Generating an oscillator signal having a desired frequency in a continuous frequency range
A method of generating a first oscillator signal having a desired frequency in a first frequency range comprises generating in a voltage controlled oscillator unit a second oscillator signal having a frequency in a second frequency range of at least one octave. The method further comprises selecting said second continuous frequency range to have a lower endpoint in said first frequency range and an upper endpoint above said range; and selectively using the oscillator signal unchanged or dividing it by a division ratio selected from integer powers of the number 2 to obtain said first oscillator signal. By centering the VCO higher than otherwise required and using an additional divider, so that the VCO signal can selectively be used unchanged or divided, a sufficient margin below as well as above the desired range for e.g. drift and tolerances of the VCO is achieved. It also simplifies the VCO design.
1. A method of generating a first oscillator signal having a desired frequency in a first continuous frequency range, the method comprising:
generating in a voltage controlled oscillator unit with at least one voltage controlled oscillator a second oscillator signal having a frequency in a combined second continuous frequency range of at least one octave;
selecting said second continuous frequency range to have a lower endpoint in said first frequency range and an upper endpoint above said first frequency range;
selectively using said second oscillator signal unchanged or dividing said second oscillator signal by a division ratio selected from a group of division ratios comprising integer powers of the number 2 to obtain said first oscillator signal;
comparing the actual frequency of said first oscillator signal with said desired frequency; and
selecting said division ratio in dependence of the result of the comparison, wherein the step of selecting said division ratio comprises:
tuning the voltage controlled oscillator unit to a frequency at an endpoint of said second continuous frequency range;
selecting an initial division ratio from said group of division ratios so that the frequency of said first oscillator signal is within said first frequency range; and
adjusting, if possible, the frequency of the voltage controlled oscillator unit so that the frequency of said first oscillator signal equals said desired frequency, and otherwise changing the division ratio and adjusting the frequency of the voltage controlled oscillator unit so that the frequency of said first oscillator signal equals said desired frequency.
2. A method according to claim 1 , wherein said second continuous frequency range is selected so that its upper endpoint is √{square root over (2)} times the upper endpoint of said first frequency range.
3. A method according to claim 1 , wherein the group of division ratios comprises the ratios 2 and 4.
4. A voltage controlled oscillator arrangement for generating a first oscillator signal having a desired frequency in a first continuous frequency range, the arrangement comprising:
a voltage controlled oscillator unit with at least one voltage controlled oscillator, the unit being configured to generate a second oscillator signal having a frequency in a combined second continuous frequency range of at least one octave;
wherein said second continuous frequency range has been selected to have a lower endpoint in said first frequency range and an upper endpoint above said first frequency range; and the arrangement further comprises:
means for selectively using said second oscillator signal unchanged or dividing said second oscillator signal by a division ratio selected from a group of division ratios comprising integer powers of the number 2 to obtain said first oscillator signal;
means for comparing the actual frequency of said first oscillator signal with said desired frequency; and
means for selecting said division ratio in dependence of the result of the comparison, wherein the means for selecting said division ratio is configured to:
tune the voltage controlled oscillator unit to a frequency at an endpoint of said second continuous frequency range;
select an initial division ratio from said group of division ratios so that the frequency of said first oscillator signal is within said first frequency range; and
adjust, if possible, the frequency of the voltage controlled oscillator unit so that the frequency of said first oscillator signal equals said desired frequency, and otherwise change the division ratio and adjust the frequency of the voltage controlled oscillator unit so that the frequency of said first oscillator signal equals said desired frequency.
5. A voltage controlled oscillator arrangement according to claim 4 , wherein said second continuous frequency range has been selected so that its upper endpoint is √{square root over (2)} times the upper endpoint of said first frequency range.
6. A voltage controlled oscillator arrangement according to claim 4 , wherein the group of division ratios comprises the ratios 2 and 4.