Harmonizing Circuit Design and EMC DesignPart 14 EMC Overview (2) What is Electromagnetic Compatibility?

Hello! I’m Inagaki, at ROHM.

In the previous 13th article, I set out to present an overview of electromagnetic compatibility (EMC), but space limitations intruded. In this 14th installment, I would like to continue this summary of electromagnetic compatibility (EMC).

I think the reader has already gained an understanding of electromagnetic interference (EMI) and electromagnetic susceptibility (EMS). Here I want to discuss transmission paths of such electromagnetic noise. As already explained in the introductory articles, electromagnetic noise can be categorized as either conducted noise that is conducted on a printed circuit board (PCB) or in wires between PCBs, or as radiated noise that propagates in the air from a device under test (DUT), either directly or else using PCB wiring or the like as an antenna. In general, noise up to 30 MHz or so is handled as conducted noise, and noise above 30 MHz is handled as radiated noise. That is not to say that there is a clear-cut demarcation at 30 MHz, but this is a good rule of thumb. Hence physical phenomena relating to electromagnetic compatibility (EMC) can be broadly classified into the following four categories.

I have explained that electromagnetic interference (EMI) and electromagnetic susceptibility (EMS) must both be considered; in terms of physical phenomena, this means ensuring that the four states listed above do not occur. This is quite difficult. In fact, international standards for electromagnetic compatibility (EMC) are also categorized in this same way. The electromagnetic compatibility (EMC) for purchase specifications provided by customers is specified using this same system, and there are still more detailed international standards for each.

There are also international standards for electromagnetic compatibility (EMC) for different product groups, with representative standards for each. These may be briefly summarized as follows.

Representative International Standards for Electromagnetic Compatibility (EMC)

Upon viewing the radiation and conduction frequency conditions, the reader may do a double-take. While describing it as a “rule of thumb”, I stated above that “in general noise up to 30 MHz or so is conducted, and noise above 30 MHz is radiated”. However, among actual international standards there are many that specify conduction up to 1 GHz, and some that specify radiation starting from 150 kHz. Conduction tests that specify frequencies above 30 MHz should be understood as meaning that the measurement range includes not only a pure conduction component, but also radiation up to higher frequencies (using a conduction measurement circuit). There are also customers with their own proprietary standards, and there are not a few standards that extend the upper frequency limit to still higher frequencies.

These international standards are being revised every few years. This is because, as with laws, rules, regulations and the like, if a problem with electromagnetic compatibility (EMC) arises that results in a serious incident, revision of frequency ranges and modification of measurement limit values are studied by different organizations such as the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO) so as to prevent such occurrences in advance, and the relevant international standards are revised and disseminated.

Thank you very much for your attention.