Design007 Magazine


Issue link:

Contents of this Issue


Page 32 of 65

November 2016 • The PCB Design Magazine 33 VIAS, MODELLING, AND SIGNAL INTEGRITY Now, back to vias. I always like to look at subjects in an alternate way, as presenting the information in an unconventional method forces you to think a little more. In this case, the thoughts should become easier. Imagine for a start that the board is not 63 mils thick, but 6 inches thick. Then turn the board vertically in your mind so you send the signal "along" your imaginary via. What does it experience? Well, whilst the signal path may be a cylin- der (or maybe a cylinder with fins if you have left non-functional pads on the via) and be a reasonable outbound path, the return path for a single-ended via is far from straightforward. The now horizontal (in your mind) via will traverse over a series of power and ground plane edges interspersed with insulators. What on earth is the return current going to do now? Think back to the simple microstrip example where I posed the question of a slot in the plane: it forms a slot antenna. The same is true here, and there are as many slot antennae as signal/ Figure 3: Energy continues to propagate until… Figure 5: Without a return via the return current will attempt to radiate between the planes. Figure 4: …Until meeting a slot in the return path (3), which causes energy to radiate (4).

Articles in this issue

Archives of this issue

view archives of Design007 Magazine - PCBD-Nov2016