Techniques for Improved Continuous and Discrete Tuning Range in Millimeter-Wave VCOs

Millimeter-wave voltage-controlled oscillators (VCOs) require small tank inductors due to large parasitic capacitances contributed by MOS switches and cross-coupled pair. This significantly increases the effect of routing inductance on the uniformity of tuning range. In this brief, mathematical analysis has been carried out to explain tuning behavior in the presence of routing inductance. A symmetrically distributed SWCB is proposed, which provides a uniform discrete tuning range, leading to a 3.6× reduction in the varactor size compared to traditional implementations. Two VCOs with different tank structures have been implemented in a Texas Instruments proprietary 130-nm BiCMOS technology. Measurement results show an oscillation frequency of 23.5 GHz with a phase noise performance of -111 dBc/Hz at 1-MHz offset from the carrier, leading to an figure of merit of -181 dBc/Hz. A layout structure that enhances continuous tuning range is validated on a third fabricated VCO through a measured 300% improvement in continuous tuning range.