Multi-varactor approach for improved VCO gain

A voltage-controlled oscillator comprising:

• a varactor connection comprising:
• a plurality of varactor stages;
• wherein for two or more varactor stages of the plurality of varactor stages, each respective varactor stage of the two or more varactor stages includes a respective set of one or more switched varactors and a respective set of one or more non-switched varactors;
• wherein for each respective varactor stage of the two or more varactor stages, the respective varactor stage is configured such that a digital control signal controls how many switched varactors in the respective set of one or more switched varactors are connected to a tuning source;
• wherein for a first varactor stage of the two or more varactor stages, a first switched varactor included in the first varactor stage is configured to be connected to the tuning source based on a first bit of the digital control signal;
• wherein for a second varactor stage of the two or more varactor stages, a second switched varactor included in the second varactor stage is configured to be connected to the tuning source based on the first bit of the digital control signal, and
• wherein the varactor connection is configured to maintain a gain of the voltage-controlled oscillator irrespective of the tuning voltage from the tuning source, wherein the gain of the voltage-controlled oscillator is defined as a rate of frequency change with tuning voltage.

A circuit comprising:

• a first varactor stage configured to be biased at a first voltage level;
• wherein the first varactor stage includes a first varactor sub-stage, a second varactor sub-stage, and a third varactor sub-stage;
• wherein the second varactor sub-stage includes a first switch that is configured to connect a first varactor and a second varactor to a tuning source in response to a first control signal;
• wherein the third varactor sub-stage includes a second switch that is configured to connect a third varactor and a fourth varactor to the tuning source in response to a second control signal;
• a second varactor stage configured to be biased at a second voltage level that is different than the first voltage level;
• wherein the second varactor stage includes a fourth varactor sub-stage, a fifth varactor sub-stage, and a sixth varactor sub-stage;
• wherein the fifth varactor sub-stage includes a third switch that is configured to connect a fifth varactor and a sixth varactor to the tuning source in response to the first control signal;
• wherein the sixth varactor sub-stage includes a fourth switch that is configured to connect a seventh varactor and an eighth varactor to the tuning source in response to the second control signal.