Electronic Design - How to design to reduce PCB electromagnetic interference

The frequency of electronic devices increases with the increase of electronic signals and processors, and electronic systems are complex devices with various components and many subsystems. High density and high speed can increase the radiation of the system, while low pressure and high sensitivity can reduce the immunity of the system. Therefore, electromagnetic interference (EMI) is a real threat to the safety, reliability and stability of electronic equipment. When designing electronic products, the design of the PCB board is very important to solve the EMI problem.

This article mainly explains what PCB design should pay attention to, so as to reduce the electromagnetic interference problem of PCB board.

Definition of electromagnetic interference (EMI) Electromagnetic interference (Emi, electromagnetic interference) can be divided into radiated and conducted interference. Radiated interference is a source of interference, where space acts as a medium to interfere with its signal to another power grid. Conducted interference is the use of conductive media as a medium to interfere with signals on one power grid to another power grid.

In the design of high-speed systems, integrated circuit pins, high-frequency signal lines and various types of plugs are common sources of radiation interference in PCB board design. The electromagnetic waves they emit are electromagnetic interference (EMI). Affect normal operation.

PCB board design techniques for electromagnetic interference (EMI) Today's PCB board design techniques include solutions to many EMI problems, such as EMI suppression coatings, appropriate EMI suppression components, and EMI simulation design. The above video introduces ways to reduce EMI.

Now let us briefly introduce these PCB technologies.

Tip 1: Common mode EMI interference source (for example, the voltage drop formed at both ends of the inductance of the decoupling path when a transient voltage is formed at the power confluence)

-With low-value inductors in the power layer, the transient signal synthesized by the inductance is reduced, and the common mode EMI is reduced.

-Reduce the length of the connection from the power plane to the IC power pin.

-Use 3-6 mil PCB layer spacing and FR4 dielectric material.

Tip 2: electromagnetic shielding

-Try to place the signal line on the same PCB layer and close to the power layer or connection layer.

-The power plane should be as close as possible to the ground plane

Tip 3: Layout of components (different layouts will affect the interference and anti-interference ability of the circuit)

-Perform block processing according to different functions in the circuit (such as demodulation circuit, high-frequency amplifier circuit and mixer circuit, etc.). In the process of separating strong and weak electrical signals, digital and analog signal circuits are separated

-The filter network of each part of the circuit must be connected to the nearest one, which can not only reduce the spokes, but also improve the anti-interference ability of the circuit and reduce the chance of interference.

-Disturbance-susceptible components should be arranged as much as possible to avoid interference sources, such as CPU interference on the data processing board.

Tip 4: Wiring precautions (unreasonable wiring may cause cross interference between signal wires)

-There should be no wires near the PCB board frame to avoid disconnection during the production process.

-The power cord should be wide and the loop resistance will be reduced.

-The signal line should be as short as possible to reduce the number of holes.

-Corner wiring cannot use the right-angle method, and an angle of 135° should be preferred.

-Digital circuit and analog circuit should be isolated by ground wire, digital ground wire and analog ground wire should be separated, and finally connected to the power supply to reduce electromagnetic interference is an important part of PCB board design. As long as you design more in this regard, it will naturally EMC testing in product testing will be more qualified.