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Technical articles on electronics, EMC and PCB design.
EMC
1. Introduction – why a small change can make great differences in the plot Did this happen to you. You go to the testing lab. you do a full RE scan and the scan looks great. Then you - Rotate the EUT 90° - Lift a cable - Move the EUT by 20 cm - Change cable routing And the emissions plot change
Francesco Poderico · · 3 min read
EMC
When I debug EMC problems on a DC/DC converter, I use a very simple test to understand whether the dominant mechanism is Differential Mode (DM) or Common Mode (CM). The test is simple: I increase the load and observe what happens to the emissions. If: - The peak frequencies stay the same,
Francesco Poderico · · 3 min read
EMC
Introduction In switch‑mode DC‑DC converters, not all currents are equal from an EMC, signal integrity, or reliability perspective. A critical distinction must be made between low di/dt current paths and high di/dt current paths. Misidentifying these paths is one of the most common root c
Francesco Poderico · · 4 min read
Electronics
Optocouplers are widely used in isolated power supplies to transfer feedback information across an isolation barrier. In schematics, they appear as a clean and robust solution: no galvanic connection, clear separation between primary and secondary, and good noise immunity. In practice, optocouplers
Francesco Poderico · · 3 min read
EMC
This is one of the most common layout mistakes I see during EMC reviews. The schematic is correct.The common-mode choke is correctly placed at the interface. But the PCB layout shows a solid ground plane directly underneath the choke. Imagine a GND plane below the chocke. The intention is usua
Francesco Poderico · · 3 min read
EMC
Introduction When I develop a new product, I usually already have a good idea which EMC test is more likely to cause problems. Based on my experience, I decide which test to run first. That may seems excessive, but believe me, you may save a lot of time and money by choosing in which orders y
Francesco Poderico · · 5 min read
EMC
Pre-compliance vs full compliance (and why it matters more than you think) Look, I'm just going to say it: Radiated Emissions (RE) and Conducted Emissions (CE) are the two EMC tests that'll tell you almost everything you need to know about your product. Think of them like getting an X-ray. On
Francesco Poderico · · 2 min read
EMC
How This Article Started I was reviewing a design for a customer a while back, and they had this active capacitor circuit being used as an EMI filter. My customer looked at the schematic and asked me, "Francesco, what is this?" I couldn't help myself – I smiled and said, "That's a 1 Farad capacit
Francesco Poderico · · 4 min read
EMC
In around 90% of CE (Conducted Emission) issues on the mains input, the solution is simple: just add a common-mode (CM) filter.Most of the time, I use Würth Elektronik filters — they’re reliable and predictable. However, every once in a while, something strange happens.Instead of reduci
Francesco Poderico · · 3 min read
EMC
If you are an electronic designer engineer you may want to read this article.... Surge and transient immunity testing often reveals weaknesses that are hard to predict during design. In one of my recent EMC test sessions, I encountered a case that perfectly illustrates why component-level surge r
Francesco Poderico · · 4 min read
Electronics
Introduction Varistors (typically MOVs) are widely used on mains lines for surge / transient protection. Under normal conditions they are passive, but when high‐voltage transients (switching surges, lightning induced, line overvoltage) occur, the varistor conducts, clamps the voltage and absorb
Francesco Poderico · · 2 min read
EMC
Today I want to talk about how apparently short PCB tracks can still create big EMC problems—especially when they carry a clock in the 20–30 MHz range. A very common setup You’ve got a clock source (XO or MCU clock out) driving something like a USB/Ethernet transceiver or an SPI flash
Francesco Poderico · · 3 min read
EMC
What I’m trying to show you today is counterintuitive. If you’re failing radiated emissions around 200–230 MHz by just 3–4 dB, there’s a simple way to flip that fail → pass: increase your clock frequency. Yes— increase it. Before we get there, please grasp one key point about
Francesco Poderico · · 4 min read
PCB
Scope: Why some products show broadband radiated emissions from 30 MHz–1 GHz, why issues often persist up to 400 MHz–1 GHz even on multilayer boards, and how to prove and fix the root cause fast. 1) What “broadband” really means in RE On the plot, broadband looks like a wide hum
Francesco Poderico · · 4 min read
EMC
Scope: How to read narrowband features on the RE plot (100–1000 MHz is where they often pop up) and trace them back to clocks, harmonics, and reflections. Part 3 will cover semi‑narrowband and broadband cases. 1) Two spectral families to watch - Narrowband rows: tall, thin lines at disc
Francesco Poderico · · 3 min read
EMC
Goal: Use the radiated emissions (RE) plot to quickly identify the likely noise source and prove it with simple, low‑risk tests. 1) Start by slicing the spectrum When you receive an RE plot from the test lab, don’t stare at the whole thing at once. Break it into three working bands: - 30–15
Francesco Poderico · · 4 min read
PCB
