A low-noise figure and quasi-constant Q in DCS band tunable active filter

This work focuses on the implementation of a tunable active filter with an almost constant quality factor. Especially for monolithic microwave integrated circuits, active filters are typically implemented by realizing active inductors, which compensates losses typical of real ones; however, these just show good inductance in a narrow band, usually reducing Q for changes of frequency and making tunability harder. The proposed circuit involves an active capacitance approach, using active component to compensate for inductors losses and making the system voltage-tunable using a varactor, keeping the Q almost unvaried. Also, good noise performances are obtained compared to other common active filter approaches.