Phase-locked loop
View Patent ↗A phase-locked loop for generating an output signal including a signal generator arranged to generate an output, a comparison unit arranged to compare the output with a reference signal so as to provide a digital signal, and a loop filter arranged to generate a control signal for controlling the signal generator in dependence on the digital signal. The loop filter includes a proportional path having a digital filter arranged to generate a first component of the control signal for controlling the phase of the output generated by the signal generator, and an analogue integral path arranged to generate a second component of the control signal for controlling the frequency of the output generated by the signal generator.
1. A phase-locked loop for generating an output signal comprising:
a signal generator arranged to generate the output signal;
a comparison unit arranged to compare the output signal with a reference signal so as to provide a digital signal;
a loop filter arranged to generate a control signal for controlling the signal generator in dependence on the digital signal, the loop filter comprising:
a proportional path comprising a digital filter arranged to generate a first component of the control signal for controlling the phase of the output signal generated by the signal generator; and
an analogue integral path arranged to generate a second component of the control signal for controlling the frequency of the output signal generated by the signal generator.
2. A phase-locked loop as claimed in claim 1 , wherein the digital filter comprises a finite impulse response filter.
3. A phase-locked loop as claimed in claim 2 , wherein the integral path comprises a charge pump and an integrator.
4. A phase-locked loop as claimed in claim 3 , wherein the integrator comprises a capacitor.
5. A phase-locked loop as claimed in claim 1 , wherein the integral path comprises a charge pump and an integrator.
6. A phase-locked loop as claimed in claim 5 , wherein the integrator comprises a capacitor.
7. A phase-locked loop as claimed in claim 1 , wherein the comparison unit comprises a binary phase detector.
8. A phase-locked loop as claimed in claim 7 , wherein the comparison unit is arranged to sample the output signal at a rate, the frequency of the output being dependent on said rate.
9. A phase-locked loop as claimed in claim 8 , said rate being dependent on a rate control signal.
10. A phase-locked loop as claimed in claim 1 , wherein the comparison unit is arranged to sample the output signal at a rate, the frequency of the output being dependent on said rate.
11. A phase-locked loop as claimed in claim 10 , said rate being dependent on a rate control signal.
12. A phase-locked loop as claimed in claim 1 , wherein the frequency of the reference signal is greater than 1 GHz.
13. A phase-locked loop as claimed in claim 1 , wherein the signal generator comprises a ring oscillator.
14. A phase-locked loop as claimed in claim 1 , wherein the signal generator includes a divider arranged to receive and frequency divide the output signal from the signal generator, the output signal being the said divided output.
15. A circuit comprising:
a phase-locked loop according to claim 1 ; and
an amplifier having a modulation bandwidth, wherein the bandwidth of the phase-locked loop is greater than the modulation bandwidth of the amplifier.
16. A method for generating an output signal comprising:
generating the output signal at a signal generator;
comparing the output signal with a reference signal so as to provide a digital signal;
at a loop filter, generating a control signal for controlling the signal generator in dependence on the digital signal, the loop filter comprising:
a proportional path comprising a digital filter to generate a first component of the control signal for controlling the phase of the output signal generated by the signal generator; and
an analogue integral path to generate a second component of the control signal for controlling the frequency of the output signal generated by the signal generator.