ABSTRACT
In this chapter, the authors introduce a method to broaden a tuning range of a CMOS LC-tank oscillator without sacrificing its area. The single-tank oscillator employs a strongly coupled transformer-based tank and forces the tank to oscillate either in a differential mode or common mode. The oscillator can be realized as a one-port or a two-port structure. However, only the two-port structure will guarantee a reliable start-up at the first Differential Mode (DM) resonance, thus preventing the mixed DM oscillation. However, in that transformer, the Common Mode (CM) current in the two windings of the primary inductor has opposite direction, thus canceling each other’s flux. Consequently, the CM primary inductance would be smaller than the DM one.
