As the frequency of electronic devices is getting higher and higher, the implementation of electromagnetic radiation standards for electronic products in the world is becoming more and more strict. How to ensure that EMI/EMC problems can be found and solved in the design stage in a limited time is very important. The PCB is often the core component of an electronic system. A PCB board designed with careful electromagnetic interference can greatly reduce signal instability and signal instability caused by impedance mismatch, transmission line problems, and signal coupling. At the same time, it can also reduce the electromagnetic radiation emission interference, and greatly improve the stability and reliability of the system. This paper will use the embedded system motherboard as the platform, using EMIStream simulation software, and using the source-side series termination impedance method to analyze the electromagnetic interference problem of embedded high-speed motherboard.
1 Electromagnetic compatibility
1.1 Electromagnetic compatibility and electromagnetic interference
ElectromagneTIc compaTIbility (EMC) refers to the ability of a device or system to operate in its electromagnetic environment without causing unacceptable electromagnetic interference to any device in its environment. Therefore, EMC includes two requirements: on the one hand, the electromagnetic interference (EMI) generated by the equipment during its normal operation cannot exceed a certain limit; on the other hand, it refers to the electromagnetic presence of the appliance in its environment. Interference has a degree of immunity (EMS), ie electromagnetic sensitivity.
Electromagnetic interference (EMI) refers to the degradation of the performance of equipment, systems or propagation channels due to electromagnetic disturbances. Electromagnetic interference formation requires three elements:
(1) Electromagnetic interference source: Any electronic device or natural phenomenon that generates electromagnetic interference.
(2) Coupling approach: The electromagnetic interference energy is transmitted to the channel or medium of the interfered device.
(3) Disturbed sensitive equipment: Equipment subject to electromagnetic interference.
The coupling path of electromagnetic interference can be divided into conduction coupling and radiation coupling. Conductive coupling primarily refers to electromagnetic coupling that is transmitted along a power or signal line. There are various connections between devices in the electronic system or between the unit circuits in the electronic device, such as power lines, wires for transmitting signals, and common ground lines, etc., so that the electromagnetic energy of a device or unit circuit may be along this Class-like wires are transmitted to other devices and unit circuits to cause interference; radiated coupling refers to electromagnetic interference that propagates into the device through space. The power supply circuit of the interference source, the input/output signal circuit, and the control circuit can form a radiation antenna under certain conditions. If the outer casing of the interference source flows through a high-frequency current, the outer casing itself becomes a radiating antenna. In PCB boards, electromagnetic energy typically exists in two forms, differential mode EMI and common mode EMI.
1.2 Harm of electromagnetic interference
(1) Hazards to electronic systems and equipment. Electromagnetic interference may cause a limited degradation of the performance of the system or equipment, and may even cause the system or equipment to malfunction. If the interference is severe, the system or equipment may malfunction or be damaged.
(2) Hazards to weapons and equipment. Modern radio transmitters and radars generate very strong electromagnetic radiation fields. This kind of radiation field can cause the sensitive electronic detonating device installed in the weapon system to run out of control and start prematurely; the guided missile will cause deviation from the flight trajectory and increase the distance error; the aircraft will cause the operating system to be unstable and the heading is not allowed. Height display error, radar antenna tracking position offset, etc.
(3) The harm of electromagnetic energy to the human body. Once the electromagnetic radiation enters the human cell tissue, it will cause biological effects, namely local thermal effects and non-thermal effects. Electromagnetic radiation causes symptoms of human body diseases: dizziness, fatigue, memory loss, palpitations, excessive sweating, hair loss and sleep disorders.
Therefore, electromagnetic radiation has become one of the environmental pollution contents that must be controlled. Many countries have formulated the "Sanitary Standard for Electromagnetic Wave Irradiation".
1.3 EMC standards and specifications
(1) International level, such as IEC standards;
(2) at the conference level, such as CISPR publications;
(3) CE level, such as the European Harmonized Standard EN;
(4) National level, such as national GB, FCC, etc.;
(5) Military standards, such as the national military standard GJB, the US military standard MIL.
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