A 28-GHz Low Phase Noise Class-C Transformer VCO With 187-dBc/Hz FoM in 90-nm SiGe BiCMOS

This article presents a 27.9-28.8-GHz voltage-controlled oscillator (VCO) in a 90-nm SiGe BiCMOS process. The VCO consists of class-C active devices and a transformer tank. A transformer tank model which captures all parasitic capacitance is formulated. Several transformer design examples are studied and compared with an LC tank in terms of quality factor and tuning range. The VCO achieves a state-of-the-art phase noise of $-$ 111.5 dBc/Hz at 1-MHz offset. The figure-of-merit (FoM) is 187 dBc/Hz, and the flicker corner is 82 kHz with a power consumption of 24.7 mW. Potential applications include phase-locked loops (PLLs) for wireless systems at 28, 60, and 90 GHz.