Frequency to digital conversion

1. A method of processing an input signal having an input signal phase including:

determining a number of transitions of the input signal within a period having a start and an end; and

determining a relative beginning phase of the input signal at the start of the period including:

generating a first reference signal having a first reference signal frequency and a first reference signal phase synchronized with the start of the period; and

detecting a first time interval required for the input signal phase to have a first specified relationship to the first reference signal phase;

determining a relative ending phase of the input signal at the end of the period including:

generating a second reference signal having a second reference signal frequency and a second reference signal phase synchronized with the end of the period; and

detecting a second time interval required for the input signal phase to have a second specified relationship to the second reference signal phase;

determining an input signal temporal characteristic from the number of transitions and the relative beginning phase and the relative ending phase.

2. A method as recited in claim 1 wherein the temporal characteristic is the period of the input signal.

3. A method as recited in claim 1 wherein the temporal characteristic is the frequency of the input signal.

4. A method as recited in claim 1 wherein the first reference signal phase is offset from the start of the period.

5. A method as recited in claim 1 , further including using the frequency determination in a frequency-locked loop.

6. A method as recited in claim 1 , further including using the frequency determination in a phase-locked loop.

7. A method as recited in claim 1 , wherein detection of the first interval includes:

obtaining a plurality of samples of the input signal at a plurality of times relative to the first reference signal; and

selecting a sample corresponding to the input signal phase having a specified relationship to the first reference signal.

8. A method as recited in claim 1 , further including obtaining a sample of the input signal at a plurality of times using one or more flip flops.

9. A method as recited in claim 1 , wherein detection of the first interval includes:

obtaining a plurality of samples of the input signal at a plurality of times relative to the first reference signal; and

selecting a sample corresponding to the input signal phase having a specified relationship to the first reference signal, wherein a change in the value of samples indicates the sample to be selected.

10. A method as recited in claim 1 , wherein detection of the first interval includes:

obtaining a plurality of samples of the input signal at a plurality of times relative to the first reference signal; and

selecting a sample corresponding to the input signal phase having a specified relationship to the first reference signal, wherein a change in the value of samples indicates the sample to be selected, including:

examining the group of samples of the input signal for error; and

correcting the group of samples of the input signal for error.

11. A method as recited in claim 1 , wherein detection of the first interval includes:

obtaining a plurality of samples of the input signal at a plurality of times relative to the first reference signal; and

selecting a sample corresponding to the input signal phase having a specified relationship to the first reference signal, wherein a change in the value of samples indicates the sample to be selected and the plurality of samples of the input signal are filtered in a manner that is robust to error.

12. A method as recited in claim 1 , wherein the first reference signal includes a plurality of first reference subsignals shifted in phase with respect to each other.

13. A method as recited in claim 1 , wherein the input signal includes a plurality of input subsignals shifted in phase with respect to each other.

14. A method as recited in claim 1 , wherein the first reference signal includes a plurality of first reference subsignals shifted in phase with respect to each other generated by a ring oscillator.

15. A method as recited in claim 1 , wherein the first reference signal includes a plurality of first reference subsignals shifted in phase with respect to each other generated with tunable delay elements.

16. A method as recited in claim 1 , wherein the input signal includes a plurality of input subsignals shifted in phase with respect to each other generated by a Johnson Counter.

17. A method as recited in claim 1 , wherein an estimated value is used for the number of transitions of the input signal within a period having a start and an end.

18. A method as recited in claim 1 , wherein:

the first reference signal includes a plurality of first reference subsignals shifted in phase with respect to each other; and

the first reference signal has a variable phase relationship with the first reference subsignals.

19. A method as recited in claim 1 , further including:

the first reference signal includes a plurality of first reference subsignals shifted in phase with respect to each other;

the input signal includes a plurality of input subsignals shifted in phase with respect to each other; and

a subset of all combinations of first reference subsignals and input subsignals is used.

20. A method as recited in claim 1 , further including:

determining a relative number of beginning input signal cycles at the beginning of the period;

determining a relative number of ending input signal cycles at the end of the period; and

determining the number of input signal cycles within the period by subtracting the beginning input signal cycles from the ending input signal cycles.

21. A method as recited in claim 1 , further including:

determining the number of input signal cycles within the period by adding the number of transitions of the input signal and the relative ending phase of the input signal, and subtracting the relative beginning phase of the input signal.

