The Facts of Resonance and Effects of Decoupling Capacitors in Printed Circuit Board

In this study, the phenomenon of resonance due to the finite size printed circuit board is presented. This paper also illustrates a systematic scheme that can determine suitable locations to place decoupling capacitors by using a commercial electromagnetic solver, SPEED2000. In order to find proper locations to place decoupling capacitors, we first connected a Gaussian pulse in between power and ground pins. The spatial distribution between power and ground planes is shown in a SPEED2000 window. Adding the decoupling capacitors in the location corresponding to the higher voltage difference between power and ground planes, the power and ground noise will be reduced and the resultant structure has a better characteristic of signal integrity. The effect of decoupling capacitor in power/ground bounce reduction and resonance frequency shifting is presented in this study. To present the significance of decoupling capacitors, the behavior model, I/O Buffer Information Specification (IBIS), was linked to the board. The results of simulation show that the waveforms of receiver suffering from the simultaneous switching noise are improved considerably after systematically placing the decoupling capacitors.