CRYSTAL OSCILLATOR FREQUENCY CALIBRATION

• US 20090195322A1
• Filed: 01/31/2008
• Published: 08/06/2009
• Est. Priority Date: 01/31/2008
• Status: Abandoned Application

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Yan, Hongbo, Filipovic, Daniel Fred
• Application Number:
  US12/023,796
• Publication Number:
  US 20090195322A1
• Time in Patent Office: Days
• US Class Current: 331/44
• CPC Class Codes: H03L 1/022 by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature H03L1/021 takes precedence

Abstract

Techniques are disclosed for estimating a frequency of a crystal oscillator based on temperature. In an embodiment, the oscillator frequency is computed using a polynomial approximation. Techniques are disclosed for deriving and periodically updating the coefficients used in the polynomial approximation.

Claims

1. A method for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the method comprising;

measuring a first temperature T 1 and a corresponding oscillator frequency Fm(T1);

measuring a second temperature T2 and a corresponding oscillator frequency Fm(T2);

computing the coefficient c0′

based on Fm(T1); and

computing the coefficient c1′

based on T1, T2, Fm(T1), and Fm(T2).

2. The method of claim 1, the computing the coefficient c0′

comprising taking the difference between Fm(T1) and an initial term F_init(T1).

3. The method of claim 2, the initial term F_init(T1) comprising a term c0_init and a coefficient c1_init times T1.

4. The method of claim 1, the computing the coefficient c1′

comprising dividing the difference between Fm(T2) and Fm(T1) by the difference between T2 and T1.

5. The method of claim 4, wherein the difference between T1 and T2 is at least one degree Celsius.

6. The method of claim 4, further comprising turning on a heat source after measuring T1 and before measuring T2.

7. The method of claim 6, wherein the heat source is a power amplifier.

8. The method of claim 1, further comprising computing multiple estimates of c0′

and c1′

.

9. The method of claim 8, further comprising averaging together the multiple estimates of c0′

and c1′

.

10. The method of claim 8, further comprising updating estimates of c0′

and c1′

using an infinite impulse response (IIR) filter.

11. The method of claim 4, the polynomial further comprising a coefficient c2′

times a second-order function of T and a coefficient c3′

times a third-order function of T, the method further comprising;

computing the coefficients c2′ and

c3′

based on c1′

.

12. The method of claim 11, the computing the coefficient c2′

comprising multiplying c1′

by a term m_c2′

.

13. The method of claim 11, the computing the coefficient c3′

comprising multiplying c1′

by a term m_c3′

.

14. The method of claim 13, further comprising updating the term c0′

by taking the difference between Fm(T1) and F′

(T1), wherein F′

(T1) comprises the pre-updated term c0′

, and the computed coefficients c1′

, c2′

, and c3′

.

15. The method of claim 13, further comprising computing multiple estimates of c0′

, c1′

, c2′

, and c3′

.

16. The method of claim 15, further comprising averaging together the multiple estimates of c0′

, c1′

, c2′

, and c3′

.

17. The method of claim 15, further comprising updating estimates of c0′

, c1′

, c2′

, and c3′

using an infinite impulse response (IIR) filter.

18. The method of claim 15, further comprising updating estimates of c0′

, c1′

, c2′

, and c3′

by minimizing a mean-squared error between;

     1) a frequency estimate based on candidate estimates of c0′

, c1′

, and

     2) the measured frequency Fm(T1).

19. The method of claim 18, the frequency estimate based on candidate estimates of c0′

, c1′

utilizing estimates for c2′ and

c3′

linearly related to the candidate estimates of c0′ and

c1′

.

20. The method of claim 1, wherein the computing the estimates of c0′

and c1′

is done at a factory.

21. A method for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the method comprising;

entering a state FIELD0, operations in the state FIELD0 comprising computing the coefficient c0′

if the measured temperature T is within a first range of temperatures; and

entering a state FIELD1, operations in the state FIELD1 comprising computing the coefficient c1′

if the measured temperature T is within a second range of temperatures.

