Voltage-controlled oscillator circuit for direct modulation

A system comprising:

• a phase comparator circuit;
• a charge pump;
• a loop filter circuit;
• a fractional-n frequency divider;
• and
• a voltage controlled oscillator (VCO ) circuit, the VCO circuit comprising:
• a) a variable capacitor for coarsely tuning the VCO circuit, the variable capacitor providing one of a plurality of capacitance values, each of the plurality of capacitance values corresponding to a distinct frequency band, each of the plurality of capacitance values providing a frequency/voltage characteristic for the VCO that is sufficiently linear to implement direct modulation for the frequency band;
• b) a varactor for fine tuning the VCO circuit;
• c) a series capacitor having a capacitance value to linearize a frequency/voltage characteristic of the varactor sufficient to implement direct modulation for a specified channel frequency within the frequency band;
• and
• d) at least one resistor to couple an input voltage to the VCO circuit, the at least one resistor dampening external noise, wherein the input voltage comprises a reference voltage and a control voltage.

A method for tuning a voltage-controlled oscillator (VCO) circuit, comprising:

• coarsely tuning the VCO circuit to implement direct modulation for a frequency band;
• finely tuning the VCO circuit using a varactor;
• and
• linearizing a frequency/voltage characteristic of the varactor sufficient to implement direct modulation for a specified channel frequency within the frequency band, wherein linearizing the frequency/voltage characteristic of the varactor is performed by a capacitor arranged in series with the varactor.

A device comprising:

• a voltage-controlled oscillator (VCO) circuit, the VCO circuit comprising:
• a) a variable capacitor for coarsely tuning the VCO circuit, the variable capacitor providing one of a plurality of capacitance values, each of the plurality of capacitance values corresponding to a distinct frequency band, each of the plurality of capacitance values providing a frequency/voltage characteristic for the VCO that is sufficiently linear to implement direct modulation for the frequency band;
• b) a varactor for fine tuning the VCO circuit;
• c) a series capacitor having a capacitance value to linearize a frequency/voltage characteristic of the varactor sufficient to implement direct modulation for a specified channel frequency within the frequency band;
• and
• d) at least one resistor to couple an input voltage to the VCO circuit, the at least one resistor dampening external noise, wherein the input voltage, comprises a reference voltage and a control voltage.

A system comprising:

• a phase comparator circuit;
• a charge pump;
• a loop filter circuit;
• a fractional-n frequency divider;
• and
• a voltage controlled oscillator (VCO ) circuit, the VCO circuit comprising:
• a) a variable capacitor for coarsely tuning the VCO circuit, the variable capacitor providing one of a plurality of capacitance values, each of the plurality of capacitance values corresponding to a distinct frequency band, each of the plurality of capacitance values providing a frequency/voltage characteristic for the VCO that is sufficiently linear to implement direct modulation for the frequency band, wherein the variable capacitor is a plurality of switchable capacitors, each capacitor coupled to a binary switch that allows the capacitor to be turned on or off;
• b) a varactor for fine tuning the VCO circuit;
• and
• c) a series capacitor having a capacitance value to linearize a frequency/voltage characteristic of the varactor sufficient to implement direct modulation for a specified channel frequency within the frequency band.