a voltage - controlled oscillator that can achieve low phase noise while ensuring stable oscillation startup and stable oscillation maintenance even under low supply voltage conditions . the voltage - controlled oscillator includes an lc parallel resonant circuit , whose impedance varies with a control input voltage and a negative resistance circuit for introducing negative resistance into the lc parallel resonant circuit , wherein the negative resistance circuit includes at least : a first amplifier circuit , provided in parallel with the lc parallel resonant circuit and having a first pair of transistors cross - coupled via a capacitor , that achieves class - c amplifier operation by biasing the gate of each transistor in the first transistor pair with a first bias voltage ; and a similarly configured second amplifier circuit that achieves class - c amplifier operation by biasing the gate of each transistor with a second bias voltage which is different from the first bias voltage .