Method for suppression of spurs from a free running oscillator in frequency division duplex (FDD) and time division duplex (TDD) wireless systems
View Patent ↗Embodiments of this disclosure include methods in which spurs generated by the drifting of an oscillation frequency of an oscillation signal provided by a free-running oscillator may be minimized and/or eliminated from an output signal of a phase locked loop (PLL). Methods include minimizing the mixing gain between the oscillation signal and a power signal provided to the PLL. The oscillation signal and the power signal may be mixed in a phase frequency detector (PFD) included in the PLL. The minimizing of the mixing gain for the PFD also minimizes the degrading effect that the spurs have on the overall performance of the communications device. The mixing gain may be minimized by minimizing the impedance provided at nodes included in the PFD where the oscillation signal and the power signal mix. The mixing gain may also be minimized by maximizing the power supply rejection ratio for the PFD.
1. A communications device, comprising:
a reference oscillator configured to provide a reference signal that is operating at a reference frequency; and
a reference phase-locked loop (PLL) configured to:
receive a power signal,
provide a target signal that is operating at a target frequency, and
mix the power signal with the reference signal such that the target signal tracks the reference signal when the communications device is engaged in a communications channel that is operating at a communications channel frequency to adjust a power level of a plurality of spurs coupled to the target signal when the reference frequency is different from the communications channel frequency.
2. The communications device of claim 1 , wherein the target frequency is configured to be proportional to the reference frequency.
3. The communications device of claim 2 , wherein the reference frequency comprises:
a center frequency of the communications channel.
4. The communications device of claim 3 , wherein the reference signal is configured to fluctuate.
5. The communications device of claim 1 , wherein the reference PLL comprises:
a phase frequency detector (PFD) configured to adjust an impedance of the PFD to adjust a mixing gain generated from mixing the power signal with the reference signal.
6. The communications device of claim 5 , wherein the impedance of the PFD comprises:
a capacitance of the PFD.
7. The communications device of claim 6 , wherein the PFD is further configured to minimize the mixing gain generated from the mixing of the power signal with the reference signal and each harmonic of the reference signal by minimizing the capacitance of the PFD to minimize a power level of the plurality of spurs that is coupled onto the target signal.
8. The communications device of claim 5 , wherein the impedance of the PFD is adjusted based on a selection of a plurality of active devices for the PFD.
9. The communications device of claim 5 , wherein the impedance of the PFD is adjusted by adjusting a power rejection ratio for the PFD.
10. The communications device of claim 5 , wherein the PFD is further configured to adjust the mixing gain generated from the mixing of the power signal with the reference signal to adjust the power level of the plurality of spurs.
11. A method, comprising:
receiving a reference signal that is operating at a reference frequency;
receiving a power signal; and
mixing the power signal with the reference signal such that a target signal tracks the reference signal when a communications device is engaged in a communications channel that is operating at a communications channel frequency to adjust a power level of a plurality of spurs coupled to the target signal when the reference frequency is different from the communications channel frequency.
12. The method of claim 11 , further comprising:
adjusting an impedance of a phase frequency detector (PFD) to adjust a mixing gain generated from the mixing.
13. The method of claim 11 , further comprising:
adjusting a power rejection ratio for a phase frequency detector to adjust a mixing gain generated from the mixing.
14. A communications device, comprising:
a reference oscillator configured to provide a reference signal that is operating at a reference frequency; and
a reference phase-locked loop (PLL) comprising a phase frequency detector (PFD), the PFD being configured to:
receive a power signal,
provide a target signal that is operating at a target frequency, and
mix the power signal with the reference signal such that the target signal tracks the reference signal when the communications device is engaged in a communications channel that is operating at a communications channel frequency to adjust a power level of a plurality of spurs coupled to the target signal when the reference frequency is different from the communications channel frequency.
15. The communications device of claim 14 , wherein the PFD comprises:
a plurality of critical nodes configured to provide a mixing location for mixing the power signal with the reference signal; and
a plurality of active devices configured to provide a mixing gain generated from the mixing of the power signal with the reference signal,
wherein the plurality of active devices is further configured to adjust the mixing gain generated from the mixing of the power signal with the reference signal to adjust a power level of a plurality of spurs coupled to a target signal.
16. The communications device of claim 15 , wherein the PFD is further configured to adjust an impedance of the PFD to adjust the mixing gain generated from the mixing the power signal with the reference signal.
17. The communications device of claim 16 , wherein the PFD is further configured to minimize the mixing gain generated from the mixing of the power signal with the reference signal and each harmonic of the reference signal by minimizing a capacitance of the PFD to minimize the power level of the plurality of spurs coupled to the target signal.
18. The communications device of claim 16 , wherein the impedance of the PFD is adjusted based on a selection of the plurality of active devices for the PFD.
19. The communications device of claim 16 , wherein the impedance of the PFD is adjusted by adjusting a power rejection ratio for the PFD.
20. The communications device of claim 16 , wherein the PFD is further configured to adjust the mixing gain generated from the mixing of the power signal with the reference signal to adjust the power level of the plurality of spurs.