A 4-Port-Inductor-Based VCO Coupling Method for Phase Noise Reduction

A 4-port-inductor-based voltage-controlled oscillator (VCO) coupling technique is introduced to improve VCO phase noise performance. The analysis of the stability of oscillation modes and the phase noise performance of a coupled oscillator is provided as theoretical fundamental. Four-port inductors are compared with typical two-port inductors, and their superior performance over the latter is demonstrated through analysis and measurements. The design strategies of coupled VCOs using 4-port inductors are discussed. Two coupled VCO topologies, the NMOS-cross-coupled-pair coupled VCO (NCVCO) and the complementary-cross-coupled-pair coupled VCO (CCVCO), are proposed and compared with the conventional NMOS-cross-coupled-pair VCO (NVCO). Prototype designs have been demonstrated to verify the analysis. The 12.8-GHz CCVCO design achieves phase noise of -116 dBc/Hz at 1-MHz offset, a tuning range of 31.4%, and FOM and FOM(T) of 184 and 194, respectively.