Many beginners are puzzled by EMI design. In fact, I was the same at the beginning, but after doing a few designs, I gradually got some experience.
First of all, it is necessary to be clear about a concept in the brain - in high frequency, the impedance of free space is 377 ohms. For the space radiation in general EMI, it is because the circuit of the signal is comparable to the space impedance. Thus the signal "radiates" through the space. Knowing this, all you have to do is lower the impedance of the signal loop.
The main way to control the impedance of the signal loop is to shorten the length of the signal and reduce the area of ​​the loop. Secondly, take reasonable terminations and control the reflection of the loop. In fact, one of the easiest ways to control the signal loop is to cover the key signal (the grounding distance is the closest distance on both sides, especially for the double panel, because the double-sided microstrip model has 150 ohms and free space. The cloth phase is up and down, and the ground can provide impedance of several tens of ohms. Please note that since the trace itself has impedance in the high frequency, it is better to use the ground plane or the ground line to connect the hole to the ground plane multiple times. Many of my designs are designed to avoid excessive radiation of the clock signal after the package is used.
The other is to avoid the signal traversing the segmented area. Many engineers signal to the ground, but sometimes forget that the wire has been passed through these areas, resulting in the signal loop bypassing a large area, which invisibly increases the wiring. length.
For the part of EMI conduction, the key point is to use bypass capacitors and decoupling capacitors. The bypass capacitor (providing an AC short-circuit line) must be placed on the chip power pin and ground (plane) with the shortest connection. The decoupling capacitor should be placed where the current demand changes the most, avoiding the noise (inductance) of the trace, so that the noise is coupled out from the power supply and the ground. Of course, the rational use of magnetic beads in series can "absorb" (convert into thermal energy) these noises. Inductors can sometimes be used to filter out noise, but please note that the inductor itself also has a frequency response range, and the package also determines its frequency response...
These are some of the most basic experiences. For EMI design, you need to really understand your own design, where to focus on care, what is the problem in what place, what is the alternative, you need to pre-organize.
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