A 3.9–4.5GHz class-C VCO with accurate current injection based on capacitive feedback

A class-C VCO with dual negative feedback architecture is proposed to break the trade-off between amplitude stability of oscillation and bias current flicker noise. Inherent dynamic biasing of this architecture maximizes available voltage swing and provides robust current control without any additional circuits. To inject current exactly at the peak of oscillation, a capacitive feedback technique is proposed which improves phase noise performance further by compensating current injection delay caused due to cross-coupled pair parasitics. This VCO has been implemented in 130nm BiCMOS technology using BJT based cross-coupled pair. It exhibits phase noise performance of −131dBc/Hz @ 1MHz offset when running at 3.9GHz. It exhibits a 14% tuning range, and presents an FoM of 184dBc/Hz.