PCB electromagnetic interference suppression design
Source: InternetPublisher:走马观花 Keywords: Electromagnetic anti-interference PCB printed board Updated: 2023/11/17
The design of printed boards is an important part of making electronic products. With the rapid development of electronic technology, the density of PCBs is getting higher and higher, and the quality of PCB design has a great impact on the ability to resist interference. If the design is unreasonable, electromagnetic interference will occur, which will affect the performance of the circuit and even prevent it from working properly.
1. Electromagnetic interference mainly includes
1. There are inductance effects, resistance effects, conductance effects, and mutual inductance effects between parallel wires. A changing current in one wire will inevitably affect the other wire, causing interference.
2. The printed wires on the printed board, the external connecting wires and even the component leads may become antennas that transmit or receive interference signals. This cannot be ignored especially in the printed board design of high-frequency circuits.
3. The constant magnetic field generated by magnetic components in the circuit, such as speakers, electromagnets, permanent magnet meters, etc., and the sudden magnetic field generated by transformers, relays, etc. will also have an impact on the printed board.
2. Methods to Suppress Electromagnetic Interference
Electromagnetic interference cannot be completely avoided, but when designing printed boards, some measures can be taken to suppress the intensity of interference, improve the anti-interference ability of the unit circuit itself, and avoid or reduce interference.
1. Key points for laying out wires that are susceptible to interference.
Generally, low-level, high-impedance wires are susceptible to interference, and should be as short as possible during wiring: wires used for input and output terminals should be avoided as adjacent as possible, and it is best to add a ground between the wires. lines to avoid feedback coupling. The effect of parallel lines is proportional to the length. Wire them in order according to the direction of the signal, and avoid circuitous interleaving. Stay away from interference sources, try to stay away from power lines, high-level wires: when you really can't avoid the interference source, you can't run it in parallel with it, double-sided panels pass through each other, and single-panel flying wires transition. As shown in Figure 1.
1. Electromagnetic interference mainly includes
1. There are inductance effects, resistance effects, conductance effects, and mutual inductance effects between parallel wires. A changing current in one wire will inevitably affect the other wire, causing interference.
2. The printed wires on the printed board, the external connecting wires and even the component leads may become antennas that transmit or receive interference signals. This cannot be ignored especially in the printed board design of high-frequency circuits.
3. The constant magnetic field generated by magnetic components in the circuit, such as speakers, electromagnets, permanent magnet meters, etc., and the sudden magnetic field generated by transformers, relays, etc. will also have an impact on the printed board.
2. Methods to Suppress Electromagnetic Interference
Electromagnetic interference cannot be completely avoided, but when designing printed boards, some measures can be taken to suppress the intensity of interference, improve the anti-interference ability of the unit circuit itself, and avoid or reduce interference.
1. Key points for laying out wires that are susceptible to interference.
Generally, low-level, high-impedance wires are susceptible to interference, and should be as short as possible during wiring: wires used for input and output terminals should be avoided as adjacent as possible, and it is best to add a ground between the wires. lines to avoid feedback coupling. The effect of parallel lines is proportional to the length. Wire them in order according to the direction of the signal, and avoid circuitous interleaving. Stay away from interference sources, try to stay away from power lines, high-level wires: when you really can't avoid the interference source, you can't run it in parallel with it, double-sided panels pass through each other, and single-panel flying wires transition. As shown in Figure 1.
2. Avoid wire loops.
Loop wires on printed circuit boards are equivalent to single-turn coils or loop antennas, which enhance the inductance effect and antenna effect. When wiring, avoid looping areas as much as possible. as shown in picture 2.
Loop wires on printed circuit boards are equivalent to single-turn coils or loop antennas, which enhance the inductance effect and antenna effect. When wiring, avoid looping areas as much as possible. as shown in picture 2.
3. Key points of feedback wiring:
Feedback components and wires connect the input and output. Improper wiring can easily introduce interference.
As shown in Figure 3 of the amplifier circuit, the feedback wire crosses the amplifier base resistor. Parasitic coupling may occur, affecting circuit operation. The layout of the circuit shown in Figure 4 places the feedback component in the middle and the output wires away from the front-end components to avoid interference.
Feedback components and wires connect the input and output. Improper wiring can easily introduce interference.
As shown in Figure 3 of the amplifier circuit, the feedback wire crosses the amplifier base resistor. Parasitic coupling may occur, affecting circuit operation. The layout of the circuit shown in Figure 4 places the feedback component in the middle and the output wires away from the front-end components to avoid interference.
4. Set up the shielded ground wire.
There are the following forms of setting up the shielded ground wire in the printed board:
(1) Large-area shielded ground wire
, as shown in Figure 5. The shielded ground wire cannot be used as a signal ground wire, but can only be used for shielding.
There are the following forms of setting up the shielded ground wire in the printed board:
(1) Large-area shielded ground wire
, as shown in Figure 5. The shielded ground wire cannot be used as a signal ground wire, but can only be used for shielding.
(2) Set up a dedicated ground ring
as shown in Figure 6, and lay the ground wire around the input signal line to avoid interference to the input line. This shielded ground wire can be single-sided, double-sided, or on another layer.
as shown in Figure 6, and lay the ground wire around the input signal line to avoid interference to the input line. This shielded ground wire can be single-sided, double-sided, or on another layer.
(3)
In shielded wire high-frequency circuits, the distribution parameters of printed wires have a great influence on the signal, and impedance matching is not easy. Special shielded wires can be used locally for connection, as shown in Figure 7.
In shielded wire high-frequency circuits, the distribution parameters of printed wires have a great influence on the signal, and impedance matching is not easy. Special shielded wires can be used locally for connection, as shown in Figure 7.
The capacitor leads cannot be too long, especially high-frequency bypass capacitors cannot have leads. In addition, you should also pay attention to:
(1) When there are contactors, relays, buttons and other components in the printed circuit board, large spark discharge will be generated during operation, and an RC circuit must be used to absorb the discharge current. Generally, R takes 1~2K, and C takes 2.2~4.7μF.
(2) The input impedance of the CMOS circuit is very high and is susceptible to induction, so the unused terminals must be grounded or connected to a positive power supply when in use.
Printed circuit boards are the most basic components of electronic products. Interference suppression on printed circuit boards is a highly skilled job and requires a lot of experience accumulation. As long as we follow some rules in design and pay attention to the accumulation and summary of experience and technology, we will be able to design a PCB board with excellent performance.
(1) When there are contactors, relays, buttons and other components in the printed circuit board, large spark discharge will be generated during operation, and an RC circuit must be used to absorb the discharge current. Generally, R takes 1~2K, and C takes 2.2~4.7μF.
(2) The input impedance of the CMOS circuit is very high and is susceptible to induction, so the unused terminals must be grounded or connected to a positive power supply when in use.
Printed circuit boards are the most basic components of electronic products. Interference suppression on printed circuit boards is a highly skilled job and requires a lot of experience accumulation. As long as we follow some rules in design and pay attention to the accumulation and summary of experience and technology, we will be able to design a PCB board with excellent performance.
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