Phase lock loop with phase interpolation by reference clock and method for the same

1. A phase lock loop (PLL) comprising:

a phase-interpolation controller for generating a phase-interpolation control signal from an input clock;

a phase/frequency detector for detecting a phase difference between a second reference clock and a feedback clock and outputting a phase error signal to represent the phase difference;

a loop filter for filtering the phase error signal to generate a first control signal;

a phase-interpolated oscillator for generating an output clock under a phase interpolation by a first reference clock controlled by the phase-interpolation control signal and an oscillation condition controlled by the first control signal;

a divide-by-N circuit for dividing down the output clock by a factor of N to generate the feedback clock, where N is an integer; and

a variable delay module, coupled to the phase/frequency detector, for delaying the input clock by an amount controlled by a second control signal to generate the second reference clock.

2. The PLL of claim 1 , the variable delay module further comprising:

a delay controller, for receiving the input clock and the output clock and thereby generating the second control signal; and

a variable delay cell, coupled to the phase/frequency detector and the delay controller, for delaying the input clock by the amount controlled by the second control signal to generate the second reference clock.

3. The PLL of claim 2 , the delay controller comprising:

a mixer for performing a frequency mixing between the input clock and the output clock to generate a correlation signal; and

a low-pass filter for filtering the correlation signal to generate the second control signal.

4. The PLL of claim 1 , wherein at least one of the first reference clock and the second reference is generated in accordance with the input signal.

5. A phase lock loop (PLL) comprising:

a phase-interpolation controller for generating a phase-interpolation control signal from an input clock;

a phase/frequency detector for detecting a phase difference between a second reference clock and a feedback clock and outputting a phase error signal to represent the phase difference;

a loop filter for filtering the phase error signal to generate a first control signal;

a phase-interpolated oscillator for generating an output clock under a phase interpolation by a first reference clock controlled by the phase-interpolation control signal and an oscillation condition controlled by the first control signal;

a divide-by-N circuit for dividing down the output clock by a factor of N to generate the feedback clock, where N is an integer; and

a fixed delay circuit, coupled to the phase-interpolated oscillator, for delaying the input clock to generate the first reference clock to the phase-interpolated oscillator.

6. The PLL of claim 5 , the phase-interpolated oscillator comprising:

a phase interpolator for performing a phase interpolation between the output clock and the first reference clock with an interpolation factor controlled by the phase-interpolation control signal to generate an interpolated clock; and

a variable delay line, coupled to the phase interpolator and the loop filter, for delaying the interpolated clock according to the first control signal to generate the output clock.

7. The PLL of claim 6 , the phase interpolator comprising:

at least a first transistor for receiving the output clock;

at least a second transistor for receiving the first reference clock;

a common load circuit coupled to said first transistor and said second transistor;

a biasing circuit, for establishing a first biasing condition for said first transistor and a second biasing condition for said second transition in accordance with the phase-interpolation control signal.

8. The PLL of claim 7 , wherein said first transistor is a part of a first differential pair and said second transistor is a part of a second differential pair.

9. A phase lock loop (PLL) comprising:

a phase-interpolation controller for generating a phase-interpolation control signal from an input clock;

a phase/frequency detector for detecting a phase difference between a second reference clock and a feedback clock and outputting a phase error signal to represent the phase difference;

a loop filter for filtering the phase error signal to generate a first control signal;

a phase-interpolated oscillator for generating an output clock under a phase interpolation by a first reference clock controlled by the phase-interpolation control signal and an oscillation condition controlled by the first control signal; and

a divide-by-N circuit for dividing down the output clock by a factor of N to generate the feedback clock, where N is an integer;

wherein the phase-interpolation controller comprising:

a flip-flop for receiving the input clock and outputting the phase-interpolation control signal; and

an inverter chain for receiving the phase-interpolation control signal and outputting a reset signal to reset the flip-flop.

10. A method of phase locking comprising:

generating a phase-interpolation control signal;

detecting a phase difference between a second reference clock and a feedback clock and outputting a phase error signal to represent the phase difference;

filtering the phase error signal to generate a first control signal;

generating an output clock under a phase interpolation controlled by the phase-interpolation control signal and an oscillation condition controlled by the first control signal;

dividing down the output clock by a factor of N to generate the feedback clock, where N is an integer; and

delaying an input clock by a controlled amount by a second control signal to generate the second reference clock.

11. The method of claim 10 , further comprising:

generating the second control signal according to a relation between the input clock and the output clock.

12. The method of claim 11 , the step of generating the second control signal further comprising:

performing a frequency mixing between the input clock and the output clock to generate a correlation signal; and

filtering the correlation signal to generate the second control signal.

13. A method of phase locking comprising:

generating a phase-interpolation control signal;

detecting a phase difference between a second reference clock and a feedback clock and outputting a phase error signal to represent the phase difference;

filtering the phase error signal to generate a first control signal;

generating an output clock under a phase interpolation controlled by the phase-interpolation control signal and an oscillation condition controlled by the first control signal;

dividing down the output clock by a factor of N to generate the feedback clock, where N is an integer; and

delaying the input clock to generate a first reference clock.

14. The method of claim 13 , further comprising:

performing a phase interpolation between the output clock and the first reference clock with an interpolation factor controlled by the phase-interpolation control signal to generate an interpolated clock; and

delaying the interpolated clock according to the first control signal to generate the output clock.

15. The method of claim 10 , the step of generating the phase-interpolation control signal comprising:

generating the phase-interpolation control signal according to the input clock.

16. The method of claim 15 , the step of generating the phase-interpolation control signal comprising:

generating a reset signal according to the phase-interpolation control signal to reset the step of generating the phase-interpolation control signal.

17. The method of claim 10 , wherein the phase-interpolation control signal and at least one of the first reference clock and the second reference are generated in accordance with the input signal.