A Fully Decoupled LC Tank VCO Topology for Amplitude Boosted Low Phase Noise Operation

Abstract

This paper describes a general technique for reducing oscillator phase noise in LC voltage-controlled oscillators (VCOs). Phase noise is reduced using a circuit topology that decouples the LC tank from the active devices using capacitive transformers, thereby achieving a higher amplitude of oscillation not limited by the transistor breakdown voltage. Moreover, the proposed VCO topology reduces active device noise injection into the tank by further improving phase noise. As proof of concept, two VCOs operating at 16-19 GHz and 31.8-39.6 GHz, respectively, are implemented in the Global Foundries (GF) 130-nm SiGe BiCMOS 8HP technology (fT/fMAX of 200/280 GHz). The lower frequency VCO achieves a phase noise of -110 dBc/Hz at a 1-MHz offset from a 17-GHz carrier while the higher frequency VCO achieves a phase noise of -103.2 dBc/Hz at a 1-MHz offset from a 36-GHz carrier. The higher frequency VCO was also implemented in a second, more advanced GF 130-nm SiGe BiCMOS 8XP technology (fT/fMAX of 260/320 GHz), yielding a further average phase noise improvement of 1.9 dB over the 8HP version.