A 550-μW Capacitor-Assisted Transformer-Based VCO Achieving 204-dBc/Hz FoMA at 1-MHz Frequency Offset

Abstract

This letter presents a capacitor-assisted transformer (CTF)-based voltage-controlled oscillator (VCO) that achieves a low flicker-noise corner with submilliwatt power consumption and compact chip area. By introducing a small assisting capacitor into the transformer, the higher order tank impedance is reshaped from the second-resonance region toward the third-resonance region, resulting in a more symmetric effective impulse sensitivity function (ISF) and hence reduced flicker-noise upconversion without incurring extra area overhead. Fabricated in a 90-nm CMOS process, the proposed VCO operates from 6.5 to 7.63 GHz while consuming 0.55 mW. Measurements show a minimum flicker-noise corner of 270 kHz and a phase noise of −131.3 dBc/Hz at 10-MHz offset. The core occupies 0.025 mm2, achieving a peak area-normalized figure of merit (FoM ${}_{A}$ ) of 204.3 dBc/Hz at 1-MHz offset.