about Electronic connector How much do you know about electromagnetic interference problems? If you ask how to prevent and deal with electromagnetic interference problems of connectors, you can say a few points. I'm afraid few people can answer such professional questions. At present, the clock frequency of the electronic system is several hundred MHz, and the front and rear edges of the pulses used are in the sub nanosecond range. High quality video circuits are also used for sub nanosecond pixel rate. These higher processing speeds indicate that industrial defense is constantly challenged. below Dessau Electronics to talk to you about the connector electromagnetic interference.
The oscillation rate on the circuit becomes faster (rise/fall time), the voltage and current amplitude become larger, and the problems become more. Therefore, it is more difficult to solve electromagnetic compatibility (EMC).
Before the two wave nodes of the circuit, the rapidly changing pulse current represents the so-called differential mode noise source. The electromagnetic field around the circuit can be coupled to other components and invade the connection part. The noise through inductive or capacitive coupling is common mode interference. The RF interference current is the same as each other, and the system can be modeled as consisting of a noise source, a "victim circuit" or a "receiver" and a loop (usually a backplane). Several factors are used to describe the size of the interference: the intensity of the noise source, the size of the surrounding area of the interference current, and the rate of change.
As a result, noise is almost always co modal, although unwanted interference is likely to occur in the circuit. Once the cable is connected between the input/output (I/O) connector and the chassis or ground plane, when some RF voltage occurs, the RF current of several milliamperes can be enough to exceed the allowable emission level.
Coupling and propagation of noise
Common mode noise is caused by unreasonable design. Some typical reasons are that the length of individual wires in different pairs is different, or the distance to the power plane or chassis is different. Another reason is the defect of components, such as magnetic induction coils and transformers, capacitors and active devices (such as application specific integrated circuits (ASICs)).
Magnetic components, especially the so-called "iron core choke" type energy storage inductor, are used in power converters and always produce electromagnetic fields. The air gap in the magnetic circuit is equivalent to a large resistance in the series circuit, where more electric energy is consumed.
Therefore, the iron core choke coil is wound on the ferrite rod, generating strong electromagnetic field around the rod, and the strongest field near the electrode. In switching power supply with tracing structure, there must be a gap on the transformer, in which there must be a strong magnetic field. The most suitable element to maintain the magnetic field is the spiral tube, which makes the electromagnetic field distribute along the length of the tube core. This is one of the reasons why helical structure is preferred for magnetic components operating at high frequencies.
Improper decoupling circuits often become interference sources. If the circuit requires a large pulse current, and the need for small capacitance or very high internal resistance cannot be guaranteed during local decoupling, the voltage generated by the power supply circuit will drop. This is equivalent to ripple, or the rapid change of voltage between terminals. Due to the packaged stray capacitance, interference can be coupled to other circuits, causing common mode problems.
When the common mode current pollutes the I/O interface circuit, this problem must be solved before passing through the connector. For different applications, it is recommended to use different methods to solve this problem. In the video circuit, the I/O signal is single ended and shares the same common loop. To solve this problem, use a small LC filter to filter out the noise.
In the low-frequency serial interface network, some stray capacitors are enough to shunt the noise to the backplane. The interface of differential drive, such as Ethernet, is usually coupled to the I/O area through the transformer, and the coupling is provided at the center tap on one or both sides of the transformer. These center taps are connected to the backplane through high-voltage capacitors to shunt the common mode noise to the backplane so that the signal is not distorted.
Common mode noise in the I/O area
There is no general solution to all types of I/O interfaces. The main goal of designers is to design circuits well, but they often ignore some details that are regarded as simple. Some basic rules can minimize the noise before reaching the connector:
1) Set the decoupling capacitor next to the load.
2) The loop size of fast changing front and rear edge pulse current shall be the smallest.
3) Keep high current devices (i.e. drivers and ASICs) away from I/O ports.
4) Measure signal integrity to ensure minimum overshoot and undershoot, especially for critical signals with large current (such as clock and bus).
5) The use of local filtering, such as RF ferrite, can absorb RF interference.
6) Provide low impedance bonding on the backplane or the reference in the I/O area is on the backplane.
Even if the industrial protection engineer takes many of the precautions listed above to reduce RF noise in the I/O area, it cannot be guaranteed that these precautions can successfully meet the emission requirements. Some noise is conducted interference, that is, common mode current flows on the internal circuit board. This interference source is between the backplane and the circuit.
Therefore, the RF current must flow through the path with the lowest impedance (between the backplane and the carrier signal line). If the connector does not exhibit a sufficiently low impedance (at the junction with the backplane), the RF current flows through stray capacitors. When the RF current flows through the cable, it will inevitably generate emissions.
This is the introduction to "Electromagnetic Interference Problems of Connectors". After reading this, you should have a basic understanding of this related problem. If you still have something you don't understand, you can send us an email, and we will arrange professionals to quickly answer your questions and provide professional advice. Finally, I hope every electronic connector practitioner can work smoothly and purchase the desired RF products.
Deso Hardware Electronics, at RF connector With 13 years of production and R&D experience in the field, it can quickly solve various production design problems and provide personalized customization services. All RF products of the company have passed the ISO certification, and are committed to providing quality assurance service within one year, meeting the international general environmental requirements. Customers can purchase with confidence.
