Reading time ( words)
I recently spoke with Ken Wyatt, founder of Wyatt Technical Services and an expert on signal integrity and EMC. I asked him to discuss his AltiumLive 2022 presentation, which focuses on reducing EMI, particularly in the wireless arena, where self-generated emissions are often a fact of life. Ken also explains how mistakes early in the design cycle can lead to EMI problems later, especially if the stackup is not designed with EMC in mind.
Andy Shaughnessy: How’s it going, Ken?
Ken Wyatt: Well, it’s going great here in Colorado. We’ve got wonderful weather and just snowed a couple days ago. But the sun is out and we’re doing well, and I’m working on several presentations for this quarter.
Shaughnessy: Well, I understand you have a presentation for AltiumLive. Why don’t you tell us about it?
Wyatt: Sure. Seems like the past five years or so, I’ve been working with a number of clients who are trying to incorporate wireless into their new or existing products. A lot of these clients are also not only incorporating things like Wi-Fi and GPS, but cellular LTE in particular. And they are finding out about the challenges of self-generated EMI coming from various energy sources on their circuit boards, affecting the receiver sensitivity.
If they’re using cellular, the cellular providers require a certain sensitivity before the company’s products are allowed onto their system. And this self-generated EMI is causing such a receiver desense that a lot of these products don’t comply with the sensitivity requirements. I’ll be talking about that, in general, and then we’ll be identifying some of these energy sources that are typically on the circuit boards.
Shaughnessy: So, when you say “self-generated,” then you’re basically saying it’s a self-inflicted wound, right?
Wyatt: That’s one way to put it.
Shaughnessy: I mean, this is something you have some control over, theoretically.
Wyatt: Yes, but this issue of internal, self-generated EMI is kind of a new one for a lot of designers. It turns out that it’s more often the broadband energy sources, like processors and memory buses, DC-to-DC converters, and narrow band sources like USB or ethernet clocks, which can encroach into the receiver pass band on these wireless receivers.
I discuss how to quiet these sources and some of the mitigations. In particular, it turns out that DC-to-DC converters really seem to be the dominant energy source so we’re going to be talking a whole lot about how to quiet those. And because the converters today are running between 1-3 MHz switching speeds they have very fast edges. And most of them have some amount of ringing. And so we’ll be looking at how to deal with this, as well as circuit board design. There is a component of circuit board design in the talk, and we’ll be talking about stackups and proper layout techniques to ensure your circuit board design itself is reduced for EMI and internal couplings.
Shaughnessy: Right. So when you’re dealing with wireless, you’ve got to have the board stackup and all the basic stuff, so to speak, set right.
Wyatt: Yes. When you’re dealing with multiple technologies, like audio, digital, and RF on the same board, you really can’t make any dumb mistakes. So many engineers don’t understand how important stackup is on your board and we’ll be talking about that. The last half of the presentation will be all about DC-to-DC converters and how to characterize and mitigate them in various ways. We’ll be presenting our Top 10 Tips for reducing EMI from DC-to-DC converters which, I think, will be an interesting segment of the presentation.
Shaughnessy: That’s good. I know the designers love Top 10s. I guess because they’re very graphically oriented. They love snapshots like that, things they can easily remember.
Wyatt: Well, a lot of these techniques are not original, but some of them might be new information. Between my local wireless compliance test lab and me, we’ve developed some rather unique ways of identifying which DC-to-DC converters are coupling into the receiver. This has been a good experiment, so I’ll be talking all about that.
Shaughnessy: It’s like some of the simplest parts of board layout can end up causing you exponentially more trouble if you’re dealing with wireless.
Wyatt: Yes. Wireless is really a whole different animal. And you’ve got sensitive receivers and you’ve got very strong energy sources on the same board. And it’s a challenge for any designer trying to incorporate wireless. So, that’s really what the talk is all about.
Shaughnessy: What would be some advice you’d give a young engineer or somebody just now getting into wireless?
Wyatt: Well, you have to understand how signals propagate in circuit boards. That’s probably the biggest takeaway for a lot of engineers. And when you understand how signals propagate, that dictates the stackup. And once you get the stackup correct, then it’s a matter of just partitioning out where the RF section is, the digital sections, and any audio or video.
One of the case studies we’ll be looking at is a wearable device with video and some experiments I did on it using one of the mitigation techniques. So, that’ll be part of the talk. But I think the biggest takeaway or lesson to be learned is you’ve got to understand how signals propagate. And, fortunately, we have a couple other great speakers on the program, Dan Beaker and Rick Hartley, who will go into much more detail on circuit board design for low EMI.
Shaughnessy: Is there anything else you want to mention? Anything we haven’t talked about?
Wyatt: I think that about covers it.
Shaughnessy: Great. Thanks for speaking with me.
Wyatt: Thank you, Andy.
Watch Kenneth Wyatt's presentation "Characterizing & Troubleshooting Wireless and IoT Self-Generated EMI" below.