Apparatus and method for improving lock time
An apparatus is provided to improve lock time of a phase locked loop, wherein the apparatus comprises: a ring oscillator including at least two delay stages, wherein each delay stage has a controllable delay; and a multiphase frequency monitor coupled to the ring oscillator to monitor frequency at an output of at least two delay stages of the ring oscillator.
1. A frequency or phase locked loop comprising:
a phase detector or a phase frequency detector to receive a reference clock and a feedback clock;
a divider coupled to the phase detector or the phase frequency detector, wherein the divider is to generate the feedback clock;
an oscillator coupled to the divider, wherein the oscillator comprises at least two delay stages coupled together in a ring formation, wherein each delay stage has an adjustable propagation delay; and
a frequency monitor coupled to the at least two delay stages, wherein the frequency monitor is to determine a frequency of a signal at an input and/or an output of the at least two delay stages, wherein the frequency monitor comprises:
a first counter coupled to the output of a first delay stage of the at least two delay stages; and
a second counter coupled to the output of a second delay stage of the at least two delay stages.
2. The frequency or phase locked loop of claim 1 , further comprising a circuitry to adjust delay of the at least two delay stages according to outputs of the first and second counters.
3. The frequency or phase locked loop of claim 1 , further comprising: a first sampler to sample an output of the first counter; and a second sampler to sample an output of the second counter.
4. The frequency or phase locked loop of claim 3 , wherein the first sampler and the second sampler sample the output of the first counter and the output of the second counter using a clock which is slower than the reference clock.
5. The frequency or phase locked loop of claim 4 , wherein the divider is a first divider and wherein the frequency or phase locked loop further comprises a second divider to divide the reference clock to generate the clock.
6. The frequency or phase locked loop of claim 1 , further comprising logic to generate an average frequency based on respective frequencies of the at least two delay stages.
7. The frequency or phase locked loop of claim 6 , wherein the logic compares the average frequency with a target frequency to determine whether to increase or decrease a coarse code which is used to increase or decrease the adjustable propagation delay of each delay stage.
8. The frequency or phase locked loop of claim 1 , further comprising a lock detector coupled to the phase detector or a phase frequency detector, wherein the lock detector is to monitor one or more outputs of the phase detector orthe phase frequency detector to determine whether the frequency or phase locked loop is phase or frequency locked.
9. The frequency or phase locked loop of claim 1 , further comprising a sigma-delta modulator coupled to the divider.
10. A frequency or phase locked loop comprising:
a time-to-digital converter to receive a reference clock and a feedback clock;
a divider coupled to the time-to-digital converter, wherein the divider is to generate the feedback clock;
an oscillator coupled to the divider;
a circuitry coupled to the oscillator, wherein the circuitry is to tap intermediate nodes of the oscillator to determine frequency of signals at the intermediate nodes; and
logic to adjust a frequency of the oscillator according to a comparison of an average of the frequency of signals at the intermediate nodes and a target frequency of the oscillator.
11. The frequency or phase locked loop of claim 10 , wherein the oscillator includes a plurality of delay stages, wherein the frequency or phase locked loop comprises:
a first counter coupled to an output of a first delay stage of the plurality of delay stages; and
a second counter coupled to an output of a second delay stage of the plurality of delay stages.
12. The frequency or phase locked loop of claim 11 , further comprising: a first sampler to sample an output of the first counter; and a second sampler to sample an output of the second counter.
13. The frequency or phase locked loop of claim 12 , wherein the first sampler and the second sampler sample the output of the first counter and the output of the second counter using a clock which is slower than the reference clock.
14. The frequency or phase locked loop of claim 13 , further comprising a second divider to divide the reference clock to generate the clock.
15. The frequency or phase locked loop of claim 10 , further comprising a lock detector coupled to the time-to-digital converter, wherein the lock detector is to monitor an output of the time-to-digital converter to determine whether the frequency or phase locked loop is phase or frequency locked.
16. A frequency or phase locked loop comprising:
a phase detector or a phase frequency detector to receive a reference clock and a feedback clock;
a divider coupled to the phase detector or the phase frequency detector, wherein the divider is to generate the feedback clock;
an oscillator coupled to the divider, wherein the oscillator comprises at least two delay stages coupled together in a ring formation, wherein each delay stage has an adjustable propagation delay;
a frequency monitor coupled to the at least two delay stages, wherein the frequency monitor is to determine a frequency of a signal at an input and/or an output of the at least two delay stages; and
a sigma-delta modulator coupled to the divider.