Return Vias, Buildup Layers and the Latest FPGAs

摘要

WHERE SIGNALS NEED return vias, component vendors often do most of the work. Let's look at a PCI Express differential pair, starting with a standard connector, showing its pinout but not its body. (I'll cover the connector body in a moment.) The signal pin assignments are also standardized. FIGURE 1 shows a through-pin component. The two sides of the differential pair (marked P and N) are close to ground pins. There's some differential coupling between the P and N pins, and the ground pins create returns in the Z dimension, just like ground planes do for traces.