EMI Bites

EMC filters are critical for managing electromagnetic interference (EMI) in electronic designs, ensuring compliance and reliable performance.

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​𝐁𝐮𝐭 𝐚𝐫𝐞 𝐲𝐨𝐮 𝐮𝐬𝐢𝐧𝐠 𝐭𝐡𝐞 𝐫𝐢𝐠𝐡𝐭 𝐟𝐢𝐥𝐭𝐞𝐫 𝐭𝐨𝐩𝐨𝐥𝐨𝐠𝐲 𝐟𝐨𝐫 𝐲𝐨𝐮𝐫 𝐚𝐩𝐩𝐥𝐢𝐜𝐚𝐭𝐢𝐨𝐧?

To understand EMC filter design, it’s essential to differentiate it from traditional filter design, as used in applications like communication systems or audio processing. Traditional filters focus on precise signal shaping, with well-defined passbands, stopbands, and transition regions. EMC filters, instead, prioritize broadband noise suppression over precision.

My latest article, EMC Filter Topologies: "𝘌𝘔𝘐 𝘊𝘰𝘯𝘵𝘳𝘰𝘭 𝘚𝘵𝘳𝘢𝘵𝘦𝘨𝘪𝘦𝘴 𝘪𝘯 𝘌𝘭𝘦𝘤𝘵𝘳𝘰𝘯𝘪𝘤𝘴 𝘋𝘦𝘴𝘪𝘨𝘯", dives into five key EMC filter configurations, and their roles in emissions and susceptibility control.

EMI Bites: Uniform Instantaneous Impedance for Reflection-Free PCBs

A common PCB design flaw is varying trace widths or layout geometry, which alters the instantaneous impedance of a signal’s propagation path.

In a 50-ohm trace, any deviation from this characteristic impedance—due to inconsistent trace dimensions or layer changes—causes potential signal reflections.

These reflections can impair signal integrity, produce common mode currents, and escalate EMI, jeopardizing EMC compliance.

The solution?

A common PCB design oversight?

Ignoring how signal frequency shapes return currents, which can spike EMI and degrade signal integrity.

For high-speed signals, return currents follow the path of least impedance, staying directly under the trace where frequency-dependent inductance dominates.

For low-speed signals, the resistive part takes over, driving currents along the shortest path to close the loop back to the source.

Misjudging these paths can lead to larger loops, radiating EMI.

EMI Bites: A Common Mistake That Spikes EMI in PCBs

I often see a simple mistake during EMI reviews: long traces connecting pads in PCB designs add impedance, hurting signal integrity and boosting EMI.

These traces create large current loops that generate common mode currents—unwanted noise highly effective at radiating EMI.

The fix?

Place a via right next to the pad (or on it) to connect to the Return Reference Plane (RRP).