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EMC electromagnetic compatibility and signal integrity

Jun 7, 2017



The growing number of electronic devices and wireless technologies providing ever-increasing performances and speeds requires a set of common standards to ensure EMC electromagnetic compatibility.

Ever since Michael Faraday’s discovery in 1831 of the phenomenon of magnetic induction, which James Maxwell later integrated in his well-known set of equations, we know that any change in an electric current produces a magnetic effect in its vicinity.

The multimedia services that we now enjoy are based on high-speed wired (Gigabit Ethernet, USB 3.0, HDMI) or wireless connections, and we also find fast buses (PCI Express, SGMII, USB, DDR3 memories) inside the communications devices, connecting integrated circuits to each other by means of printed circuit board tracks. All of these communication interfaces are capable of transmission rates of between 1 and 10 Gbps, which presents two problems: on the one hand, signal interference, and on the other, signal distortion. The first, Electromagnetic Compatibility, or EMC, is regulated by strict European-wide standards. The second is known under the term “signal integrity” and is the responsibility of designers because it directly affects the functionality of the product itself. Ideally, we would hope that signals travelling long distances would neither radiate any electromagnetic energy nor experience waveform deterioration. However, a certain degree of both phenomena will always occur. The challenge is to stay within legally established thresholds and to maintain the bit error rate at a low enough value to allow for correction.

In the same way that a highway or a high-speed railway line must be designed to avoid potholes, sharp bends, gradient changes, road narrowing, etc., so too must the printed circuit board layout  allow signals (our passengers) to travel unhindered without unexpected events, confusion or shocks. With high-speed circuitry, we pay attention to the symmetry of differential signals (to cancel out the common-mode component and therefore its radiation) as well as characteristic impedance along the entire transmission path (to eliminate reflections and, consequently, power loss or echo distortion).

A few years ago, high-speed communication interfaces were based on combining parallel signals, like PCI, with high impedance terminations. The norm today are serial buses installed on differential transmission lines terminated by their own characteristic impedances, which confine the electromagnetic field to a smaller volume of space and come close to the physical speed limits of printed circuit boards.

While radiofrequency and digital electronics have long been completely separate disciplines, nowadays the boundaries are disappearing. Developers of both technologies must observe the same physical principles and often employ the same simulation tools and measuring instruments.

Teldat devices use fast communication buses and meet and exceed all CE marking requirements for EMC Electromagnetic Compatibility.



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