A Programmable Bandpass Filter with Simultaneously Reconfigurable Working Frequency and Bandwidth
A sharp-rejection programmable bandpass filter (BPF) with transmission zeros (TZs) and simultaneous continuous-type reconfiguration in terms of center frequency and bandwidth is presented. With the user-predefined filtering responses, it promises to simplify modern RF system architectures and adapts to flexible front-end designs. The proposed controllable BPF is composed of two building blocks, namely the resonant-inverter (RI) and the shunt resonator. The BPF programmability relies on the adaptive change of the resonances in these two circuit parts. When the shunt resonances that define the overall TZs move out of the frequency span defined by the even-odd-mode-RI-subnetwork natural frequencies, the bandwidth increases; if all the resonances are shifted with their relative spacing maintained, the center frequency is varied for constant absolute bandwidth. A proof-of-concept reconfigurable BPF design example is implemented, showing a highly flexible bandwidth tuning ratio of 5:1 and center-frequency tuning ratio of 2:1.