Balun has 3 basic functions

Balun (Balun in English) is a three-port device, or a broadband RF transmission line transformer that realizes the connection between a balanced transmission line circuit and an unbalanced transmission line circuit by converting matched inputs to differential outputs. Balun's function is to make the system with different impedances or compatible with differential / single-ended signaling, and used in modern communication systems such as mobile phones and data transmission networks.

Balun has 3 basic functions:

1. Switch current or voltage from unbalanced to balanced

2. Common-mode current rejection through certain configurations

3. Impedance conversion through certain structures (impedance ratio is not equal to 1: 1)

There are many types of baluns, some of which are used for impedance conversion, and some are used to connect transmission lines with different impedances. Impedance conversion baluns allow impedance matching, DC isolation, and matching of balanced ports to single-ended ports. The common mode choke is also a kind of balun in a sense because it can eliminate the common mode signal. Baluns are used in push-pull amplifiers, wideband antennas, balanced mixers, balanced frequency multipliers and modulators, phase shifters, and any circuit design that needs to transmit two lines with equal amplitude and 180 degrees phase difference.

The most common use of baluns is to connect unbalanced signals to balanced transmission lines for long-distance transmission. Compared with single-ended signaling using coaxial cables, differential signaling using balanced transmission lines is less affected by noise and crosstalk, can use lower voltages, and is more cost-effective. Therefore, baluns can be used as an interface between local video, audio, and digital signals and long-distance transmission lines.

Balun's uses include:

– Radio and baseband video

– Radar, transmitter, satellite

– Telephone network, wireless network modem / router