Grounding and shielding to reduce PCB noise

Role of grounding: a solid ground (preferably a ground plane in a PCB) gives a low-impedance, short return path for every signal, which reduces the loop area, common-impedance coupling and ground bounce. Separate analog, digital and power grounds, joined at one point, prevent noisy currents from flowing through sensitive circuits. Ground fill around traces and guard traces reduces crosstalk.

Role of shielding: shielding blocks the electric, magnetic or radiated fields between noise source and victim. On a PCB, a metal can or enclosure placed over a noisy (oscillator, switching regulator) or sensitive (RF, low-level analog) section, a ground guard ring with stitched vias, and shielded cables for off-board signals prevent noise emission and pickup. A shield must be connected to ground to be effective (electrostatic shield).

Together, grounding gives the correct return path and reference, while shielding keeps external and internal fields from coupling; the result is lower EMI and noise in the PCB.