I am working on a device based on the STM32WB55xx line of microcontrollers.
In the latest revision of the PCB, I altered the antenna filter and chip antenna components to better match the device documentation. However, the device is now failing to connect to a phone over Bluetooth, while the previous version connects just fine. I'm looking for feedback on the schematic design, so we can try to determine whether our bug is in hardware or in firmware.
Here is the original Bluetooth antenna schematic:
And here is my new antenna schematic:
Here's the microcontroller datasheet guidance on the RF subsystem:
Finally, here is an excerpt from the ST AN5165 reference document, which specifies the antenna filter specific to the 100-ball BGA package type we're using:
Is there anything I'm missing at the schematic level? I think I have implemented ST's guidance correctly. If the schematic looks okay, I intend to post a follow-up question focused on layout.
On page 40 of AN5165, the document reads:
"As a conclusion, the IPD reference MLPF-WB55-01E3 can replace the RF output network of the STM32WB for the QFN packages (an antenna filter is still needed) for a 2-layer PCB."
Does this imply that the output filter from the microcontroller and the input filter to the antenna are two separate filters? I assumed that there should be one filter between the microcontroller and the chip antenna, but now that it's not working, I'm revisiting my assumptions. I'm noticing that the original schematic has the Murata bandpass filter chip, and then an additional pi filter before the antenna.
Do I need to add an additional filter stage between the ST IPD chip and the antenna? Or does my schematic look okay as is?