Page 56

June, 2019

Filtering out Common Mode Noise in Congested Environments with Monolithic EMI Filters

By Jeff Elliott A

multitude of factors combine to increase the amount of “noise” interference that can dis- turb the functionality and even damage elec-

tronic devices, starting with the sheer number used in our vicinity at any given time. Today’s automobiles provide a prime exam-

ple. In a single vehicle you can find Wi-Fi, Bluetooth, satellite radio, GPS systems, LED lights, air conditioning, power steering, anti-lock brakes, rear-view cameras, and other instrumen- tation. Numerous items also operate using DC motors, including power seats, adjustable mirrors, windshield wipers, power windows, and sunroofs. This same example could also apply to

devices that range from Wi-Fi or Bluetooth- enabled appliances, such as washing machines, espresso machines, medical instruments, and even medical implants. To protect these systems, the industry has

typically employed shielding, along with EMI fil- ters in various configurations to eliminate unwant- ed noise. However, even some of the traditional solutions for eliminating EMI/RFI are no longer sufficient, given increases in operating circuit fre- quency, noises of higher frequencies that expand the affected frequency range and the miniaturiza- tion of electronic devices that shrink the distance between source and victim. If that wasn’t enough, many electronic

devices are more easily affected by noise, even with less energy, due to circuits that operate at lower voltages. This is leading many OEMs to avoid options such as two-capacitor differential, three-

MID AMERICA Taping and Reeling, Inc.

capacitor (one x-cap and two y-caps), feed-through filters, common mode chokes, or combinations of these for more ideal solutions, such as monolithic EMI filters that deliver superior noise suppression in a substantially smaller package.

EMI/RFI Noise When electronic devices receive strong elec-

tromagnetic waves, unwanted electric currents can be induced in the circuit and cause unintended

low, if it is mixed with the radio waves used for broadcasting and communication, it can cause loss of reception, abnormal noise in sound, or disrupted video in places where the radio waves for broadcast- ing and communication are weak. If the energy is too powerful, electronic devices can be damaged. Sources of noise include natural, such as elec-

trostatic discharge, lighting and other sources, and artificial noise such as contact noise, leaking from devices that use high frequencies, unwanted emis- sion (e.g. harmonic emission from digital circuit, emission from switching power supplies) and others. Noise can even be generated from a circuit

inside an electronic device and cause interference with another circuit in the same electronic device. Usually, EMI/RFI noise is common mode

noise, so the solution to all but eliminate unwant- ed high frequencies is to use an EMI filter, either as a separate device or embedded in circuit boards. This also helps OEMs meet regulatory standards that exist in most countries that limit the amount of noise that can be emitted.

Johanson Dielectrics’ monolithic EMI filters.

operations —or interfere with intended operations. EMI/RFI can come in the form of conducted or

radiated emissions. When EMI is conducted, it means the noise travels along the electrical con- ductors. Radiated EMI occurs when noise travels through the air as magnetic fields or radio waves. Even if the energy applied from the outside is


EMI Filters EMI filters normally consist of passive com-

ponents, such as capacitors and inductors, con- nected together to form circuits. “The inductors allow DC or low-frequency

currents to pass through, while blocking the harm- ful unwanted high-frequency currents. The capac- itors provide a low impedance path to divert the high frequency noise away from the input of the fil-

Continued on next page AUTOMATE YOUR


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