Contact Us   
Your Position: Home > News > Company News

Why lan transformers are the standard design for Ethernet ports in communications equipment?

2022-10-31 10:50:18      view:

Ethernet hardware interfaces, as physical layer interconnect components in Ethernet network transmission systems, have gradually formed a set of standard interface designs and specifications over a long period of time in hardware system design. As a key component, the ethernet transformer also has its own defined specifications and is closely related to the PHY driver part in the system board design. Some inadvertent changes in use may cause unpredictable consequences.

 

In our communication equipment, network transformers play a role in the end, whether it is necessary to choose.

The answer is: less network transformer is fine, but it would be better to use on. From the working principle, it is possible to consider not to use, directly connected to the RJ45 connector, is also workable. However, the cost of the whole machine will be greatly reduced.

1. The transmission distance is very limited value, when the input level of different network ports, there will also be affected.

2. from external factors on the PHY interference and direct damage is also very large.

When the device PHY output signal sent to 100 meters or even longer will have a large loss of DC component. And if the external network cable is directly connected to the chip, from the external large pulse voltage and static electricity, it is easy to cause damage to the chip. The network transformer filters the differential signal from the PHY with a differential mode coupling coil to enhance the signal, and couples it to the other end of the connected cable through the conversion of the electromagnetic field. This not only makes no physical connection between the network cable and the PHY but also transmits the signal, isolates the DC component of the signal, and allows the transmission of data in the device.

 

Network transformer common mode signal suppression

When the differential-mode signal passes through the network transformer, when the common-mode signal passes through the transformer

When the common-mode signal passes through the network transformer, it presents a high impedance g to the common-mode signal, which is a signal of equal size and polarity at the two inputs, so it will not pass the common-mode signal to the secondary line. However, the coupling capacitance Cww between transformers provides a pathway for the common-mode signal transfer.

In order to prevent the common mode signal on the transformer coupled to the secondary through the coupling capacitor Cww channel, we use the center tap in the design to provide a path for the common mode signal drain (in the design of the entire equipment network port, most hardware engineers will use the center tap to increase the filtering circuit, or the location of the common mode inductor reserved on the differential signal alignment of the network port)

 

To sum up: network transformer in the design of communication equipment network port to meet the function (differential signal transmission) premise, not only can play the role of anti-turbulence protection for the back-end circuit, but also can suppress the common mode radiation noise.

Therefore, the network transformer is the standard design of the Ethernet port of communication equipment!