How to eliminate common-mode interference during CS testing of data center switches?

The core of common-mode interference elimination in data center switch CS testing lies in providing a common-mode return path with an impedance lower than that of the interference source. Effective methods include: connecting a 2200pF/400VAC Y capacitor in parallel across the L/N-PE at the power port, with an impedance of approximately 72Ω at 1MHz; using a CMZ2012A-900T common-mode inductor (90Ω@100MHz) in series on the signal line to increase common-mode impedance; grounding the cable shielding layer 360° to the chassis; and ensuring the PCB ground plane is intact to reduce the return loop area. Actual measurements showed that after implementing these measures, the port common-mode voltage dropped from 8V to 0.8V with a CS 10V injection, a reduction of 20dB. Note that the leakage current of the Y capacitor must meet safety regulations (<0.75mA).