Thermal-relief “spokes” help solderability, but they add inductance and cut slots in your reference plane—exactly where high-frequency return current needs a short, wide path. For HDMI, PCIe, and other multi-GHz links, prefer solid connections to ground on anything that carr
Francesco Poderico · · 2 min read
EMC
Quick Recap of Part 1 In Part 1, we explored how a simple change in antenna orientation can help you tell whether a radiated emission is coming from your PCB or from the attached cables .By running both vertical and horizontal measurements
Francesco Poderico · · 2 min read
EMC
Any electronic product must be compliant with the appropriate EMC (Electromagnetic Compatibility) therefore the designer engineer should select the right EMC standard right at the beginning. This increases your chances that your product will pass EMC testing and be legally placed on the market in re
Francesco Poderico · · 13 min read
EMC
In this post, I’ll share a powerful debugging technique you can use to identify the source of emissions in the 30 MHz to 300 MHz range. In this specific band, the test setup you use during EMC measurements is critically important. I’ve seen customers fail tests simply because of issues with how the
Francesco Poderico · · 3 min read
EMC
The RS422 and RS485 standards are well known in the industry for their reliability and noise immunity. However, they do hide the seeds for narrowband emissions, at least in some industries like for example the defense industry when you need to meet the MIL STD 461, and the tollerated radiated emissi
Francesco Poderico · · 2 min read
Electronics
In one of my previous blogs, I discussed the importance of adding common mode filtering to power cables. Nevertheless, even the best filtering may not be enough to pass CE. When this occurs, most EMC testing houses recommend using "low frequency" ferrites, like Fair-Rite's excellent Material 31, whi
Francesco Poderico · · 3 min read
EMC
The following tips may be helpful if you're designing a solution that uses a 10/100 LAN Ethernet port. Some very common Ethernet PHY (sometimes) causes a particular issue at 1GHz, I've seen the same problem at 250 MHz and 500 MHz, but 1GHz is the most problematic, if you don't know what to do, becau
Francesco Poderico · · 3 min read
EMC
Let's learn how to fix emissions due to clock lines. Over the course of my career, I have helped many companies resolve EMC issues. One of the most common causes of failing EMC (but hard to fix if you don't know what to do) is due to the clock line. For example, some MCUs require interfaces to some
Francesco Poderico · · 5 min read
EMC
In terms of EMI, it is very difficult to have a product that is both efficient and low noise. Today I'd like to discuss some typical issues you may encounter when designing an efficient power supply. As you can see, I have not used the word DC/DC converter, but power supply, since this issue may als
Francesco Poderico · · 3 min read
EMC
Last year I worked with Cryptalab on the design of a quantum random number generator card. SSL/TSL experts know how important this is in today's world. Visit their website at https://cryptalabs.com/ to learn more about this excellent product There is a detail in this kind
Francesco Poderico · · 2 min read
EMC
In my previous post, I explained why there are emissions in DC-DC converters that are insulated and how to minimize them. I have also explained in detail the three main mechanisms that are responsible for emissions. This has allowed us to see how we can reduce the emissions from these 3 differe
Francesco Poderico · · 3 min read
EMC
As I mentioned in two previous posts, I have discussed the emission path of an insulated DCDC converter below the frequency of 80 MHz. It has been shown how a capacitor placed between the pins Vout- and Vin- can reduce the emissions from the DC-DC converter. After that, we have analyzed the emission
Francesco Poderico · · 2 min read
EMC
Hello again! The previous post demonstrated how an insulated DCDC converter can generate unwanted emissions at frequencies below 80 MHz. The next step is to analyze two more mechanisms in more detail. There are many similarities between these mechanisms, but before I begin to tell you about them, it
Francesco Poderico · · 3 min read
EMC
As a matter of fact, it is quite common these days that we need some amount of insulation between our electronics and the outside world. If you had designed a PoE product, for example, you would typically have an insulation of 1.5kV in your product. In most cases, the insulation voltage is determine
Francesco Poderico · · 3 min read
EMC
The 2023 was the busies time ever. Because of all the projects I had, I barely had time to write articles for EMC. In this year, I've already got 25 EMC designs to fix and a few products to design. In any case, I'll try to be as active as I can, and share some of my design knowledge with you. You sh
Francesco Poderico · · 2 min read
EMC
The use of good ECAD is crucial to the design and development of high-quality electronic products. ECAD can provide a variety of benefits, such as reduced design cycle time and error minimization.offer various benefits, reduced design cycle time, and One essential aspect of ECAD, which I consider cr
Francesco Poderico · · 3 min read
PCB