22. The method of claim 21, the computing the coefficient c0′

comprising;

taking a difference between a measured frequency fm and a calculated frequency fcal to generate a first difference term, wherein fcal is calculated from a previous estimate of the coefficient c0′ and

the measured temperature T.

23. The method of claim 22, the computing the coefficient c0′

further comprising;

weighting a difference between the first difference term and a previous estimate of the coefficient c0′

by a weighting constant; and

adding the weighted difference to the previous estimate of c0′

.

24. The method of claim 23, the computing the coefficient c1′

comprising;

measuring temperatures T2 and T1, and corresponding frequencies Fm(T2) and Fm(T1);

dividing the difference between Fm(T2) and Fm(T1) by the difference between T2 and T1 to generate a first quotient;

weighting the first quotient by a weighting constant; and

adding the weighted quotient to the previous estimate of c1′

.

25. The method of claim 24, operations in the state FIELD0 further comprising waiting for a first predetermined time period before checking if the measured temperature T is within the first range of temperatures, operations in the state FIELD1 further comprising waiting for a second predetermined time period before checking if the measured temperature T is within the second range of temperatures.

26. The method of claim 25, further comprising transitioning from FIELD0 to FIELD1 if c0′

has been computed a first predetermined number of times in FIELD0.

27. The method of claim 25, further comprising transitioning from FIELD0 to FIELD1 if the difference between a current estimate of c0′

and a previous estimate of c0′

is less than a predetermined value.

28. The method of claim 25, further comprising transitioning from FIELD0 back to FIELD1 if a predetermined condition is met.

29. The method of claim 25, further comprising entering a state FIELD3, operations in the state FIELD3 comprising computing the coefficient c3′

if the measured temperature T is within a fourth range of temperatures, operations in the state FIELD3 further comprising waiting for a fourth predetermined time period before checking if the measured temperature T is within the fourth range of temperatures.

30. The method of claim 29, the computing the coefficient c3′

comprising determining an estimate of c3′

that minimizes a mean-squared error between;

     1) a frequency estimate based on the updated values of c0, c1, c2, and a candidate estimate of c3′

, and

     2) the measured frequency Fm(T1).

31. The method of claim 30, further comprising IIR filtering the estimate of c3′

with a previous estimate of c3′

.

32. The method of claim 31, further comprising transitioning from FIELD1 to FIELD3 if c1′

has been computed a second predetermined number of times.

33. The method of claim 31, further comprising transitioning from FIELD1 to FIELD3 if the difference between a current estimate of c1′

and a previous estimate of c1′

is less than a predetermined value.

34. An apparatus for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the apparatus comprising;

a temperature measurement unit for measuring a first temperature T 1 and a second temperature T2;

a frequency measurement unit for measuring corresponding oscillator frequencies Fm(T1) and Fm(T2); and

a computing module for computing the coefficient c0′

based on Fm(T1), and for computing the coefficient c1′

based on T1, T2, Fm(T1), and Fm(T2).

35. The apparatus of claim 34, the computing module computing the coefficient c0′

by taking the difference between Fm(T1) and an initial term F_init(T1).

36. The apparatus of claim 34, the computing module computing the coefficient c1′

by dividing the difference between Fm(T2) and Fm(T1) by the difference between T2 and T1.

37. The apparatus of claim 34, the polynomial further comprising a coefficient c2′

times a second-order function of T, the computing module further computing the coefficient c2′

by performing a linear operation on the computed coefficient c1′

.

38. The apparatus of claim 37, the polynomial further comprising a coefficient c3′

times a third-order function of T, the computing module further computing the coefficient c3′

by performing a linear operation on the computed coefficient c1′

.

