Datasheet

V
+
GND
SIGNAL IN
RETURN PATH
V
+
GND
LMH6559
www.ti.com SNOSA57C –APRIL 2003–REVISED MARCH 2013
Figure 51.
In this arrangement the power lines have been routed in order to avoid ground loops and to minimize sensitivity
to noise etc. The same technique is valid when routing a high frequent signal over a board which has no ground
plane. In that case is it good practice to route the high frequency signal alongside a ground trace. A still better
way to create a pcb carrying high frequency signals is to use a pcb with a ground plane or planes.
Discontinuities In A Ground Plane
A ground plane with traces routed over this plane results in the build up of an electric field between the trace and
the ground plane as seen in Figure 48. This field is build up over the entire routing of the trace. For the highest
performance the ground plane should not be interrupted because to do so will cause the field lines to follow a
roundabout path. In Figure 52 it was necessary to interrupt the ground plane with a crossing trace. This
interruption causes the return current to follow a longer route than the signal path follows to overcome the
discontinuity.
Figure 52.
If needed it is possible to bypass the interruption with traces that are parallel to the signal trace in order to reduce
the negative effects of the discontinuity in the ground plane. In doing so, the current in the ground plane closely
follows the signal trace on the return path as can be seen in Figure 53. Care must be taken not to place too
many traces in the ground plane or the ground plane effectively vanishes such that even bypasses are
unsuccessful in reducing negative effects.
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