100BASE-T1 Ethernet EMI: Keeping Differential Symmetry to Limit Common-Mode Noise

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100BASE-T1 is a single-pair Ethernet technology delivering 100 Mbit/s over one balanced twisted pair, suited to robots, vehicles, and distributed sensor systems where cable weight and packaging matter. Because transmit and receive share the same conductors, impedance discontinuities, imbalances, parasitic capacitance, and layout errors can degrade both signal integrity and EMC. The article stresses preserving electrical symmetry along the whole path from PHY pins through PCB traces, coupling networks, connectors, and cable to the remote node, since asymmetry converts differential energy into common-mode current that radiates and increases susceptibility. It recommends controlled differential impedance, continuous reference planes, matched component values, and careful placement of common-mode chokes near the media interface, with connector and shield termination also affecting overall EMC performance.

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