RF Transceivers Need Baluns and ST has the Winning Technology

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In our recent post on the new S2-LP sub-1Ghz RF transceiver, we discussed the growing importance of this kind of RF communication technology for IoT Smart Things and Smart Cities. The different RF encoding techniques, frequency bands and protocols require specific optimizations for the applications we use every day. All require different RF transceivers to drive the antenna in transmit and detect signals in receive mode. The common point for all these transceivers, whether they are sub-1GHz, Bluetooth Low-Energy, Wi-Fi or other standard, is that they all require baluns. With its range of  RF IPD (Integrated Passive Discrete) baluns, ST is supporting the future of mobile, wearable and IoT applications, where multiple connectivity chips, and protocols, mean even more RF complexity. By providing improved performance, simplifying the design, and reducing the size and cost, ST is leading the RF chipset specific balun market thanks this IPD technology.

What is a Balun and Why Do We Need Them?

Balun is an acronym for “balanced to unbalanced”. Very simply, in telecommunication, as well as professional audio, “balanced” refers to a transmission composed of two identical but inverted signals. Its main advantage is its ability to single out noise and limit the effect of interference. On the contrary, an unbalanced line will only carry one signal. When a Bluetooth antenna receives a signal, (diagram below), it is unbalanced. However, the signal outputted from the antenna to the RF circuit must be balanced to protect its integrity from noise. The balun acts as a go-between, taking the unbalanced signal and sending a balanced one, making sure there’s only a minimal power loss in the process.

Baluns and the need for a matching network

Fig2. The need for a matching network

Choosing the right balun can be complex. Conventional discrete baluns are available in a variety of impedance ratios, typically for 50Ω unbalanced to an integer multiple of 50Ω balanced. However, because RF ICs often have arbitrary (and complex) impedance characteristics, it is also necessary to insert a matching network between the chip and the balun to obtain an optimal power match. In addition, active RF circuits always generate out-of-band radiation, and because of FCC and CE standards, it is often necessary to also add harmonic RF filters between the balun and the antenna.

How are Baluns and Matching Networks Made?

There are several options to design a circuit integrating baluns and matching networks. Fig 5 compares the four main options: active ciruits, discrete surface mounted devices (SMD), low-temperature co-fired ceramic (LTCC) packages, and ST’s approach: the Integrated Passive Device (IPD) on a glass substrate.

balun circuit.

Fig 5 Comparison of technologies for balun circuit.

 *The resistive losses in on-chip components are too high to be useful in most applications.

The IPD approach can also integrate both the harmonic filters and matching network in the same chip as the balun. As a result, one of the main benefits of IPD baluns is the reduction of the number of components along with the board space reduction. Hence, as the RF circuit becomes simpler, the value proposition of ST’s components extends far beyond their performance. As a result, we no longer need to be RF experts to implement RF communications.

BALF-NRG-01D3 for BLUENRG transceiver

Fig 7. Example of BALF-NRG-01D3 for BLUENRG transceiver, design & layout simplification.

Choosing the right balun, with the correct transceiver matching and harmonic filtering, is now simple. ST has a wide range of solutions for most of the RF transceivers available on the market today. To simplify your next RF design, find out more about our IPD baluns on ST’s website.