Over the last ten years, I have seen so many PCBs fail conductive immunity that I could write a book about it. In most cases, the errors are caused by bad designs and a lack of understanding of the ground plane's role. Since I keep seeing people recommend designing 2 layers PCBs to save a few pence,
Francesco Poderico · · 2 min read
EMC
These days, we tend to encounter circuits with microcontrollers that incorporate AD/DA converters as a part of their design. As an example, Infineon has a very powerful PSoC with integrated digital blocks, operational amplifiers, etc., which is one of the most powerful PSoCs on the market today, I t
Francesco Poderico · · 2 min read
PCB
As part of my job, I have been analyzing PCB layouts that have been designed by third parties. Whenever I do this, it is interesting to see what typical mistakes people make when they are doing this. As an example, for some reason, when there is a differential signal, such as USB, RS485, etc., peopl
Francesco Poderico · · 3 min read
Electronics
There is a feeling in me that sometimes the old books are better than the new ones. As an example, a book by Hnatek called Design of Solid State Power Supplies might be one of those gems that shouldn't be missed in your library if you are interested in solid-state power supplies. This old book s
Francesco Poderico · · 3 min read
Electronics
PDN design is not an easy task, and it can be challenging. One of the most common mistakes is to follow so-called "rules of thumb" that work 90% of the time, but not 100%, so it is your responsibility to determine when these rules are valid or not. Adding a 100 nF capacitor to each power pin in para
Francesco Poderico · · 2 min read
PCB
In today's world, ribbon cables are widely used as a way to interconnect PCBs with each other. They are low-cost and very easy to install. In spite of this, they come at a price. It is very important that you know how to choose how the current flows on each pin, otherwise, you may get into a lot of
Francesco Poderico · · 3 min read
EMC
My current client has four heatsinks in his design, so in my solution, I'm designing some precautions to minimize emissions in the final design. In my experience, this error is very common, so I would like to discuss it one more time. I hope you won't make the same mistake again in your design. The
Francesco Poderico · · 3 min read
EMC
Back in the day, when testing was conducted for EMC, it was possible to perform tests, such as immunity tests, during which the device would degrade. Let's say, for example, that you were performing an RF immunity test of a light controller, and during this test, the light flickered a little bit. As
Francesco Poderico · · 2 min read
EMC
The CAN interface is the most common BUS inside a car. Some years back, I was introduced to the CAN bus by a good friend of mine from Argentina, who came to the UK for a few years and needed an electronic engineer for his company. I am so grateful to Roman Di Lullo for coming to the UK and creating
Francesco Poderico · · 3 min read
EMC
Radiated emissions from a product don't always turn out the way we want. And having a plan for troubleshooting emissions when they exceed or are near the limits is a smart idea. If you follow me on my blog, you should know by now that I often share design tips that aren't widely known or not widely
Francesco Poderico · · 4 min read
Electronics
In a previous article, I discussed the common mode coupling on the PoE (Power Over Ethernet) DCDC converter that I discussed a few months back. It is a similar mechanism that happens when we design our own AC/DC converters. Based on some of the comments that I have received, it seems clear that for
Francesco Poderico · · 2 min read
Electronics
EMC is considered by many to be a "black magic" for a number of reasons. In some cases, it may be the case that you obtain unexpected emissions from components you were not expecting to have. Oftentimes, the problem lies in the fact that we tend to ignore what we call "parasitic components" such as
Francesco Poderico · · 2 min read
EMC
Today, it is common for a product to contain a motherboard and several daughter boards. In the following example, let us imagine that we have a daughterboard that has some high-speed signals on it. In order to minimize ground bounce on both the motherboard and the daughterboard, what is the best str
Francesco Poderico · · 2 min read
EMC
A couple of months ago, I was testing EMC for a medical product. As the product is enclosed within a metallic enclosure, I was concerned about potential emissions from the enclosure during operation. This is something that I have discussed with the testing engineer, and he stated, "Francesco, don’t
Francesco Poderico · · 4 min read
Electronics
I visited Scotland on holiday, a beautiful country! There is so much history in Edinburgh, and I also enjoyed visiting Glasgow. It is difficult for a consultant engineer to stop working entirely, as you can imagine. I received a call from an IT company that already has a product on the market, and
Francesco Poderico · · 2 min read
Electronics
A few years ago, I worked on digital radio for a customer. It was a very complex design, but the reward for an electronic engineer such as me was enormous. It was a pleasure to work on every single part of the design. As I recall, I bought a few books to ensure that I was doing a good job, and the
Francesco Poderico · · 3 min read
PCB
