By creating one solid ground plane around power and signal traces, a low impedance shield is created to protect against noise. All boards in this app note were four-layer PCBs. Ground pours were created around power and signal traces on every layer, with one middle layer being entirely ground plane with no power or signal traces. This prevents unwanted interference from both entering and leaving sensitive areas of the circuit due to a decreased return-path resistance. Note that when flooding the ground planes, do not use thermal reliefs. Flood over all same net holes and vias.