Voltage-Controlled Oscillator

1 . A calibration circuit for a voltage-controlled oscillator comprising:

a first counter for counting the number of cycles of a reference signal;

a second counter for counting the number of cycles of a feedback signal produced by the voltage-controlled oscillator, wherein the second counter is adapted to produce a difference value representative of the difference between the frequency of the reference signal and the frequency of the feedback signal;

a memory comprising a plurality of memory locations storing a plurality of the difference values and associated capacitor selections; and

a capacitor bank selectable by the associated capacitor selections in the memory, wherein the capacitor bank is connected to an input of the voltage-controlled oscillator.

2 . The calibration circuit of claim 1 , further comprising a sweeper for selecting possible values of the capacitor selections.

3 . A method for the calibration of a voltage-controlled oscillator comprising:

selecting a capacitor selection in a capacitance bank connected to an input of the voltage-controlled oscillator;

measuring the difference frequency between a frequency of a reference signal and a frequency of a feedback signal produced by the voltage-controlled oscillator;

storing a value representative of the difference frequency in a memory together with the capacitor selection.

4 . The method of claim 3 , further comprising repeating the method with a new capacitor selection, measuring a changed difference frequency and storing a further value representative of the changed difference frequency in the memory together with the new capacitor selection.

5 . The method of claim 4 , further comprising repeating the method until all of the possible capacitor selections have been selected.

6 . A phase-locked loop for aligning an output phase of a voltage-controlled oscillator with the input phase of the voltage-controlled oscillator comprising:

a phase/frequency detector for detecting changes in the output phase of the voltage-controlled oscillator compared with the input phase of the voltage-controlled oscillator;

a selectable capacitor bank attached to an input of the voltage-controlled oscillator

a look-up table for storing a plurality of values representative of the difference between the output phase of the voltage-controlled oscillator and the input phase of the voltage-controlled oscillator and for storing a plurality of values of capacitor selections adapted to select capacitors in the selectable capacitor bank.

7 . The phase-locked loop according to claim 6 , wherein the phase/frequency detector has as input integer values and fractional values from a sigma-delta divider.

8 . The phase-locked loop according to claim 6 , further comprising a plurality of selectable voltage-controlled oscillators with a plurality of selectable capacitor banks.

9 . The phase-locked loop according to claim 6 , further comprising at least one frequency divider attached to the output of a voltage-controlled oscillator.

10 . A method of adjusting the frequency of a voltage controlled oscillator comprising:

measuring a difference value between the output phase of the voltage-controlled oscillator and the input phase of the voltage-controlled oscillator;

using the difference value to look up in a memory a capacitor selection;

using the capacitor selection to change a capacitance value at a capacitor bank attached to an input of the voltage-controlled oscillator.

11 . The method of claim 10 , further comprising

pre-storing a plurality of difference values in the memory by choosing a plurality of capacitance values at the capacitance bank and measuring the difference values between a phase of a reference signal and the output phase of the voltage-controlled oscillator.

12 . The method of claim 10 , further comprising

choosing a capacitor selection having a difference value closest to the measured difference value.

13 . A computer program product embodied on a computer-readable medium and comprising executable instructions for the manufacture of a calibration circuit for a voltage-controlled oscillator comprising:

a first counter for counting the number of cycles of a reference signal;

a second counter for counting the number of cycles of a feedback signal produced by the voltage-controlled oscillator, wherein the second counter is adapted to produce a difference value representative of the difference between the frequency of the reference signal and the frequency of the feedback signal;

a memory comprising a plurality of memory locations storing a plurality of the difference values and associated capacitor selections; and

a capacitor bank selectable by the associated capacitor selections in the memory, wherein the capacitor bank is connected to an input of the voltage-controlled oscillator.

14 . The computer program product of claim 12 , wherein the executable instructions are programmed in a hardware description language selected from the group consisting of Verilog, VHDL and RTL.