Evaluating Class Two Permissive Change Triggers for Encapsulated Modules
Class Two Permissive Changes are triggered when physical, antenna, or firmware modifications alter RF emissions or RF exposure without exceeding original grant limits.
Ground Plane Return Paths
Meaning
Electrical circuit routes for the return of current to its source determine the electromagnetic compatibility and signal integrity of a printed circuit board. Ground plane return paths follow the route of least impedance, which often mirrors the signal trace on the adjacent layer at high frequencies. Any interruption in this route causes radiation and noise.
Impedance Control
The continuity of the reference plane ensures that the characteristic impedance of the transmission line remains stable. Ground plane return paths that are narrow or winding introduce inductance that degrades the signal.
Noise Mitigation
Stray currents moving through unintended areas of the board create electromagnetic interference. Well defined ground plane return paths confine the electromagnetic fields between the signal trace and the copper. This confinement protects sensitive analog components from digital switching noise.
Designers avoid placing slots or holes in the ground layer directly beneath high speed traces to ensure the return current does not have to diverge.
Via Placement
Stitching vias connect different layers to provide a low resistance route for the current. When signals transition between layers, ground plane return paths must jump as well. Placing a ground via near the signal via maintains the loop area at a minimum.