Filtering out Common Mode Noise with Monolithic EMI Filters

March 13, 2019

Jeff Elliot

(Image courtesy: Johanson Dielectrics Inc.)

Strong electromagnetic waves can create unwanted electrical currents in electronic devices. Sources of electromagnetic interference (EMI), also known as radio-frequency interference (RFI) or simply “noise,” can occur naturally (electrostatic discharge, lighting, and other sources) and can be produced artificially (contact noise leaking from high frequency devices, harmonic emission from digital circuits, emission from switching power supplies). Noise can even be generated from one circuit inside an electronic device and cause interference with another circuit in the same device.

Numerous factors can contribute to interference levels that have the potential to disturb or damage electronic devices, starting with the sheer number used in our vicinity at any given time. Today’s automobiles are a prime example. In a single vehicle you can find Wi-Fi, Bluetooth, satellite radio, Global Positioning System (GPS) equipment, light emitting diode (LED) illumination, air conditioning, power steering, anti-lock brakes, rear-view cameras, and other instrumentation. Numerous items also operate using dc motors, including power seats, adjustable mirrors, windshield wipers, power windows, and sunroofs. This same example also applies to items ranging from Wi-Fi- or Bluetooth-enabled appliances like washing machines, espresso machines, medical instruments, and even medical implants.

Some OEMs are finding that the traditional solutions for eliminating EMI/RFI are no longer sufficient given increases in operating circuit frequency, noises of higher frequencies that expand the affected frequency range, and the miniaturization of electronic devices that shrink the distance between source and device. This is leading many OEMs to employ monolithic EMI filters instead of traditional options.

Jeff Elliott is a Torrance, California-based technical writer. He has researched and written about industrial technologies and issues for the past 20 years.