Analysis of electromagnetic compatibility issues in power supply internal systems

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Analysis of electromagnetic compatibility issues in power supply internal systems [Copy link]

Current electronic products are constantly developing towards high performance. From multi-functional mobile phones, high-end digital cameras, to various game consoles, their functional complexity is increasing compared to the past. In addition to digital circuits, many communication functions are also integrated into them, such as Bluetooth, etc. After inheriting such a wide range of functions, in addition to ordinary radiation, internal EMC issues have also been a very hot topic of discussion in recent years. There are several reasons for the generation of EMI in the internal power supply system. First, the high-speed chips of mobile terminals continue to generate low voltage operation, which reduces the working margin of EMC. Second, the sharing of equipment and digital equipment. Third, the increase in interface communication speed. Fourth, the popularization of electronic control in automotive applications. Next, let's briefly introduce the electromagnetic compatibility issues of the internal system of the power supply. Take a laptop computer as an example. Since it has digital circuits and communication circuits, the internal circuits will generate some radiation, and the noise can be easily received by the surrounding antennas. After receiving these noises, the receiving sensitivity of the circuit will be affected. This is what we often call the electromagnetic compatibility problem of the internal system. These are several principles for generating sensitivity. The main EMC paths may cause the surrounding noise to affect the EMC compatibility problem inside the system. Let's briefly talk about the EMC compatibility of the internal system. EMC is divided into far-field and near-field effects. A simple analysis of the antenna can help solve this problem.

Next, let's start with the subsequent topic of the decreased sensitivity of the tablet computer. Since the noise generated by various circuits at work affects the antenna's receiving sensitivity, when the voice and video are broadcast in the upper right corner, it will receive relatively large noise energy. Red represents when it is working, and blue represents when it is in standby mode. The noise will be much lower when it is in standby mode. The picture in the lower left corner is in a tablet terminal. When the high-definition camera is working, the (English) antenna will receive noise energy. Similarly, red represents the noise during work, and blue represents the noise energy in standby mode. Finally, when the LCD is working, we see the noise energy. Red represents when the LCD is lit, and blue represents when the LCD is backlit. This is a popular smart phone. It has a 3G antenna, a high-definition camera, and a CPU chip. These may generate high-frequency radiation noise. If this radiation noise is coupled and received by the 3G antenna, it will affect the receiving sensitivity of the 3G antenna. The second is a tablet computer. In many cases, a tablet computer is used as a multimedia terminal for audio and video processing. Therefore, when playing music, it will definitely affect the use of customers. The noise in common tablet terminals, the power supply of digital circuits, and the general problems of antenna and audio placement are very important for us to find solutions and countermeasures when problems occur. This is the battery, this is the main processing chip and power management chip, and this is an audio circuit, and above is a high-definition camera. Among the currently commonly used tablet high-definition, the RF part uses a 3G module. Its receiving antenna may be very close to components or chips with relatively high noise energy. Therefore, if such electronic products are used for office work, there will be internal electromagnetic compatibility problems, which will significantly reduce the receiving sensitivity of the antenna. This is a mainstream smartphone. The noise on it mainly comes from the power management chip, followed by the main chip. Therefore, we must effectively suppress the noise energy of 800-900. It can be found that this solution is the most effective for overall noise suppression. The second one is also a smartphone. We will try some other methods to suppress noise. This is the curve of the sensitivity of the receiving end. Obviously, the sensitivity has been significantly improved. This is the audio chip and audio cable mentioned earlier. This is the LCD backlight control chip. A related current is added to its power supply. We analyze the noise energy of the tablet computer. The red one is before the addition, and the blue one is after the addition. It is found that the noise energy will have a very obvious suppression effect after the addition. This means that the noise source comes from these two locations. The following lists the EMC components used in the countermeasures just now. The 0202 added to the audio cable in the tablet computer will not have much impact on the sound quality when used in the audio stage. This is the common-mode circuit board produced on the LCD. Its length and width are no more than one millimeter. It is processed using a fine photolithography thin-film process.