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What is Ethernet Transformer used for?

Views : 205
Author : CETUS INTL
Update time : 2023-06-01 14:07:36
In Ethernet equipment, when connecting RJ45 through PHY, a ethernet transformer will be added in the middle. Some transformers have a center tap connected to the power supply, and some are connected to the capacitor to ground. And when connected to the power supply, the power supply value can be different, 3.3V, 2.5V, 1.8V, what is the function of this transformer?

What is Ethernet Transformer used for?

Here is a rough summary
:
1. Why are some of the center taps connected to power and some to ground? This is mainly determined by the UTP port drive type of the PHY chip used. This drive type consists of two types, voltage drive and current drive. If it is driven by voltage, it must be connected to the power supply; if it is driven by current, it must 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.

2. Why are different voltages connected to the power supply? This is also determined by the UTP port level specified in the PHY chip data used. What level is determined, you have to connect the corresponding voltage. That is, if it is 2.5V, pull it up to 2.5V, and if it is 3.3V, pull it up to 3.3V.

3. What is the role of this transformer, can it not be connected? Theoretically, it can be connected directly to the RJ45 without a transformer, and it can work normally, but the transmission distance will be limited, and it will also be affected when it is connected to a network port of a different level. Moreover, the external interference to the chip is also very large. When connected to the ethernet transformer, it is mainly used for signal level coupling. First, the signal can be enhanced to make the transmission distance longer; second, the chip end is isolated from the outside, the anti-interference ability is greatly enhanced, and the chip is greatly protected (such as lightning); third: when connected When connecting to network ports with different levels (for example, some PHY chips are 2.5V, some PHY chips are 3.3V), it will not affect each other's equipment.

In general, the ethernet transformer mainly has the functions of signal transmission, impedance matching, waveform restoration, signal clutter suppression and high voltage isolation.

signal transmission

Data mercury is also called a ethernet transformer or can be called a network isolation transformer. It plays two main roles on a network card. One is 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 different levels through the conversion of the electromagnetic field. Connect the other end of the network cable; one is to isolate the different levels between different network devices connected by the network cable, so as to prevent different voltages from being transmitted through the network cable from damaging the equipment. In addition, data mercury can also play a certain role in lightning protection for equipment.

When the signal voltage (differential mode signal) is applied to the two feet of the transformer, a voltage is induced on the secondary end of the transformer through magnetic circuit coupling. For the signal voltage, since the signal currents flowing through the two windings of the CMC at the same time are equal in size and opposite in direction, magnetic fluxes in opposite directions are generated in the iron core magnetic circuit of the CMC, which cancel each other out and do not affect the differential mode signal transmission. At this time, the two windings of the CMT flow currents of the same size and direction, so that the CMT acts as a large resistor, which hinders the passage of the differential mode signal and has little impact on the transmission of the carrier signal. So the differential mode signal is directly coupled to the load. For the common mode signal, it is mainly coupled to the secondary through the distributed capacitance of the primary and secondary of the transformer. At this time, the two windings of the CMC flow currents with the same size and the same direction. At this time, the CMC is equivalent to a large The resistor prevents the transmission of the common-mode signal, while the two windings of the CMT flow equal and opposite currents, which is equivalent to a short circuit for the common-mode signal, so that the common-mode signal will basically not be transmitted, but will be coupled to the load In this way, the carrier signal can be well transmitted, and the common-mode interference signal can be suppressed.