Design and Analysis of 55-63-GHz Fundamental Quad-Core VCO With NMOS-Only Stacked Oscillator in 28-nm CMOS

This article presents a 55-63-GHz fundamental multicore voltage-controlled oscillator (VCO) in a 28-nm bulk CMOS process. The single-core VCO utilizes stacking and magnetic coupling of two NMOS-based resonators, which increases the tank energy for phase noise reduction while maintaining low voltage swings for reliability. In the multi-core configuration, the oscillators are coupled in a way that also simplifies LO distribution toward the transmitter and receiver. The potential parasitic modes that occur both in single-core and multi-core configurations are suppressed by design. The implicit common-mode (CM) impedance control is utilized to reduce phase noise without any large extra tail inductor as used in a conventional complementary oscillator. The distributed nature of energy restoring elements in the proposed stacked oscillator also offers robust parasitic mode suppression compared to alternative implementation based on a conventional complementary oscillator. The working range of the prototype is between 55 and 63 GHz corresponding to a tuning range of 13.4% with power consumption varying from 15.3 to 12 mW across the tuning range. The prototype achieves the best phase noise of -95 and -121.7 dBc/Hz at 1- and 10-MHz offsets from the carrier at 55GHz. The corresponding peak figure of merits (FOMs) achieved are 178 and 185 dBc/Hz at 1- and 10-MHz offsets from the carrier.