Eliminating EMI Through ShieldingOne of the most common approaches to dealing with this pesky foe is to use some type of shield in your connector/cable system. Contrary to popular belief, a board-to-board connector shield is not designed to shield the contacts from radiating noise. Instead, the shield minimizes the noise voltage between ground planes. These shields often take the form of ground pins surrounding the high speed pins. At high frequencies, ground connections are not electrical shorts, rather they can act as inductors. These can develop a small noise voltage across the boards, creating problems. Hence, shielding is necessary. For cabled systems, requirements can be slightly different. Key elements of a shielded cable include cable braiding, separable interfaces, and circumferential mating to the chassis. The shielding performance of the cable is only as good as its weakest link. For this reason, it is crucial that all three of these methods are implemented correctly.
EMI and SamtecIn the connector/cable industry, many manufacturers may offer what is known as “psychological shielding.” Unfortunately, most of the time, this proves to be just what it sounds like — psychological. True, there may be a shiny piece of metal surrounding your connector, and yes that cable you have been eyeing up may have ferrite beads, but what are these really good for? At Samtec, protection against EMI is important to us. Working both in-house at our Harrisburg Design Center and through various partners, Samtec tests its connectors and cables using methods such as:
- Raw cable shielding tests
- HFSS Shielding Performance
- TRP Simulation Models
- Shielding Room/Dual Reverb Chambers (see photo)