Systems and methods for using a phase locked loop (PLL) to provide multiple output signals
View Patent ↗A phase locked loop (PLL) provides output signals at multiple frequencies. In particular, the PLL includes a phase detector and two voltage controlled oscillators (VCOs). One of the VCOs is selectively enabled depending on a desired output signal. The phase detector receives a reference signal and a feedback signal from the enabled one of the two VCOs. The phase detector outputs a control signal that controls the VCO that provided the feedback signal.
1. A phase locked loop (PLL) comprising:
a phase detector configured to:
receive a reference input signal and one of two feedback signals; and
output a control signal;
a first voltage controlled oscillator (VCO) configured to:
receive the control signal and output a first one of the two feedback signals; and
receive a first enable signal that activates the first VCO; and
a second VCO configured to:
receive the control signal and output a second one of the two feedback signals; and
receive a second enable signal that activates the second VCO such that only one of the first VCO and the second VCO are active at a time.
2. The PLL of claim 1 , further comprising a loop filter communicatively positioned between the phase detector and the first VCO.
3. The PLL of claim 1 , wherein the first VCO comprises a voltage controlled crystal oscillator.
4. The PLL of claim 1 , wherein the first one of the two feedback signals comprises a first frequency and the second one of the two feedback signals comprises a second frequency different than the first frequency.
5. The PLL of claim 1 , further comprising a divider communicatively positioned between the first VCO and a phase comparator in the phase detector.
6. The PLL of claim 1 , wherein the phase detector comprises a mixer.
7. The PLL of claim 1 , wherein the phase detector comprises a differential amplifier.
8. The PLL of claim 1 , further comprising a resistor network coupled to the phase detector and the first VCO.
9. The PLL of claim 8 , further comprising a second resistor network coupled to the phase detector and the second VCO.
10. The PLL of claim 8 , wherein the resistor network is configured to provide a fixed voltage to the phase detector.
11. A method of operating a phase locked loop (PLL), comprising:
while providing a first reference signal to a phase detector:
enabling a first voltage controlled oscillator (VCO);
providing a first control signal from the phase detector to the first VCO to generate a first feedback signal to the phase detector;
while providing a second reference signal to the phase detector:
enabling a second VCO;
providing a second control signal from the phase detector to the second VCO to generate a second feedback signal to the phase detector.
12. The method of claim 11 , further comprising filtering the first control signal and the second control signal with a loop filter.
13. The method of claim 11 , further comprising dividing the first reference signal and the second reference signal.
14. The method of claim 11 , further comprising dividing the first feedback signal and the second feedback signal.
15. The method of claim 11 , further comprising extracting a first clock signal to serve as the first reference signal.
16. The method of claim 15 , further comprising extracting a second clock signal to serve as the second reference signal, wherein the second clock signal is different than the first clock signal.
17. A wireless distribution system (WDS), comprising:
a plurality of remote units comprising a transceiver comprising a phase locked loop (PLL) comprising:
a phase detector configured to:
receive a reference input signal and one of two feedback signals; and
output a control signal;
a first voltage controlled oscillator (VCO) configured to:
receive the control signal and output a first one of the two feedback signals; and
receive a first enable signal that activates the first VCO; and
a second VCO configured to:
receive the control signal and output a second one of the two feedback signals; and
receive a second enable signal that activates the second VCO such that only one of the first VCO and the second VCO are active at a time;
a head-end unit (HEU), the HEU coupled to the plurality of remote units via a plurality of communications media, respectively, and configured to:
distribute a plurality of downlink communications signals to the plurality of remote units via the plurality of communications media, respectively;
receive a plurality of uplink communications signals from the plurality of remote units via the plurality of communications media, respectively; and
generate a plurality of communications signals based on the plurality of uplink communications signals, wherein each of the plurality of communications signals corresponds to a signal channel and a remote unit among the plurality of remote units communicating on the signal channel; and
a signal processing circuit comprising a signal input communicatively coupled to a plurality of signal sources, respectively.
18. The WDS of claim 17 , wherein the PLL further comprises a loop filter.
19. The WDS of claim 17 , wherein the first VCO comprises a voltage controlled crystal oscillator.
20. The WDS of claim 17 , wherein the HEU is coupled to the plurality of remote units via a plurality of optical fiber-based communications media, respectively, wherein:
the HEU is further configured to:
receive a plurality of radio frequency (RF) downlink communications signals;
convert the plurality of RF downlink communications signals into a plurality of optical downlink communications signals, respectively;
distribute the plurality of optical downlink communications signals to the plurality of remote units via the plurality of optical fiber-based communications media, respectively;
receive a plurality of optical uplink communications signals from the plurality of remote units via the plurality of optical fiber-based communications media, respectively; and
convert the plurality of optical uplink communications signals into a plurality of RF uplink communications signals, respectively; and
the plurality of remote units is further configured to:
receive the plurality of optical downlink communications signals via the plurality of optical fiber-based communications media, respectively;
convert the plurality of optical downlink communications signals into the plurality of RF downlink communications signals, respectively;
receive the plurality of RF uplink communications signals;
convert the plurality of RF uplink communications signals into the plurality of optical uplink communications signals, respectively; and
provide the plurality of optical uplink communications signals to the HEU via the plurality of optical fiber-based communications media, respectively.