What is electromagnetic interference? Electromagnetic interference (EMI) is an electrical noise that interferes with cable signals and reduces signal integrity. EMI is typically generated by electromagnetic radiation sources such as motors and machines.
What is the cause of electromagnetic interference?We often hear electromagnetic interference, but how does electromagnetic interference come about? In fact, the factors that cause interference are very complicated. There are two modes of interference, namely common mode and differential mode. The “common mode†interference refers to the existence of the line, including the conduction test caused by the field induction, etc. For the secondary and the line, all they feel are common mode interference.
Electromagnetic interference, both conducted and radiated. Conducted interference refers to the coupling (interference) of signals on one electrical network to another electrical network through a conductive medium. Radiated interference refers to an interference source that couples (interferes) its signal to another electrical network through space. In high-speed PCB and system design, high-frequency signal lines, integrated circuit pins, various types of connectors, etc. may become radiation interference sources with antenna characteristics, which can emit electromagnetic waves and affect other systems or other subsystems in the system. normal work. The so-called "interference", electromagnetic compatibility refers to the meaning of the device after the interference is reduced and the interference source to the device.
Type of electromagnetic interferenceElectromagnetic interference EMI (ElectromagneTIc Interference), there are two types of conducted interference and radiated interference.
Conducted interference refers to the coupling (interference) of signals on one electrical network to another electrical network through a conductive medium.
Radiated interference refers to an interference source that couples (interferes) its signal to another electrical network through space.
In high-speed PCB and system design, high-frequency signal lines, integrated circuit pins, various types of connectors, etc. may become radiation interference sources with antenna characteristics, which can emit electromagnetic waves and affect other systems or other subsystems in the system. normal work.
1. Electromagnetic interference source
Sources of electromagnetic interference include microprocessors, microcontrollers, transmitters, electrostatic discharges, and transient power actuators such as electromechanical relays, switching power supplies, lightning, and the like. In a microcontroller system, the clock circuit is the largest broadband noise generator, and this noise is spread throughout the spectrum. With the development of a large number of high-speed semiconductor devices, the edge jump rate is very fast, and this circuit will generate harmonic interference of up to 300 MHz.
2. Coupling path
The noise is coupled to the conductor that is most easily passed through the circuit, as shown in the figure for analyzing the electromagnetic interference mechanism. If a wire passes through a noisy environment, the wire senses ambient noise and passes it to the rest of the circuit. Noise enters the system through the power line, and the noise carried by the power line is transmitted to the entire circuit, which is a coupling situation.
Coupling also occurs in circuits with shared load (impedance). For example, two circuits share a wire that provides power or a ground wire. If one of the circuits requires a large burst of current, and the two circuits share the power line, equivalent to the same internal resistance of the power supply, the imbalance of the current will cause the power supply voltage of the other circuit to drop. The effect of this coupling can be reduced by reducing the common impedance. However, the internal resistance of the power supply and the grounding conductor are fixed. If the grounding is unstable, the return current flowing in one circuit will cause the ground potential to change in the grounding circuit of the other circuit. The fluctuation of the ground potential will seriously reduce the low level of the analog-to-digital converter, operational amplifier and sensor. The performance of analog circuits.
In addition, electromagnetic wave radiation is present in each circuit, which forms a coupling between circuits. When the current changes, electromagnetic waves are generated. These electromagnetic waves can couple into nearby conductors and interfere with other signals in the circuit.
3. receiver
All electronic circuits can be subject to electromagnetic interference. Although some of the electromagnetic interference is directly accepted by means of radio frequency radiation, most electromagnetic interference is accepted by transient conduction. In digital circuits, critical signals such as resets, interrupts, and control signals are most susceptible to electromagnetic interference. Control circuits, analog low-level amplifiers, and power conditioning circuits are also susceptible to noise.
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