Electromagnetic interference analysis and suppression measures

This article will analyze the generation mechanism of electromagnetic emission and magnetic field interference in electronic products, and introduce various technical measures to effectively suppress and prevent interference. When electronic and electrical products are working normally, they also radiate electromagnetic disturbance to the surrounding space. The radiated disturbance field strength often exceeds the limit in certain frequency bands and will affect the normal operation of the surrounding electronic equipment and itself. Therefore, understanding the reasons for exceeding the standard and the suppression methods of electromagnetic emission and magnetic field interference are very important for the electromagnetic compatibility (EMC) design of the product. 01 Mechanism of electromagnetic emission and magnetic field interference 1) Electromagnetic emission of various digital circuit chips and high-frequency analog circuit chips during the operation, due to the unreasonable design of PCB wiring or the connection of various parts of the product, an antenna effect is generated, which is caused by electromagnetic waves. Radio frequency interference. When the electromagnetic wave energy reaches a certain value, it will affect the normal operation of the surrounding electronic equipment and itself. 2) The magnetic field interferes with the internal power line of the product and the magnetic field generated by the inductive components working at high frequency through radiation, which interferes with the operation of the product, causing work disorder. 02 Electromagnetic emission and suppression of electronic products In electronic products, the frequency of the transition edge of the digital circuit chip port signal can reach hundreds of megahertz, and some analog circuit signal frequencies reach more than megahertz, and these digital or analog signals may pass through the wire Conducted interference or radiated interference into the air affects the electronic equipment itself and interferes with other electronic equipment. The basic measures to suppress electromagnetic emissions are as follows. 2.1 Reduce the energy of interference signals 1) Reduce the hopping rate of digital signals or reduce the transmission speed of digital signals without affecting the overall working performance of the product; 2) Adopt SMD components to shorten the external lead of high-frequency working chips Feet, reduce the length of the high-frequency signal transmission line, which can suppress the antenna effect and reduce the radiated energy of the high-frequency signal. 2.2 Isolate the propagation path of interference signals Grounding in electronic equipment is one of the important methods to suppress electromagnetic noise and prevent electromagnetic interference. The simplest and effective isolation method is shielding, also known as 'shielding groundingThere are three commonly used shielding methods: 1) Use magnetically permeable metal material shell packaging, the shell is reliably grounded (earth); 2) Local circuits or IC chips that are prone to high-frequency radiation plus metal shields, and the shields are connected to signal ground; ) The two sides of the traces that transmit high-speed digital signals or high-frequency analog signals in the circuit board are coated with copper and connected to signal ground to achieve isolation from other signal lines. 2.3 The filter filter can not only suppress the conducted interference from electronic equipment, but also suppress the conducted interference introduced from the power grid. EMI (electromagnetic interference) filters are mainly used to suppress interference. The EMI filter is composed of a linear component circuit and is installed between the power line and the electronic equipment. It allows the power frequency to pass, and prevents high-frequency noise from passing, which plays an important role in improving the reliability of the equipment. 1) Connect decoupling capacitors or decoupling resistor capacitors directly between the power pins of the circuit chip to filter out high-frequency interference signals that enter the chip through the power traces; 2) Set a power filter on the product's AC 220 V power input to prevent The high frequency interference generated when the product is working enters the power grid. Enter the pricing page https://www./