Center frequency and bandwidth tunable filter employing MEMS digitally tunable capacitors

This paper proposes a novel multi-pole bandpass filter that is suitable for applying micro electromechanical systems (MEMS). The proposed bandpass filter employs parallel resonance circuits with tunable capacitors, and can independently tune its center frequency and bandwidth by only tunable capacitors. The proposed bandpass filter comprises tunable ring resonators which are coupled by J-inverters. Since the tunable resonator can change its bandwidth by itself, it is not required to tune the characteristics of the J-inverters for changing the bandwidth, which helps to simplify a bandwidth tuning scheme. This paper shows the circuit configuration of the proposed filter. A two-pole filter is fabricated using MEMS digitally tunable capacitors. Measured results show that the fabricated bandpass filter changed its bandwidth from 1.7% to 7.4% at the center frequency of 1.77 GHz, and changed its center frequency from 1.37 GHz to 1.77 GHz.