Designing of high-Q slow-wave coplanar strips for CMOS MMICs

In contrast to conventional coplanar transmission lines, slow-wave coplanar transmission lines offer higher quality factor and smaller on-chip area. Among coplanar transmission lines, coplanar strips have the advantage of higher level of integration and a balanced structure that has favourable features for integrated voltage controlled oscillators (VCO) and low noise and power amplifiers. In this article, the affect of geometrical dimensions of slow-wave coplanar strips on the quality factor, characteristic impedance, and on-chip wavelength are investigated. Based on the presented guidelines mm-wave slow-wave coplanar strips operating at 60 GHz in a standard CMOS process were optimised for a 50 Ω characteristic impedance with a 250% improvement in quality factor of 31.