A 3-GHz Inverse-Coupled Current-Reuse VCO Implemented by 1:1 Transformer

A voltage-controlled oscillator (VCO) based on a current-reuse (CR) topology is proposed. By inversely coupling two CR VCOs through tank inductors, the proposed VCO inherits the good phase noise performance of CR VCO, and meanwhile can realize differential outputs and alleviate the disturbance of VCO to the power supply and ground. Also, the proposed VCO achieves a phase noise improvement due to the electro-magnetic coupling of a transformer. Fabricated in the 180-nm CMOS process, the core circuit of the proposed VCO occupies an area of
$0.4\times0.32$
mm
²
. Under a supply voltage of 1.2 V, the measured tuning range is 2.88–3.61 GHz (22.5%). The phase noise at 1-MHz offset varies between −126.7 and −123 dBc/Hz among the tuning range. The figure of merit (FoM) is in the range of 188.1–190.7 dBc, at 1-MHz offset.