[Repost] What are the key points to follow in EMC processing?

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[Repost] What are the key points to follow in EMC processing? [Copy link]

EMC has become a "metaphysics" for many novices in the design of electronic circuit systems. The main reason is that it is easy to say but difficult to deal with. Simply put, it is internal and external interference. It is difficult to deal with it and it is often a mess and you can't find the problem point. Whether it is an ordinary circuit system or a high-speed circuit system, it is very necessary for us to deal with EMC. So today I will share an article to learn a few key points. In fact, following these principles can greatly reduce the probability of EMC problems.

1. Power system processing:

One principle: There must be the concept of source and impedance. The source needs to reach the IC to the maximum extent and then return from the ground as quickly as possible.

[color=rgb(25, This is the design division of the PDN system. The key point of the switching power supply design lies in the processing of the switching current loop. The loop should be small!

For copper coating: avoid the RF part from interfering with the digital GND noise through coupling, digital circuit abnormality, and pay attention to the coupling interference problem in the radiation area.

Avoid the formation of a large source loop and bridge the Plane layer.

For the copper coating of the Plane layer, pay attention to leaving gaps at the edges to reduce the influence of edge effects.

Place the decoupling capacitor nearby to reduce parasitic inductance and avoid decoupling failure.

Note that the difference between the AC path and the DC path lies in the coupling.

Regarding the grounding of the signal ground and the bracket, the purpose of grounding is to provide a discharge path for interference, and the purpose of the loop opening is to avoid the formation of a large loop antenna and cause EMI interference.

2. Signal considerations

The spectrum of the high-speed signal is shown in the figure above. Our goal is to transmit all the energy to the receiving end.

Impedance equivalent of transmission line:

Microstrip line model:

Coupling model of differential signal:

Impedance of transmission line:

Several termination matching:

3. Layout

Wiring:

The principle of wiring is to reduce process interference based on the shortest distance and minimum impedance.

The reason for the formation of the eye diagram is the superposition effect of a series of digital signals, which reflects the quality of the transmission signal.

Simple 3W principle.

Special attention to the wiring of the crystal oscillator:

Fourth, ESD problem

ESD problem is very common and is an important cause of chip damage, especially in the production process, TVS is the best protection device.

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led2015

Thanks for sharing. In the past, when testing EMC, I always saw that the curve exceeded the standard, and it was a waste of time to change it again and again.