1.6.1 Shielding and Grounding

• Shielding is important for all circuits, it prevents electrical noise from creating false digital signals, and from corrupting analog signals.

• Shielding is accomplished through a number of methods:

- sheet metal (iron) enclosures keep electromagnetic interference out, or in.

- shielded cables

- RF chokes

- bypass capacitors

• Cables can be shielded two different ways:

- twisted pairs - two wires that are used for a signal (signal and common) are twisted once per inch or more. As a result, any inductive magnetic field induces a current one way for one twist, and the other way for the next twist - hence cancelling out the induced current.

- shielding sheaths - cable bundles are often covered by a metal foil, or braided wire to provide a general protection for the cable. This shield is to be connected at one end (not two) of the cable to drain off any induced currents.