Electromagnetic Interference (EMI) has become part of our lives, do you want to deal with? Many people believe that the wide application of electronic solutions is a good thing because it brings comfortable, safe enjoyment to our lives, and bring medical services to our side. However, these solutions also generate EMI signals with electron hazards.
The source of the EMI signal is various, including some of our electronic devices. Cars, trucks and heavy vehicles themselves are generators of EMI signals. The problem is that these EMI sources are located in the same - vehicle, which will affect audio devices, automatic door controllers, and other devices. However, this type of EMI noise present in the vehicle is foreseeable.
However, what about the mobile phones in the 21st century, what is the situation? Each electronic device has its advantages and disadvantages. Today, the use of mobile phones allows us to easily contact friends, family and business partners anywhere. However, the phone will also generate EMI signals, which is only the beginning of the problem. The development of mobile phones has exceeded its basic function and has more smartphone functions. This EMI noise is completely unpredictable for interference of the surrounding equipment and circuitry. The phone needs to rely on high RF energy, so even if the relevant requirements are met, it is also an unexpected EMI source to interfere with the surrounding sensitive equipment.
Printed circuit boards, clock circuits, oscillators, digital circuits, and processors are also in the internal EMI source. Some electromechanical devices for current execution switching operations also produce EMI during critical operation. These EMI signals do not necessarily have a negative impact on other electronic devices. The spectral components and strength of the EMI signal determine whether it will have unexpectedly for sensitive circuits.
You can simplify the spectrum components of a digital signal into frequency and rise time. The clock or system frequency is established the time baseline of the circuit, but its edge rate forms an interference harmonic. Figure 1 shows a spectral component of a 10 MHz square wave. The edge rate of the 10 MHz signal is 10 ns. Note that the magnitude of these harmonics in Figure 1 decreases with the frequency. In general, the potential EMI of this signal is:
FMAX = 1 / (πxtrise)
The results of the 10NS edge rate of about 31.8 MHz. The graph shows that the last obvious harmonic appears at 30MHz. At the same time, the results of the 1NS edge rate is 318 MHz max frequency (shown in Figure 2). If your circuit is easily affected by the frequency generated in the 318 MHz band, the EMI harmonics may cause your circuit to interfere.
Figure 1: Analog EMI signal for 10NS lifting time signal
Figure 2: Analog EMI signal for 1 ns lifting time signal
In fact, the better approach is to eliminate interference signals in the source without letting it pass your circuit. For vehicles, there are more and more components to start using plastics. However, when you want to find a low impedance ground or implement signal mask, this has become a problem. Once the signal transmission is "free", they "wander around", so that they enter your sensitive system, eventually bring serious damage.
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