EMI and EMC in Circuit Board Design | Printed Circuit Podcast Episode 23
Hi everyone. Thanks for tuning in to the Printed Circuit podcast where we discuss trends, challenges and opportunities across the printed circuit engineering industry. I'm your host, Steph Chavez. In this episode, we'll focus on EMI, EMC and signal integrity and power integrity. And here to join me in this discussion is John Kraemer, an electromagnetic compatibility engineer with a very impressive history in this industry. Thanks for being here. Hey, thanks for having me.
John, can you give us a brief introduction of yourself? Well, I recently retired from Collins Aerospace as a senior technical fellow for electromagnetic compatibility. My focus as a technical fellow was on innovation for EMI control and providing company wide leadership in the area of designing for EMI control and the achievement of EMC at the circuit board level, the product level, and at the system level. My responsibilities also included troubleshooting the company's toughest EMI problems somewhere at the circuit board level, while others were at the product level and system level.
Still having a passion and interest in EMC area, I'm now doing consulting and short term contract work in the areas of designing for EMI control and troubleshooting. I'm also still serving in technical leadership positions within the IEEE EMC Society. That's a great background and I can attest to John's background and his experience because I've had the luxury and the honor of working with John in my stint when I worked at Collins Aerospace. So he and I definitely have did a lot of hard core collaboration. So I'm very excited about this. So John, can you tell me what is EMI and EMC and Signal Integrity and Power Integrity? EMI stands for electromagnetic interference, which is the bad thing.
We don't want interference, whether it be at the circuit board level between equipment within a system or from the environment, such as the case with lightning or electrostatic discharge. There are two aspects of EMI. The first is where a circuit, a circuit assembly or a piece of equipment is susceptible to interference. This is called susceptibility. In a defense aerospace world where we work staff and immunity in other product design areas.
The second aspect of EMI is emissions control emissions, which could potentially interfere with radio receivers. Emission control is generally quantified and qualified at the equipment level. Conducted and radiated emissions from equipment must be below limits specified by regulatory agencies. EMI is also a concern within a piece of equipment where one item is an emitter or source of interference. And another item is the victim of interference.
A common example is a digital processor that produces energy at the same frequency used by a Bluetooth receiver on the circuit board. There are many possible paths for that energy to couple from the processor to the radio circuit. They include the power distribution system, cross-talk between credit conductors, coupling via overlapping power planes and radiation from circuit board traces to the receiver’s antenna.
You really have to know what you're doing during layout to prevent this type of EMI problem. EMC, on the other hand, stands for electromagnetic compatibility. It's a desired outcome. Everything is electromagnetically compatible. No interference between circuits on the same circuit board, no interference between circuit boards, no interference between equipment items, and no interference or degrading effects from the environment, which can include energy from radio transmitters, lightning and electrostatic discharge to name a few. Signal integrity, often called SI, focuses on ensuring that the digital signals on a circuit board and their associated routing and interconnect possesses the required properties to allow reliable operation.
These properties include signal level, transmission time source and low termination characteristics, delay in isolation from other signals, which is known as crosstalk. Many of these items are also important with analog and radio circuit designs. Signal integrity on the printed circuit board equates to going beyond analysis of the schematic. It includes the component shown on the schematic as well as the cop around the circuit board connecting the sources and loads.
Power Integrity called PI focuses on the power distribution network on the circuit board to ensure that the integrated circuits, most notably processors, memory and RF transmitters, have the power available immediately when needed. In today's world, it's not uncommon for integrated circuit device to command over 100 amps in the range of 18 to 3 volts for a brief instant to support a lot of simultaneous switching actions, if that power is not immediately available, System reliability can suffer. Power integrity also involves ensuring that instantaneous power demands of one device does not adversely affect the power characteristics and power quality present in other devices. That's great, John. You laid out a great foundation to get an understanding.
