Concept

During the process of rectifying the product, we will first consider the key factors that affect EMC, which enables us to quickly identify the problem and improve efficiency. The key factors mainly include voltage, frequency and grounding. 

1) Voltage - The higher the power supply voltage, the greater the voltage amplitude and the more emissions will occur. However, a low power supply voltage will affect the sensitivity. 

2) Frequency - Higher frequencies generate more emissions, and periodic signals also generate more emissions. In high-frequency digital systems, current spike signals are generated when the devices switch; in analog systems, current spike signals are generated when the load current changes. For example, for sensitive components (such as MOS transistors, high-frequency transformers), etc.:

3) Grounding - For circuit design, there is nothing more crucial than a reliable and perfect power system. Among all EMC issues, the main problem is caused by improper grounding. 

There are three methods for signal grounding: single-point, multi-point and hybrid. 

At frequencies lower than 1 MHz, the single-point grounding method can be adopted, but it is not suitable for high frequencies.

In high-frequency applications, it is advisable to use multiple grounding points.

Mixed grounding is a method where single-point grounding is used for low-frequency applications and multiple-point grounding is used for high-frequency applications. 

The ground layout is crucial. The ground circuits for high-frequency digital circuits and low-level analog circuits must not be mixed together.