Wide frequency range clock generation with phase interpolation

1. An apparatus comprising:

a circuit configured to:

scale a phase control value from an external phase control resolution of an external clock frequency to an internal phase control resolution of an internal clock frequency to generate a target phase control value;

determine a difference between a current phase control value and the target phase control value;

determine a phase step value based on the difference;

modify a current phase control value based on the phase step value;

generate a phase controlled clock signal at the internal clock frequency using the modified phase control value; and

divide the phase controlled clock signal at the internal clock frequency to generate a phase controlled clock signal at the external clock frequency.

2. The apparatus of claim 1 , comprising the circuit further configured to:

generate the phase controlled clock signal at the internal clock frequency by offsetting a phase of the phase controlled clock signal at the internal clock frequency from a phase of an internal clock signal by the modified phase control value.

3. The apparatus of claim 1 , comprising the circuit further configured to:

output the phase controlled clock signal at the external clock frequency as a phase-locked-loop output clock.

4. The apparatus of claim 1 , comprising the circuit further configured to:

determine another difference between the modified phase control value and the target phase control value;

determine another phase step value based on the other difference;

modify the modified phase control value based on the other phase step value to generate another modified control phase value; and

generate the phase controlled clock signal at the internal clock frequency using the other modified phase control value.

5. The apparatus of claim 1 , comprising the circuit further configured to:

perform the determining the phase step value by determining a direction of the phase step based on a result of a modulo operation on the difference between a modified phase control value and the target phase control value.

6. The apparatus of claim 1 , comprising the circuit further configured to:

perform the scaling based on the ratio of the external clock frequency to the internal clock frequency to generate target phase control value.

7. The apparatus of claim 1 , further comprising:

the internal clock frequency being faster than the external clock frequency, a ratio of the internal clock frequency to the external clock frequency being a power of two.

8. The apparatus of claim 1 , comprising the circuit further configured to:

receive a ratio value specifying a ratio of the internal clock frequency to the external clock frequency as a power of two; and

perform the divide of the phase controlled clock signal at the internal clock frequency to generate the phase controlled clock signal at the external clock frequency based on the received ratio value.

9. An apparatus comprising:

an internal clock configured to generate an internal clock signal at an internal clock frequency;

a digital to phase circuit configured to:

scale a phase control value from an external phase control resolution of an external clock frequency to an internal phase control resolution of the internal clock frequency to generate a target phase control value;

determine a difference between a current phase control value and the target phase control value;

determine a phase step value based on the difference;

modify a current phase control value based on the phase step value;

generate a phase controlled clock signal at the internal clock frequency using the modified phase control value; and

a frequency divider configured to:

divide the phase controlled clock signal at the internal clock frequency to generate a phase controlled clock signal at the external clock frequency.

10. The apparatus of claim 9 , comprising the digital to phase circuit further configured to:

generate the phase controlled clock signal at the internal clock frequency by offsetting a phase of the phase controlled clock signal at the internal clock frequency from a phase of the internal clock signal by the modified phase control value.

11. The apparatus of claim 10 , comprising the digital to phase circuit further configured to:

determine another difference between the modified phase control value and the target phase control value;

determine another phase step value based on the other difference;

modify the modified phase control value based on the other phase step value to generate another modified control phase value;

generate the phase controlled clock signal at the internal clock frequency using the other modified phase control value.

12. The apparatus of claim 11 , comprising the digital to phase circuit further configured to:

perform the determining the phase step value by determining a direction of the phase step based on a result of a modulo operation on the difference between a modified phase control value and the target phase control value.

13. The apparatus of claim 12 , comprising the digital to phase circuit further configured to:

perform the scaling based on the ratio of the external clock frequency to the internal clock frequency to generate target phase control value.

14. The apparatus of claim 10 , further comprising

the internal clock frequency being faster than the external clock frequency, a ratio of the internal clock frequency to the external clock frequency being a power of two.

15. The apparatus of claim 9 , comprising the frequency divider further configured to:

receive a ratio value specifying a ratio of the internal clock frequency to the external clock frequency as a power of two; and

perform the divide of the phase controlled clock signal at the internal clock frequency to generate the phase controlled clock signal at the external clock frequency based on the received ratio value.

16. A method comprising:

scaling a phase control value from an external phase control resolution of an external clock frequency to an internal phase control resolution of an internal clock frequency to generate a target phase control value;

determining a difference between a current phase control value and the target phase control value;

determining a phase step value based on the difference;

modifying a current phase control value based on the phase step value;

generating a phase controlled clock signal at the internal clock frequency using the modified phase control value;

dividing the phase controlled clock signal at the internal clock frequency to generate a phase controlled clock signal at the external clock frequency.

17. The method of claim 16 further comprising:

the generating the phase controlled clock signal at the internal clock frequency being performed by offsetting a phase of the phase controlled clock signal at the internal clock frequency from a phase of an internal clock signal by the modified phase control value.

18. The method of claim 17 further comprising:

outputting the phase controlled clock signal at the external clock frequency as a phase locked loop output clock.

19. The method of claim 17 further comprising:

determining another difference between the modified phase control value and the target phase control value;

determining another phase step value based on the other difference;

modifying the modified phase control value based on the other phase step value to generate another modified control phase value;

generating the phase controlled clock signal at the internal clock frequency using the other modified phase control value.

20. The method of claim 17 further comprising:

the determining the phase step value determines a direction of the phase step based on a result of a modulo operation on the difference between a modified phase control value and the target phase control value.