Phase locked loop, transceiver device and method for generating an oscillator signal
View Patent ↗A phase locked loop has a controlled oscillator for outputting an oscillator signal depending on a control signal. A comparator generates a comparison result from a comparison between a reference frequency signal and a feedback signal derived from the oscillator signal. The phase locked loop also has a filter block for filtering the comparison result and for deriving the control signal from the comparison result, where the filter block has a loop filter and a rejection filter for the frequency-selective attenuation of at least one first interference frequency in the comparison result.
1. A phase locked loop, comprising:
a digital controlled oscillator configured to generate an oscillator signal, and having an oscillator input and an oscillator output;
a comparator, having a comparator first input coupled to a reference input, a comparator second input coupled to the oscillator output, and a comparator output; wherein the comparator is configured to generate an unwanted periodic pattern as a function of the oscillator signal, where the unwanted periodic pattern includes at least a first interference frequency; and
a filter block having a filter block input coupled to the comparator output and having a filter block output coupled to the oscillator input, the filter block comprising a loop filter and a rejection filter, wherein the rejection filter comprises a notch filter comprising an at least second-order recursive filter having one or more filter coefficients for rejecting at least the first interference frequency,
wherein the notch filter comprises a plurality of at least second-order recursive filters connected in series which have one or more filter coefficients for rejecting the first interference frequency and further interference frequencies.
2. The phase locked loop of claim 1 , wherein the notch filter comprises a cascaded integrator comb filter.
3. The phase locked loop of claim 1 , wherein the filter block output is coupled to the oscillator input via a sigma-delta modulator.
4. The phase locked loop of claim 1 , wherein the oscillator output is coupled to the comparator second input via a frequency divider.
5. A phase locked loop, comprising:
a digital controlled oscillator configured to output an oscillator signal based on a control signal;
a comparator operable to generate a comparison result from a comparison between a reference frequency signal and a feedback signal derived from the oscillator signal, the comparison result including an unwanted periodic pattern having at least a first interference frequency; and
a filter block configured to filter the comparison result and configured to derive the control signal from the comparison result, the filter block comprising a loop filter and a notch filter for the frequency-selective attenuation of at least the first interference frequency in the comparison result, the notch filter comprising an at least second-order recursive filter which has one or more filter coefficients for the frequency-selective attenuation of the first interference frequency,
wherein the notch filter further comprises a plurality of at least second-order recursive filters connected in series having one or more filter coefficients for the frequency-selective attenuation of the first interference frequency and further interference frequencies.
6. The phase locked loop of claim 5 , wherein the notch filter further comprises a cascaded integrator comb filter.
7. The phase locked loop of claim 5 , further comprising a sigma-delta modulator configured to derive the control signal from the filtered comparison result.
8. The phase locked loop of claim 5 , further comprising a frequency divider configured to derive the feedback signal from the oscillator signal.