Multiple synthesized clocks from a single clock source
View Patent ↗A system for generating multiple synthesized clocks having an input terminal for receiving a reference signal, a phase locked loop circuit coupled to the input signal terminal, where the phase locked loop circuit is capable of generating a plurality of output signals that are frequency locked to the reference signal and having a plurality of different phases, a phase rotator coupled to the phase locked loop circuit, where the phase rotator generates an even greater plurality of phases.
1. A method of generating multiple synthesized clocks, the method comprising:
receiving a reference signal;
generating a plurality of signals that are frequency locked to the reference signal and that have a plurality of different phases;
assigning a relative weighting to the plurality of signals to form a plurality of weighted signals; and
combining the weighted signals to form a first output signal, wherein the relative weighting determines an output phase of the first output signal.
2. The method of claim 1 , further comprising:
assigning a second relative weighting to the plurality of signals to form a second plurality of weighted signals; and
combining the second weighted signals to form a second output signal, wherein the second relative weighting determines an output phase of the second output signal.
3. The method of claim 2 , wherein said output phase of said second output signal is different from said output phase of said first output signal.
4. The method of claim 1 , wherein generating the plurality of signals includes:
receiving a feedback signal;
comparing a first frequency of the reference signal and a second frequency of the feedback signal;
generating an error signal based on a difference between the first frequency and the second frequency;
low pass filtering the error signal to remove high frequency noise;
generating an output signal having a frequency based on a voltage of the error signal; and
feeding back the output signal to provide the feedback signal.
5. The method of claim 4 , further including dividing the frequency of the output signal by a divisor to provide the second frequency of the feedback signal.
6. The method of claim 1 , wherein generating the plurality of signals is performed using a plurality of delay buffers.
7. The method of claim 1 , wherein generating the plurality of signals is performed using eight delay buffers.
8. The method of claim 1 , further comprising controlling a difference between phase states of the first output signal.
9. The method of claim 8 , wherein controlling the difference between the phase states of the first output signal is performed based on a parts per million count signal.
10. The method of claim 9 , further comprising:
assigning a second relative weighting to the plurality of signals to form a second plurality of weighted signals;
combining the second weighted signals to form a second output signal, wherein the second relative weighting determines an output phase of the second output signal; and
controlling a difference between phase states of the second output signal based on a second parts per million count signal.
11. The method of claim 1 , wherein generating the plurality of signals includes generating the plurality of signals that are frequency locked to the reference signal and that have eight different phases, and combining the weighted signals includes combining the weighted signals to form the first output signal having sixty four different phases.
12. The method of claim 1 , wherein generating the plurality of signals includes generating the plurality of signals that are frequency locked to the reference signal and that have eight different phases, and combining the weighted signals includes combining the weighted signals to form the first output signal having 128 different phases.
13. A system comprising:
a phase locked loop circuit configured to generate a plurality of signals that are frequency locked to a reference signal and that have a plurality of different phases; and
a phase rotator coupled to the phase locked loop circuit to provide an output signal having a phase based on the plurality of signals.
14. The system of claim 13 , further comprising an additional phase rotator coupled to the phase locked loop circuit to provide another output signal having a phase based on the plurality of signals.
15. The system of claim 13 , wherein the phase locked loop circuit further comprises:
a phase detector to receive the reference signal;
a charge pump coupled to an output of the phase detector;
a low pass filter coupled to an output of the charge pump;
a voltage controlled oscillator circuit coupled to an output of the low pass filter; and
a divider circuit coupled to an output of said voltage controlled oscillator circuit to provide a feedback signal to the phase detector.
16. The system of claim 15 , wherein the voltage controlled oscillator circuit further comprises a plurality of delay buffers configured to generate the plurality of signals having the plurality of phases.
17. The system of claim 16 , wherein the voltage controlled oscillator circuit includes eight delay cells.
18. The system of claim 15 , wherein a voltage controlled oscillator frequency is a multiple of a frequency of the reference signal, and the divider circuit determines the multiple.
19. The system of claim 13 , wherein the phase rotator is coupled to a logic control unit, wherein the logic control unit controls a rotation speed of the phase rotator.
20. The system of claim 19 , wherein the logic control unit includes:
a logic control circuit;
a counter to receive bit counts from the logic control circuit;
a decoder coupled to the counter to decode the bit counts to provide an output count; and
a latch coupled to the decoder and the phase rotator, wherein the latch detects the output count and provides the output count to the phase rotator.
21. The system of claim 20 , wherein the logic control circuit is coupled to a parts per million (“PPM”) input terminal, wherein the PPM input terminal supplies a PPM input count to the logic control circuit including:
a count accumulator, wherein the count accumulator supplies the bit counts to the counter; and
a sign latch to increase or decrease the bit counts.
22. The system of claim 21 , further comprising an additional phase rotator coupled to the phase locked loop circuit to provide another output signal having a phase based on the plurality of signals, and the additional phase rotator is coupled to an additional logic control circuit coupled to another PPM input terminal.
23. The system of claim 20 , wherein the counter is a six bit counter.
24. The system of claim 20 , wherein the decoder decodes six bits of data to provide sixty four bits of data.
25. The system of claim 13 , wherein the phase rotator provides sixty four phases based on eight phases provided by the phase locked loop circuit.
26. The system of claim 13 , wherein the phase rotator provides 128 phases based on eight phases provided by the phase locked loop circuit.