You can’t wave a wand and magically cure conduction noise… But you can find the cause and countermeasures! (Part 1)

Hello, everyone. I’m Akatani, a manager for EMI test & solution service.

Today, I would like to talk a little bit about conducted emission suppression, which many of you might have struggled with during product development.

There are two types of transmission paths for noise. One is the emission radiated directly from a noise source into the air. And another is the emission conducted through electric conductors such as PCB wirings , cables and cases.

Although radiated emission and conducted emission are closely related, today’s discussion will focus on conducted emission.

Conducted emission is measured by an EMI receiver or similar equipment via a Line Impedance Stabilization Network (LISN), which extracts noise components superimposed on a EUT’s (Equipment under test) power cable.

There are two types of LISN; one is V-type LISN which detect both differential mode noise and common mode noise at a time, another is Δ-type LISN which can detect them separately. V-type LISN is often used as a standardized measurement method for conducted emission, while Δ-type LISN can be an extremely effective tool during EMI suppression measures.

By the way, you may often hear the term “Mains Terminal Interference Voltage”. In this case, it generally means the measurement is done by a V-type LISN.

We have both V-type LISN and Δ-type LISN, and when you use our anechoic chamber rental service, you can also use them.



The left side of the photo is a V-type LISN and the right side is a Δ-type LISN.

I’m sorry to start off with a long introduction. It’s time to get to the point.

At a product design stage, you surely keep in mind EMI suppression and reflect some measures to your design like these,

  • Signal patterns acting as noise source should be compact as much as possible.
  • Put EMI filters close to an input and output of a power supply in order to confines noise energy to as small an area as possible.
  • Provide a firm ground plane on a PCB to make wirings functioning as micro-strip lines especially for a wiring acting as noise source. (Unless you use a multi-layer PCB, it might be difficult to provide a ground plane, though.)
  • To prevent harmonic components generates, blunt the edges of signals which can be noise source. (Be careful not to increase switching losses in a power supply.)
  • Bond a surface ground of a PCB and an inner layer ground by multiple via holes in order to strengthen the ground effect.
  • Employ shielding to noise source.

Many of you know these things and reflect them to the design. Despite all those efforts, you often cannot meet a standard requirement for conducted and radiated emission.

That’s it for today and in the next blog, we’ll tell you why that happens! Please continue to enjoy next article with case studies.

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