Theoretically speaking, it can work normally without connecting the network transformer and directly connecting to the RJ.However, the transmission distance will be limited, and it will also be affected when it is connected to a network port of a different level. And the external interference to the chip is also great. When the network transformer is connected, it is mainly used for signal level coupling.
1. Strengthen the signal to make the transmission distance farther;
2. Isolate the chip end from the outside, enhance the anti-interference ability, and increase the protection of the chip (such as lightning strike);
3. When connected to different levels (such as Some PHY chips are 2.5V, and some PHY chips are 3.3V), it will not affect each other’s devices.
In general, the network transformer mainly has the functions of signal transmission, impedance matching, waveform repair, signal clutter suppression and high voltage isolation.