A 4.7-to-6.4 GHz VCO is designed in 45 nm bulk CMOS using an above-IC inductor on top of the active circuitry, yielding 28% area reduction. The inductor is shielded from the circuitry, using the top metal layers of the CMOS back- end, which enables the proposed 3D integration for low-cost performance extension. The fully integrated VCO consumes just 400 microW, achieves a FoM of 185 dB, and occupies and area of only 0.12 mm2