An embodiment of the voltage controlled oscillator is provided. The oscillator comprises a first inductor set, a second inductor set, a second capacitor, a voltage source and a negative resistance element. The inductance of the second inductor set is k times the inductance of the first inductor set. The voltage source applies an ac voltage to the second inductor set. The negative resistance element is coupled to the second inductor set to provide a negative resistance to resonate the second capacitor at the second inductor set.