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1. What is a reference design?
A reference design is an optimized layout for a specific RF use case that integrates the host processor on board.
This page gives an overview of the main characteristics of these reference designs. More details are available in the data brief DB5558. Additionally, the integration of the STM32U5 host and some design guides are described in the application note AN6316.
2. Reference design descriptions
2.1. 4-Layer reference board (-B and -U version)
This design consists of 2 boards: B2413 stamp board and B2416 Interface board.
A zip file containing the Altium database, manufacturing files and the BOM is available here.
2.1.1. Stamp board B2413
- A small board measuring 20x34 mm, including a host STM32U575AIIQ (BGA169 package) and the ST67W611M1 for both -U and -B versions.
2.1.2. Interface board B2416
- An interface board (mini-board format, 43 x 50 mm) that contains the B2413 board, the reset and user button for the U5, and a connector for the STLinkV3.
This board serves as an interface to flash the module, send UART commands and power the board.
There are two possible configurations:
- Connect an STLinkV3 (blue circle) which provides UART connection as well as 5 V supply
or
- Connect UART_FTDI (green circle) and an external supply (red circle).
The default power supply configuration is:
- all VDD = 3.3 V from the LDO supplied by the 5 V of the STLinkV3:
The 5 V can also come from the external connector TP5 and all VDD can be supplied externally via connectors JP1 to JP4 with the proper soldering bridge configuration. For more details refer to the schematics.
For debugging purpose, this set of boards can be plugged on a mezzanine boards (MB1801) that routes signals to a Morpho connector:
Note: These boards are only delivered with the STM32WBA and STM32WB09 Nucleo-64 boards
In this configuration, the B2413 stamp board is supplied by the MB1801. For more details, refer to the schematics,
2.2. 4-Layer reference board (-P version)
2.2.1. B2414 and B2415 boards description
Two reference design are available for the -P version:
- B2414 board with a single antenna path.
- B2415 board for RX diversity (two antennas).
A zip file containing the Altium database, manufacturing files and the BOM is available here.
The PCB stack-up is identical to the B2413 board. Regarding the schematics and the layout, the only differences are:
- RF tracks from Pin 31 "RF I/O" to antennas or RF switch for the B2415 board.
- ANT_SEL pin (Pin 1) connected to the control pin 6 of the RF switch BGS12WN6.
2.2.2. RX Diversity description
This feature is used to recover radio performances in environments of difficult reception:
- Antenna cross-polarization.
- Multiple reflections on the radio path.
- Multipath fading.
Using two antennas placed in different configurations (e.g. orthogonal) can reduce these effects.
An algorithm based on RSSI measurements during the preamble determines which antenna provides optimal performance.
In terms of hardware requirements, the Pin 1 (ANT_SEL) controls a switch for antenna selection:
Logical control of the ANT_SEL pin:
The following figure shows which antenna path is selected based on the logic of the RF switch:
- ANT1 is selected if the CTRL (ANT_SEL) signal equals 0.
- ANT2 is selected if the CTRL (ANT_SEL) signal equals 1.
A multimeter can be used to check the state value (0 or 3.3V) on Pin 1 of the stamp board.
RF path losses and isolation of the switch:
The ST67W611M1A6P is programmed to deliver a TX output power of 20 dBm A spectrum analyzer is connected to the SMA connectors ANT1 and ANT2 to measure the power in the antennas plane:
The antenna diversity performs on-time antenna selection during connection setup using scan-based selection.
The activation of this feature is done by sending the following CLI commands:
- wifi_antenna [ mode [0: disable; 1: static; 2: dynamic]]
For more details, refer to the CLI documentation.