EMI resulting from a signal via transition through DC power bus-effectiveness of focal SMT decoupling

Signal vias are commonly used in multilayer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current has to jump from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in power bus noise, and can produce an EMI problem as well. Numerical methods, such as finite-difference time-domain (FDTD), moment methods (MoM), and partial element equivalent circuit (PEEC), were employed herein to study this problem. The modeled results were supported by the measurements. In addition, the EMI mitigation approach of adding decoupling capacitors was investigated with the FDTD method.