SLLU149E June 2011 – February 2016 TUSB7320 , TUSB7340
High frequency return signal/current is defined as the path that a signal follows back to its original source as all signals flow in a closed loop. Minimizing the loop area of the closed loop is beneficial for both EMI (Electro-Magnetic Interference) reduction and signal integrity.
The best way to minimize loop area is to always have a signal reference their nearest solid ground or power plane. Obstructions to the return signal will cause signal integrity problems like reflections, crosstalk, undershoot and overshoot.
Signals can reference either power or ground planes, but ground is preferred. Without solid plane references, single ended and differential impedance control is very hard to accomplish; crosstalk to other signals may happen as the return signals will have no other path. This type of crosstalk is difficult to troubleshoot.
Symmetric pairing of solid planes in the layer stackup can significantly reduce warping of the PCB during the manufacturing process. Warping of the PCB is crucial to minimize on boards that utilize BGA components.