Spiral Inductors With Floating Low-Loss RF Shields for <inline-formula> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> Resonator Applications

Abstract

A method for designing $LC$ tank circuits to improve energy efficiency and reduce layout area is described. The approach uses a projected shield that is floating, overlaps the trace of the overlying inductor, and adds capacitance to the tank’s inductor. Capacitance is distributed along the spiral traces, and the layout area is thus decreased. In this paper, we investigate the properties of spiral inductors with and without projected shielding, and compare the method with similar circuits including those with floating shields shaped as patterned ground shields. In addition, a measurement methodology for $LC$ tank resonators is developed and presented. Test structures are implemented as microstrip spiral inductors and evaluated as $LC$ tank circuits that resonate between 100 and 500 MHz. The $Q$ values of shielded structures are up to 7% greater than those without shields, and area savings for $LC$ resonators—compared with side-by-side layouts of $L$ and $C$ —are up to 35%.