Power Plane Filter Using Higher Order Virtual Ground Fence

Abstract

The virtual ground fence (VGF) has been recently proposed to filter power plane noise in gigahertz frequency range. The VGF has distinct advantages over existing approaches, such as power islands and electromagnetic bandgap structures: The IR drop is not increased; transmission-line return-path discontinuities can be avoided; and the design procedure is simple. The basic VGF is created by using quarter-wave resonators referenced to the power or the ground plane. At the design frequency, the resonator creates an ac short circuit between the power and ground planes. An array of such resonators can be placed in electrically short intervals to create a VGF. Power plane noise will then ideally be shorted to ground at the location of the VGF. The operation principle is similar to the series resonance of a decoupling capacitor, which is usually ineffective in the gigahertz frequency range. This paper proposes a new design procedure for determining the number of quarter-wave resonators needed, their characteristic impedances, and their placement on the board. The design approach is based on the well-known insertion loss method in microwave filter theory, which allows for higher order VGF designs consisting of multiple rows of resonators.