Method for using digital PLL in a voltage regulator

1. A digital phase locked loop circuit, comprising:

at least one input for receiving a reference signal;

a phase frequency detector for determining a phase difference between the reference signal and a feedback signal and generating a digital representation of an amount of the phase difference between the reference signal and the feedback signal;

a digital filter circuit for generating a counter value responsive to the digital representation of the phase difference;

a counter circuit for generating an output pulse including coarse phase information and fine phase information each time the counter circuit goes below a predetermined value, wherein an initial counter value is established responsive to the counter value;

wherein the feedback signal is established responsive to the coarse phase information;

an analog phase interpolator for generating a synchronization signal responsive to the coarse phase information and the fine phase information; and

an output for providing the synchronization signal to a switching voltage regulator to enable generation of a PWM signal at the switching voltage regulator.

2. The digital phase locked loop circuit of claim 1 , further including circuitry for providing the reference signal, the circuitry enabling selection of either an external synchronization pulse or an internal synchronization pulse.

3. The digital phase locked loop circuit of claim 2 , wherein the circuitry for providing the reference signal further comprises:

a multiplexer connected to receive the external synchronization pulse and the internal synchronization pulse and provide the reference signal as an output responsive to a control signal;

a programmable divider circuit for generating the internal synchronization pulse from an internally provided clock signal, a frequency of the internal synchronization pulse established by a selectable input to the programmable divider circuit; and

control logic for providing the control signal enabling the multiplexer to select between the external synchronization pulse and the internal synchronization pulse.

4. The digital phase locked loop circuit of claim 1 , wherein the digital filter circuit further comprises:

a frequency circuit path for accumulating a frequency of the digital representation of the phase difference;

a phase circuit path for accumulating a phase of the digital representation of the phase difference; and

an adder circuit for adding the accumulation from the frequency circuit path with the accumulation from the phase circuit path to generate the counter value.

5. The digital phase locked loop circuit of claim 4 , wherein the frequency circuit path further comprises:

a first gain circuit for selectively gain controlling the digital representation of the phase difference; and

a first accumulator circuit for accumulating a frequency of the gain controlled digital representation of the phase difference.

6. The digital phase locked loop circuit of claim 4 , wherein the phase circuit path further comprises:

a second gain circuit for selectively gain controlling the digital representation of the phase difference; and

a second accumulator circuit for accumulating a phase of the gain controlled digital representation of the phase difference.

7. The digital phase locked loop circuit of claim 6 , wherein the analog phase interpolator generates the delayed synchronization signal by applying the fine phase information to the coarse phase information.

8. An apparatus, comprising:

a digital phase locked loop circuit for generating a synchronization signal, wherein the digital phase locked loop circuit further comprises:

at least one input for receiving a reference signal;

a phase frequency detector for determining a phase difference between the reference signal and a feedback signal and generating a digital representation of an amount of the phase difference between the reference signal and the feedback signal;

a digital filter circuit for generating a counter value responsive to the digital representation of the phase difference;

a counter circuit for generating an output pulse including coarse phase information and fine phase information each time the counter circuit goes below a predetermined value, wherein an initial counter value is established responsive to the counter value;

wherein the feedback signal is established responsive to the coarse phase information;

an analog phase interpolator for generating a synchronization signal responsive to the coarse phase information and the fine phase information;

an output for providing the synchronization signal to a switching voltage regulator to enable generation of a PWM signal at the switching voltage regulator; and

a voltage regulator for providing a regulated voltage, wherein a PWM signal of the voltage regulator is generated responsive to the synchronization signal.

9. The apparatus of claim 8 , further including circuitry for providing the reference signal, the circuitry enabling selection of either an external synchronization pulse or an internal synchronization pulse.

10. The apparatus of claim 9 , wherein the circuitry for providing the reference signal further comprises:

a multiplexer connected to receive the external synchronization pulse and the internal synchronization pulse and provide the reference signal as an output responsive to a control signal;

a programmable divider circuit for generating the internal synchronization pulse from an internally provided clock signal, a frequency of the internal synchronization pulse established by a selectable input to the programmable divider circuit; and

control logic for providing the control signal enabling the multiplexer to select between the external synchronization pulse and the internal synchronization pulse.

11. The apparatus of claim 8 , wherein the digital filter circuit further comprises:

a frequency circuit path for accumulating a frequency of the digital representation of the phase difference;

a phase circuit path for accumulating a phase of the digital representation of the phase difference; and

an adder circuit for adding the accumulation from the frequency circuit path with the accumulation from the phase circuit path to generate the counter value.

12. The apparatus of claim 11 , wherein the frequency circuit path further comprises:

a first gain circuit for selectively gain controlling the digital representation of the phase difference; and

a first accumulator circuit for accumulating a frequency of the gain controlled digital representation of the phase difference.

13. The apparatus of claim 11 , wherein the phase circuit path further comprises:

a second gain circuit for selectively gain controlling the digital representation of the phase difference; and

a second accumulator circuit for accumulating a phase of the gain controlled digital representation of the phase difference.

14. The digital phase locked loop circuit of claim 8 , wherein the analog phase interpolator generates the delayed synchronization signal by applying the fine phase information to the coarse phase information.