● Learn about the differences between Broadband and Narrowband EMI.
● Gain a greater understanding of the methods that produce EMI and how to mitigate them.
● Learn more about the classifications of EMI and its standards.
The electromagnetic spectrum.
Electromagnetic Interference (EMI) is a disruption (interference) produced by one electronic device that affects another through the electromagnetic (EM) fields created by its operation. Although there is a myriad of disruptive phenomena that designers in the field of electronics must contend with, EMI is usually at the top of the preventative to-do list.
Categories of Electromagnetic Interference (EMI)
Various forms of EMI can adversely affect circuits. These various EMI or RFI (radio frequency interference) forms can manifest in a multitude of ways. However, like power loss, they should not be part of the design.
Although there are numerous sources of EMI, it fundamentally resides within two categories or source types: naturally occurring or human-produced. In addition to the two category types, EMI has a veritable list of characteristics. These characteristics vary and are dependent on the method and source producing the disruption.
As I am sure you are aware, EMI is an unwelcome phenomenon, and its mitigation or elimination is paramount to device performance and functionality.
Types of Electromagnetic Interference (EMI)
We categorize EMI into its various types with regard to three determining factors:
Source or method of production.
Length of occurrence or the duration of the EMI.
The frequency range of the interference or the bandwidth of the EMI.
The following is a more detailed examination of these three criteria of EMI categorization.
Method of Production
Naturally occurring EMI comes from a variety of sources such as lightning, electrical storms, or even cosmic noise, to name a few. As the name implies, this EMI is produced by naturally occurring phenomena.
Human-produced EMI typically includes other electrical devices, electrical circuits, and even switching currents.
Duration of EMI
Continuous interference: EMI typically derived from an electrical circuit that continuously emits a signal. This category can include phenomena like background noise as well, which is also continuous whether it is naturally occurring or human-produced.
Impulse noise: Any unwanted signal in a communication circuit. This type of EMI can be naturally occurring or human-produced. It typically includes phenomena such as lightning, electrostatic discharges, and current switching systems.
Frequency Range or Bandwidth of EMI
Narrowband EMI: As you may know, the bandwidth of EMI is a reference to its range of frequencies in which the EMI spans. We refer to Narrowband EMI as a narrow band of interference frequencies or even a single interference frequency. Narrowband EMI signals occupy a minute portion of the radio frequency spectrum. These signals are generally CW (continuous sine waves) that can occur either intermittently or continuously. Narrowband EMI can be the result of spurious emissions such as harmonic outputs of narrowband communication transmitters. It can also emanate from oscillators, signal generators, test equipment, and even power-line hum.
Broadband EMI: A Broadband EMI signal can distribute its energy throughout hundreds of megahertz or more. These types of signals are composed of narrow pulses with short rise and fall times. Characteristically, broadband signals divide into impulse and random sources. They can occur intermittently, transiently, or continuously. Broadband EMI can arise from radar and communication transmitters (emissions), ignition systems, electric switch contacts, PCs, thermostats, voltage regulators, pulse generators, and intermittent ground connections.
The Origin of EMI Standards
Like most technological standards, EMI standards arise from a military background. The need to protect electronic devices and circuits from EMI spans as far back as the 1950s. Therefore, it is only logical that the focus on preventative and mitigating measures be at the forefront for today’s design engineers.
The military is all too familiar with the effects of EMI since it is responsible for critical equipment failures that lead to loss of life. Currently, with the advancements in health-related solutions like Cardiac Implantable Electronic Devices (CIEDs), these standards are even more vital.
These, along with various other scenarios, validate the need for adherence to EMC (electromagnetic compatibility) and EMI standards. Although these standards vary by country, continent, and even economic region, these standards provide a baseline of acceptable parameters. There are two primary standards, and they are European IEC 60601, which governs control, lab, and measurement equipment, and 60950, which regulates IT equipment.
In the USA, there is a significant focus on unintentional emissions. The FCC’s Title 47, Part 15 (47 CFR 15) governs this classification of interference. Also, with regard to this standard, there are two classifications for electronic devices:
Class A: Devices designated for use in office environments, industrial settings, and everywhere except in-home use.
Class B: Devices designated for home use and other user settings.
Guidelines for Mitigating EMI and EMC Issues
While of course, guidelines for designing away from EMI and EMC issues, as well as understanding where the locations of these issues may arise is important; however, just as important are understanding the tools available for resolving these issues. We’re talking quick and reliable modeling capabilities to merge mechanical structures such as connectors and cables can yield holistic EMI diagnosis. And we’re talking accurate s-parameter modeling to augment the analysis from any tool. And we’re talking about the need to handle 5G, automotive, HPC applications, or anything that emergent technologies are willing to throw at you.
The Use of Shielding
Both EMI and EMC shielding provides protection for signal transmissions from external noise as well as preventing information loss. The primary objective of EMI and EMC shielding is to mitigate the effects of both RFI and EMI on electronic circuitry. Typically, we utilize metallic screens to absorb EMI.
Impedance Matching Designs
When designing a PCB, the design must incorporate accurate line impedance that matches the source impedance. This technique naturally suppresses EMI, and it also controls the signal rise and fall times.
Spacing is always a critical concern, however, when addressing EMI, it requires an even higher degree of diligence. One of these primary concerns is line or trace spacing. Since EMI propagates through the board’s edges, your design should include PCB traces that bend at a 450 angle to the board’s edges.
Try to utilize striplines instead of microstrips as well as avert layer changes and routing high-speed signals over the slots. Finally, incorporate designs that keep differential traces near one another.
In the field of electronics, proper grounding is paramount to all functionality. Therefore, designs that effectively apply ground planes are vital to the reduction of EMI and EMC. Take care when splitting ground paths and try to utilize large, continuous ground reference planes to connect it to the ground plane with the ground vias. Also, be sure to include a return path for the ground plane.
During high-speed signal transmissions, the utilization of low-pass filters for mitigation with ferrite-core inductors will reduce EMI and EMC issues. Designers utilize decoupling capacitors to increase switching between ground and IC power connections, thus, shunting the interference caused by other circuits through the capacitor.
5G or RF Antennas
Antennas, and therefore antenna arrays as we progress our designs into more 5G or RF fields, will require careful arrangement to ensure isolated elements. This prevents crosstalk to the receiver function of another antenna from the transmitter of the current piece. Using absorbers and proper EMI shielding can work wonders to achieve this minimal and prevention of crosstalk.
Sensitive Component Spacing
DFM (design for manufacture) practices are always in concert with component placement. The same is true of EMI and EMC mitigation practices. Therefore, a proper PCB design must account for the location of any oscillators to minimize interference with other circuits or components. Place high-speed components away from input and output connections or other possible interfering signals.
EMI as a whole is one of the singular most disruptive phenomena in existence to electronic circuitry. The mitigation of EMI is paramount to the functionality, performance, and lifecycle of all electronic devices. Whether it is narrowband or broadband EMI, the above practices will minimize and eliminate EM emissions at their source. Furthermore, they will also promote better designing practices, which in turn increases profits for your company.
CAD tools can be a big help in producing high-quality designs.
To properly mitigate EMI in your circuit designs, working through every angle is going to be of paramount importance. In sensitive designs, you cannot be careful enough to identify and navigate through EMI sources or vulnerabilities.
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