S2-LP with Balun and RF Front-End

[Chalumo]

Hello,

I am currently reviewing the S2-LP transceiver for high-bitrate/long-range communication in the 915MHz band. To achieve that, I want to interface an S2-LP with a Skyworks SE2435L front-end, as shown in the FK915V1 Evaluation board. I would like to know if it is possible to use a Balun from ST like the BALF-SPI2-03D3 to match the impedance of the transceiver with the front end. I am asking this question because in the FK915V1 schematic, the RX and TX paths are distinct, whereas using the Balun implies connecting the PAIN and TR pins of the front end together.

Can this approach yield good result or am I wrong?

Also, what is the recommended balun for the S2-LP, BALF-SPI2-03D3 or BALF-SPI2-01D3 ?

Thank you,

Robin

[liaifat85]

The SE2435L has distinct control pins for switching between TX and RX modes. When using a balun, you’d need to carefully manage the control logic to avoid unwanted signals and potential interference.

[Chalumo]

Thank you for your answer. So you think using a Balun with the front-end should not be a problem because the front-end will never be in TX and RX mode simultaneously, so tying the PA-IN and TR pins to the ANT pin of the Balun is fine ?

[Philippe SIMONNET · Accepted solution]

Hi Robin,

I will not recommend using IPD balun with external PA as IPD as only "Antenna" output which is not possible to connect to PA where you have PA IN (Tx) pin and Rx pin.

this is why on STEVAL-FKI915v1 we have specific matching SMD components to connect S2-LP to Skyworks PA.
IPD components (like BALF-SPI2-02D3/BALF-SPI2-01D3) are done to connect output of IPD to antenna directly.

Regards

Philippe