RJ45 network transformer manufacturer tells you common mode, differential mode noise and EMC?

There are two types of noise on the cable: radiation source noise and conduction noise caused by switching power cable and data signal cable. The selection of RJ45 connector for Ethernet is divided into common mode noise and differential mode noise. Differential mode conducted noise is the noise current in the same path as data signal current or switching power supply current caused by the internal noise working voltage of electronic products. The way to reduce this kind of noise is to connect differential mode choke coil, series capacitor or low-pass filter composed of capacitor and inductor on the power line and plug to reduce high-frequency noise.

The electric field intensity caused by such noise is inversely proportional to the distance from the cable to the observation point, to the square meter of frequency, and to the total area of current and current loop. Therefore, the way to reduce the price of RJ45 connector is to add LC low-pass filter at the data signal input end to block the noise current from flowing to the cable; shield the cable or bias flat cable to transmit the return current and data signal current in the adjacent transmission line, so as to reduce the total area of the loop.

The common mode conducted noise is caused by the noise current flowing between the ground and the cable by the Ethernet RJ45 connector manufacturer through the parasitic capacitance between the ground and the machine equipment under the driver of the noise working voltage in the machine equipment.

The way to reduce the common mode conducted noise is to connect the common mode choke coil in series in the power line or plug, the power capacitor between the ground and the transmission line, and form LC filter to carry out the filter, so as to filter out the common mode conducted noise.