With the rapid development of microelectronics technology, electronic devices are more and more widely used, and the integration of electronic systems is getting higher and higher. However, in complex electromagnetic environments, electronic systems have obvious sensitivity and vulnerability to electromagnetic interference. In order to reduce failures and prevent accidents, electronic equipment must be designed for electromagnetic compatibility. As long as the electrical and electronic equipment is energized, electromagnetic fields, electromagnetism, and magnetoelectricity are generated. Therefore, the electromagnetic environment is very complicated. On the one hand, it is required to use the electronic equipment without causing pollution to the surrounding electromagnetic environment, and on the other hand, the electronic equipment is required. In the actual electromagnetic environment application, there is no performance degradation or failure to cause a serious accident. Therefore, it is necessary to study the electromagnetic compatibility of electronic equipment and control and protect against electromagnetic interference [1-2]. Based on the importance of electromagnetic compatibility design, some of the related issues are discussed below.
1 Common electromagnetic interference phenomena and their analysis
Electromagnetic and its induction phenomena are ubiquitous, so the electromagnetic working environment of electronic systems is very complicated. From the perspective of engineering applications, electromagnetic interference can be classified according to the operating frequency. For example, in general power grids, harmonic signal voltage fluctuations, grid frequency changes and low-frequency induced voltages, grid voltage imbalance, short-term power grid fluctuations and short-term interruptions, etc., low-frequency conducted interference, low-frequency radiation interference of magnetic fields and electric fields; Due to the oscillation transients of the induced continuous wave voltage and current and the high frequency conduction interference caused by the one-way transient, the electromagnetic field (continuous wave, transient) interferes with the high frequency radiation caused by the magnetic field and the electric field; the electrostatic discharge due to the insulation property of the material Interference, etc. The above mentioned interferences contain most of the electromagnetic interference phenomena in engineering applications.
In the anti-interference performance analysis of electronic systems, it is necessary to comprehensively analyze the inherent characteristics of the system and its application environment. The types of electromagnetic interference that may occur in an electronic circuit system are: for example, due to the common impedance coupling of the circuit loop, the mutual interference of the circuit is caused; since there is a changing electric field between the interference source and the interference object, a capacitive coupling may be formed. Capacitive interference, because it will generate interference voltage; the variation of electric and magnetic field strength of space electromagnetic wave may cause interference between conduction current and conduction voltage caused by induced potential; in alternating magnetic field interference source, current change may lead to inductive component An induced voltage is generated thereon, thereby causing inductive interference and the like.
2 Electromagnetic compatibility and its design mechanism
2.1 Electromagnetic compatibility
With the wide application of electrical and electronic equipment in modern production, the connection of equipment is more and more complicated, the power is getting larger and larger, the number is increasing sharply, the requirements for equipment are getting higher and higher, the frequency band is widening, and the equipment sensitivity is higher. Therefore, electromagnetic compatibility issues have become more important. Electromagnetic compatibility (EMC, ElectromagneTIcCompaTIbility) means an electronic system in an electromagnetic environment. Nothing else can constitute an unacceptable electromagnetic interference capability, and the device or system can work normally. Electromagnetic compatibility technology involves communications, computing, electronics, production, military, and all aspects of life. It is an interdisciplinary subject that is rapidly evolving. Electromagnetic compatibility is a science that studies the coexistence of different devices without affecting each other under the conditions of limited space, finite time and limited spectrum resources. It can be seen from the above definition of electromagnetic compatibility that the meaning of electromagnetic compatibility includes: the device does not cause unacceptable interference to other devices around, and itself is not affected by interference of other devices. Electromagnetic compatibility research involves many aspects, firstly, the research on the characteristics of electromagnetic interference sources; secondly, the research on electromagnetic emission intensity, interference mechanism and electromagnetic interference suppression method, and time-frequency domain characteristics of electromagnetic interference, third, special It is worth noting that the equipment itself is resistant to electromagnetic interference. Finally, how to evaluate electromagnetic compatibility such as electromagnetic radiation and conduction characteristics, what equipment and measurement methods are used to measure electromagnetic interference, and how to process measurement data and measurement results. From a broader perspective, it also covers electromagnetic compatibility within and between systems. Electromagnetic compatibility research includes natural and man-made electromagnetic interference sources, such as lightning and electrostatic discharge, which are natural electromagnetic interference sources. Measurements of interference sources include measurement of open field, radiation, conduction and pulse interference (electric surge, fast transient pulse). Group and electrostatic discharge), shielding, grounding, bonding and filtering in the technical aspects of electromagnetic compatibility, including special design techniques to suppress electromagnetic interference.
2.2 Anti-electromagnetic interference design mechanism
To constitute electromagnetic interference, it must have three conditions at the same time: First, there must be interference sources, no interference sources exist, it is obviously impossible to generate electromagnetic interference to the equipment; Second, there are channels that propagate electromagnetic interference, otherwise it is impossible to form a pair The electromagnetic interference of the equipment; Third, the equipment should be able to receive the interference signal and directly affect the normal operation of the equipment. Therefore, even if the equipment receives the interference, if the technical measures are taken, the interference to the equipment can be eliminated. For example, a robust device is immune to electromagnetic interference. The anti-electromagnetic interference design mechanism is to adopt electromagnetic compatibility design, so that the above three conditions are not available at the same time, so as to improve the anti-electromagnetic interference of the equipment.
Take the anti-jamming design of electronic equipment as an example. Because the high-frequency interference in the equipment is particularly prominent, firstly, the RF energy emitted by the equipment is controlled to be as small as possible so as not to interfere with other equipment. Secondly, in order to avoid external interference, the equipment must be as far as possible. Reduce the RF energy entering the device. Electromagnetic interference can be realized by means of radiation or conduction transmission. If the interference source energy is directly radiated to the control line, the signal line and the power line enter the device, the device can directly interfere with the device through a coupling path such as a common signal, a control cable or a public power line. normal work. Therefore, in the device port or sensitive circuit, common mode or differential mode anti-interference measures can be used to minimize the impact on it, reduce the radiation and conduction energy, and improve the anti-interference performance of the device. The anti-electromagnetic interference design mechanism is to eliminate At the same time meet the above three prerequisites [3-4]. Based on this, the technical measures for its anti-electromagnetic interference design can be various. With the advancement of technology, the technical measures that can be taken will be more and more abundant to ensure the electromagnetic compatibility of equipment design.
3 Anti-interference design strategy
Anti-electromagnetic interference design is to use comprehensive technical measures to ensure the correct performance of electronic devices in a complex electromagnetic spectrum environment. According to the anti-electromagnetic interference design mechanism, the first is to suppress the interference source to prevent electromagnetic interference; the second is to take anti-electromagnetic interference measures to block the interference propagation path; finally, to reduce the sensitivity of electronic equipment to interference, or to improve the electronic equipment Bar performance to prevent and suppress electromagnetic interference. For the electronic system cable connector, printed board layout, signal layout, to suppress interference electromagnetic interference signals that may be introduced in the wiring, components, filters, grounding and bypass, isolation, circuit impedance control, filtering, solution Anti-electromagnetic interference measures such as coupling, sealing, grounding, shielding, and correct wiring.
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