39. An apparatus for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the apparatus comprising;

means for measuring a first temperature T1 and a second temperature T2;

means for measuring corresponding oscillator frequencies Fm(T1) and Fm(T2);

means for computing the coefficient c0′

based on Fm(T1), and for computing the coefficient c1′

based on T1, T2, Fm(T1), and Fm(T2).

40. A computer program product for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the product comprising;

computer-readable medium comprising;

code for causing a computer to measure a first temperature T1 and a corresponding oscillator frequency Fm(T1);

code for causing a computer to measure a second temperature T2 and a corresponding oscillator frequency Fm(T2);

code for causing a computer to compute the coefficient c0′

based on Fm(T1);

code for causing a computer to compute the coefficient c1′

based on T1, T2, Fm(T1), and Fm(T2).

41. An apparatus for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the apparatus comprising;

means for entering a state FIELD0, operations in the state FIELD0 comprising computing the coefficient c0′

if the measured temperature T is within a first range of temperatures; and

means for entering a state FIELD1, operations in the state FIELD1 comprising computing the coefficient c1′

if the measured temperature T is within a second range of temperatures.

42. The apparatus of claim 41, the computing the coefficient c0′

comprising taking a difference between a measured frequency fm and a calculated frequency fcal to generate a first difference term, wherein fcal is calculated from a previous estimate of the coefficient c0′ and

the measured temperature T.

43. A computer program product for computing coefficients for use in a polynomial approximation of a crystal oscillator frequency, the polynomial comprising a term c0′

and a coefficient c1′

times a measured temperature T of the crystal oscillator, the product comprising;

computer-readable medium comprising;

code for causing a computer to enter a state FIELD0, operations in the state FIELD0 comprising computing the coefficient c0′

if the measured temperature T is within a first range of temperatures; and

code for causing a computer to enter a state FIELD1, operations in the state FIELD1 comprising computing the coefficient c1′

if the measured temperature T is within a second range of temperatures.

44. The computer program product of claim 43, the code for causing a computer to compute the coefficient c0′

comprising code for causing a computer to take a difference between a measured frequency fm and a calculated frequency fcal to generate a first difference term, wherein fcal is calculated from a previous estimate of the coefficient c0′ and

the measured temperature T.

45. The computer program product of claim 43, the code for causing a computer to compute the coefficient c0′

further comprising;

code for causing a computer to weight a difference between the first difference term and a previous estimate of the coefficient c0′

by a weighting constant; and

code for causing a computer to add the weighted difference to the previous estimate of c0′

.

46. The computer program product of claim 45, the code for causing a computer to compute the coefficient c1′

comprising;

code for causing a computer to measure temperatures T2 and T1, and corresponding frequencies Fm(T2) and Fm(T1);

code for causing a computer to divide the difference between Fm(T2) and Fm(T1) by the difference between T2 and T1 to generate a first quotient;

code for causing a computer to weight the first quotient by a weighting constant; and

code for causing a computer to add the weighted quotient to the previous estimate of c1′

.

47. The computer program product of claim 46, operations in the state FIELD0 further comprising waiting for a first predetermined time period before checking if the measured temperature T is within the first range of temperatures, operations in the state FIELD1 further comprising waiting for a second predetermined time period before checking if the measured temperature T is within the second range of temperatures.

48. The computer program product of claim 47, the computer-readable medium further comprising code for causing a computer to transition from FIELD0 to FIELD1 if c0′

has been computed a first predetermined number of times in FIELD0.

49. The computer program product of claim 48, the computer-readable medium further comprising code for causing a computer to enter a state FIELD3, operations in the state FIELD3 comprising computing the coefficient c3′

if the measured temperature T is within a fourth range of temperatures, operations in the state FIELD3 further comprising waiting for a fourth predetermined time period before checking if the measured temperature T is within the fourth range of temperatures.

50. The computer program product of claim 49, the computer-readable medium further comprising code for causing a computer to transition from FIELD1 to FIELD3 if c1′

has been computed a second predetermined number of times.