Shenzhen PCB design company PCB engineer notes

EMC problem

At the time of layout, you should also pay attention to EMC suppression! ! This is very difficult to grasp, distributed capacitance is always there! !

How to ground!

PCB design originally had to consider a lot of factors, different environments need to consider different factors. In addition, I am not a PCB engineer, the experience is not rich :)))

Ground segmentation and tandem

Grounding is one of the important means to suppress electromagnetic interference and improve the EMC performance of electronic equipment. Proper grounding not only improves the ability of the product to suppress electromagnetic interference, but also reduces the external EMI emissions of the product.

Grounding purpose

A. Safety considerations, that is, protective grounding;

B. Provide a stable zero potential reference point (signal ground or system ground) for the signal voltage;

C. Shield grounding.

Basic grounding method

There are three basic grounding methods in electronic equipment: single-point grounding, multi-point grounding, and floating.

Shenzhen PCB design company engineers pay attention

Single point grounding

Single point grounding is the entire system, only one physical point is defined as the ground reference point, and other points that need to be grounded are connected to this point.

Single point grounding is suitable for circuits with lower frequencies (below 1 MHZ). If the operating frequency of the system is so high that the working wavelength is comparable to the length of the system ground lead, the single-point grounding method is problematic. When the length of the local line is close to 1/4 wavelength, it is like a transmission line with a short circuit at the end. The current and voltage of the ground line are distributed in standing wave, and the ground line becomes a radiating antenna, but it cannot function as a "ground". .

In order to reduce the grounding impedance and avoid radiation, the length of the ground wire should be less than 1/20 wavelength. In the processing of the power circuit, a single point grounding can generally be considered. For PCBs with a large number of digital circuits, because of their high level of harmonics, single-point grounding is generally not recommended.

Multi-point grounding

Multi-point grounding means that each grounding point in the equipment is directly connected to the ground plane closest to it so that the length of the grounding lead is the shortest.

The multi-point grounding circuit has a simple structure, and the high-frequency standing wave phenomenon that may occur on the grounding line is significantly reduced, and is suitable for applications with a high operating frequency (>10 MHz). However, multi-point grounding may cause many ground loops to form inside the device, thus reducing the ability of the device to resist external electromagnetic fields.

As an engineer of Shenzhen PCB Design Company, we must pay attention to the above matters.