A printed circuit is an antenna for transmitting and receiving energy.
A raging fraternity party with thumping house music can be annoying as the morning hours approach. Noise suppression ordinances to the rescue! The partiers have two choices: quiet down or get shut down.
In that sense, the fraternity party is like building an electronic circuit. If our machines make too much “noise” in any part of the spectrum, it’s game over.
Just like kids can stop trampling everyone’s lawn and come inside, shut the doors, windows, shutters and even the fireplace flue, we can also contain unwanted spectral emissions. Left unchecked, a printed circuit is an antenna for transmitting and receiving energy from within and outside the board.
Even a well-designed PCB has compromises. Our goal is to be ready to react to spurious emissions that take us beyond the allowable threshold. We start with a power budget, and a noise floor, and our electronics must comply with those design criteria while meeting regulatory requirements.
As we bring different functions aboard, the problems in the near field multiply. We think of high-speed transmission lines as the focus of our EMI abatement efforts. They are seen as the cause of the problem, owing to their signal rise times or a harmonic of that momentary event.
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