So exactly what makes a PCB design a high speed design? Sure it’s about things happening quickly, but it’s not just about the clock rate used on the board. A design is a high speed design when it includes devices with fast edges, devices that switch state so quickly that the transition is complete before the signal can travel along the route and reach the target pin. In this situation the signal can be reflected back to the source pin, degrading or destroying the original signal data.

 

A signal with a fast edge can also radiate from the route and couple into adjacent routes, or radiate further and become electromagnetic interference (EMI), resulting in the product failing to meet mandatory emission standards.