Frequency generator with a phase locked loop
AssigneeFraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
InventorsNiels Christoffers, Rainer Kokozinski, Bedrich Hosticka, Stephan Kolnsberg
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Abstract
A frequency generator with a phase locked loop includes a loop filter, the transfer function of which has a pair of complex conjugated poles. The present invention provides an optimum and greatly improved compromise, in particular as opposed to the prior art, between phase noise and settling time of the phase locked loop of the frequency generator.
Claims18
A frequency generator, comprising:
- a phase locked loop with a loop filter,
- wherein the loop filter is formed such that a transfer function of the loop filter has a pair of complex conjugated poles.
A method of generating an oscillating output signal with an output frequency from a reference signal with a reference frequency, comprising the steps of:
- generating the oscillating output signal;
- generating a comparison signal from the oscillating output signal, wherein a comparison frequency of the comparison signal differs from the output frequency by a frequency factor;
- comparing the comparison frequency with the reference frequency or a phase of the comparison signal with a phase of the reference signal, in order to generate an oscillator control signal, which depends on the difference of the comparison frequency and the reference frequency or on the difference of the phase of the comparison signal and the phase of the reference signal;
- filtering the oscillator control signal with a loop filter, in order to obtain a filtered oscillator control signal, wherein the transfer function of the loop filter comprises a pair of complex conjugated poles;
- and
- controlling the output frequency of the output signal depending on the filtered oscillator control signal.
A method of designing a frequency generator with a phase locked loop with a loop filter, comprising the steps of:
- determining a maximum phase noise of the phase locked loop and a frequency offset, wherein the phase noise of the phase locked loop is to be no more than equal to the maximum phase noise at the frequency offset from a carrier frequency;
- calculating a maximum magnitude of a transfer function HPLL(s) of the phase locked loop at the frequency offset from the maximum phase noise and the frequency offset;
- determining a pair of complex conjugated poles of a transfer function HLF(s) of the loop filter so that the magnitude of the transfer function, HPLL(s) of the phase locked loop for the determined pair of complex conjugated poles is equal to the maximum magnitude and the settling time of the phase locked loop is minimal.
A computer program with program code for performing, when the computer program is executed on a computer, the method of designing a frequency generator with a phase locked loop with a loop filter, comprising the steps of:
- determining a maximum phase noise of the phase locked loop and a frequency offset, wherein the phase noise of the phase locked loop is to be no more than equal to the maximum phase noise at the frequency offset from a carrier frequency;
- calculating a maximum magnitude of a transfer function HPLL(s) of the phase locked loop at the frequency offset from the maximum phase noise and the frequency offset;
- determining a pair of complex conjugated poles of a transfer function HLF(s) of the loop filter so that the magnitude of the transfer function HPLL(s) of the phase locked loop for the determined pair of complex conjugated poles is equal to the maximum magnitude and the settling time of the phase locked loop is minimal.
An apparatus for designing a frequency generator with a phase locked loop with a loop filter, comprising:
- a maximum phase noise determinator for determining a maximum phase noise of the phase locked loop and a frequency offset, wherein the phase noise of the phase locked loop is to be no more than equal to the maximum phase noise at the frequency offset from a carrier frequency;
- a calculator for calculating a maximum magnitude of a transfer function of the phase locked loop at the frequency offset from the maximum phase noise and the frequency offset;
- and
- a pole determinator for determining a pair of complex conjugated poles of a transfer function of the loop filter, for which the magnitude of the transfer function of the phase locked loop is equal to the maximum magnitude and the settling time of the phase locked loop is minimal.
Dependencies are inferred from the claim text.