Learning a new technology will always encounter various problems, and learning EMC is no exception.
EMC (electromagnetic compatibility) includes two parts: EMS (electromagnetic sensitivity) and EMI (electromagnetic interference). What we usually say is to solve the problem of external radiation interference of electronic equipment, or how to prevent equipment and electronic components from being interfered by external electromagnetic waves.
In learning EMC, we should attach importance to the basic knowledge, such as the introduction theory of electromagnetic wave and electromagnetic field. We have an urgent desire to learn. In practice, we can communicate with many people. The learning and communication effect of several people is much better than that of one person.
Here are the common compatibility problems and specific solutions of EMC engineers for learning notes.
Why does the ground wire and power line of digital circuit often have a large noise voltage? How to reduce these noise voltages?
Answer: The digital circuit will absorb a large amount of current instantaneously when it is working. When these transient currents flow through the power line and ground wire, due to the existence of the inductance of the power line and ground wire, a large backlash voltage will be generated, which is the observed noise voltage.
One way to reduce these noise voltages is to reduce the inductance of the power line and ground wire, such as the use of grid ground, ground wire surface, power line surface, etc., and the other is to use an appropriate decoupling capacitor (energy storage capacitor) on the power line.
In practice, it is common to twist multiple strands of wires as high-frequency conductors, which is said to reduce the RF impedance of wires. Why?
In this way, the surface area of the wire is increased, thus reducing the high-frequency resistance.
When designing the electromagnetic compatibility of circuits or circuit boards, special attention should be paid to the processing of key signals. What are the key signals here?
From the perspective of electromagnetic emission, key signal lines refer to periodic signals, such as local oscillator signal, clock signal, address low bit signal, etc; From the perspective of sensitivity, key signals refer to signals that are very sensitive to external electromagnetic interference, such as low-level analog signals.
How to prevent electrochemical corrosion at the bonding point?
Select the metal with the electrochemical potential close to, or seal the contact part with the environment to isolate the electrolyte.
What is lapping and how many lapping methods?
The low impedance (RF) connection between metal components is called lapping. The lapping methods include welding, riveting, screw connection, electromagnetic sealing gasket connection, etc.
Please list as many ways as possible to reduce the RF impedance of the ground wire?
Try to use conductors with large surface area to reduce the resistance of high-frequency current; Try to make the conductor shorter to reduce resistance and inductance; Plating silver on the conductor surface to reduce the surface resistance; Multiple conductors are connected in parallel to reduce inductance.
Why are some ground wires grounded through capacitance or inductance in some imported prototypes?
Answer: To make the ground wire system present different ground wire structures for signals of different frequencies.
What is the root cause of ground wire interference?
Answer: The impedance of the ground wire is the root cause of the ground wire problem. Because of the existence of the ground wire impedance, when the current flows on the ground wire, it will generate voltage and form potential difference.
When we design the circuit, we assume that the potential of each point on the ground wire is the same, and the ground wire potential is the reference potential for the whole system to work. The difference between the actual ground wire potential and the assumed conditions leads to various ground wire problems.
When analyzing electromagnetic interference problems, what definition is often used to describe ground wire?
The ground wire should be defined as the return wire of the signal.
When there are many wires passing through the panel, filter connectors or filter array boards are often used. What problems should be paid attention to when installing filter connectors or filter array boards?
The electromagnetic sealing gasket shall be installed between the filter connector or filter array board and the chassis panel or the gap shall be glued with conductive tape to prevent electromagnetic leakage at the gap.
