Phase-locked loop outputs with reduced reference spurs and noise
In some examples, a circuit is described. The circuit may include a voltage-controlled oscillator that may be configured to generate an output signal. The circuit may also include a control signal generation unit that may be configured to generate a control signal based on the output signal. The control signal generation unit may also be configured to provide the control signal to the voltage-controlled oscillator. The voltage-controlled oscillator and the control signal generation unit may be part of a phase-locked loop (PLL) included in the circuit. The circuit may also include a feed-forward network. The feed-forward network may be configured to provide a portion of the control signal to the voltage-controlled oscillator. The voltage-controlled oscillator may generate the output signal based on the control signal from the control signal generation unit and the portion of the control signal from the feed-forward network.
1. A circuit comprising:
a voltage-controlled oscillator configured to generate an output signal;
a control signal generation unit coupled to the voltage-controlled oscillator, and configured to generate a control signal based on the output signal and to provide the control signal to the voltage-controlled oscillator; and
a feed-forward network, coupled to the voltage-controlled oscillator and to the control signal generation unit, the feed-forward network configured to receive the control signal and to provide a portion of the received control signal to the voltage-controlled oscillator, the voltage-controlled oscillator configured to generate the output signal based on the control signal from the control signal generation unit and the portion of the received control signal provided from the feed-forward network.
2. The circuit of claim 1 , wherein the control signal generation unit comprises a phase frequency detector configured to determine a phase difference between the output signal and a reference signal, the control signal being based on the phase difference between the output signal and the reference signal.
3. The circuit of claim 2 , wherein the portion of the received control signal provided by the feed-forward network to the voltage-controlled oscillator includes a fundamental frequency of the reference signal or a first harmonic frequency of the reference signal.
4. The circuit of claim 1 , wherein the feed-forward network includes:
a voltage regulator coupled to the voltage-controlled oscillator and configured to provide a reference voltage signal to the voltage-controlled oscillator; and
a filter coupled to the voltage regulator and configured to filter the received control signal to remove at least a direct current component of the received control signal and direct the filtered received control signal to the voltage regulator.
5. The circuit of claim 4 , wherein the voltage-controlled oscillator is configured to generate the output signal based on the control signal from the control signal generation unit, the portion of the filtered received control signal provided from the feed-forward network, and the reference voltage signal configured to be generated by the voltage regulator.
6. A circuit comprising:
a control signal generation unit configured to generate a control signal based on a phase difference between an output signal and a reference signal, the control signal including an alternating current component;
a feed-forward network comprising a voltage regulator coupled to the control signal generation unit and configured to receive the control signal and to generate a reference voltage signal that includes at least a portion of the alternating current component of the control signal as received from the control signal generation unit; and
a voltage-controlled oscillator coupled to the control signal generation unit and to the voltage regulator, and configured to generate a tuning signal based on the control signal and the reference voltage signal generated by the feed-forward network and configured to generate the output signal based on the tuning signal.
7. The circuit of claim 6 , wherein an amplitude of an alternating current component of the tuning signal is less than an amplitude of the alternating current component of the control signal resulting from a cancellation between the alternating current component of the control signal and the at least the portion of the alternating current component of the control signal included in the reference voltage signal.
8. The circuit of claim 6 , wherein the voltage-controlled oscillator includes a transistor with a gate, a source, and a drain, the gate configured to receive the control signal and the source configured to receive the reference voltage signal generated by the feed-forward network.
9. The circuit of claim 8 , wherein the drain is configured to output the tuning signal based on the control signal received at the gate and the reference voltage signal received at the source.
10. The circuit of claim 6 , wherein the feed-forward network further comprises a filter communicatively coupled between the control signal generation unit and the voltage regulator, the filter configured to filter the control signal to remove at least direct current components of the control signal and direct the filtered control signal toward the voltage regulator.
11. The circuit of claim 6 , wherein the at least a portion of the alternating current component of the control signal included in the reference voltage signal is a pass-band filtered portion of the alternating current component of the control signal.
12. The circuit of claim 11 , wherein frequencies of the pass-band filtered portion of the alternating current component of the control signal includes a fundamental frequency of the reference signal or a first harmonic frequency of the reference signal.
13. The circuit of claim 11 , wherein a lower frequency of the pass-band filtered portion of the alternating current component of the control signal is higher than a loop bandwidth of the control signal generation unit and the voltage-controlled oscillator.
14. A circuit comprising:
a control signal generation unit configured to generate a control signal based on a phase difference between an output signal and a reference signal, the control signal including an alternating current component; and
a voltage-controlled oscillator coupled to the control signal generation unit and configured to:
receive the control signal from the control signal generation unit,
generate a tuning signal based on the received control signal and a reference voltage signal that includes at least a portion of the alternating current component of the control signal, and
generate the output signal based on the tuning signal.
15. The circuit of claim 14 , wherein an alternating current component of the tuning signal is based on the alternating current component of the control signal and the at least a portion of alternating current component of the control signal included in the reference voltage signal.
16. The circuit of claim 14 , further comprising a feed-forward network comprising a voltage regulator coupled to the voltage controlled oscillator and configured to generate the reference voltage signal.
17. The circuit of claim 16 , wherein the feed-forward network further comprises a filter communicatively coupled between the control signal generation unit and the voltage regulator, the filter configured to filter the control signal to remove at least direct current components of the control signal and direct the filtered control signal toward the voltage regulator.
18. A method to reduce noise in an output of a phase-locked loop, the method comprising:
generating a control signal based on a phase difference between an output signal and a reference signal, the control signal including an alternating current component;
generating a reference voltage signal that includes at least a portion of the alternating current component of the control signal;
generating a tuning signal based on the control signal and the reference voltage signal; and
generating the output signal based on the tuning signal.
19. The method of claim 18 , wherein an alternating current component of the tuning signal is based on the alternating current component of the control signal and the at least a portion of the alternating current component of the control signal included in the reference voltage signal.
20. The method of claim 18 , further comprising filtering the control signal to remove direct current components of the control signal.