Which principle about cable layout helps minimize interference in mixed-signal runs?

• A. Keep data lines and power lines in the same trench to simplify routing.
• B. Route data lines close to power lines to minimize length differences.
• C. Keep data lines shielded only if adjacent to unshielded power lines.
• D. Keep data and power conductors physically separated and maintain adequate spacing.

Answer: (D)

Keep data paths physically separated from power conductors and maintain adequate spacing. This simple layout principle reduces the opportunities for interference to couple into the signal lines. When data lines run close to or alongside power lines, switching currents in the power conductors can induce noise in the data lines through capacitive and inductive coupling, and ground bounce from high-power traces can corrupt digital signals. By separating them and avoiding long parallel runs, you lower crosstalk, improve impedance control, and lessen radiated EMI, all of which help preserve signal integrity in mixed-signal systems.

The other ideas fall short because putting data and power in the same trench increases proximity and coupling, routing data lines near power lines tends to worsen interference rather than minimize it, and shielding should be planned as part of the overall layout rather than applied only when adjacent to unshielded power lines.