Switching-induced substrate noise and mixed-signal receiver design

We use a stochastic model of the switching current to describe the power spectral density of current noise waveforms induced by digital switching events. We discuss common impedance paths, particularly arising from non-ideal properties of electronic packages, that couple this noise into the substrate of an integrated circuit. We derive estimates of the noise spectrum for modest digital power and typical package characteristics and evaluate the noise in the context of RF mixed-signal designs. Common TQFP packages show significantly worse noise performance than BGA packages with low inductance substrate ground, and are less suitable for demanding applications. The adoption of differential design methods can eliminate this source of common-mode noise, at the expense of added power or higher noise figure.