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.
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.
- 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 MLPF-NRG-01D3 tailored for our BLUENRG-LP and BLUENRG-LPS (BLUENRG-3x5Vx, BLUENRG-3x5Ax, BLUENRG-332xx, BLUENRG-3x5Mx) Bluetooth® low energy 2.4GHz radios, in a 1.2 mm² footprint.
- 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.
- Other available baluns include:
- BAL-UWB-01E3 optimized for the UWB DW1000 RF IC from Decawave.
- BALF-ATM-01E3 for ATSAMR21E18.
- BALF-NRF01D3, BALF-NRF01E3, BALF-NRF01J5, and BAL-NRF02D3 series, optimized for Nordic Semi-BLE RF type ICs.
Discover our Balun portfolio for STM32WL
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.
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 | MLPF-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 |
