Issue link: https://resources.pcb.cadence.com/i/1541046
20. Preventing Ground Loops and Unintentional Return Paths How To Implement 1. Map all intentional and possible ground connections: f Identify every planned ground connection: planes, chassis/earth, cable shields, connectors, mounting holes. f Trace possible alternative return paths, including mounting hardware, shielded enclosures, and power supply returns. 2. Establish a single, low-impedance ground reference: f Use a star or "single-point" ground connection between analog, digital, and power grounds whenever possible. f For multi-board or system designs, designate one ground reference at the main power supply or input, and prevent other chassis or cable shield returns from forming loops. 3. Tie cable shields to ground at only one end (unless system design dictates otherwise): f For signal cables, connect the shield to ground at the source end (typically chassis) and leave it floating at the device end to prevent loop currents. For some EMC-critical designs, both ends may be tied, but only with careful return path control. 4. Avoid running critical signals over slots, splits, or gaps in ground planes: f Maintain a continuous, unbroken return path directly beneath every signal, especially high-speed and sensitive analog traces. f Use stitching vias at every plane transition or where signals cross domains. 5. Isolate mounting holes and mechanical fasteners as needed: f If mounting hardware or enclosure is grounded, use insulating washers or non-plated holes to prevent unwanted ground return paths through the chassis. 6. Document ground domain boundaries and intent: f Mark analog, digital, chassis, and shield grounds clearly in the schematic and layout. Use net names and keepouts to prevent accidental copper "bridges." 7. Validate ground paths with both simulation and physical measurement: f Use circuit simulation, field analysis, or simple ohmmeter checks on prototypes to verify ground continuity and absence of loops. Common Pitfalls, Their Impact, and How to Avoid Them Common Pitfall How to Avoid it Allowing multiple low-impedance ground paths between boards or systems Causes unpredictable current flow and noise coupling – Use star topology for connecting multiple ground planes and via stitching across different layers. Tying cable shields at both ends without consideration Can create strong loop antennas and EMI problems – Check that grounds are at the same potential, otherwise ground at one end or use a hybrid (capacitive or ferrite) connection. Letting signals cross ground plane splits or gaps Increases noise susceptibility and radiated emissions – Keep signals over continuous reference planes or if crossing a split is unavoidable, add stitching vias next to the trace. Not isolating mechanical hardware from sensitive circuits Can inject or pick up noise uninten- tionally – Use insulating washers and keep sensitive circuits away from mounting holes.