An oscillator circuit is described comprising a piezoresistive resonator and a phase changing devices. Oscillator circuits with piezoresistive resonators do have the advantage that they can perform self-sustaining oscillation without additional active devices as e.g. transistors since they can be used as amplifiers. Phase changing devices as capacitors, coils and further piezoresistive resonator are used in order to compensate the π/2 phase shift of the piezoresistive resonator.