Analysis and Design of a Double-Quadrature CMOS VCO for Subharmonic Mixing at Ka-Band

In this paper, we analyze the potentials of a four-phase 14-GHz CMOS voltage-controlled oscillator, tailored to a sub-harmonic receiver, for signal processing at Ka-band. When mild phase accuracies between in-phase and quadrature down-converted signals are required, the four-phase oscillator displays roughly the same phase noise figure-of-merit as quadrature oscillator counterparts. However, the operation at half-frequency leads to an improved performance due to a higher quality factor of the tuning varactors, and because the local oscillator circuitry and signal path run at different frequencies, relaxing coupling issues. A detailed time-variant analysis of phase noise in multiphase oscillators is introduced and validated by both simulations and experiments. Prototypes realized in a 65-nm technology occupy an active area of 0.5 mm² and show the following performances: a 26% frequency tuning range (from 12.2 to 15.9 GHz), maximum phase error from pi/4 of 2deg, and a phase noise of -110 dBc/Hz at 1 MHz from 14 GHz, while consuming 18 mA from 0.8-V supply.