Analysis and Design of Coupled PLL-Based CMOS Quadrature VCOs

A novel architecture to implement quadrature voltage-controlled oscillators (QVCOs), based on the coupled phase-locked loop (CPLL) technique, is presented. The proposed solution allows to overcome the trade-off between low phase noise and small quadrature error, typical of conventional QVCOs. Both figure-of-merit (FoM) can then be optimized simultaneously. Within the CPLL bandwidth, the QVCO phase noise is even improved by 3 dB with respect to the phase noise of the standalone free-running oscillators in the loop. Prototypes realized in a 28 nm bulk CMOS technology operate from 24 to 29.2 GHz (a 20% tuning range) and show a −134 dBc/Hz phase noise at 10 MHz offset from the 24 GHz carrier. The measured average quadrature error across the tuning range is 0.9°. The QVCO dissipates 60 mW; its FoM is −184 dBc/Hz. The QVCO core area amounts to 0.2 mm2.