All-digital frequency synthesis with DCO gain calculation

• US 20030133522A1
• Filed: 11/22/2002
• Published: 07/17/2003
• Est. Priority Date: 11/27/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Leipold, Dirk, Staszewski, Robert B., Wallberg, John
• Granted Patent: US 8,000,428 B2
• Time in Patent Office: Days
• US Class Current: 375/345
• CPC Class Codes: H03L 2207/50 All digital phase-locked loop
• CPC Class Codes: H03L 7/085 concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal H03L7/10 takes precedence; circuits for comparing the phase or frequency of two mutually-independent oscillations H03D13/00
• CPC Class Codes: H03L 7/0991 the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider H03L7/0995 takes precedence; fixed oscillators with means for selecting among various phases H03L7/0814

Abstract

An all-digital frequency synthesizer architecture is built around a digitally controlled oscillator (DCO) that is tuned in response to a digital tuning word (OTW). In exemplary embodiments: (1) a gain characteristic (K_DCO) of the digitally controlled oscillator can be determined by observing a digital control word before and after a known change (Δf_max) in the oscillating frequency; and (2) a portion (TUNE_TF) of the tuning word can be dithered (1202), and the resultant dithered portion (d_k^TF) can then be applied to a control input of switchable devices within the digitally controlled oscillator.

Claims

1. A method of estimating a gain characteristic of a digitally controlled oscillator in a frequency synthesizer, comprising:

providing a digital control word that includes information for use in tuning the digitally controlled oscillator;

obtaining a first value of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at a first frequency;

changing the operating frequency of the digitally controlled oscillator from said first frequency by a predetermined frequency change amount;

after said changing step, obtaining a second value of the digital control word produced by the frequency synthesizer; and

using the first value, the second value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

2. The method of claim 1, wherein said first value obtaining step includes obtaining a first plurality of values of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at said first frequency, said using step including using the first plurality of values, the second value, and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

3. The method of claim 2, wherein said using step includes producing from the first plurality of values a representative value which represents the first plurality of values, and using the representative value, the second value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

4. The method of claim 3, wherein the representative value is an average value of the first plurality of values.

5. The method of claim 2, wherein said second value obtaining step includes obtaining a second plurality of values of the digital control word produced by the frequency synthesizer, said using step including using the first plurality of values, the second plurality of values and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

6. The method of claim 5, wherein said using step includes producing from the first plurality of values a first representative value that represents the first plurality of values, and using the first representative value, the second plurality of values and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

7. The method of claim 6, wherein the first representative value is an average value of the first plurality of values.

8. The method of claim 6, wherein said using step includes producing from the second plurality of values a second representative value which represents the second plurality of values, and using the first representative value, the second representative value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

9. The method of claim 8, wherein the first representative value is an average of the first plurality of values.

10. The method of claim 9, wherein the second representative value is an average of the second plurality of values.

11. The method of claim 8, wherein said using step includes determining a difference between the first and second representative values.

12. The method of claim 11, wherein said using step includes determining a ratiometric relationship between the frequency change amount and said difference.

13. The method of claim 1, wherein said using step includes using the first value, the second value and the frequency change amount to produce a current estimate of the gain characteristic, and combining the current estimate of the gain characteristic with a previous estimate of the gain characteristic to produce a desired estimate of the gain characteristic.

14. The method of claim 13, wherein said combining step includes applying to the current estimate and the previous estimate respective weighting factors to produce respective weighted estimates, and combining the weighted estimates to produce the desired estimate.

15. The method of claim 1, wherein said first frequency is for effectuating a desired communication on a communication link, and said frequency change amount is associated with modulation of a communication symbol on the communication link.

16. The method of claim 15, wherein said frequency change amount corresponds to one of a symbol-to-symbol change and a carrier-to-symbol change.

17. The method of claim 1, wherein said digital control word is one of an oscillator tuning word for directly tuning the digitally controlled oscillator and a further digital word from which said oscillator tuning word is derived.

18. The method of claim 1, wherein said first frequency is for effectuating transfers of information blocks on a communication link, and including performing said first value obtaining step, said changing step, said second value obtaining step and said using step immediately before selected ones of said information block transfers.

19. The method of claim 18, including performing said first value obtaining step, said changing step, said second value obtaining step and said using step immediately before each of said information block transfers.

20. The method of claim 18, wherein said information blocks are data packets.

21. An apparatus for estimating a gain characteristic of a digitally controlled oscillator in a frequency synthesizer, comprising:

an input for receiving a digital control word that includes information for use in tuning the digitally controlled oscillator;

a selector coupled to said input for selecting a first value of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at a first frequency, said selector further for selecting a second value of the digital control word produced by the frequency synthesizer after the operating frequency of the digitally controlled oscillator has changed from said first frequency by a predetermined frequency change amount; and

an estimator coupled to said selector for using said first value, said second value and said frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

22. The apparatus of claim 21, wherein said selector is further for selecting a first plurality of values of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at said first frequency, said estimator further for using the first plurality of values, the second value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

23. The apparatus of claim 22, wherein said estimator includes a calculator for producing from the first plurality of values a representative value which represents the first plurality of values, said estimator further for using the representative value, the second value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

