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A balun is a type of transmission line transformer. This two-port component is placed between a source and load when a differential symmetric RF functional block needs to be connected to a single-ended block.

These transformers are made by winding a strip-line on a high-permeability core substrate. Because of the high impedance of the winding, the balanced output terminals are isolated from the unbalanced input terminals.

The most straightforward way to build a balun is with a two-winding transformer-based design, with one side grounded and the other side floating (differential). A balun can be used in either direction, so it can perform single-ended to balanced transformation, and the reverse.

Two-winding transformer-based balun design

The key features of baluns include frequency range, bandwidth, insertion loss, magnitude imbalance, phase imbalance, linearity, distortion, and power rating. Size and cost are also important design considerations.

ST’s baluns use our monolithic RF IPD process to integrate high-quality RF passive components on a single glass substrate. ST’s RF IPD baluns are optimized for high RF integration and improve system performance. They simplify RFIC-to-antenna matching networks and their integrated harmonic filters aid compliance with major EMC regulations like CCC, FCC, ETSI, and ARIB.

Where are balun used?

ST’s RF IPD baluns are used on many antennas and their feedlines to transform a balanced line to an unbalanced one. They usually integrate the matching impedance and optimize the RF power transmission to maximize performance. They usually occupy a very small footprint, less than 1 mm² for the complete function.

ST’s RF IPD balun integration example
Our solutions are tailored for:
  • Bluetooth® low energy 2.4 GHz radios
  • IEEE 802.15.4-based specification including Zigbee
  • Sub-1GHz RF transceivers
  • Sigfox wireless connectivity
  • LoRa wireless connectivity

Which balun do i need?

Our wide range of integrated baluns includes companion chips for ST’s latest transceivers, such as:

These and other baluns designed for other transceivers from various manufacturers significantly help reduce RF complexity and provide an optimized link budget.

Other available baluns include:

ST companion chips for Wireless ICs - RF IPD

Associated RF Transceiver Matched Balun
Companion Chip
Frequency (MHz) Integrated filter Size Package
SPIRIT 1 BALF-SPI-01D3 868-915 Yes 1.4 mm x 2.0 mm CSP
SPIRIT 1 BALF-SPI-02D3 433 Yes 1.4 mm x 2.0 mm CSP
S2-LP BALF-SPI2-01D3 868-915 Yes 2.1 mm x 1.55 mm CSP
S2-LP BALF-SPI2-02D3 433 Yes 2.1 mm x 1.55 mm CSP
(QFP32 and CSP34)
BALF-NRG-01D3 2400 Yes 1.4 mm x 0.85 mm CSP
BlueNRG-1 (QFP32 and CSP34)
BlueNRG-2 (QFN32 and CSP34)
2400 Yes 1.4 mm x 0.85 mm CSP and
Thin CSP
Associated RF Microcontroller Matched Low Pass Filter
Companion Chip
Frequency (MHz) Integrated filter Size Package
STM32WB55Cx/Rx, STM32WB50Cx, STM32WB35Cx,
STM32WB30Cx BLE 5.0
MLPF-WB-01E3 2400-2500 Yes 1.5 mm x 1.0 mm Bumpless CSP
(LTCC assy-like)
STM32WB55Vx BLE 5.0 MLPF-WB55-02E3 2400-2500 Yes 1.5 mm x 1.0 mm Bumpless CSP
(LTCC assy-like)


What are the main benefits of using ST baluns?

ST baluns simplify solution designs and optimize performance. Our technology for passive integration on a high resistivity substrate ensures higher system integration. It improves reliability, and significantly reduces bill-of-materials in comparison with alternative discrete solutions.

Benefits of ST’s RF IPD technology