Oscillator with differential tunable tank circuit

An oscillator comprising:

• a tank circuit including an inductance and a differentially tunable capacitance coupled to the inductance;
• a negative-impedance circuit coupled to the tank circuit;
• and
• first and second outputs;
• wherein the differentially tunable capacitance comprises:
• first and second control inputs;
• first and second varactors coupled respectively between the first output and the first control input and between the second output and the first control input;
• and
• third and fourth varactors coupled respectively between the first output and the second control input and between the second output and the second control input.

An oscillator comprising:

• first and second supply nodes;
• first and second differential tuning inputs for receiving first and second tuning voltages;
• a differentially tunable tank circuit having first and second output nodes coupled between the first and second supply nodes and to the first and second differential turning inputs, with the tank circuit including:
• a differentially tunable impedance means for providing an impedance based on a difference between the first and second tuning voltages.

An oscillator comprising:

• first and second supply nodes;
• a tank circuit;
• a current source coupled between the tank circuit and the first supply node;
• and
• a current sink coupled between the tank circuit and the second supply node.

A tunable capacitance circuit comprising:

• first and second nodes;
• first and second control inputs for receiving first and second complementary control voltages;
• first and second varactors coupled respectively between the first node and the first control input and between the second node and the first control input;
• and
• third and fourth varactors coupled respectively between the first node and the second control input and between the second node and the second control input.

A method of tuning an oscillation frequency of an oscillator having a total capacitance, comprising:

• providing first and second control signals;
• changing a first portion of the total capacitance based on the first control signal;
• and
• changing a second portion of the total capacitance based on the second control signal;
• and
• wherein changing the first portion based on the first control signal comprises changing the bias voltage on a varactor.

A method of operating an oscillator having a total capacitance, the method comprising:

• changing a first portion of the total capacitance in response to a noise signal;
• and
• offsetting at least a portion of the change in the first portion of the total capacitance;
• and wherein offsetting at least a portion of the change in the first portion of the total
• capacitance comprises increasing or decreasing a second portion of the total capacitance in response to the noise signal.