The frequency of electronic signals and processors in electronic devices is increasing, and the electronic system has been a complex device including a variety of components and many subsystems. High density and high speed will aggravate the radiation of the system, and low voltage and high sensitivity can reduce the system's disturbance. Therefore, electromagnetic interference (EMI) is a real threat to the safety, reliability and stability of electronic devices. When we design electronic products, the design of PCB board is very important to solve the problem of EMI.
EMI (Electro MagneTIc Interference) can be divided into radiation and conduction interference. Radiation interference is the interference source that interferes with its signal to another network by space as a medium. The conduction interference is to disturb the signal on an electric network to another electric network by conducting media as media. In the design of high-speed system, integrated circuit pins, high frequency signal lines and all kinds of connectors are common radiation interference sources in the design of PCB boards. The electromagnetic waves emitted by them are electromagnetic interference (EMI), and their own and other systems will affect normal work.
PCB board design techniques for electromagnetic interference (EMI)
There are many solutions to EMI problems in PCB board design techniques, such as EMI suppression coating, appropriate EMI suppression parts and EMI simulation design. Now simply explain these skills.
1. A common mode EMI interference source (such as a voltage drop formed at both ends of the inductor of the decoupling path, such as the transient voltage formed by a power supply confluence).
With a low value inductor in the power layer, the transient signal produced by the inductor will be reduced, and the common mode EMI is reduced.
Reduce the length of the power layer to the IC power pin connection.
Using 3-6 mil PCB layer spacing and FR4 dielectric material.
2, electromagnetic shielding
Try to put the signal on the same PCB layer and close to the power layer or the ground.
The power layer should be as close to the ground as possible.
3. The layout of the parts (the different layout will affect the interference and anti-interference ability of the circuit).
According to the different functions of the circuit, block processing (such as demodulation circuit, high frequency amplifying circuit and mixing circuit) is adopted. In this process, the strong and weak electrical signals are separated, and the digital and analog signal circuits are separated.
The filter network of each part must be connected nearby, so that it can not only reduce the spoke, but also improve the anti-interference ability of the circuit and reduce the chance of being disturbed.
The distracted parts should avoid interference sources as far as possible, such as the interference of CPU on the data processing board.
4. Consideration of wiring (unreasonable wiring will cause cross interference between signal lines)
There can not be the border of the line close to the PCB plate, so as to avoid the broken line in the production.
The power line is wide, and the loop resistance will be reduced.
The signal line is as short as possible and reduces the number of holes.
The corner of the wiring can not be used right angle method, should be 135 degree angle as the best.
The digital and analog circuits should be isolated from the ground lines, and the digital ground lines and the analog ground lines should be separated and finally connected to the power supply.
Reducing electromagnetic interference is an important part of the PCB board design, so long as it is designed to be more easily qualified on this side of the product test such as the EMC test.