How should the filtering of the communication port of the power measurement switch (PMS) be designed?

The filtering design for various communication ports of PMS (RS485, CAN, Ethernet, etc.) aims to suppress externally transmitted conducted interference and internally radiated noise while ensuring signal integrity. The design needs to be customized for the interface type. For differential buses such as RS485/CAN, the core of the filter is a common-mode inductor, such as the CML3225A-510T (51μH), whose low differential-mode impedance does not affect the signal, and high common-mode impedance suppresses noise. Small capacitors (such as 100pF) can be connected in parallel before and after the common-mode inductor to ground to form a low-pass filter, but attention must be paid to the effect of the capacitor on the signal edges. For high-speed interfaces such as Ethernet, RJ45 connectors with integrated filtering and protection (with transformer and common-mode choke) should be used. All filtering components should be placed close to the communication connector. On the PCB layout, the filter input and output traces should be separated to avoid coupling. At the same time, good decoupling should be provided for the transceiver power pins (0.1μF ceramic capacitors should be placed nearby). The filtering effect can be verified by measuring conducted emissions (CE) at the port, with the goal of suppressing noise from 150kHz to 30MHz below the limits of EN 55032 Class B.