A wide frequency range CMOS active inductor for UWB bandpass filters

A CMOS active inductor that exhibits wide-frequency range inductive impedance with a high quality factor (Q) is presented. The inductor is designed using negative impedance obtained in a cross-coupled transistor pair that is a part of the feedback loop consisting of common gate and common drain stages. Then, a tunable ultra-wideband (UWB) bandpass filter (BPF) is designed by cascading two such inductors back-to-back through a varactor. The proposed active inductor and the BPF are designed and simulated in 90 nm CMOS digital process. The inductor exhibits inductive impedance in the range from few MHz to over than 20 GHz and achieves Q-factor of 600. The designed BPF shows a -3 dB bandwidth of 2.25 GHz with a tuning range of 5 GHz.