DESIGN OF HIGH QUALITY CMOS ACTIVE INDUCTANCES USING INTEGRATED TRANSFORMERS

摘要

The most important problem for the realization of a fully integrated RF CMOS front end comes from the low quality of the passive integrated devices. In this paper a circuit topology which allows to compensate for the intrinsic low quality of CMOS integrated inductors is presented. Employing a magnetic coupling between primary and secondary coils of a transformer, and taking the maximum advantage of the limited transconductance gain of MOS devices for compensating the losses of the integrated magnetic structures, a behaviour of a quite "ideal inductance" is obtained. To prove the validity of such an approach, a transformer based active inductance was designed employing a 0.35 μm CMOS technology by AMS and using both electromagnetic and circuital simulations. An equivalent "almost ideal" inductance of 6 nH at a centre frequency of 2.4 GHz was obtained. The circuit needs a bias current less than 1 mA operating with a supply voltage of 3.3 V. Moreover, two control voltages allow to tune the maximum quality factor of the inductance and to change the frequency at which it occurs in a relatively wide range.