Virtual ground fence options for shielding power plane noise

This paper demonstrates possible design approaches for the virtual ground fence, a novel design concept for shielding power plane noise. The basic idea of a virtual ground fence is replacing discrete capacitors with quarter-wave stubs. This allows decoupling of power plane noise in the GHz spectrum. Such noise filtering is critical in a mixed-signal system, where there is switching noise generated by the digital VLSI. This noise easily propagates to the sensitive RF IC if not filtered. The virtual ground fence consists of quarter-wave transmission-line stubs that act as short circuits at their design frequency. An array of such stubs can then be considered as a ground fence. Hence the power plane of the RF IC is effectively placed inside a Faraday cage, and isolated from the noise in the environment. Controlling noise enables designing faster and smaller electronic systems.