Learn about RF balun transformers and features

The balun (a contraction of balanced-unbalanced) is a two-port component placed between a source and load when a differential, balanced RF functional block must connect to a single-ended, ground-referenced one. Although it is often “glossed over” in RF discussions because it does not add obvious value to the RF signal chain, this passive component is essential in common situations.

For example, it is needed when a single-ended power amplifier (PA) is driving a dipole-antenna element (balanced load) or a whip antenna (single-ended) is feeding a differential front-end amplifier. You are probably familiar with the mass-market, low-cost balun used to connect a rooftop, over-the-air 300 Ω dipole antenna for broadcast TV to a run of 75 Ω coaxial cable, which then connected to the TV set itself (some older TVs assumed the dipole antenna was located at the TV, and so only had a pair of 300 Ω, balanced-screw-terminal inputs, in which case another balun would be needed to make the reverse transformation from coax to TV input). 

However, the need for baluns extends beyond TVs and their antennas: in recent years, RF ICs are increasingly using differential configurations for their internal topology, because this provides improved noise immunity and better overall RF performance, and at a very-low-cost increment due to the nature of IC designs.

Baluns are not new or even relatively recent components. They have been used since the earliest days of wireless telephony to resolve the single-ended/balanced dilemma. Now, the growth in portable, handheld, and IoT applications means there is enormous demand for tiny, relatively low-power baluns. These can be constructed using ceramic-based fabrication similar to that used for bandpass filters, directional couplers, and SAW-type oscillators.

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