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Digital Circuit Boards: Mach 1 GHz by Ralph Morrison

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5.14 Grounding as Applied to Electronic Hardware

In electronic hardware, a conducting plane is often called a ground. This is not a power industry term. In some analog designs (below 100 kHz), there may be several different grounds or reference conductors. These grounds or commons may or may not be directly earthed. In general, these conductors are used in the processing of non-power-related signals. When these reference conductors are inside of hardware, they are not controlled by the National Electrical Code (NEC). In commercial products, this grounding is controlled by UL or its equivalent. The terms signal common or signal reference conductor are preferred over the term ground.

A cell phone may have a conducting plane used as a return path for forward transmission. Obviously, this conductor is not grounded or earthed in any way. This plane is certainly not controlled by the NEC. These “grounds” control the flow of field energy within the device. In some ways, it is unfortunate that we use the same word to describe all of these different conducting surfaces. The semantics problem gets even more complicated when we add adjectives such as signal ground, digital ground, power ground and output ground, and safety ground. These adjectives have little effect on making a facility electrically quiet.

N.B.
Nature does not read the labels we place on conductors. She also does not read color codes.

The ground conductor used in a digital circuit is used as a current path (return path) ...

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