What is the role of RJ45 with transformer?

In an Ethernet device, when the PHY is connected to the RJ45 with a transformer, the base adds a network transformer. Some transformer bases are connected to the power supply, and some are connected to the ground. And when connected to the power supply, the power supply value can be different, 3.3V, 2.5V, 1.8V. What is the effect of this transformer?

Here is an approximate answer:

1. Why is the base tap connected to the power supply? Some grounding? This is primarily the resolution of the UTP port drive type used with the PHY chip. There are two types of drive, voltage drive and current drive. The voltage drive should be connected to the power supply; if the current is driven, it can be connected directly to the ground! So with regard to different chips, the connection of the base tap is closely related to the PHY. For details, please refer to the chip's datasheet and refer to the planning. 2. Why do you connect different voltages when you connect the power supply? This is also the regular UTP port level resolution in the PHY chip material used. The level of the resolution, you have to pick up the corresponding voltage. That is, if it is 2.5v, it will be pulled up to 2.5v, and if it is 3.3v, it will be pulled up to 3.3v. RJ45 network connector

3. What is the effect of this transformer? Can you not pick it up? In theory, it can be connected to the RJ45 without the need for a transformer, and it can work normally. However, the transmission interval is very limited, and it will also have an impact when connected to a different level network port. And the external interference on the chip is also very large. When connected to a network transformer, it is primarily used for signal level coupling. First, it can enhance the signal to make the transmission interval farther; secondly, the chip end and the external barrier can be greatly enhanced, and the anti-interference can be greatly enhanced, and the maintenance effect (such as lightning strike) is added to the chip; When the network port is not the same level (if the PHY chip is 2.5V and some PHY chips are 3.3V), it will not affect the mutual devices. RJ45 connector

In general, network transformers have the effects of signal transmission, impedance matching, waveform correction, signal clutter suppression, and high voltage blocking.

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