So as we evolved this conversation. So that's awesome. I love the way you described that. So tell me why signal integrity and power integrity have become critical, Are must do items to ensure product EMC compliance During the past decade? Well, with today's technology, there's often an extremely large density of high speed switching and integrated devices on the circuit board. High speed and high density translate to the potential for a lot of EMI emissions as community issues. High speed
translates to high frequency content in shorter wavelengths. When the dimension of a copper feature such as the length of a trace or the diagonal dimension of a component pad on your circuit board becomes longer than 1/10 of a wavelength, they cannot be electrically ignored. Rather, they take on the electrical characteristics of a component such as a capacitor inductor, transmission line or antenna, and will affect the signal as it runs from the source to the load. With today's technology, the signal frequency contact is high enough to cause the copper on the board to look like an electrical component, which will affect the quality of the signal. Of course, if the copper happens to look like an antenna, it could be a mechanism for receiving or transmitting EMI thus designed for signal integrity, allows a proper transfer of energy between devices on the circuit board, both from an electrical perspective and from a timing perspective. If energy is not transferred as desired, it may turn into excessive heat or electromagnetic emissions, which are released from the circuit board by radiation or conduction.
Once this high frequency energy is released, it's very hard to contain it within the equipment item. This often results in EMI emission compliance failures and endless weeks of troubleshooting and expensive fixes before your product can be shipped. It can also result in interference to radio circuits inside your equipment item. Excessive emissions can also be released due to power integrity issues. So for emissions control, with today's technology, it's important to get the signal integrity, power, integrity, aspects of your circuit board done correctly. Signal integrity and power integrity at the circuit board level are also important in regards to immunity and prevention of susceptibility at the equipment level where before you ship EMC compliance testing is performed.
Having good signal integrity and good power integrity can be compared to being in good health. If you're healthy, you have greater immunity and are less susceptible to disease and sickness. You can do your job reliably day in and day out, no matter what sicknesses are going around. If you're healthy, the same is true for circuits. If the signals in power have a high level of integrity or health, they will be less susceptible and more immune to interference.
In the old days, signaling speed and density was notably less than it is today, and signal integrity and power integrity were not on the top items to consider. At the equipment level for EMC compliance. Back then we called circuit boards, printed wiring boards or P.W BS. Since the copper really didn't matter that much, it was just wiring. That is not true today in the world of printed circuit boards or PCBs. The copper features not only connect, but they often have the characteristics of a component other than a simple wire.
As a matter of fact, the IEE EMC Society changed the annual symposium name from Symposium on EMC to Symposium on EMC and SIPI in 2017. Just to illustrate how important signal integrity and power integrity have become for controlling EMI and achieving product level EMC compliance. That's amazing and what you described of dealing with issues with EMI power integrity. I mean, there's nothing worse than chasing the dragon. That phrase that I use when you're in the lab as an engineer and your circuit is actually on, but it's actually the performance of the board itself that you're having to battle with of why things aren't functioning.
And a lot of it has to do with the performance of how the signals interact with each other, whether they're a positive or a negative in that aspect. And I love your analogy of what you use to describe the health of a body, the human body, and then the health of a healthy circuit That's spot on. I could truly visualize that.
So tell me, what is the importance of addressing EMC, SI and PI during the PC design process? To start with, And what you alluded to it is ultimately the circuit board that contains the devices that will be susceptible to interference. It is also these devices that source the energy PI frequency energy, which can be the source of electromagnetic emissions. As mentioned before, with today's high speed and high frequency signals, the printed circuit board copper is not merely the equivalent of a wire connecting component pins, but rather that copper is a bunch of circuit elements. That copper trace often needs to be designed as a transmission line to allow the correct energy transfer and to prevent immunity reducing crosstalk. The capacitance and inductance and resistance of the power copper is of utmost importance for ensuring adequate power delivery. So it all starts at the printed circuit board.
