High efficiency harmonic voltage controlled oscillator (VCO)

A method comprising:

• generating a voltage signal across a tank circuit of a voltage controlled oscillator;
• and
• introducing a negative resistance to sustain oscillation of the voltage signal of the voltage controlled oscillator at a desired frequency, wherein the negative resistance introduces a current into the tank circuit substantially at a peak of the voltage signal;
• passing the current through one of a first pair of transistors each having a gate, drain, and a source, wherein the gates of the first pair of transistors are cross-coupled with the drains of the first pair of transistors, the one of the first pair of transistors being turned on when a voltage at the gate of one of the first pair of transistors is greater than a first threshold voltage;
• and
• passing the current through one of a second pair of transistors each having a gate, drain, and a source, the gate of one of the second pair of transistors being coupled to the gate of the one of the first pair of transistors, the one of the second pair of transistors being turned on when a voltage at the gate of the second pair of transistors is greater than a second threshold voltage, the second threshold voltage higher than the first threshold voltage.