Decision-directed phase detector

1. A decision-directed phase detector, comprising:

a first comparator configured to compare an input signal including clock and data components with a reference signal set to a clock crossover value, and to generate a first compared output signal designating a transition of the input signal through the clock crossover value;

a phase detector configured to receive the first compared output signal and generate a phase adjustment signal;

a second comparator configured to compare the input signal with the reference signal set to a positive offset clock crossover value of the clock crossover value offset by a positive offset value, and to generate a positive offset compared output signal designating a transition of the input signal through the positive offset clock crossover value; and

a transition detection circuit to generate a valid transition signal to route the phase adjustment signal to a clock generation circuit when the positive offset compared output signal transitions over a clock period.

2. The decision-directed phase detector of claim 1 , further comprising a third comparator configured to compare the input signal with the reference signal set to a negative offset clock crossover value of the clock crossover value offset by a negative offset value, and to generate a negative offset compared output signal designating a transition of the input signal through the negative offset clock crossover value.

3. The decision-directed phase detector of claim 2 , wherein the transition detection circuit is further configured to generate the valid transition signal to route the phase adjustment signal to the clock generation circuit.

4. The decision-directed phase detector of claim 3 , further comprising a validation circuit configured to receive both the transition of the positive offset compared output signal and the transition of the negative offset compared output signal over the clock period.

5. The decision-directed phase detector of claim 1 , further comprising a selector for passing one of the phase adjustment signal or a common mode input signal to the clock generation circuit based on the valid transition signal.

6. The decision-directed phase detector of claim 1 , wherein the phase detector comprises an Alexander phase detector.

7. The decision-directed phase detector of claim 6 , further comprising at least one flip-flop coupled to the output of the Alexander phase detector, the at least one flip-flop configured to match delays through the transition detection circuit.

8. A method, comprising:

comparing an input signal including clock and data components with a reference signal set to a clock crossover value, and generating a first compared output signal designating a transition of the input signal through the clock crossover value;

receiving the first compared output signal and generating a phase adjustment signal;

comparing the input signal with the reference signal set to a positive offset clock crossover value of the clock crossover value offset by a positive offset value, and generating a positive offset compared output signal designating a transition of the input signal through the positive offset clock crossover value; and

generating a valid transition signal to route the phase adjustment signal to a clock generation circuit when the positive offset compared output signal transitions over a clock period.

9. The method of claim 8 , further comprising:

comparing the input signal with the reference signal set to a negative offset clock crossover value of the clock crossover value offset by a negative offset value; and

generating a negative offset compared output signal designating a transition of the input signal through the negative offset clock crossover value.

10. The method of claim 9 , wherein the generating a valid transition signal further comprises generating the valid transition signal to route the phase adjustment signal to the clock generation circuit.

11. The method of claim 10 , further comprising receiving both the transition of the positive offset compared output signal and the transition of the negative offset compared output signal over the clock period.

12. The method of claim 8 , further comprising passing one of the phase adjustment signal or a common mode input signal to the clock generation circuit based on the valid transition signal.

13. The method of claim 8 , wherein the generating the phase adjustment signal uses an Alexander phase detector.

14. The method of claim 13 , further comprising latching an output of the Alexander phase detector to match delays while generating the valid transition signal.

15. A decision-directed phase detector, comprising:

means for comparing an input signal including clock and data components with a reference signal set to a clock crossover value, and means for generating a first compared output signal designating a transition of the input signal through the clock crossover value;

means for receiving the first compared output signal and means for generating a phase adjustment signal;

means for comparing the input signal with the reference signal set to a positive offset clock crossover value of the clock crossover value offset by a positive offset value, and means for generating a positive offset compared output signal designating a transition of the input signal through the positive offset clock crossover value; and

means for generating a valid transition signal to route the phase adjustment signal to a clock generation circuit when the positive offset compared output signal transitions over a clock period.

16. The decision-directed phase detector of claim 15 , further comprising:

means for comparing the input signal with the reference signal set to a negative offset clock crossover value of the clock crossover value offset by a negative offset value; and

means for generating a negative offset compared output signal designating a transition of the input signal through the negative offset clock crossover value.

17. The decision-directed phase detector of claim 16 , wherein the means for generating a valid transition signal further comprises means for generating the valid transition signal to route the phase adjustment signal to the clock generation circuit.

18. The decision-directed phase detector of claim 17 , further comprising means for receiving both the transition of the positive offset compared output signal and the transition of the negative offset compared output signal over the clock period.

19. The decision-directed phase detector of claim 18 , further comprising means for passing one of the phase adjustment signal or a common mode input signal to the clock generation circuit based on the valid transition signal.

20. The decision-directed phase detector of claim 15 , wherein the means for generating the phase adjustment signal is an Alexander phase detector.