Varactor circuit and voltage-controlled oscillation

A voltage-controlled oscillator, comprising:

• a varactor circuit coupled in parallel with an inductor circuit at a first output node and a second output node;
• a first pair of cross-coupled transistors coupled to the varactor circuit and the inductor circuit at the first output node and the second output node;
• a bias transistor coupled between the first pair of cross-coupled transistors and ground;
• and
• a gate of the bias transistor coupled for receiving a bias voltage;
• wherein the varactor circuit includes:
• a first varactor, a second varactor, a third varactor, and a fourth varactor;
• a first source-drain node of the first varactor and a second source-drain node of the second varactor are coupled to a first input node;
• a first gate node of the first varactor is coupled to the first output node;
• a second gate node of the second varactor is coupled to the second output node;
• a third gate node of the third varactor and a fourth gate node of the fourth varactor are coupled to a second input node;
• a third source-drain node of the third varactor is coupled to the first output node;
• a fourth source-drain node of the fourth varactor is coupled to the second output node;
• and
• a resistance bridge coupled to the first gate node, the second gate node, the third source-drain node, and the fourth source-drain node;
• the resistance bridge including at least one common mode voltage node, and capacitors coupled for DC decoupling of a common mode voltage at the at least one common mode voltage node from a first sinusoidal voltage and a second sinusoidal voltage respectively at the first output node and the second output node;
• wherein the resistance bridge includes:
• a first resistor and a second resistor coupled to one another between the first gate node and the second gate node at a first common mode voltage node of the at least one common mode voltage node;
• a third resistor and a fourth resistor coupled to one another between the third source-drain node and the fourth source-drain node at a second common mode voltage node of the at least one common mode voltage node;
• and
• wherein the capacitors include:
• a first capacitor coupled between the first output node and the first gate node:
• a second capacitor coupled between the second output node and the second gate node;
• a third capacitor coupled between the first output node and the third source-drain node;
• and
• a fourth capacitor coupled between the second output node and the fourth source-drain node.

A method for providing a programmable voltage-controlled oscillation, comprising:

• providing a first control voltage to a first pair of varactors;
• providing a second control voltage to a second pair of varactors;
• wherein the first control voltage has a first voltage range;
• wherein the second control voltage has a second voltage range;
• wherein the first voltage range and the second voltage range are associated with a gate-to-source voltage range of high capacitive gain range;
• wherein the first control voltage and the second control voltage in combination provide a differential input;
• operating the first pair of varactors in a first mode;
• operating the second pair of varactors in a second mode;
• wherein the first mode and the second mode are complementary modes;
• wherein the differential input in combination with the complementary modes provides the high capacitive gain range associated with operation of the first pair of varactors and the second pair of varactors in combination;
• providing a resistance bridge coupled to a first varactor and a second varactor of the first pair of varactors, and to a third varactor and a fourth varactor of the second pair of varactors;
• the resistance bridge including at least one common mode voltage node, and capacitors coupled for DC decoupling of a common mode voltage at the at least one common mode voltage node from a first sinusoidal output voltage and a second sinusoidal output voltage respectively at a first output node and a second output node;
• wherein the resistance bridge includes:
• a first resistor and a second resistor coupled to one another between the first varactor and the third varactor;
• a third resistor and a fourth resistor coupled to one another between the second varactor and the fourth varactor;
• the first resistor, the second resistor, the third resistor, and the fourth resistor coupled to one another at the at least one common mode voltage node to couple the common mode voltage to each of the first varactor, the second varactor, the third varactor, and the fourth varactor;
• and
• wherein the capacitors include:
• a first capacitor coupled between the first output node and the first varactor;
• a second capacitor coupled between the second output node and the second varactor;
• a third capacitor coupled between the first output node and the third varactor;
• and
• a fourth capacitor coupled between the second output node and the fourth varactor;
• and
• outputting the first sinusoidal output voltage and the second sinusoidal output voltage having a frequency programmed responsive to the differential input and having a programmable frequency range responsive to the high capacitive gain range.