VIIP PCB Mixed-Signal Interference Solutions: Discussion on Power Filter and Layout Optimization Strategies

I. Definition of Electromagnetic Interference

Electromagnetic Interference (EMI) refers to any electromagnetic phenomenon that occurs when voltage and current are present in a conductive medium or in the presence of an electromagnetic field, which can degrade the performance of a device, equipment, or system, and may also have adverse effects on living organisms or substances. It is mainly divided into two types: conducted interference and radiated interference. Conducted interference refers to coupling (interference) a signal from one electrical network to another through a conductive medium; while radiated interference refers to coupling (interference) a signal from the interference source to another electrical network through space.

II. Generation of Electromagnetic Interference

The generation of electromagnetic interference mainly stems from internal interference and external interference. Internal interference primarily originates from mutual interference among various components within electronic devices, such as interference caused by leakage currents generated by distributed capacitance and insulation resistance in power lines, impedance coupling among signal lines, power lines, and transmission lines, or interference caused by mutual inductance between conductors. External interference refers to factors outside electronic devices or systems that interfere with circuits, equipment, or systems, such as lightning strikes or switching operations of nearby electrical equipment.

III. Strategies for Suppressing Electromagnetic Interference

1. Power Filter

A power filter is a filtering circuit composed of capacitors, inductors, and resistors, mainly used to filter out specific frequency points in the power line or frequencies beyond that point, thus obtaining a power signal at a specific frequency or eliminating the power signal after a specific frequency. The main principle of a power filter is impedance matching network, which effectively attenuates electromagnetic interference by increasing impedance matching between the input and output sides of the power filter and the power and load sides. Therefore, correctly selecting and using power filters can to some extent address the electromagnetic interference issues of devices.

2. Coupling of External Interference (Input and Output)

Coupling of external interference mainly occurs at the input and output ends of the filter. To reduce this coupling, it is necessary to design the input and output circuits of the filter reasonably and optimize the layout and grounding method of the filter. For example, common-mode chokes or differential-mode capacitors can be added at the input end to filter out common-mode or differential-mode interference.

3. Switch Tubes

As important components in electronic devices, the changing operating states of switch tubes may generate electromagnetic interference. To reduce this interference, switch tubes with lower electromagnetic radiation can be selected, or the electromagnetic interference they produce can be reduced by optimizing the drive circuit and operating mode of the switch tubes.

4. Transformers

Transformers may generate electromagnetic interference during operation, mainly due to changes in their magnetic fields. To reduce this interference, transformers with low magnetic leakage and low noise can be selected, or the electromagnetic interference they produce can be reduced by optimizing the layout and grounding method of the transformers.

5.  Diodes and Energy Storage Inductors

Diodes and energy storage inductors are widely used in electronic devices, but changes in their operating states may also generate electromagnetic interference. To reduce this interference, diodes and inductors with excellent electrical performance can be selected, or their electromagnetic interference can be reduced by optimizing their operating circuits and layouts.

6. PCB Layout and Routing

      The layout and routing of PCBs have a significant impact on electromagnetic interference. To reduce electromagnetic interference, it is necessary to optimize the layout of PCBs by separating high-frequency signal lines and sensitive signal lines as much as possible to reduce coupling between them. Additionally, routing should be designed reasonably to avoid excessively long, thin, or complex traces to minimize electromagnetic radiation and crosstalk.

In conclusion, while power filters are an effective means to address equipment interference issues, it is also necessary to combine other strategies to suppress electromagnetic interference, such as optimizing the coupling of external interference, switch tubes, transformers, diodes, energy storage inductors, PCB layout, and routing. Only by comprehensively and effectively addressing equipment electromagnetic interference issues can the best interference suppression results be achieved in practical applications. It is important to select appropriate strategies based on the specific conditions of the equipment and the characteristics of the interference sources.