Abstract: Voltage controlled oscillators are disclosed. The voltage controlled oscillator includes an inductive circuit, a cross-coupled N-type transistor pair, and a cross-coupled P-type transistor pair. The inductive circuit includes two inductive windings stacked together, and is configured to generate a pair of differential resonance signals. The cross-coupled N-type transistor pair is coupled in series with the inductive circuit, and configured to receive the pair of differential resonance signals to generate a first oscillation signal. The cross-coupled P-type transistor pair is coupled in series with the inductive circuit, and configured to receive the pair of differential resonance signals to generate a second oscillation signal. The first oscillation signal and second oscillation signal include substantially the same frequency and are out-of-phase to each other.