Matching network for antenna design for STM32WL33

[leahjoseph]

Hello,

While using a unit as a receiver module, is the matching network required for the Tx pins as well?

Also, since there is no data being transmitted, how should the VFBSD pin (power pin for the RF section) be connected in this case?

Regards,

Leah

[AJ_1]

Hi Leah,

I don't know if you'll get a response from an official ST employee, but in case you don't, I wanted to pass along my knowledge.

If you have no need to ever transmit, the TX pins don't need to be connected. Section 29.3.7 of the reference manual (RM0511) even shows example implementations where the TX or TX_HP pin is disconnected. So I'm sure you can leave both disconnected.

However, since they are tied together, removing the TX matching network could potentially mess with the tuning of the RX network. I don't understand that well enough to say whether or not it will be an issue. (But if you do, please teach me!)

Regarding VFBSD, if you aren't using it to pull either TX line high it doesn't need to be involved in the RF networ; you don't need C14, C15, or L8. However, the VFBSD still needs to be powered with either an inductor or by directly connecting it to VDD. Look at section 5.5 of the reference manual for more details.

PS: I'm interested in learning more about calculating the matching network when TX and RX are directly tied together (as shown in your schematic). Did you calculate those component values yourself? Or is that from a reference design?

[STTwo-32]

Hello @leahjoseph 

If you want to use only the RX feature, you can remove the corresponding TX network components. Regarding the VFBSD pin, in this case, no connection with the PA is required, but only with the VLXSD pin.

Best Regads.

STTwo-32