In Ethernet design, magnetics are an essential component, providing signal conditioning and protection for stable data transmission. The Ethernet specification actually mandates them. But why are they so important? Let’s check it out in detail today.

Based on what I know about Ethernet communication, magnetics are crucial in three main areas. First, they provide galvanic isolation, electrically isolating the Ethernet device from the cable to prevent voltage spikes, surges, and power transients from damaging sensitive electronics. This is important as two circuits driven by an ethernet cable can be very long. So there can be ground potential variations that get solved via isolation. Second, they aid in signal conditioning, as Ethernet relies on differential signaling that can be affected by noise and interference. Magnetics help filter out common-mode noise, reduce crosstalk, and balance the signal for more reliable transmission. Lastly, they contribute to EMI reduction, minimizing electromagnetic interference and ensuring clean, efficient data transmission over long cables.
Now Magnetics in Ethernet can be handled in two ways.
External/Discrete Magnetics: Here, magnetics are placed as discrete components on the PCB, external to the RJ45 connector. This meant more PCB space was used for the transformers and inductors. The good thing is that designers have more flexibility in choosing specific magnetics for their application.
Integrated Magnetics: These are RJ45 connectors with the magnetics built directly into the port. This saves board space, simplifies design, reduces signal routing issues, and helps improve reliability. It has better EMC shielding as it’s inside the Ethernet metal shield. The solution is usually as per standard specs and is slightly expensive but gets the job done.
Takeaway? Whether you choose external or integrated magnetics depends on your design needs. The key is to find the right balance between flexibility, space, and cost for your project.
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