In EVAL Kit of ST25RU3993, why do we give Buffer positive supply, internally regulated to Low Power DIfferential Power output (0 dBm )

[Akshit Dangi]

In the schematic for EVAL Kit why we have used Inductors and why we have given Buffer positive supply, { internally regulated } to RF Output of both Internal Amplified and also for Low power Amplifier. PFA image attached.

Secondly why they have used the 82pF capacitor before inputting every IC?

[Bart Herse · Accepted solution]

Hi Akshit Dangi,

VDD_B and VDD_PA are needed to bias the RF output stages of the reader IC.

The inductors act as chokes that block the RF signal not reaching VDD_B and VDD_PA.

The 82pF capacitors are DC blocking caps preventing the DC voltage to propagate to the remainder of the RF path.

Note that some Baluns offer also a DC bias input. You can use such a feature as well instead .

Cheers,

B