Feature: Automotive
Filtering out common-mode noise in
automotive environments By Jeff Elliott, Torrance, California-based technical writer. He has researched and written about industrial technologies and issues for the past 15 years
W
ith growing design complexities in shrinking packages, several factors
are combining to increase the amount of noise interference that impairs the design’s functionality and can even damage components. A prime example is today’s automobiles.
In a single vehicle there are Wi-Fi, Bluetooth, satellite radio, GPS, LED lighting, air conditioning, power steering, anti-lock brakes, rear-view cameras and other systems that continue to grow in number and functionality. Many in- vehicle systems need DC motors, to power seats, windows, sunroofs, mirrors, windshield wipers and more. To prevent interference between
them, the industry typically employs shielding along with EMI filters in various configurations. Sadly, some of the traditional solutions for eliminating
EMI/RFI are no longer sufficient, given increases in operating-circuit frequencies, higher-frequency noise generation and the reduced distances between noise- impacting components. If that wasn’t enough, many electronic
devices are more sensitive to noise, even at low power, due to circuits operating at lower voltages. Tis has led OEMs to abandon certain
options such as two-capacitor differentials, three-capacitor (one X-cap and 2 Y-caps) feed-through filters, common-mode chokes, or any combination of these, for more appropriate solutions such as monolithic EMI filters that deliver superior noise suppression in substantially smaller packages.
EMI/RFI noise Electromagnetic waves can cause unwanted currents in electronic devices, interfering with functions or causing unwanted operations altogether. EMI/RFI emissions can be conducted or radiated. When conducted, the noise
26 September/October 2020
www.electronicsworld.co.uk
travels along the electrical conductors, whereas radiated EMI occurs when noise travels through the air as magnetic fields or radio waves. Even if the energy applied from the
outside is low, if mixed with broadcasting and communication radio waves, it can cause loss of reception, audible noise in the sound, or disrupted video. If stronger, this energy can damage electronic devices. Sources of noise can be of natural
origin, such as electrostatic discharge, lightning and other sources, or artificial, such as contact noise, leakage from high- frequency devices, unwanted emissions (e.g. harmonic emission from digital circuits, emission from switching power supplies), and others. Electronic devices also generate noise internally, causing interference to neighbouring circuits. Usually, EMI/RFI noise is common-
mode noise, so the solution will be to eliminate unwanted high frequencies with an EMI filter, either as a separate device or embedded in the circuit board. Tis also
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