How do the Stm32wl55 SubGHz_Phy Radio driver PA Config Settings conform to AN5457 section 5.1.2?

[TBlan.2]

Hi,

we are working on an own hardware design with the STM32WL55.

According to AN5457, section 5.1.2, I am supposed to select a Power mode (Low or High), and then a maximum output power for which I would want to optimize my design. With that maximum output power in mind I would then get optimal PA settings from table 2. Those settings are what I use in firmware when I adjust the RF matching network in hardware. Using different PA settings can change the PA output impedance, so when I have adjusted the network once, I must make sure to always use those same PA settings on that hardware.

In radio_driver.c from the SubGHz_Phy middleware of the STM32Cude Firmware for the STM32WL55 (version 1.1.0) (STM32Cube_FW_WL_V1.1.0\Middlewares\Third_Party\SubGHz_Phy\stm32_radio_driver\radio_driver.c) in the function SUBGRF_SetTxParams, lines 647 to 654, the radio driver selects different PA settings depending on the selected output power. If i understand AN5457 correctly, that could change the PA output impedance and therefore lead to the RF matching network no longer being well adjusted to the PA output.

What gives? Is that a bug in the driver? Did I understand everything correctly? How am I supposed to proceed? Can I use that driver on my own hardware?

Thank you,

Thomas

[YBOUV.1 · Accepted solution]

Hi,

You understood correctly.

In the CubeWL1.1.0, the optimum settings are 'frozen' to 22dBm for HP and 15dBm for LP output.

The settings could be updated in the lines you mention with the settings described in AN5457 (section 5.1.2) depending on you matching network optimized for you output power.

The flexibility is added in the upcoming CubeWL1.2.0 (end of Feb) as a new BSP function.

Hope it answers

[TBlan.2]

Sounds great, thank you. I'll look forward to version 1.2.0.