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What is a Network Transformer?

Views : 230
Author : CETUS INTL
Update time : 2023-06-01 14:01:34
The network transformer is a transformer component that is available in all levels of network equipment in a limited local area network.

Network transformer (Ethernet Transformer), also known as data mercury module, is an indispensable part of the network card circuit, it mainly includes the middle tap capacitor, transformer, autotransformer, common mode inductor.

It is also called network isolation transformer, Ethernet transformer, network filter, network port transformer, LAN transformer and so on.
RJ45 and network transformer

The function of the Network Transformer
First, to transmit data, it filters the differential signal sent by the PHY with a differential-mode coupled coil coupling filter to enhance the signal, and couples it to the other end of the connecting network cable of different levels through the conversion of the electromagnetic field;

Second, electrical isolation and lightning protection
When any CMOS process chip is working, the signal level generated is always greater than 0V (depending on the chip process and design requirements), and the PHY output signal will have a large DC component loss if it is sent to a place of 100 meters or even longer. . Moreover, if the external network cable is directly connected to the chip, electromagnetic induction (thunder) and static electricity can easily cause damage to the chip.

Furthermore, the grounding method of the equipment is different, and the different grid environment will cause the 0V levels of the two parties to be inconsistent. In this way, the signal is transmitted from A to B. Since the 0V level of the A equipment is different from the 0V level of the B point, this may cause a big difference. Current flows from a device with a higher potential to a device with a lower potential.

The network transformer filters the differential signal sent by the PHY with a differential-mode coupled coil coupling filter to enhance the signal, and couples it to the other end of the network cable through the conversion of the electromagnetic field. In this way, there is no physical connection between the network cable and the PHY and the signal is transferred, the DC component in the signal is cut off, and data can also be transmitted in devices with different 0V levels. The network transformer itself is designed to withstand the voltage of 2KV~3KV. Also played a role in lightning protection. Some friends' network equipment is easy to be burned out during thunderstorms. Most of them are caused by unreasonable PCB design, and most of them burnt the interface of the equipment. Few chips are burned because the transformer plays a protective role.

Isolation transformers can meet the insulation requirements of IEEE802.3, but cannot suppress EMI.

Third, Common mode rejection
Each wire in a twisted pair is wound around each other in a double helix. The magnetic field generated by the current flowing through each wire is constrained by the helical shape.

The current direction of the wires determines the degree of noise emitted by each pair of wires. The degree of emission caused by the differential mode and common mode current flowing on each pair of wires is different, and the noise emission caused by the differential mode current is relatively small, so the noise is mainly determined by the common mode current.

1. Differential mode signal in twisted pair
For differential mode signals, the current on each wire is transmitted on a pair of wires in opposite directions. If the pair of wires were evenly wound, these opposing currents would generate equal and oppositely polarized magnetic fields, causing their outputs to cancel each other out.

2. Common mode signal in twisted pair
The common-mode current flows in the same direction on the two wires and returns to ground through the parasitic capacitance Cp. In this case, the currents generate magnetic fields of equal magnitude and same polarity, and their outputs cannot cancel each other out. The common-mode current generates an electromagnetic field on the surface of the twisted wire, which acts like an antenna.

3. Common mode, differential mode noise and its EMC
There are two types of noise on cables: radiation noise and conduction noise generated from power cables and signal cables. These two categories are divided into common mode noise and differential mode noise. Differential mode conduction noise is the noise current generated by the internal noise voltage of electronic equipment and the same path as the signal current or power supply current. The way to reduce this noise is to connect differential mode choke coils in series on the signal line and power line, connect capacitors in parallel, or use capacitors and inductors to form a low-pass filter to reduce high-frequency noise.

The electric field intensity generated by this noise is inversely proportional to the distance from the cable to the observation point, proportional to the square of the frequency, and proportional to the current and the area of the current loop. Therefore, the way to reduce this radiation is to add an LC low-pass filter at the signal input to prevent noise current from flowing into the cable.
Classification of Network Transformers
According to the type of structure, the products can be divided into two categories:
a. Discrete LAN Magnetics Module;
b. RJ45 connector with integrated magnetic transformer module (RJ45 Connector with Integrated Magnetics,ICMs);
Products can be divided into two categories according to customer welding type:
a. Surface Mount Components (SMT, Surface Mount Type)
b. Plug-in components (TH,Through-Hole Type)

What is a Network Transformer?

According to the transmission rate, the products can be classified into four categories:
a. 10Base-T,
b. 10/100Base-T,
c. 1000 Base-T,
d. 10G Base-T.
(Base-T: Baseband, twisted pair. In short, Base-T is a local area network (LAN) standard that operates at a bps rate. It is often called Fast Ethernet and uses UTP (unshielded dual Twisted wire) copper cable. There are three basic implementations of Fast Ethernet: Base-FX, Base-T, and 1Base-T4. Each specification is the same except for the interface circuit, which determines which interface they use A type of cable. In order to realize the clock/data recovery (CDR) function, Base-T uses the 4B/5B Manchester encoding (Manchester Encoding) mechanism.)
Main Applications of Network Transformers
Network transformer products are mainly used in: RJ45 network card, Ethernet switch, network router, ADSL, VDSL digital equipment, EOC terminal, EPON/GPON triple play equipment, POE power receiving equipment, FILT optical fiber loop equipment, network set-top box, smart TV , IP camera, SDH/ATMSDH/ATM, PC motherboard, computer peripheral, industrial motherboard, network server, telecommunication base station smallcell and other equipment.