How to eliminate common-mode interference in I/O modules?

The key to eliminating common-mode interference from I/O modules lies in blocking its flow path and reducing its amplitude. First, common-mode chokes, such as the CML4532A-510T or CMZ3225A-510T, must be used at all external interfaces, including power, communication, and signal ports. These devices present high impedance to common-mode noise, effectively suppressing its input or output to the module. Second, safety Y capacitors should be added at the ports to short-circuit common-mode noise to chassis ground or protective ground. For floating ground systems, a high-voltage ceramic capacitor or varistor should be connected between signal ground and chassis ground to provide a discharge path for high-frequency noise. Inside the module, sensitive circuits such as AI or communication interfaces should be powered by isolated power supplies, such as DC-DC isolation modules, to cut off the conduction loop of common-mode current. In PCB design, a complete ground plane should be provided, ensuring that the grounding pins of all interface filters are connected to this ground plane with the shortest path, forming a low-impedance noise return path. For common-mode interference introduced by long cables, common-mode ferrite cores can be used at the cable entry point for additional suppression.