I've observed over and over that the material costs for a printed circuit board that is done right is no different than for when done wrong for EMC signal integrity and power integrity. As I mentioned before, once high frequency undesired energy is conducted or radiated off of the printed circuit board, it is very difficult and often expensive to control it at the equipment level to allow product level EMC compliance. I couldn't echo that more this many a times where I've seen EEs are down in the lab or in the EMI chamber doing battle and trying to figure out what went wrong or how to control that.
And you really need to understand what you're doing. This is why when I talk about printed circuit board design, you really need to master your craft as a designer, as well as mastering your tool. And then of course, then you have addressing the performance of the board as well as the manufacturability or reproducibility of the board. The three key successes that you need to achieve when you think about designing circuit boards. So tell me, what are some of the items? Or some of the things you recommend for PCB design tools and processes for ensuring SI/PI success? Well, first, you should start your design with signal integrity pre layout tools that allow you to model your devices, input and outputs with circuit terminations and the printed interconnect with specific cross-section dimensions and links to help you determine your base copper stack up in cross-section dimensions. HyperLynx SI as a good pre layout tool that can help you make that needed tradeoffs and set you up for signal integrity success in layout.
I found the HyperLynx SI pre lay out two or three very easy to use. Can get you started on defining what you need for more thicknesses between layers and the dimensions cross-section dimensions of your traces. Of course, I strongly recommend that post layout tools such as what's contained in HyperLynx SI and HyperLynx PI be used to check signal integrity on critical and representative circuit nets as well as evaluate the board's power delivery network. You can use these tools right in your layout environment to evaluate what if changes. After all, design is an art of tradeoffs, and these tools can help you find the win win tradeoffs with high speed and high grade density situations. You may find that you will have to change the copper layout and component placement to obtain the needed power integrity characteristics.
Again, this can be done with HyperLynx PI, right in the design tool layout environment for quick feedback. In my experience I found that HyperLynx SI and PII add the optimum mix of capability and ease of use for most situations. I do want to emphasize the first step for achieving EMC is getting signal integrity and power integrity right. You need to do that first.
Achieving EMC may require a bit more regarding in your layout. I couldn't agree with you more. One of the things that I always stress is Multi-Discipline and Multi-Domain collaboration. I mean your layout designer as well as your EMC engineer or SI engineer along with your EE and your mechanical engineer. We all have to be in sync and be in collaboration. When you think about how the board comes together, because I've seen circuits that are resurfaced at work and prove when tested, but the layout that a designer may have had may have missed something during the layout of that particular design he's working on And then you get it in the lab and for whatever reason, it's not working.
That's definitely a challenge. So tell me, what about EMC? Do you have any recommendations for PCB design tools and processes for enhancing EMC success in your PCB layout? Well, as I mentioned, the layout, features and constraints needed for EMC are in addition to what's needed for good signal integrity and power integrity. Often the must have layout attributes for successful EMC can be checked using a rule based layout checker and EMC engineer can provide specific rules and rule parameters regarding the copper design on a circuit board for a particular end product type and technology.
I found that HyperLynx DRC, DRC stands for Design rule checker, is the best tool for a post layout check for compliance to EMC design rules. Custom rules can be authored and the rule parameters can be easily changed to Accommodate your end product Type, the compliance situation, and overall product EMI control approach as recommended by the EMC engineer. The particular EMC rules and their pass fail parameters should be communicated to the board of designers before layout to allow them to be incorporated into the layout tools constraint editor. It should be noted that the EMC rules and parameters are based on a mix of experience and simulation for a particular technology, product type, compliance situation, and overall product.
EMI Control Approach. Hyperlinks DRC comes with a bunch of built in rules with parameters that provide a good starting point. The EMC engineer can recommend which rules to use and suggest the parameters for each.
Again, based mostly on his or her experience with the end product type, the EMC compliance requirement details and the technologies being used. The EMC engineer is typically involved with the EMC compliance testing. Thus, he or she sees what works and what doesn't. And that can be fed back into the specifics for the EMC design rules and their parameters that will be used by HyperLynx DRC.
