Matching circuit

[DurandA]

Hi @prasad-dot-ws,

Thanks you for sharing a proper footprint of the Espressif antenna design. I found it through your ESP32 Forum post.

When using the antenna, do you add a matching circuit like below? If yes, how do you chose the value of the inductors/capacitors?

Many thanks!

[DurandA]

This matching circuit is called a Pi-network and here is a guide on how to use it (requires a VNA).

[prasad-dot-ws]

Hey @DurandA,

Yes, I did use matching circuit for the antenna. I used the recommended values for ESP WROOM 32 module. However, as you may know this is more or less PCB fabrication process dependant. Most of the PCB fabricators provide an impedance calculator so that you can calculate the impedance and match with the required impedance stated by the silicon manufacturer.

[https://cart.jlcpcb.com/impedanceCalculation?_ga=2.187928104.1246244105.1590089135-901229049.1590089135](JLC PCB)

Below quote is from ESP32 datasheet,

The typical value of ESP32’s Wi-Fi radio output impedance is different between chips in different QFN packages. For ESP32 chips with a QFN 6×6 package, the value is 30+j10 Ω. For ESP32 chips with a QFN 5×5 package, the value is 35+j10 Ω

Having all that said, Using recommended values from ESP WROOM 32 module worked perfectly fine for me with JLC PCB.

Best Regards,
Prasad.

[DurandA]

Thank you very much for the extensive answer.

I am using the ESP32-PICO-D4 system-in-package which is a bit different (and also the only ESP32 available in JLCPCB SMT assembly right now). It is a 7x7 QFN package that also include a flash as well as most passives. From its schematic, it also includes a Pi-network to match 50Ω:

Also, the datasheet is a bit confusing as it states:

For the modules that use IPEX antennas, the output impedance is 50Ω. For other modules without IPEX antennas, users do not need to concern about the output impedance.

I had a look at two boards which use the same 3D antenna, and they seem to use quite different values for the Pi-network.

ESP32-PICO-KIT:

TinyPICO:

I'm not sure how bad it will be if I use one of the values above (or no matching network at all) with the Espressif PCB antenna. I read that too much signal reflection can be destructive to the transceiver.