Q-enhancing technique for rf CMOS active inductor

A design technique for realising a very-high Q CMOS active inductor operating in the RF-band is described in this paper. The proposed active inductor is based on double-feedback transconductor topology in which negative feedback is used to realise inductive input impedance while positive feedback is employed to produce a negative resistance for canceling the inductor loss, hence an enhancing of the Q factor. In order to verify the effectiveness of the proposed technique, a very-high Q (Q>1,000) second-order bandpass filter has been implemented. Simulation results show that the filter exhibits stable Q factor of 12,000, the resonant frequency can be tuned from 1.007 GHz to 1.023 GHz and the input-referred third-order intercept point (IIP3) of -25 dBm (at 1.023 GHz centre frequency and 12,000 Q factor) under a 3.3 V supply voltage.