24. The apparatus of claim 23, wherein the representative value is an average value of the first plurality of values.

25. The apparatus of claim 22, wherein said selector is further for selecting a second plurality of values of the digital control word produced by the frequency synthesizer after said change in said operating frequency of the digitally controlled oscillator, said estimator further for using the first plurality of values, the second plurality of values and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

26. The apparatus of claim 25, wherein said estimator includes a calculator for producing from the first plurality of values a first representative value that represents the first plurality of values, said estimator further for using the first representative value, the second plurality of values and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

27. The apparatus of claim 26, wherein the first representative value is an average of the first plurality of values.

28. The apparatus of claim 26, wherein said calculator is further for producing from the second plurality of values a second representative value which represents the second plurality of values, said estimator further for using the first representative value, the second representative value and the frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

29. The apparatus of claim 28, wherein the first representative value is an average of the first plurality of values.

30. The apparatus of claim 29, wherein the second representative value is an average of the second plurality of values.

31. The apparatus of claim 28, wherein said calculator includes a subtractor for determining a difference between said first and second representative values, said estimator including an arithmetic circuit coupled to said subtractor for determining a ratiometric relationship between said frequency change amount and said difference.

32. The apparatus of claim 21, wherein said estimator is further for using the first value, the second value and the frequency change amount to produce a current estimate of the gain characteristic, said estimator including an input for receiving a previous estimate of the gain characteristic, and said estimator including a combiner coupled to said last-mentioned input for combining the previous estimate of the gain characteristic with the current estimate of the gain characteristic to produce a desired estimate of the gain characteristic.

33. The apparatus of claim 32, wherein said combiner is further for applying to the current estimate and the previous estimate respective weighting factors to produce respective weighted estimates and for combining the weighted estimates to produce the desired estimate.

34. A data processing apparatus, comprising:

a data processor for performing digital data processing operations;

a man/machine interface coupled to said data processor for permitting a user to communicate with said data processor;

a frequency synthesizer coupled to said data processor for producing a periodic signal having a desired frequency for use in transferring data produced by said data processor; and

said frequency synthesizer including an estimation apparatus for estimating a gain characteristic of a digitally controlled oscillator in said frequency synthesizer, said estimation apparatus including an input for receiving a digital control word that includes information for use in tuning the digitally controlled oscillator, a selector coupled to said input for selecting a first value of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at a first frequency, said selector further for selecting a second value of the digital control word produced by the frequency synthesizer after the operating frequency of the digitally controlled oscillator has changed from said first frequency by a predetermined frequency change amount, and an estimator coupled to said selector for using said first value, said second value and said frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

35. The apparatus of claim 34, provided as one of a cellular telephone, a Bluetooth apparatus, and a laptop computer.

36. The apparatus of claim 34, wherein said man/machine interface includes one of a tactile interface, a visual interface and an audio interface.

37. The apparatus of claim 34, wherein said periodic signal is for use in transferring said data on a communication link, and said frequency change amount is associated with modulation of a communication symbol on the communication link.

38. The apparatus of claim 37, wherein said frequency change amount corresponds to one of a symbol-to-symbol change and a carrier-to-symbol change.

39. The apparatus of claim 34, wherein said periodic signal is a clock signal for said data processor.

40. A frequency synthesizer apparatus, comprising:

a control loop for producing a digital control word;

a digitally controlled oscillator coupled to said control loop for producing in response to said digital control word a periodic signal having a desired frequency; and

an estimation apparatus coupled to said control loop for estimating a gain characteristic of said digitally controlled oscillator, said estimation apparatus including a selector for selecting a first value of the digital control word produced by the control loop while the digitally controlled oscillator is operating at a first frequency, said selector further for selecting a second value of the digital control word produced by the control loop after the operating frequency of the digitally controlled oscillator has changed from said first frequency by a predetermined frequency change amount, and an estimator coupled to said selector for using said first value, said second value and said frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

41. A data processing apparatus, comprising:

a data processor for performing digital data processing operations;

a frequency synthesizer coupled to said data processor for producing a periodic signal having a desired frequency for use in transferring data produced by said data processor; and

said frequency synthesizer including an estimation apparatus for estimating a gain characteristic of a digitally controlled oscillator in said frequency synthesizer, said estimation apparatus including an input for receiving a digital control word that includes information for use in tuning the digitally controlled oscillator, a selector coupled to said input for selecting a first value of the digital control word produced by the frequency synthesizer while the digitally controlled oscillator is operating at a first frequency, said selector further for selecting a second value of the digital control word produced by the frequency synthesizer after the operating frequency of the digitally controlled oscillator has changed from said first frequency by a predetermined frequency change amount, and an estimator coupled to said selector for using said first value, said second value and said frequency change amount to estimate the gain characteristic of the digitally controlled oscillator.

42. The apparatus of claim 41, provided as one of a microprocessor, a digital signal processor and an RF front end apparatus.

43. A method of estimating a gain characteristic of a digitally controlled oscillator in a phase-locked loop, comprising:

perturbing an oscillating frequency of the digitally controlled oscillator; and

observing a response of the phase-locked loop to said perturbing step.