Solving the electromagnetic compatibility issues of polychlorinated biphenyls

There are two main types of PCB interference. One comes from inside the PCB. This is mainly due to signal crosstalk along the transmission path caused by parasitic coupling between adjacent circuits and field coupling of internal components. For example, capacitors on PCBs, especially those used for high-frequency applications. We can consider it as an LCR circuit because when a capacitor operates in the circuit, it usually produces equivalent inductance and impedance. Capacitors have self resonant frequencies. At self resonant frequency, capacitors are capacitive. Above the self resonant frequency, capacitance is inductive and impedance increases with increasing frequency.
Another type of electromagnetic interference comes from outside the PCB and is divided into two types: radiation interference and sensitive components. The radiation mainly comes from the harmonic source of the clock and other periodic signals. Some electronic devices or instruments also generate second harmonics due to voltage and power jumps.
To avoid PCB electromagnetic interference, the following points should be taken into consideration:
1. Reasonable design drawings
When designing a circuit board, the first thing to do is to design a schematic diagram. Design schematics are generally operated by Altium Designer software, and all components used can be filtered in the schematic library. If there are no components to select in the schematic library, you can draw them yourself.
After drawing the schematic, automatic detection is required to check for obvious errors during the drawing process. After completing the schematic, the printed circuit board can be designed. The results of automatic routing are often unsatisfactory and require manual routing. When designing printed circuit boards, electromagnetic compatibility has become an important technical requirement to consider. The reasonable layout of components and circuits in printed circuit boards can effectively reduce electromagnetic interference problems.
2. Choose capacitors with lower equivalent inductance and resistance
The issue of cross-talk should also be noted. Crosstalk is the energy coupling between one wire and another. According to the Faraday electromagnetic induction phenomenon, when a wire passes through an electric current, a magnetic field is generated around the wire. The interaction of magnetic fields between different wires can cause crosstalk. Mutual inductance is one of the mechanisms that generate crosstalk, and its magnitude is proportional to the current in the wire.
3. Limit periodic signals to the smallest possible area
Mutual capacitance is another mechanism that generates crosstalk. Cross talk is generated by the coupling of two electrodes through an electric field. The solution is to limit periodic signals to the smallest possible range and block parasitic coupling paths with the outside world. Filters can be used if necessary; The external sensitivity mainly includes radio frequency interference and electrostatic discharge. To solve this problem, shielding, good grounding, and filtering methods can be used.