PCB interference is mainly divided into two types. One type comes from within the PCB, mainly due to the influence of parasitic coupling between adjacent circuits and field coupling of internal components, resulting in signal crosstalk along the transmission path. For example, capacitors on PCBs, especially those used in high-frequency situations. We can consider it as an LCR circuit, because when a capacitor actually works in a circuit, it generally produces equivalent inductance and impedance, and the capacitor has a self resonant frequency. At the self resonant frequency, the capacitor exhibits capacitance. When the frequency is higher than the self resonant frequency, the capacitance appears inductive, and the impedance increases with the increase of frequency.

　　Another type of electromagnetic interference comes from the outside of the PCB, which is further divided into two types: radiation interference and sensitive element problems. Radiation mainly comes from harmonic sources of clocks and other periodic signals, and some electronic devices or instruments generate second harmonics due to voltage and power supply fluctuations.