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balun logo

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.

Applications

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
  • Human Machine Interface
  • Sigfox
  • ZigBee
  • Bluetooth Low Energy
  • LoRa
  • 802.15.4 OpenThread
  • ISM Radio SubGHz
  • WM-BUS

Product types

    Our wide range of integrated baluns includes companion chips for ST’s latest transceivers covering sub-giga Hertz applications (433 MHz) to Bluetooth applications (2.5 GHz), such as:
  • The BALF-NRG-02D3 tailored for our BlueNRG-1 and new BlueNRG-2 Bluetooth® low energy 2.4GHz radios, in a 1.2 mm² footprint.
  • The BALF-SPI2-01D3 (868-927 MHz) and the new BALF-SPI2-02D3 (433-470 MHz), designed to be used with ST’s S2-LP sub-1GHz RF transceiver.
  • The BALF-SPI2-01D3 is instead tailored for sigfox wireless connectivity.
  • The BALFHB-WL-0xD3 and BALFLB-WL-0xD3 are designed and optimized for STM32WL series.

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

Discover our portfolio

balfhb-wl-01d3 balfhb-wl-02d3 balfhb-wl-03d3 balfhb-wl-04d3 balfhb-wl-05d3 balfhb-wl-06d3

Benefits

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

Characteristics

ST companion chips for Wireless ICs - RF IPD

Companion Chips to SPIRIT

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

Companion Chips to STM32WL

Associated RF Transceiver Matched Balun
Companion Chip
Frequency (MHz) Output Power PCB Layers Integrated filter Package
STM32WL BGA BALFHB-WL-01D3 864-928 22dBm 4 Yes CSP
STM32WL QFN BALFHB-WL-02D3 864-928 22dBm 4 Yes CSP
STM32WL QFN BALFHB-WL-03D3 864-928 22dBm 2 Yes CSP
STM32WL BGA BALFHB-WL-04D3 864-928 15dBm 4 Yes CSP
STM32WL QFN BALFHB-WL-05D3 864-928 15dBm 4 Yes CSP
STM32WL QFN BALFHB-WL-06D3 864-928 15dBm 2 Yes CSP
STM32WL BGA BALFLB-WL-07D3 470-530 17dBm 4 Yes CSP
STM32WL QFN BALFLB-WL-08D3 470-530 17dBm 4 Yes CSP
STM32WL QFN BALFLB-WL-09D3 470-530 17dBm 2 Yes CSP

Companion Chips to STM32WB & BLUENRG

Associated RF Transceiver MCU package Matched Low Pass Filter
Companion Chip
Frequency (MHz) Integrated filter Size Package
STM32WB55Cx,
STM32WB55Rx,
STM32WB35xxx,
STM32WB50xxx and
STM32WB30xxx,
STM32WB15x
QFN MLPF-WB-01D3 2400-2500 Yes 1.5 mm x 1.0 mm CSP
STM32WB55Cx,
STM32WB55Rx,
STM32WB35xxx,
STM32WB50xxx and
STM32WB30xxx,
STM32WB15x
QFN MLPF-WB-01E3 2400-2500 Yes 1.5 mm x 1.0 mm Bumpless CSP
(LTCC assy-like)
STM32WB55Cx,
STM32WB55Rx,
STM32WB35xxx,
STM32WB50xxx and
STM32WB30xxx,
STM32WB15x
QFN MLPF-WB55-01E3 2400-2500 Yes 1.5 mm x 1.0 mm Bumpless CSP
(LTCC assy-like)
STM32WB5x and STM32WB1x BGA MLPF-WB55-02E3 2400-2500 Yes 1.5 mm x 1.0 mm Bumpless CSP
(LTCC assy-like)
STM32WB5x and STM32WB1x BGA MLPF-WB-02D3 2400-2500 Yes 1.5 mm x 1.0 mm CSP
BLUENRG-3x5Vx, BLUENRG-3x5Ax, BLUENRG-332xx, BLUENRG-3x5Mx QFN & BGA BALF-NRG-01D3 2400 Yes 1.4 mm x 0.85 mm CSP
BlueNRG-1 (QFP32 and CSP34)
BlueNRG-2 (QFN32 and CSP34)
QFN & BGA BALF-NRG-02D3
(Height<350ym)
2400 Yes 1.4 mm x 0.85 mm CSP and Thin CSP