With the increase in PCB traces, electromagnetic compatibility (EMC) design is our electronic engineers have to consider the issue. In the face of electromagnetic compatibility (EMC) design, when performing a product and design of electromagnetic compatibility (EMC) analysis, there are five important attributes to consider:

(1) Key device size:

The physical size of the emitting device that produces the radiation. Radio frequency (RF) current will produce electromagnetic field, the electromagnetic field will leak through the case and out of the chassis. The length of the traces on the PCB as a transmission path has a direct effect on the RF current.

(2) impedance matching:

Source and receiver impedance, and the transmission impedance between the two.

(3) Interference signal time characteristics:

Whether the problem is a continuous (periodic signal) event, or only in a specific operating cycle (for example, a single key operation or power-on interference, periodic disk-driven operation or network burst transmission).

(4) the intensity of the interference signal:

How strong the source energy level is, and how much potential it produces harmful interference.

(5) Frequency characteristics of the interfering signal:

Use the spectrum analyzer to observe the waveform, observe the problem in which the location of the spectrum, easy to find the problem lies.

In addition, some low-frequency circuit design habits need attention. For example, my custom single-point grounding is very suitable for low-frequency applications, but later found not suitable for RF signal occasions, because the RF signal occasions there are more EMI problems. It is believed that some engineers will apply a single point of grounding to all product designs without realizing that the use of such a grounding method may produce more or more complex electromagnetic compatibility (EMC) problems.

We should also pay attention to the current flow in the circuit components. Circuit Knowledge We know that current flows from high voltage to low places where current flows through one or more paths in a closed loop circuit, so a minimum loop and a very important law. For those that measure the direction of the interfering current, by modifying the PCB trace, it does not affect the load or sensitive circuit. Applications that require high impedance paths from power to load must consider all possible paths that return current that can flow.

There is also a PCB tracing problem. The impedance of the wire or trace contains the resistance R and the inductance, at high frequency impedance, there is no capacitive reactance. When the line frequency is higher than 100kHz above, the wire or alignment becomes inductance. Wires or traces that work above the audio may become RF antennas. In electromagnetic compatibility (EMC) specifications, wires or traces are not allowed to operate at a specific frequency of λ / 20 (the design length of the antenna is equal to λ / 4 or λ / 2 for a particular frequency) Be careful when designing, the alignment becomes a high-performance antenna, which makes the late debugging become more difficult.

PCB layout issues:

First, consider the size of the PCB.

PCB size is too large, with the growth of the line to reduce the anti-interference ability, cost increases, and the size is too small to cause heat dissipation and interference problems.

Second, and then determine the location of special components.

Such as clock components, the clock alignment is best not around the floor and do not walk in the key signal line up and down, to avoid interference.

Third, according to the circuit function, the layout of the PCB as a whole.

In the component layout, the relevant components as close as possible, so you can get a better anti-jamming effect.