FRACTIONAL-N OFFSET PHASE LOCKED LOOP
First Claim
1. A phase locked loop system comprising:
- loop circuitry adapted to provide an output signal based on a divided reference signal;
combiner circuitry adapted to combine an initial fractional divide value and a modulation signal to provide a combined fractional divide value; and
a fractional-N divider adapted to fractionally divide a reference signal based on the combined fractional divide value to provide the divided reference signal such that the output signal is phase modulated.
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Accused Products
Abstract
A fractional-N offset phase locked loop (FN-OPLL) is provided. The FN-OPLL includes a fractional divider, a phase detector, a loop filter, a voltage controlled oscillator (VCO), and feedback circuitry. Combiner circuitry combines an initial fractional divide value and a modulation signal to provide a combined fractional divide value. Based on the combined fractional divide value, the fractional-N divider divides a reference frequency and provides a divided reference frequency to the phase detector. The phase detector compares a phase of the divided reference frequency to a phase of a feedback signal to provide a comparison signal. The comparison signal is filtered by the loop filter to provide a control signal to the VCO, where the control signal controls a frequency of an output signal of the VCO. The output signal is processed by the feedback circuitry to provide the feedback signal to the phase detector.
29 Citations
27 Claims
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1. A phase locked loop system comprising:
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loop circuitry adapted to provide an output signal based on a divided reference signal;
combiner circuitry adapted to combine an initial fractional divide value and a modulation signal to provide a combined fractional divide value; and
a fractional-N divider adapted to fractionally divide a reference signal based on the combined fractional divide value to provide the divided reference signal such that the output signal is phase modulated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 16, 17, 26)
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- 13. The system of 11 wherein the integer multiple is selected such that there is at least a minimum offset between fractional spurs appearing in the local oscillator signal and a frequency of the local oscillator signal.
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18. A method of providing a modulated signal using a phase locked loop system comprising:
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providing an output signal based on a divided reference signal;
combining an initial fractional divide value and a modulation signal to provide a combined fractional divide value; and
fractionally dividing a reference signal based on the combined fractional divide value to provide the divided reference signal such that the output signal is phase modulated. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 27)
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Specification