Some time ago, I wrote a blog post about the design technique I use when I am solving EMC emissions for clients when I am working on their projects. As a result of some comments (from LinkedIn), I feel that the subject is not fully understood by the majority of people. As a result, I decided to rewr
Francesco Poderico · · 3 min read
Electronics
Those of you who are reading my post know that there is not much 'black magic' behind EMC and that there is always an explanation for why we fail during the EMC testing process. As a result of having a strong understanding of EMC, it is extremely satisfying to be able to pass the EMC testing for bo
Francesco Poderico · · 3 min read
PCB
I designed my first general I/O PCI card when I was a student (a few years ago now :-)). The PCI card was part of my thesis, and the design was challenging at the time. One of my professors was quite impressed with my throughput. The FIFO was bigger than I needed, and I managed to get all the data
Francesco Poderico · · 2 min read
Electronics
As we have seen in parts 1, 2, and 3, the input current loop of a DCDC converter affects both conductive and radiated emissions. Furthermore, the output current loop primarily affects radiated emissions.We then learned how an R/C snubber works and how antiparallel output capacitors can reduce radiat
Francesco Poderico · · 2 min read
Electronics
In the process of creating a new product from scratch, I always add components that I may not need in production when I am designing it. As an example, it does not cost anything to add an 0-ohm link or a "does not fit" capacitor in a critical spot where we think we might need them in the future (in
Francesco Poderico · · 3 min read
PCB
To avoid EMI and crosstalk on both PCB traces and connectors, it is crucial to understand the return path current. Previously, I discussed how a ground plane reduces EMC problems (both emission and immunity). In addition to minimising crosstalk, a ground plane helps minimise interference. You know I
Francesco Poderico · · 1 min read
Electronics
I had the pleasure of working with a customer a few years ago, who was ready to launch his product on the market. My suggestion was to go for full CE compliance before the test and to contact me only if there were any problems that occurred during the test. As the EMC house was just 15 minutes away
Francesco Poderico · · 3 min read
EMC
It was my pleasure to assist a startup company in passing EMC last month. The company now has its CE mark on their product and I am extremely pleased to hear that they have started making sales. There were quite a few mistakes made in this project, just to name a few: a poor design of the common mo
Francesco Poderico · · 3 min read
Electronics
When we design electronics, there are a few things we shouldn't skip. Often, CEOs and CTOs pressure us to design things quickly. But what is the cheapest option? Should we spend one or two extra days analyzing the board or should we run it a second time? My goal today is to discuss some design analy
Francesco Poderico · · 2 min read
PCB
When we place our bypass capacitors on a PCB, there are several factors that may affect the series inductance of the capacitor ESL when it is placed on the board. What can we do in order to minimize it during the routing of our PCB? Do you consider the footprint of the capacitor when you select the
Francesco Poderico · · 2 min read
Electronics
I spent several stimulating days last week performing EMC testing on one of my most challenging designs in the past two years. This is the first time EMC compliance has been achieved in a topology of medical products. For this particular design, the EMC house was my most critical testing location; I
Francesco Poderico · · 2 min read
PCB
Recently, a customer contacted me about the possibility of "fixing" their design from the standpoint of EMC. The board may function perfectly, but it won't pass most tests, including Conductive Immunity, Radiated Immunity, Radiated Emission, and Conductive Emission. Some people may think a ground/V
Francesco Poderico · · 2 min read
PCB
Have you ever seen corrosion on the solder joints on an old PCB? Or on the aluminium side of a power supply? Why we do have corrosion, and how can we stop it? Every time we connect different metals with different Fermi levels, the chances are you have created a diode. Zener diodes work just based o
Francesco Poderico · · 1 min read
EMC
A few years ago I was doing EMC testing for a product I designed myself. The emissions were so low that at some point the EMC house doubted the equipment was on... I had my phone with me and I showed them that was fully functional. :-) I toke this comment as a compliment, and I started to get a good
Francesco Poderico · · 2 min read
EMC
As I said in my last post, sometimes I' am contacted by companies to help them pass EMC. I like the challenge and I know that I will learn something new. In this post, I'll share some things that I do at the beginning of an investigation. When you have a product that doesn't pass EMC, most of the ti
Francesco Poderico · · 2 min read
EMC
Passing EMC compliance testing doesn't need to be as difficult as taking a degree in special relativity. I'm often contacted by small, and medium companies to help them pass EMC testing. I'm very happy about that since at the end of this experience I build strong relationships with the customer, whi
Francesco Poderico · · 1 min read
