A feedback class-C VCO with robust startup condition over PVT variations and enhanced oscillation swing

This paper presents a feedback class-C VCO with PVT-robustness and enhanced oscillation swing. The proposed VCO starts oscillation as a differential LC-VCO for robust startup, and automatically adapts to an amplitude-enhanced class-C VCO in steady-state for lower phase noise. The proposed VCO is implemented in a 0.18-μm CMOS process. The measured phase noise at room temperature is -125 dBc/Hz @ 1MHz offset with a power dissipation of 3.4 mW, from a carrier frequency of 4.84 GHz. The figure-of-merit is -193 dBc/Hz.