A systematic measurement technique to characterize bimodal oscillation for CMOS Quadrature LC-VCO

This paper presents a theoretical analysis and control procedure of the bimodal oscillation phenomenon inherent to LC-tuned Quadrature voltage-controlled oscillators (QVCOs). A systematic start-up procedure is proposed to drive the quadrature VCO (QVCO) into the desirable mode of operation by controlling its initial conditions. This is the first reported approach in the published literature to the best of author's knowledge. The theory and the proposed methodology are validated with the measurement of a 13-GHz QVCO implemented in 90 nm CMOS using NMOS current-coupling topology.