-
High-speed digital signals:
Return currents follow the signal path tightly, hugging the lowest-impedance path, which is usually the directly adjacent ground plane under the trace (due to mutual inductance). -
Low-frequency analog signals:
Return currents don’t follow the signal trace directly. They spread out, and their path is influenced by impedance, loop area, and nearby capacitive/inductive elements. You can’t always assume a narrow, clean return like in digital signals. 🔧 Rule of thumb for analog: Keep return paths short and direct to the source. Avoid creating large loop areas, which makes the system susceptible to noise pickup.