Design of a 77-GHz LC-VCO With a Slow-Wave Coplanar Stripline-Based Inductor

The objective of this paper is to demonstrate that the use of a distributed approach for the design of the inductance of an LC-tank millimeter-wave (mm-wave) voltage-controlled oscillator (VCO) can lead to higher performance. Performance is improved in both frequency tuning range and power consumption thanks to a reduction of the cross-coupled pair size. The direct comparison of VCOs designed in different technologies is not straightforward, since the performance of the varactors and the inductance widely differ for different fabrication technologies. Hence, two VCOs were designed and integrated in the same CMOS 55-nm technology by using the same varactors. A "classical" VCO using an inductor available in the technology and serving as reference, and a distributed-inductance-based VCO using a slow-wave transmission line were considered. A detailed and efficient approach is adopted for the synthesis of slow-wave transmission line-based inductance without using time-consuming EM simulations. The slow-wave VCO permits to limit the overall size linked to a distributed approach while improving the electrical performance. The experimental results on the proof-of-concept demonstrators at a working frequency of 77 GHz allow validating our proposal.