Differential inductor design incorporating multiple Q-enhancement techniques and expanded physical model

Poor inductor Q values leading to sub-standard circuit performance has motivated investigation into non-invasive, process independent, Q improvement techniques. This paper presents the first combination of three techniques in the form of a symmetric differentially driven stacked inductor with an underlying patterned ground shield. It shows that stacking a differential inductor can lead to an increase in Q or more than 40% and that the effectiveness of a patterned ground shield requires prior knowledge of substrate resistance. Novel prediction graphs are presented which provide the designer with a method of ascertaining the viability of patterned ground shields for different processes, prior to fabrication. A new physical model is also presented which emphasises the complexity of stacked inductors. Both the physically based prediction graphs and physical model match very well with measured results.