Low-phase-noise 54GHz quadrature VCO and 76GHz/90GHz VCOs in 65nm CMOS process

This paper presents new circuit topologies and design techniques for low-phase-noise CMOS mmWave Quadrature VCO (QVCO) and VCOs. A transformer coupling with extra phase shift is proposed in QVCO to decouple the tradeoff between phase noise (PN) and phase error and improve the PN performance. This technique is demonstrated in a mmWave QVCO with a measured PN of -119.2 dBc/Hz at 10 MHz offset of a 56.2 GHz carrier and a tuning range of 9.1% (FOM_T of -179 dBc/Hz). To our best knowledge, this QVCO has the lowest PN at 10 MHz offset among all the QVCOs around 50-60 GHz frequency range. In addition, an inductive divider feedback technique is proposed in VCO design to improve the transconductance linearity, resulting in larger signal swing and lower PN compared to the conventional LC VCOs. The effectiveness of this approach is demonstrated in a 76 GHz VCO and a 90 GHz VCO, both fabricated in a 65 nm CMOS process, with an FOM_T of 173.6 dBc/Hz and 173.1 dBc/Hz, respectively.