Ethernet ports on routers rely heavily on specialized components called LAN transformers (also known as Ethernet magnetics or network transformers). These small modules, typically integrated directly onto the router's PCB near the RJ45 connectors, perform several critical functions essential for reliable network communication.
The most common configurations include single-port (1x1) and multi-port (e.g., 1x2, 2x2) LAN transformers, designed to meet standards like 10/100BASE-TX and Gigabit 1000BASE-T. Key manufacturers like Pulse Electronics (now part of Yageo), Bourns, Halo Electronics (Microchip), and TDK offer widely used models. These transformers provide vital electrical isolation (typically 1500V AC or more) between the router's sensitive internal circuitry and the external Ethernet cable, protecting against voltage surges and ground loops.
Furthermore, LAN transformers ensure proper signal coupling, impedance matching (to the 100-ohm differential line), and significantly reduce electromagnetic interference (EMI) both emitted by the router and received from the environment. They incorporate common-mode chokes to suppress noise. While surface-mount (SMT) packages are now dominant for modern router designs, some legacy or specialized units might still use through-hole types. Choosing the right LAN transformer is crucial for signal integrity, compliance with EMI regulations, and overall port reliability in any router design.
