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Some general knowledge of EMC system integration

Release time:

2022-10-13 11:45

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EMC system integration manufacturers believe that in circuit design, we tend to focus on increasing wiring density or pursuing uniform layout, ignoring the impact of circuit layout on interference prevention, making a large amount of signal radiation in space to form interference, which may lead to more EMC problems. Therefore, good wiring is the key to successful design.

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EMC system integration manufacturers believe that the ground is not only a potential reference point for the circuit, but also a low-impedance circuit for the signal. A common interference on the ground is ground loop interference caused by ground loop current. Solving this interference problem is equivalent to solving most of the EMC problems. Noise on the ground mainly affects the ground level of digital circuits, and when digital circuits output low levels, they are more sensitive to noise on the ground. Interference from the ground can cause not only circuit failures, but also conducted and radiated emissions. So the key to reducing these interferences is to reduce the impedance of the ground as much as possible (for digital circuits, it is especially important to reduce the inductance of the ground). The arrangement of grounding lines should pay attention to the following points.

(1) According to the different supply voltages, ground wires are set separately for digital and analog circuits.

(2) EMC system integration manufacturers believe that the common ground wire should be as thick as possible. When using multilayer thick film process, grounding ground can be set specifically to help reduce the loop area and reduce the efficiency of antenna reception. And can be used as a shield for signal lines.

(3) Comb ground wire should be avoided. This structure makes the signal return loop very large, which will increase the radiation and sensitivity, and the common impedance between the chips may also cause circuit misoperation.

(4) EMC system integration manufacturers believe that when multiple chips are installed on the board, a large potential difference is generated on the grounding line. The grounding line should be designed as a closed loop to improve the noise tolerance of the circuit.

(5) Boards with both analog and digital functions, analog ground and digital ground are usually separate and connected only at the power supply.

EMC system integration manufacturers believe that in addition to the interference directly caused by electromagnetic radiation, electromagnetic interference caused by power lines is the most common. Therefore, the layout of power lines is also important, and the following rules should generally be observed [.

(1) EMC system integration manufacturers believe that power lines as close as possible to the ground, reduce the area of the power supply circuit, the differential mode radiation is small, which helps reduce circuit cross-talk. Do not overlap the power supply loops of different power supplies.

(2) When using a multilayer process, analog and digital power supplies are separated to avoid mutual interference. Do not overlap the digital power supply and analog power supply, otherwise it will generate coupling capacitance and destroy the isolation.

(3) The power supply layer can be completely isolated from the grounding layer. When the frequency and speed are high, a dielectric paste with low dielectric constant should be selected. The power supply layer should be close to the grounding layer and arranged below the grounding layer to shield the radiation current distributed in the power supply layer.

(4) EMC system integration manufacturers believe that the chip should be decoupled between the power supply pins and ground pins. The decoupling capacitor is a 0.01uF chip capacitor, which should be installed close to the chip to minimize the loop area of the decoupling capacitor.

(5) When choosing a chip for SMD, try to choose a chip with the power supply pin close to the ground pin, which can further reduce the power loop area of the decoupling capacitor and help achieve electromagnetic compatibility.

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