Calibration circuit for VCO

A phase-locked loop circuit, comprising:

• a phase frequency detector for detecting a phase difference between a reference input signal and a feedback signal for producing a voltage that represents the detected phase difference;
• a charge pump coupled to receive the voltage representing the detected phase difference, the charge pump for generating a DC current level responsive to the received voltage;
• a loop filter coupled to receive the DC current generated by the charge pump, the loop filter for converting the received current into a voltage level;
• a voltage controlled oscillator coupled to receive the voltage level, the voltage controlled oscillator for producing an output signal having a frequency characteristic which frequency characteristic is a function of the received voltage level;
• and
• an array of selectable capacitors formed within the phase-locked loop circuit, the selectable capacitors for adjusting the frequency characteristic of the output signal from the phase-locked loop circuit.

A method for adjusting a frequency output of a phase-locked loop circuit, comprising:

• initially coupling a first number of capacitors formed within the phase-locked loop circuit to a first node of the phase-locked loop circuit;
• evaluating one of a phase or a frequency of an output signal that is produced at a second node within the phase-locked loop circuit;
• and
• changing from the first number of capacitors to a second number of capacitors coupled to the first node to adjust the voltage level at a third node.

A method for controlling a frequency of an output signal of a phase-locked loop circuit, comprising:

• setting a capacitance value by selecting a first number of capacitors formed within the phase-locked loop circuit to provide a level of coarse frequency-control;
• sinking current out of a loop filter formed within the phase-locked loop circuit to provide fine frequency control whenever an input voltage to a voltage controlled oscillator is higher than a specified amount;
• and
• sourcing current into the loop filter for fine frequency control whenever the input voltage to a voltage controlled oscillator is lower than a specified amount.