Power and ground-reference plane impedance determination as decoupling capacitor distance increases

Power and ground-reference plane analysis traditionally has focused on the overall printed circuit board and the resonances that result from the physical size of the parallel planes. However, from a functionality point of view, the rapid impedance switching within typical ICs require a fast response in the current to the power pins of the IC. This is a local effect, since the loop inductance associated with currents from far corners of the board will be too high to provide this rapid current response. This effort characterized the impedance to this rapid current response seen by the IC power pin as the distance to the decoupling capacitor is increased, as the number of decoupling capacitors is varied, and as the diameter of the via is varied. The closest decoupling capacitor has the greatest effect on this rapid current response and dominates the response time for the IC current. This impedance can then be used to find the amount of noise voltage created locally at the IC power pins, and which can create EMI emissions.