The present invention relates to a resonator structure, such as a film bulk acoustic wave (FBAW) resonator structure, which is modified to approximate a parasitic input characteristic to a parasitic output characteristic and thus enable use of the resonator structure in a differential topology. Thereby, crystal-based resonator structures can be replaced by the proposed differential resonator structure, which enables higher integration, reduced costs and higher frequencies. A crystal based oscillator cannot handle frequencies above 40 MHz in fundamental mode.