22. A system for processing an input signal having an input signal phase including:

a processor configured to:

determine a number of transitions of the input signal within a period having a start and an end;

determine a relative beginning phase of the input signal at the start of the period;

determine a relative ending phase of the input signal at the end of the period; and

determine an input signal temporal characteristic from the number of transitions and the relative beginning phase and the relative ending phase;

a reference signal generator configured to generate a reference signal having a reference signal frequency and a reference signal phase synchronized with the start of the period; and

a detector configured to detect a time interval required for the input signal phase to have a specified relationship to the reference signal phase;

wherein the reference signal generator and the detector are used to determine either the relative beginning phase or the relative ending phase or both the relative beginning phase and the relative ending phase.

23. A system as recited in claim 22 , wherein the temporal characteristic is the period of the input signal.

24. A system as recited in claim 22 , wherein the temporal characteristic is the frequency of the input signal.

25. A system as recited in claim 22 , wherein the reference signal phase is offset from the start of the period.

26. A system as recited in claim 22 , wherein the system is used in a frequency-locked loop.

27. A system as recited in claim 22 , wherein the system is used in a phase-locked loop.

28. A system as recited in claim 22 , wherein the detector is further configured to:

obtain a plurality of samples of the input signal at a plurality of times relative to the reference signal; and

select a sample corresponding to the input signal phase having a specified relationship to the reference signal.

29. A system as recited in claim 22 , wherein the detector is further configured to obtain a sample of the input signal at a plurality of times using one or more flip flops.

30. A system as recited in claim 22 , wherein the detector is further configured to:

obtain a plurality of samples of the input signal at a plurality of times relative to the reference signal; and

select a sample corresponding to the input signal phase having a specified relationship to the reference signal, wherein a change in the value of samples indicates the sample to be selected.

31. A system as recited in claim 22 , wherein the detector is further configured to:

obtain a plurality of samples of the input signal at a plurality of times relative to the reference signal; and

select a sample corresponding to the input signal phase having a specified relationship to the reference signal, wherein a change in the value of samples indicates the sample to be selected, including:

examine the group of samples of the input signal for error; and

correct the group of samples of the input signal for error.

32. A system as recited in claim 22 , wherein the detector is further configured to: obtain a plurality of samples of the input signal at a plurality of times relative to the reference signal; and

select a sample corresponding to the input signal phase having a specified relationship to the reference signal, wherein a change in the value of samples indicates the sample to be selected and the plurality of samples of the input signal are filtered in a manner that is robust to error.

33. A system as recited in claim 22 , wherein the reference signal generator is further configured such that the reference signal includes a plurality of reference subsignals shifted in phase with respect to each other.

34. A system as recited in claim 22 , wherein the input signal includes a plurality of input subsignals shifted in phase with respect to each other.

35. A system as recited in claim 22 , wherein the reference signal generator is further configured such that the reference signal includes a plurality of reference subsignals shifted in phase with respect to each other and are generated by a ring oscillator.

36. A system as recited in claim 22 , wherein the reference signal generator is further configured such that the reference signal includes a plurality of reference subsignals shifted in phase with respect to each other and are generated with tunable delay elements.

37. A system as recited in claim 22 , wherein the input signal includes a plurality of input subsignals shifted in phase with respect to each other generated by a Johnson Counter.

38. A system as recited in claim 22 , wherein the processor is further configured to use an estimated value for the number of transitions of the input signal within a period having a start and an end.

39. A system as recited in claim 22 , wherein the reference signal generator is further configured such that:

the reference signal includes a plurality of reference subsignals shifted in phase with respect to each other; and

the reference signal has a variable phase relationship with the reference sub signals.

40. A system as recited in claim 22 , wherein the reference signal generator is further configured such that:

the reference signal includes a plurality of reference subsignals shifted in phase with respect to each other; and

the input signal includes a plurality of input subsignals shifted in phase with respect to each other; and

the detector is further configured such that a subset of all combinations of reference subsignals and input subsignals is used.

41. A system as recited in claim 22 , wherein the processor is further configured to:

determine a relative number of beginning input signal cycles at the beginning of the period;

determine a relative number of ending input signal cycles at the end of the period; and

determine the number of input signal cycles within the period by subtracting the beginning input signal cycles from the ending input signal cycles.

42. A system as recited in claim 22 , wherein the processor is further configured to:

determine the number of input signal cycles within the period by adding the number of transitions of the input signal and the relative ending phase of the input signal, and subtracting the relative beginning phase of the input signal.