I. Introduction
Under the leadership of this "epidemic storm" and "health trend", the richness of household electronic products has risen sharply, and all kinds of electronic massage products, electronic cleaning tools and the Internet of Things have driven the electromagnetic environment to become increasingly complex, and solving EMC problems has become a "core disease" for development engineers or R&D engineers when developing new products.
Second, understand the EMC problem
Here we mainly elaborate on the EMI problems that have more problems in EMC. EMI is divided into TWO parts, RE and CE, of which emi problems can be roughly power problems + clock problems + other problems, which clock problems and power problems are more common, but also the most problems, some other problems relative to these two problems are not so frequent, here are temporarily summarized into other problems.
The performance of these three types of EMC problems in the test data is also very obvious, easy to understand and distinguish. The switching frequency mainly appears in the low-frequency test, and it is also a problem point that is more difficult to rectify; the power supply harmonics generally appear in the frequency band within 200MHz, and the rectification will be relative to the switching frequency will be simpler; the high-frequency clock will generally cover the entire test frequency band, and the difficulty of rectification is mainly to see the location of the problem point. Understanding the radiation data of different problems is also an important ability to rectify EMC problems.
Third, EMC problem analysis ideas
After knowing the classification of EMC problems, we also need to know how to distinguish these problems! For example, if a test data is given to the engineers, can you simply determine the type of problem and the location of the problem point through the test data? When solving emc problems, how to quickly lock down EMC problems is more important than solving the problem itself, because the types of problems are those, but there are many ways to cause problems.
For example: a tablet computer EMC radiation 100MHz-1GHz exceeds the standard (customer requirements 6dB margin), analysis of data can be found that the main or clock signal exceeds the standard, in the case of not affecting the basic function of the device, disconnect the speaker, microphone, camera and other auxiliary functions of the line, and then test test, found that the test data did not change much, the data as shown in the following figure;
Then disconnect the screen line of the display screen, test, and find that the test data is better, the specific data is shown in the following figure;
The screen line is manually shielded and grounded, and the beads of 300 ohms are stringed on the CLK clock line to verify, and the test data is as follows;
Comparing the test data, it can be determined that the radiation problem is mainly due to the excessive length of the screen line, which is caused by the radiation exceeding the standard. In this case, the key information extraction point lies in the "clock signal exceeding the standard" and "the broken screen line data becomes better", in order to determine that the radiation source comes from the screen signal, and the processing of the screen line is only a measure to suppress the radiation path.
4. Summary
When dealing with EMC problems, it is important to analyze and understand emc test data capabilities, but how to judge and analyze the problem points is far more important than how to rectify the current EMC problem, because on different machines, EMC problem types will be similar, but the way the problem is handled is not necessarily the same, so the analysis idea of emc problems is far greater than the EMC rectification method.
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