Our collaboration, you know that we were very fortunate to address when we were working together several years ago. It is amazing how we were to easily go from Expedition to HyperLynx in our back and forth and how and the tools in going between the two different domains. It's truly amazing. You know, when you talk about collaboration and getting it right and feeding that information into the layout designer.
But what if the particulars for your project are different than something similar encountered before or are some special needs to accommodate design tradeoffs? Well, in these situations, you may need to use an advanced electromagnetic field solver to determine your needed layout attributes for signal integrity and or power integrity, as well as specifics. For the EMC rules, the HyperLynx advance field solver is a great option for these sorts of situations which require more study. So typically, what do the EMC layout rules focus on? Probably the most important rule check is centered on ensuring each signal and power trace is tracking or sees the correct reference plane from source to load. As an example, typically a digital signal must see digital ground from source to load, at high speeds even a small interruption in tracking can cause major EMI problems. Another rule check that is often important involves maintaining a minimum amount of separation between board internal signal traces and the traces for signals that leave the product.
If those traces are too close for too long of a distance, undesired high frequency processor type signals can couple to the outside world and subsequently cause EMI emission problems. The reverse coupling situation can cause EMI immunity problems or susceptibility to electrical noise from the external environment. Overlapping power plants may also be a concern regarding EMI control, especially on mixed signal boards and boards that have inputs and outputs that directly lead in product. Thus, power play and overlap constraint must be included as a rule with parameters in the EMC check. Floating copper If large enough with respect to the highest frequency content on the board, get enhanced interference coupling. Thus a rule check centered on floating copper is also often included in the EMC rule check.
Additionally, placements of components critical for EMI control, such as decoupling capacitors, bypass capacitors and traction protection devices and their routing details is almost always a rule defined area that can be checked with post layout rule based design checker such as HyperLynx DRC. Decades ago we would check these sorts of items manually. Today's boards are much more complex and denser to allow performance of the EMC checks with the old manual methods.
When we talk about the legacy methodology, when it comes to design and doing the signal integrity checks, our integrity checks are the checks for performance. I mean, today's tools are so much more powerful and those of us or those that are taking advantage of the horsepower in their respective tools, That's today's age and tomorrow's evolution And if you're not doing that, it's going to be more costly and more time consuming just to do that. If you're still implementing those legacy approaches.
So can you share some helpful hints and advice for preventing EMI problems and achieving product EMC compliance? First, I would say have a plan for EMI control and EMC compliance. I got started in EMC after college in 1982 with the US Army. One of the first things I was taught was a six PS of success. Proper prior planning prevents poor performance. I have continuously found that to be great advice.
Your plan for EMC control should have input from the design team. Since design is an art of tradeoffs, have a pre layout teen peer review and include an EMC engineer in that review so he or she can share their experiences and guide you in setting out the rules and parameters that you're going to be using for EMC control on your circuit board. Also, ask yourself, What am I doing to make sure that my circuit board will not be the cause of an emissions or immunity EMI problem. Also, make sure you properly address signal integrity and power integrity. This is a must do with today's technology.
Again, poor signal integrity and or poor power integrity equates to a high probability of any UI problem. Use pre layout and post layout tools to optimize your signal integrity and power integrity Design. Most definitely use a rule based design checker to check your layout against the important EMC rules and constraints given the complexity of the EMI requirements and how they affect overall product design approach and how technology can influence the need for layout attributes and constraints or EMI control, It is best if an experienced EMC engineer is involved with this process. And finally, never be afraid to ask for help. All of us. We all learn from each other.
I couldn't echo that more. Definitely getting the key stakeholders involved, the subject matter experts involved early at the earliest stages of The design process is is key to downstream success. You mapped it out and stated it within this discussion and I can't thank you enough for bringing all that to the table and sharing it with the audience.
That's all we have time for today. John, thanks again for sharing your insights and experience with us and your take on the topic for today. Hey, my pleasure. You're very welcome.
2024-02-25 10:24
