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What is the coupling and propagation of noise from RF connectors

Time:2018-12-12

Common mode noise is due to the unreasonable design of the RF connector. Some typical reasons are the length of individual wires in different pairs, or the distance to the power plane or chassis. Another cause is component defects such as magnetic induction coils and transformers, capacitors and active devices (such as application specific integrated circuits (ASICs)).

Magnetic components, particularly so-called "core choke" type energy storage inductors, are used in power converters to always generate an electromagnetic field. The air gap in the magnetic circuit is equivalent to a large resistance in the series circuit, where more power is consumed. Thus, the core choke coil is wound on the ferrite rod, creating a strong electromagnetic field around the rod and having the strongest field strength near the electrode. In a switching power supply using a retrace structure, there must be a gap on the transformer with a strong magnetic field. The most suitable component in which the magnetic field is maintained is a spiral tube that distributes the electromagnetic field along the length of the die. This is one of the reasons why the magnetic element operating at high frequencies preferably has a spiral structure.


Inappropriate decoupling circuits often also become sources of interference. If the circuit requires a large pulse current and local decoupling does not guarantee a small capacitance or a very high internal resistance, the voltage generated by the power supply circuit drops. This is equivalent to ripple, or equivalent to a rapid change in voltage between terminals. Due to the stray capacitance of the package, interference can be coupled into other circuits, causing common mode problems.

When the common mode current contaminates the I/O interface circuit, the problem must be resolved before passing through the connector. Different applications suggest different ways to solve this problem. In the video circuit, where the I/O signals are single-ended and share the same common loop, to solve it, use a small LC filter to filter out the noise. In a low frequency serial interface network, some stray capacitance is sufficient to shunt noise onto the backplane. Differential drive interfaces, such as Ethernet, are typically coupled to the I/O area by a transformer that is coupled at the center tap on one or both sides of the transformer. These center taps are connected to the backplane via a high voltage capacitor to shunt common mode noise to the backplane so that the signal is not distorted.

Shenzhen Tiankele Communication Technology Co., Ltd. is a professional manufacturer of RF connectors. The R&D team with more than ten years of industry experience; the industry's leading three professional laboratories of machinery, electrical and environment, and the integrated industrial chain from machining, assembly testing and electroplating. The pursuit of high quality products is the guarantee of Tiankele people to customers.

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