8

Delta I-Noise

The noise caused by the switching of digital devices on PCB power and ground distribution networks is presented in this chapter. This impulsive voltage noise is referred to as ΔI-noise. The importance of using decoupling capacitors for current switching demand of ICs and for lowering the impedance of the power distribution network is introduced and discussed. The path of the impulsive switching current is analyzed for a typical PCB. The noise produced on power and ground distribution by the switching current of a typical high-speed CMOS device is simulated for stripline and microstrip power and ground distribution networks, taking into account the inductance associated with the lead of the components present in a PCB. Main design rules are given and discussed.

The contribution given by the interplane capacitance between power and ground planes in a multilayer PCB and the action of decoupling capacitors to mitigate ΔI-noise are investigated analytically, experimentally, and by means of circuit simulations. The resonances produced by a multilayer PCB are investigated. Three models for predicting impedances and resonance frequencies in a pair of power and ground planes populated by decoupling capacitors are outlined and validated in Appendix C. These three models are based on: a set of closed-form expressions for a resonant cavity, an equivalent circuit consisting of a grid of lumped elements, and a 3D structure used as input for numerical simulations. Measurements ...

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