How to perform interference-resistant cabling for industrial servo differential signals?

Servo differential signals (such as encoder A+/A-, CANH/CANL) have a natural ability to suppress common-mode interference, but improper routing can reduce their effectiveness. Key points for interference suppression routing by Etymotic: Differential pairs must be strictly equal in length, equidistant, and tightly coupled in parallel, with a constant spacing (usually twice the line width) to maintain impedance consistency. The routing should reference a complete ground plane, avoiding crossing splits. At connector entry and exit points, differential pairs should be placed adjacent to each other, with additional grounding pins on both sides if necessary.

For long-distance transmission (>10cm), a matching resistor (typically 120Ω) should be connected in parallel at the differential pair termination and placed close to the receiving end. To enhance interference immunity, a common-mode choke (such as CML3225A-510T) can be connected in series on the differential lines, and an ESD protection device (such as ESDSM712 for RS485) can be connected in parallel to ground on the lines. Following these routing rules can reduce the impact of external common-mode interference on differential signals by more than 25dB, ensuring signal reliability in noisy industrial environments.