EMI Bites

Return currents in PCB designs are often misunderstood, yet they play a critical role in electromagnetic compatibility (EMC) and signal integrity, especially across low and high-speed signals.

Are you optimizing your layouts for these currents, or are hidden issues increasing EMI risks?

Our latest article, Effective Strategies for Managing EMI in PCBs with Low and High-Speed Signal Return Currents, explores how frequency impacts return currents and provides practical guidance for robust PCB design.

It reveals how to control return paths to minimize EMI and ensure reliable performance, whether you’re designing for low-frequency circuits or high-speed applications.

Why Read This?

A common PCB design mistake?

Placing components like the crystal oscillators too far from the pins they feed.

Crystal clock signals, with sharp edges, carry high-energy harmonics.

When traces are long, these harmonics can couple to nearby signals or the power net, spreading interference across or beyond the board, causing EMI issues.

The solution: position crystals as close as possible to their pins to shorten traces and minimize coupling risks.

Grounded? Think Again for EMI Control

A frequent design error causes electronics to fail EMC tests: pigtail connections between shielded cables and chassis.

Many assume grounding the shield prevents EMI, thinking, “Isn’t the shield now grounded?” Not exactly.

A single-point, high-impedance connection disrupts the Faraday cage effect intended to contain common mode currents.

This allows currents to escape as emissions or makes circuits susceptible to external interference, such as ESD (watch for my upcoming guide).

If you're using both layers for signals without a dedicated return and reference plane (RRP), you're very likely headed for EMC test failure.

Why?

Because radiated emissions from differential mode currents—that is, your normal operating current—are proportional to the area of the current loop.

Bigger current loop → bigger enclosed area → bigger emissions → bigger chance of failing EMC.

Are there exceptions that pass?