Electromagnetic interference (EMI) and its effects on components, circuits, and systems are a serious concern for many designs. It can cause transitory malfunctions, erratic performance, intermittent issues, system upsets, component degradation, and hard failure. EMI is a pervasive issue for many applications, especially industrial and automotive designs, and there are various industry and regulatory standards for ensuring EMI resistance which end-products must meet.
I won’t attempt to provide a guide to EMI-resistant design techniques here; it’s too big a topic to get our hands around, let alone explore in detail. Also, it has been covered extensively in everything from academic papers with interesting theoretical analysis (interesting but often not directly actionable) to hands-on pieces on how to investigate and “knock down” EMI and its consequences. Many of these references are relatively old but still quite valid since EMI, at its core, is a manifestation of Maxwell’s equations and other basic principle of physics and electronics.
Electrical disturbances can be conducted by the power and signal lines, or conveyed through the air by capacitive, magnetic, or other electromagnetic radiations. Good design practice calls for following some basic guidelines and standard techniques to minimize EMI, include line filtering, modified power-supply design, proper layout, and shielding the enclosure (Figure 1).
Figure 1 There are many ways to enhance EMI resistance; and they can be used individually or in clusters and each approach involves tradeoffs of complexity, cost and time. Source: Texas Instruments
EMI protection venues
Physical locations have a large role in EMI problems and solutions, before adding any components to attenuate it. Basic strategies include blocking disturbances as near to their source as possible—preferably before they enter the equipment—and redirect them to ground and trying to place sections that can be exposed to EMI disturbance as far as possible from sensitive circuitry.
Of course, EMI protection should be considered while designing the circuit and not left largely to post-design/prototype tests. Nonetheless, it’s very likely that design engineers will need to do more after the circuit and system are built and evaluated. In addition to layout and wire-routing changes, engineers often resort to multiple EMI-attenuation components and techniques, including bypass capacitors, resistors, ferrite beads, inductive chokes, shielding, improved grounding and ground paths, varistors, and more.
Still, there’s one tool in the EMI kit that is easy to overlook: the use of components which inherently have additional EMI resistance due to their design and fabrication. I was reminded of this by the recent introduction by Rohm Semiconductor of two new op amps, the humblest and most basic active analog component along with the transistor. The single-channel BD87581YG-C and dual-channel BD87582YFVM-C feature improved EMI immunity for automotive and industrial applications.
These components join Rohm’s BD8758xY EMARMOUR family of rail-to-rail input/output high-speed CMOS op amps first introduced in 2017. They are well-suited for high-speed sensing in harsh environments such as vehicle engine control units and anomaly detection systems for factory automation equipment. These op amps achieve an enhanced EMI performance through a combination of proprietary analog design technology and fabrication process.
Of course, it’s one thing to say better, but some numbers make the claim tangible. In this case, Rohm claims that in the ISO 11452-2 Radio Wave Emission Test conducted by vehicle manufacturers, the output voltage of standard op amps fluctuates by more than ±300 mV in all frequency bands, while it’s only ±10 mV at most in its new series. This low value can often mean that the need for EMI-related “countermeasures” such as frequency-specific filter components at each frequency of interest is eliminated, thus reducing application design effort and improving reliability.
Rohm also has some interesting graphs that show performance in four international noise evaluation tests: ISO 11452-2 Radio Wave Emission Test, ISO 11452-4 Bulk Current Injection Test, ISO 11452-9 Proximity Antenna Immunity Test; and IEC 62132-4 Direct RF Power Injection Test (Figure 2).
Figure 2 The EMARMOUR approach significantly improves EMI performance, as shown by three ISO 11452 and one IEC 62132 test results. Source: Rohm Semiconductor
Other EMI-resistant components
These op amps are not the only available EMI-resistant ICs. There are EMI-resistant interface components for the venerable RS-232 standard; the components serving RS-232 are most vulnerable to EMI due to their physical and electrical location in the system. RS-232, once the most common interface-connectivity standard, still has many legacy ports in use.
Have you ever started with an EMI-resistant component so as to improve your “odds” in an EMI-tolerant design? Have you ever switched over to such components afterward to fix a problem? Or do you think single-source components are a design and availability risk, and prefer to achieve improved EMI immunity via traditional techniques such as passive filters, shielding, layout topology, grounding, and other approaches?
- What Does Your Noise Nemesis Look Like?
- Active filtering: Attenuating switching-supply EMI
- Improve EMI rejection with a simple front-end amplifier
- Minimizing EMI in Automotive and Industrial Applications
- “Stop” in the Name of Noise: Do I Shut Off That Switching Supply?