Creating projects for hobby reasons rarely calls on electromagnetic compatibility (EMC), but it is not unheard of when a hobby project becomes a commercial product. However, strict rules and regulations surround electronic devices on the market mainly involving EMC considerations, so in this article, we will look into what EMC is and some small tips on how to improve the EMC performance of a circuit.

What Is EMC?





EMC stands for electromagnetic compatibility and it is concerned with circuit EM emissions and susceptibility to EM emissions. All circuits that switch or change voltage polarity emit EM radiation which can potentially be detected by a receiver. A classic example of EM emission is an RF transmitter circuit that generates a high-frequency oscillation which in turn creates photons with a frequency equal to the frequency of the oscillator (these EM emissions can then be detected by a radio receiver). This example of EM emission demonstrates intentional EM emission (since the goal is to send information over radio waves). However, many circuits containing microcontrollers and/or switching circuits produce EM emissions which can cause serious problems with other nearby circuits. Therefore, these emissions must be reduced as much as possible for a circuit to pass FCC and CE regulations (which is required when selling a product).

All EM emission related problems come down to three main areas:

The Emitter – Something must be creating EM emissions (possibly at unacceptable levels)



The Medium – Something must be carrying the EM emissions



The Receiver – Something must be receiving EM emissions and be failing as a result



EMC issues can be solved by removing one of the three areas above and some techniques apply to more than one area shown above. Typically, it is easier to remove emissions and mediums than it is to remove receivers since most electronic circuits that exist on the market comply with receiver regulations (circuits inside products must not be susceptible to standard emissions from sources such as WiFi, Mobile phones, and other radio equipment).

Removing Sources of EM Emission





Method 1 – Smooth Switching Circuits

Switching circuits and circuits that involve data/clock signals can cause serious problems when it comes to emission. The issue does not usually come from the switching frequency itself but from the rise and fall times from the signals. A sine wave signal in a wire will mostly emit EM radiation whose frequency is equal to the frequency of the sine wave. A square wave, however, is made up of a singular sine wave and an infinite number of sine waves at odd harmonic frequencies. Therefore, square waves have a tendency to emit radio waves not just on the frequency of the switching circuit but at many other frequencies as well. This is why spectrum analyzers are so important when trying to comply with EMC regulations (showing detected signals at different frequencies).