing unit updating the second parameter in accordance with a past parameter when the input reference timing signal is unavailable,

wherein the first and second characteristic signals are combined to produce the characteristic signal, so as to vary the control component of the input control signal.

9. The PLL of claim 8, wherein:

the first processing unit further comprises a first update determinater for determining whether the fist parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the first processing unit updates the first parameter in accordance with a past parameter; and

the second processing unit further comprises a second update determinater for determining whether the second parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the second processing unit updates the second parameter in accordance with a past parameter.

10. The PLL of claim 8, the second processing unit comprising:

an update distinction detector for detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, the second parameter being positively or negatively updated in accordance with the detected distinction.

11. The PLL of claim 2, wherein the processing unit comprises:

a first processing unit for providing a first characteristic signal included in the characteristic signal in accordance with a first parameter of a first model included in the characteristic model, the first parameter being relating to an aging characteristic of the oscillator, the first processing unit updating the first parameter in accordance with the difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively; and

a second processing unit for providing a second characteristic signal included in the characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter (i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit and a temperature in relation to the oscillator, when the input reference timing signal is available; and

(ii) in accordance with a past parameter when the input reference timing signal is unavailable,

wherein the first and second characteristic signals are combined to produce the characteristic signal, so as to vary the control component of the input control signal.

12. The PLL of claim 11, wherein the processing unit comprises:

each of the first and second first processing units comprises an adaptive filter, the first processing unit updating the first parameter of the first model using the adaptive filter thereof, the second processing unit updating the second parameter of the second model using the adaptive filter thereof.

13. The PLL of claim 11, wherein:

the first processing unit further comprises a first update determinater for determining whether the fist parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the first processing unit updates the first parameter in accordance with a past parameter; and

the second processing unit further comprises a second update determinater for determining whether the second parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the second processing unit updates the second parameter in accordance with a past parameter.

14. The PLL of claim 11, further comprising:

a temperature sensor for sensing temperature in relation to the oscillator to provide the temperature signal.

15. The PLL of claim 11, the second processing unit comprising:

an update distinction detector for detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, the second parameter being positively or negatively updated in accordance with the detected distinction.

16. The PLL of claim 2, wherein the processing unit comprises:

a first processing unit for providing a first characteristic signal included in the characteristic signal in accordance with a first parameter of a first model included in the characteristic model, the first parameter being relating to an aging characteristic of the oscillator, the first processing unit updating the first parameter in accordance with the difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively; and

a second processing unit for providing a second characteristic signal included in the characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter (i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit, a temperature in relation to the oscillator and a voltage in relation to the oscillator, when the input reference timing signal is available; and

(ii) in accordance with a past parameter when the input reference timing signal is unavailable,

wherein the first and second characteristic signals are combined to produce the characteristic signal, so as to vary the control component of the input control signal.

17. The PLL of claim 16, wherein the processing unit comprises:

each of the first and second first processing units comprises an adaptive filter, the first processing unit updating the first parameter of the first model using the adaptive filter thereof, the second processing unit updating the second parameter of the second model using the adaptive filter thereof.

18. The PLL of claim 16, wherein:

the first processing unit further comprises a first update determinater for determining whether the fist parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the first processing unit updates the first parameter in accordance with a past parameter; and

the second processing unit further comprises a second update determinater for determining whether the second parameter is updated regardless of the availability of the input reference timing signal, the determination being made in accordance with a predetermined period, wherein the second processing unit updates the second parameter in accordance with a past parameter.

19. The PLL of claim 16, further comprising:

a temperature sensor for sensing temperature in relation to the oscillator to provide the temperature signal to the second processing unit; and

a voltage detector for detecting voltage in relation to the oscillator to provide the voltage signal to the second processing unit.

20. The PLL of claim 16, the second processing unit comprising:

an update distinction detector for detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, the second parameter being positively or negatively updated in accordance with the detected distinction.

21. The PLL of claim 1, further comprising:

a converter for converting the updated frequency dependent element into voltage representing the control component of the input control signal applied to the oscillator.

22. A method for providing an accurate timing output signal when an input reference timing signal is unavailable, the method comprising the steps of:

providing an oscillator for generating an oscillation output signal in response to a control component of an input control signal;

detecting a difference between the oscillation output signal and an input reference timing signal when the input reference timing signal is available, thereby providing a difference signal;

changing the control component of the input control signal applied to the oscillator in accordance with the difference detected by the difference detector and a frequency dependent element relating to the oscillator;

providing the frequency dependent element in accordance with a characteristic model that is updateable in accordance with the difference signal when the input reference timing signal is available,

wherein a frequency of the oscillation output signal generated by the oscillator is controlled in accordance with the varied control component of the input control signal, the timing output signal being provided in accordance with the oscillation output signal.

