How to avoid the problem of EMC PCB design

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Recently often asked EMC Related issues, such as how to design in order to avoid the problem of EMC, I want to often focus on high-speed Mr shoes are the same opportunity will certainly ask this question. First, this is a systemic problem, the answer is not so good, especially for high-speed gentlemen in the field of high-speed signal focusing and non EMC expertise, but also can only answer about the truth in the field of EMC, we are constantly learning, so this article is based on some of our understanding EMC, from pcb in the design of how to avoid problems, which was not in place also please criticism, if you own a better article, also welcomed the submission to the high speed of our mr..


 

He said that at the beginning of this paper, EMC and SI, PI Closely, we will tell you a lot of time, we cannot EMC simulation, but we will from the board level to avoid some EMC problems, it actually is to try to ensure that the performance of SI and PI (this is what we do), to prevent the problem from the source EMC.
 

First of all, on signal integrity and the relationship between the EMC in front of Chen have written many articles on some sense, today we come to a simple summary, overshoot, reflection and crosstalk of SI concerns, in fact there is a direct relationship between EMC and. Signal due to impedance matching is not good, will be all kinds of reflection, reflection will have a relatively large overshoot is large, then the overshoot amplitude in addition to affect the service life of the device, but also affect the radiation, because he is the source of radiation, so the design of PCB on some key signals need to control impedance so, under the condition of impedance matching, may also need to pass to the external end of the match, the series has been mentioned in topology and end all termination methods; also need to pay attention to the problem of cross signal segmentation and segmentation problems in addition to the impedance signals across, in fact there is a return signal, said signal return EMI, many people will think of the problem, the signal return path change also produces the EMI problem; there is crosstalk between signal crosstalk is coupling That many people may take it directly and EMI equivalent, you need to avoid crosstalk between signals to increase the distance as far as possible, especially the microstrip line, also need to consider the crosstalk between the double strip line, try to avoid the upper parallel line is too long; there are some such as edge line, along the line segmentation, in fact, these is a commonplace talk of an old scholar topic, but easier said than done, if the design has some knowLEDge of SI and design from the perspective of SI, so many EMC related problems can be avoided.

 

PCB设计的EMC问题如何避免

Secondly, from the point of view of PI is to avoid a key problem of EMC, the power supply design, you can also say the product is half success. In the power integrity inside we will consider the power supply impedance, which will supply all kinds of comprehensive evaluation Capacitance The matching is reasonable, then from the whole band to ensure that the power supply network has a low impedance path, if a band of high noise impedance exceed the standard, in the corresponding frequency band will now EMI problem is likely to be excited, so we will use the corresponding frequency band capacitance to filter the noise in the previous article we have talked about Liu EMC and capacitance, was actually about the future, we have more PI related topics and so on EMC and PI of the topic we do not involve too much.

 

The other is from the stack, and the point of filtering to avoid the EMC problem. Stack is actually providing a fundamental signal framework, in this framework to meet the needs of various quality signal and power integrity requirements, of course, can guarantee the processing, then laminated to the topic of our topics; in an article on the inside is very superficial understanding about the key. Is that we need to ensure the return signal signal and reference, also is the final segmentation, how to split through what way to connect, EMC or PCB in this design is the need to pay attention to, but also the most complex. There is a low pass filter, common, high pass Band-pass and band stop filter, the need according to the different needs of different filter, in addition to Wave filterSuch as feed pass filter, L filter, P AI Type filter, T filter, common mode filter, the filter is different when the principle of hardware design has different considerations.

 

The last is the radiation shielding, because many times the chip itself is very big, the radiation is not from the chip board to eliminate, in addition to the chip or purchase small radiation chip manufacturers to ensure that most of the time we need to isolate with shielding cover, such as a mobile phone often see above each big module is an iron box to wrap up the chip, the iron box many times not to security requirements (part does not exclude the Kazakhstan), in fact, a large part of the reason is the shielding and isolation of EMI, this is based on the consideration of the EMC. Because we are a lot of mobile phone chips on the RF signal, on the one hand it is easy to interfere with other signals, on the other hand it is very easy to be disturbed, so this time with an iron box shielding them in isolation, as if some good ones have locked up alone, we all play each does not affect each other, so it is quite friendly.

The general said a lot, but also is the source to avoid radiation and EMC problems, because we all know that in order to solve the problem, you need to start from the root of the problem,

rather than no overall plan for a fundamental transformation, the EMC problem is the same, the EMC problem is complicated we need to know, where is the source of the problem, an antidote against the disease.



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read ()  •  Jan 10, 2019  •  Edit


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