nRF52 Output impedance clarification

[Arturo Arellano Arciniega]

Hi,

I've been digging through a lot of AN's about how to design a PCB antenna, in all of them an important parameter is the output impedance of the transmitter.

So, according to this blog post, the output impedance of the nRF52 is not 50ohms, but it is achieved externally with components L1 and C3 wich also forms a low pass filter. But also in the answer of this question Øyvind Karlsen said that the internal balun matches the impedance of the chip to 50ohms and L1 and C3 are only to filter unwanted frequencies (low pass filter).

It's clear that both components are needed to as a filter but wich one is right? Can I assume a 50ohm impedance after or before L1?

Thanks.

[Einar Thorsrud]

The output impedance of the nRF52 is not 50 Ω, so this answer is not correct. The correct answer would be that the output is unbalanced (due to the internal balun), but not matched. The external matching components are there for two main reasons: attenuate harmonics and match to 50 Ω. The General PCB design guidelines for nRF52 describes layout considerations and matching in more detail.

[Arturo Arellano Arciniega]

Thanks, it is clear now.