23. The method of claim 22, wherein the step of providing the oscillation characteristic comprises the step of:

providing a first characteristic signal in accordance with a first parameter of a first model, the first parameter being relating to an aging characteristic of the oscillator;

updating the first parameter in accordance with the difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively;

providing a second characteristic signal included in accordance with a second parameter of a second model, the second parameter being relating to a temperature characteristic of the oscillator;

updating the second parameter;

(i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit and a temperature in relation to the oscillator, when the input reference timing signal is available;

(ii) in accordance with a past parameter when the input reference timing signal is unavailable; and

combining the first and second characteristic signals to produce the characteristic signal, so as to vary the control component of the input control signal.

24. The method of claim 23, wherein the step of updating the second parameter comprises the step of:

detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, so that the second parameter is positively or negatively updated in accordance with the detected distinction.

25. The method of claim 23, wherein:

the step of updating the first parameter comprises the step of updating the first parameter of the first model using an adaptive filter; and

the step of updating the second parameter comprises the step of updating the second parameter of the second model using an adaptive filter.

26. The method of claim 22, wherein the step of providing the oscillation characteristic comprises the step of:

providing a first characteristic signal in accordance with a first parameter of a first model, the first parameter being relating to an aging characteristic of the oscillator;

updating the first parameter in accordance with the difference signal when the input reference timing signal is available and in accordance with a past parameter when the input reference timing signal is unavailable, respectively;

providing a second characteristic signal in accordance with a second parameter of a second model, the second parameter being relating to a temperature characteristic of the oscillator;

updating the second parameter;

(i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit, a temperature in relation to the oscillator and a voltage in relation to the oscillator, when the input reference timing signal is available; and

(ii) in accordance with a past parameter when the input reference timing signal is unavailable; and

combining the first and second characteristic signals to produce the characteristic signal, so as to vary the control component of the input control signal.

27. The method of claim 26, wherein the step of updating the second parameter comprises the step of:

detecting a distinction of the second parameter in accordance with the frequency of the oscillation output signal and the temperature in relation to the oscillator, so that the second parameter is positively or negatively updated in accordance with the detected distinction.

28. The method of claim 26, wherein:

the step of updating the first parameter comprises the step of updating the first parameter of the first model using an adaptive filter; and

the step of updating the second parameter comprises the step of updating the second parameter of the second model using an adaptive filter.

29. The method of claim 24, wherein the step of detecting a distinction comprises the step of:

detecting the sign of variation of the oscillation frequency over time, in accordance with the frequency of the oscillation output signal and the temperature, the sign being used to update the second parameter positively or negatively.

30. An apparatus for generating a reference signal for use in a cellular base station, the apparatus comprising:

a receiver for generating an input reference timing signal when a cellular signal is available;

an oscillator for generating an oscillation output signal in response to a control component of an input control signal;

a difference detector for detecting a difference between the oscillation output signal and the input reference timing signal when the input reference timing signal is generated, thereby providing a difference signal; and

a processor for varying the control component of the input control signal applied to the oscillator in accordance with the difference detected by the difference detector and a frequency dependent element relating to the oscillator, the frequency dependent element being provided in accordance with a characteristic model that is updateable in accordance with the difference signal provided by the difference detector when the input reference timing signal is generated, a frequency of the oscillation output signal generated by the oscillator being controlled in accordance with the varied control component of the input control signal.

31. The apparatus of claim 30, wherein the processor comprises:

a first processing unit for providing a first characteristic signal in accordance with a first parameter of a first model included in the characteristic model, the first parameter being relating to an aging characteristic of the oscillator, the first processing unit updating the first parameter in accordance with the difference signal when the input reference timing signal is generated and in accordance with a past parameter when the input reference timing signal is generated, respectively; and

a second processing unit for providing a second characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter (i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit and a temperature in relation to the oscillator, when the input reference timing signal is generated; and

(ii) in accordance with a past parameter when the input reference timing signal is not generated,

wherein the first and second characteristic signals are combined to produce the characteristic signal, so as to vary the control component of the input control signal.

32. The apparatus of claim 30, wherein the processor comprises:

a first processing unit for providing a first characteristic signal included in accordance with a first parameter of a first model included in the characteristic model, the first parameter being relating to an aging characteristic of the oscillator, the first processing unit updating the first parameter in accordance with the difference signal when the input reference timing signal is generated and in accordance with a past parameter when the input reference timing signal is not generated, respectively; and

a second processing unit for providing a second characteristic signal in accordance with a second parameter of a second model of the characteristic model, the second parameter being relating to a temperature characteristic of the oscillator, the second processing unit updating the second parameter (i) in accordance with the difference signal, the first characteristic signal provided by the first processing unit, a temperature in relation to the oscillator and a voltage in relation to the oscillator, when the input reference timing signal is generated; and

(ii) in accordance with a past parameter when the input reference timing signal is not generated,

wherein the first and second characteristics signals are combined to produce the characteristic signals, so as to vary the component of the input control signal.