
Signal lines placed close to or parallel to crystal oscillator and clock traces are highly susceptible to capacitive coupling interference from the clock frequency and its harmonics. Crystal oscillator circuits carry high-frequency square waves with strong electric field radiation, which can pick up noise through parasitic capacitance on nearby analog sampling lines, high-impedance input lines, or reset lines, affecting circuit performance. Mitigation measures include defining an isolation zone for the crystal oscillator circuit during PCB layout, maintaining a complete ground plane underneath and surrounding it with traces. Ensure all sensitive signal lines maintain a distance of at least 3-5 times the trace width from crystal oscillator and clock lines, and avoid long parallel traces. Clock lines themselves should be as short as possible and surrounded by ground plane to limit their radiation.