The Influence of Ethernet Transformer Connection Method on System Common-Mode Radiation

With the popularity of Ethernet, unshielded twisted pair (UTP) cables are widely used for data transmission. The common-mode (CM) noise generated in the printed circuit board (PCB) circuit is easily radiated into the space through the UTP cable, causing radiation interference. At the Ethernet port, it is the most effective and feasible way to suppress the noise entering the UTP cable from the PCB. This article takes the conventional voltage-driven PHY network port circuit as the research object. Through the analysis of the common-mode choke (CMC) and the center-tapped transformer inside the Ethernet transformer, the connection method of the Ethernet transformer is changed to achieve the optimal suppression of the CM current. This research further optimizes the filtering performance of the network port circuit without adding additional circuit components and ensuring the stable operation of the system, which has a good reference significance for the design of the Ethernet network port circuit.