What is EMI Filter?

A filter is a circuit that removes or "filters out" frequency components in a specific range. In other words, it separates the frequency spectrum of the signal into frequency components that will pass and frequency components that will be blocked.

Let us assume that we have an audio signal composed of a perfect 5 kHz sine wave. We know what a sine wave looks like in the time domain, and in the frequency domain we can only see a frequency “spike” of 5 kHz. Now let us suppose that we activate a 500 kHz oscillator to introduce high frequency noise into the audio signal. The signal seen on the oscilloscope is still just a sequence of voltages, with a value at each moment, but the signal will look different because its time domain changes must now reflect the 5 kHz sine wave and high-frequency noise fluctuations. However, in the frequency domain, sine waves and noise are separate frequency components that exist simultaneously in the one signal. Sine waves and noise occupy different parts of the signal's frequency domain representation (as shown in the figure below), which means that we can filter out noise by directing the signal through circuits that pass low frequencies and block high frequencies.



EMI Filter Solutions' Provider: ACSOON