Detailed anatomy of the role of Ethernet transformer filters

1. Network transformers are also known as network isolation transformers, Ethernet transformers, and network filters. Product types are further divided into single-port, dual-port, multi-port, 10/100BASE, 1000BASE-TX and RJ45 interface integrated network isolation transformers. The products are mainly used in: RJ45 network card, Ethernet switch, network router, ADSL, VDSL digital equipment, EOC terminal, EPON/GPON triple-network integration equipment, network set-top box, smart TV, network camera, SDH/ATMSDH/ATM, PC motherboard, Industrial motherboards and other equipment.

  

  2. The network transformer mainly has the functions of signal transmission, impedance matching, waveform repair, signal clutter suppression and high voltage isolation. The role of network transformer in Ethernet is in Ethernet equipment. When connecting RJ45 through PHY, a network transformer will be added in the middle. Some transformers have their center tap connected to ground. When connected to the power supply, the power supply value can be different, 3.3V, 2.5V, and 1.8V. Some of the center taps are connected to power, while others are connected to ground. This is mainly determined by the type of PHY chip UTP port driver used. There are two types of this drive, voltage drive and current drive. The voltage-driven one should be connected to the power supply; the current-driven one should be directly connected to a capacitor to the ground. Therefore, for different chips, the connection method of the center tap is closely related to the PHY. For details, please refer to the datasheet and reference design of the chip. When connecting to the power supply, it is necessary to connect different voltages, which is also determined by the UTP port level specified in the PHY chip data used.

  

  3. Theoretically speaking, it is possible to connect it directly to RJ45 without the need for a transformer. However, the transmission distance is very limited, and when it is connected to a different level network port, it will also have an impact. And the external interference to the chip is also very large. When connected to the network transformer, it is mainly used for signal level coupling. Can have the following effects:

   1. The signal can be enhanced to make the transmission distance longer;

   2. The chip end is isolated from the outside, the anti-interference ability is greatly enhanced, and a great protection effect is added to the chip (such as lightning strike);

   3. When connected to network ports of different levels (some PHY chips are 2.5V, some PHY chips are 3.3V), it will not affect each other‘s devices.