Lifting the veil on electromagnetic compatibility of PCB boards

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Lifting the veil on electromagnetic compatibility of PCB boards [Copy link]

Someone once said that there are only two kinds of electronic engineers in the world: those who have experienced electromagnetic interference and those who have not. With the increase in the speed of PCB traces, electromagnetic compatibility design is an issue that we electronic engineers have to consider. When facing a design, when performing EMC analysis of a product and design, there are 5 important attributes to consider: (1) Key component size: The physical size of the radiating device that generates radiation. Radio frequency (RF) current will generate an electromagnetic field, which will leak out of the chassis through the chassis. The length of the trace on the PCB as a transmission path has a direct impact on the RF current. (2) Impedance matching: The impedance of the source and receiver, and the transmission impedance between the two. (3) Time characteristics of interference signals: Is the problem a continuous (periodic signal) event, or does it only exist in a specific operation cycle (for example, a single key operation or power-on interference, periodic disk drive operation or network burst transmission). (4) Strength of interference signals: How strong is the source energy level, and how much potential does it have to produce harmful interference. (5) Frequency characteristics of interference signals: Use a spectrum analyzer to observe the waveform and observe where the problem is in the spectrum, so as to find the problem. In addition, some low-frequency circuit design habits need to be paid attention to. For example, the single-point grounding I usually use is very suitable for low-frequency applications, but after chatting with the company's experts, I found that it is not suitable for RF signal occasions, because RF signal occasions have more EMI problems. I believe that some engineers apply single-point grounding to all product designs without realizing that using this grounding method may generate more or more complex electromagnetic compatibility problems. We should also pay attention to the direction of current flow within the circuit components. With circuit knowledge, we know that current flows from high voltage to low voltage, and current always flows in a closed loop circuit through one or more paths, so a minimum loop and a very important law. For those measured interference current directions, modify the PCB traces so that they do not affect the load or sensitive circuits. For those applications that require a high impedance path from the power supply to the load, all possible paths that the return current can flow must be considered. There is also a PCB trace problem. The impedance of a wire or trace includes resistance R and inductance. At high frequencies, it is impedance, and there is no capacitive reactance. When the trace frequency is above 100kHz, the wire or trace becomes an inductor. Wires or traces working above audio may become RF antennas. In the EMC specification, wires or traces are not allowed to work below λ/20 of a certain frequency (the design length of the antenna is equal to λ/4 or λ/2 of a certain frequency). When it is not designed in that way, the trace becomes a high-performance antenna, which makes later debugging more difficult. Finally, let's talk about the layout of the PCB. First, the size of the PCB should be considered. When the size of the PCB is too large, the anti-interference ability of the system decreases with the increase of the trace, and the cost increases. If the size is too small, it is easy to cause heat dissipation and mutual interference problems. Second, determine the location of special components (such as clock components) (it is best not to lay ground around the clock trace and not to run above or below the key signal line to avoid interference). Third, layout the entire PCB according to the circuit function. In the layout of components, the related components should be as close as possible, so that a better anti-interference effect can be obtained.

btty038

Most of them are done this way. Some details are not handled very comprehensively. Every time I make a PCB, I feel that there are some unsatisfactory places and I always want to modify it

dellmeco

MSG develops and manufactures cutting-edge focusing technologies to increase the throughput and quality of microscope automation and AOI systems. Solutions from MSG in Germany include high-speed autofocus systems, dimensional measurement sensors, motor controls and optoelectronic components for 2D and 3D surfaces. Our technologies are used in a variety of industries, including automated optical inspection of semiconductors, wafers and electronics, display inspection and repair systems, and biomedical vision systems. MSG is proud of the key role it plays in basic research, improving production efficiency, or by providing solutions directly to end users or embedded technologies for OEM suppliers. Metrology Sensors GmbH develops and manufactures cutting-edge technologies to increase the throughput and quality of microscope automation and AOI systems. Our solutions include high-speed autofocus systems, dimensional measurement sensors, motor controls and optoelectronic components for 2D and 3D surfaces. Our technologies are used in a variety of industries, including automated optical inspection of semiconductors, wafers and electronics, display inspection and repair systems, and biomedical vision systems. MSG is proud of the key role it plays in basic research, improving efficiency or quality inspection in production processes, by providing solutions directly to end users or embedded technologies for OEM suppliers.

qwqwqw2088

Which category do those who have experienced electromagnetic interference and those who have not experienced electromagnetic interference belong to?