Methods and mobile communication devices for performing spur relocation for phase-locked loops

1. A method for performing spur relocation for a digital phase-locked loop in a mobile communication device, comprising:

receiving a first frequency command word corresponding to a first frequency channel of interest;

identifying a first frequency at which a first fractional spur associated with the first frequency command word starts to occur;

determining whether the first frequency is within the first frequency channel of interest;

when the first frequency is within the first frequency channel of interest, determining a second frequency command word associated with a second fractional spur that occurs at a second frequency outside the first frequency channel of interest; and

changing the frequency command word to the second frequency command word using a first programmable value, wherein a first divider of a programmable feedback divider divides the first frequency command word by the first programmable value to generate the second frequency command word, wherein a second divider of the programmable feedback divider divides an output of the digital phase-locked loop by a second programmable value, and wherein the second programmable value is equal to a product of the first programmable value and a constant in a first mode of operation.

2. The method of claim 1 , wherein the first frequency channel of interest comprises at least one of a current communication channel for a first radio associated with the digital phase-locked loop or another communication channel utilized by a second radio in the mobile communication device.

3. The method of claim 1 , wherein the first frequency command word represents a ratio between an output frequency of the digital phase-locked loop and a reference frequency and wherein the second frequency command word comprises a second fractional component different from a first fractional component of the first frequency command word.

4. The method of claim 1 further comprising:

adjusting the programmable feedback divider in the digital phase-locked loop to change the first frequency command word to the second frequency command word, the adjustable programmable feedback divider comprising a first divider and a second divider.

5. The method of claim 4 , wherein adjusting the programmable feedback divider comprises providing the first programmable value to the first divider, the first divider to divide the first frequency command word by the first programmable value to generate the second frequency command word and providing the second programmable value to the second divider, the second divider to divide an output of a digitally controller oscillator in the digital phase-locked loop by the second programmable value to generate a programmable feedback loop frequency.

6. A mobile communication device adapted to perform spur relocation for a digital phase-locked loop, comprising:

a receiver configured to determine a first frequency channel of interest and to identify a first frequency command word corresponding to the first frequency channel of interest;

control logic circuitry configured to:

identify a first frequency at which a first fractional spur associated with the first frequency command word starts to occur;

determine whether the identified first frequency is within the first frequency channel of interest; and

when the identified first frequency is within the first frequency channel of interest, determine a second frequency command word associated with a second fractional spur that occurs at a second frequency outside the first frequency channel of interest; and

a programmable feedback divider comprising a first divider and a second divider and configured to change the first frequency command word to the second frequency command word using a first programmable value, wherein the first divider is configured to divide the first frequency command word by the first programmable value provided by the control logic to generate the second frequency command word, wherein the second divider is configured to divide an output of the digital phase-locked loop by a second programmable value provided by the control logic circuitry, and wherein the second programmable value is equal to the first programmable value in a first mode of operation.

7. The mobile communication device of claim 6 , wherein the first frequency command word represents a ratio between an output frequency of the digital phase-locked loop and a reference frequency.

8. The mobile communication device of claim 6 , wherein the second frequency command word comprises a second fractional component different from a first fractional component of the first frequency command word.

9. The mobile communication device of claim 6 , wherein the digital phase-locked loop comprises:

a phase detector;

a loop filter coupled to the phase detector;

a digitally controlled oscillator coupled to the loop filter; and

a feedback path coupled to the digitally controlled oscillator and the phase detector.

10. The mobile communication device of claim 9 , wherein the first divider is coupled to an input of the phase detector.

11. The mobile communication device of claim 10 , wherein the second programmable value provided by the control logic generates a feedback loop frequency.

12. The mobile communication device of claim 11 , wherein the second programmable value is equal to a product of the first programmable value and a constant in a second mode of operation.

13. An apparatus, comprising:

a memory; and

a processor in communication with the memory, wherein the processor is configured to:

receive a first frequency command word corresponding to a first frequency channel of interest;

identify a first frequency at which a first fractional spur associated with the first frequency command word starts to occur;

determine whether the first frequency is within the first frequency channel of interest;

when the first frequency is within the first frequency channel of interest, determine a second frequency command word associated with a second fractional spur that occurs at a second frequency outside the first frequency channel of interest; and

change the first frequency command word to the second frequency command word using a first programmable value, wherein a first divider of a programmable feedback divider divides the first frequency command word by the first programmable value to generate the second frequency command word, wherein a second divider of the programmable feedback divider divides an output of a digital phase-locked loop by a second programmable value, and wherein the second programmable value is equal to a product of the first programmable value and a constant in a first mode of operation.

14. The apparatus of claim 13 ,

wherein the first frequency command word represents a ratio between an output frequency of the digital phase-locked loop and a reference frequency.

15. The apparatus of claim 13 ,

wherein the second frequency command word comprises a second fractional component different from a first fractional component of the first frequency command word.

16. The apparatus of claim 13 ,

wherein the second programmable value is equal the first programmable value in a second mode of operation.

17. The apparatus of claim 13 ,

wherein changing the first frequency command word comprises changing a first fractional component of the first frequency command word to a second fractional component that is different than the first fractional component.