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Digital Circuit Boards: Mach 1 GHz by Ralph Morrison

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5.15 Internal Grounding of a Digital Circuit Board

A question that is often asked is, where should a digital ground plane be connected (grounded) to the hardware housing? The first observation is that a metal enclosure plays a small role in controlling the fields associated with the logic. This control exists entirely with the logic ground plane and the routing of traces. It is still a good idea to connect the enclosure to the circuit ground plane, as allowing it to float raises all sorts of new issues. This connection should be made to limit equipment ground currents from flowing in the ground plane of the circuit board. This can be done by connecting the housing to the circuit common, where the secondary of the power transformer connects to the circuit board ground plane. This practice is shown in Figure 5.5.

Figure 5.5 Grounding a housing to a circuit board.

5.5
N.B.
Grounding a circuit board does not attenuate the fields that might exist near the circuit board. The ground connection might change the field configuration in areas near the connection. Multiple grounding of a circuit board ground plane to the housing is not recommended, as it invites interference currents to flow in common conductors on the board.
N.B.
When practical, board connectors should be located in one area of a board. This keeps interference currents that flow in cable shields from flowing across the ...

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