A VCO With Extra Cross-Coupling Path

This letter presents a voltage-controlled oscillator (VCO) with an extra cross-coupling path realized by a novel transformer-based resonator. The extra cross-coupling can enhance the negative
$G_{m}$
and loop gain of the cross-coupled pair. The triode time of the active device during the oscillation will be reduced, resulting in better phase noise (PN) and shorter startup time than the conventional
$LC$
-VCO. Fabricated in a CMOS 65-nm process, the proposed VCO consumes 0.9 mW average dc power under a voltage supply of 0.38 V. The 1-MHz offset PN can reach −107.15 dBc/Hz at 8.38 GHz, and the corresponding figure of merit (FoM) is −186.75 dBc/Hz. The VCO’s bandwidth is 34.1% ranging from 6.26 to 8.84 GHz, which corresponds an FoM
_T
of −197.41 dBc/Hz. Thanks to the compact layout of the transformer, the VCO occupies only 0.055 mm
²
core area, resulting in a −199.35 dBc/Hz FoM
_A
.