An oscillator circuit includes a field effect transistor and a resonant circuit having a first terminal connected to the field effect transistor. The resonant circuit includes an inductance and a capacitance and has a second terminal for connecting to a radiator. The field effect transistor includes a gate electrode coupled to a source of gate voltage, a source electrode, a drain electrode and a graphene channel disposed between the source electrode and the drain electrode and electrically connected thereto. The graphene channel is disposed relative to the gate electrode for being biased by the gate electrode into a negative differential resistance region of operation. The oscillator circuit is capable of generating a continuous wave THz frequency signal, and is further capable of being enabled and disabled by the bias applied to the gate electrode.