The frequency of electronic signals and processors in electronic devices is increasing, which the electronic system is complex device with various components and many subsystems. High density and high speed will increase the radiation, while low pressure and high sensitivity will reduce the system immunity.
Therefore, electromagnetic interference (EMI) is a threat to the safety reliability and stability of electronic equipment. When designing electronic products, PCB design is critical to solve the EMI problems.
Definition of EMI
Electromagnetic interference (EMI) can be divided into radiation and conduction interference. Radiation interference refers to the source takes space as a media to interfere electrical network with its signal. And the conduction interference is to use the conductive medium as a media to interfere another electrical network with the signals. In the high-speed system design, the integrated circuit pins, high-frequency signal traces and various types of plugs are common radiation interference sources in PCB design. The electromagnetic waves they emit are electromagnetic interference (EMI), which will affect the normal work of itself and other systems.
Tips in PCB design to avoid EMI
Nowadays, there are a lot of solutions to solve the problem of EMI, such as: EMI suppression coating, the appropriate EMI suppression parts and EMI simulation design, etc. Now let's take a brief introduction on these tips.
1. Common mode EMI interference source
In the power layer with a low value of the inductor, the inductance of the synthesis of the transient signal will be reduced, reducing the common mode EMI.
Reduce the length of the power supply to the IC power supply pin.
Use 3-6 mil PCB layer spacing and FR4 dielectric material.
2. Electromagnetic shielding
Try to place the signals on the same PCB layer, and close to the power plane or ground plane.
The power plane should be as close as possible to the ground plane
Different components distribution will affect the circuit interference and anti-interference capability. Thus, designers should do blocking according to different functions. In this process, you’d better separate the strong and weak signals, as well as digital and analog signal circuits.
The filter network of each part of the circuit must be near the connection, so not only can reduce the radiation, which can improve the circuit's anti-jamming capability and reduce the chance of being disturbed.
The parts that are susceptible to interference should avoid interference sources such as CPU interference on the data processing board.
Unreasonable layout will cause cross-interference between the signal traces.
There cannot be close to the PCB border, to avoid disconnection in manufacture.
The power line should be wide so as to reduce the loop resistance.
The signal traces are as short as possible and reduce the number of vias.
Corner layout cannot be used in the right angle, 135 °is better.
Digital circuits and analog circuits should be isolated by ground. Both digital ground and analog ground are separated, and finally connected to the power ground.