Matching network on nrf52840

[Samno]

Hello,

I am new to developing with Nordic products and I have a question regarding the components in the antenna matching network. I am designing around the QIAA QFN-73 package.

On the datasheet it gives the following for the matching network for 50 ohms:

However in the online guide for the nrf52 series, available here:

 General PCB design guidelines for nRF52 series 

It gives the following circuit:

I understand the Z1, Z2 and Z3 in the second picture are the matching network for the antenna and that is not my question. The other values for the nrf52 matching network are quite similar, so I would ordinarily go with the latest datasheet, except that there is the addition of the extra 2.2nH inductor L2. Just wondering if there is an explanation for the discrepancy that could help me understand it better, and to know which one is recommended. Appreciate any help you can give.

[Bendik Heiskel]

Hi,

The second picture shows the matching network in circuit configuration 7. This is a updated matching network that performs better when using 8dBm output power. The radio matching circuit serves double duty, it both matches the ANT pin to 50Ohm and is a lowpass filter used for attenuating the harmonic distortion, to limits within the regulatory limits. On some designes the older Pi network was not suffifcient for attenuating the harmonic frequency emission, so we now recommend using the 4 component matching network when using 8dBm output power.

Regardless of which matching network you use, the component values may need to be tweaked for your specific board layout to make sure the emission are within the regulatory limits. This is done after the board is produced, by measuring the output power of the fundamental and harmonic frequencies.

You can get your design reviewed before have the boards produced to help catch any issues with the RF part of the design before hand. Just create a new private ticket and share your schematic and layout, and one of our engineers will give feedback on the design.

 

Best regards,

Bendik

[Samno]

Thank you very much. I am new to developing with Nordic so I am sure I will have many more questions for you in the near future. This project is very time constrained so I appreciate the customer support.