A double tuned Ku-band SiGe-MMIC VCO with variable feed-back capacitor

A double tuned Ku-band SiGe-MMIC voltage-controlled oscillator (VCO) with variable feedback capacitor is presented. The proposed VCO employs series varactors in feed-back paths in addition to varactors in tank circuit. By controlling both varactors, this VCO achieves wide tuning range compared to the conventional LC cross-coupled VCO. Furthermore, appropriately biased MOS varactors for feed-back paths realize linear tuning performance. The proposed configuration is experimentally validated with a 0.35 mum SiGe-BiCMOS fully integrated VCO. The oscillation frequency of the fabricated VCO varies 14.3 GHz to 16.2 GHz with 12.5% tuning range, which is increased by 120% from that of the conventional LC cross-coupled VCO.