Hi Nordic Forum!

We're currently tuning our antenna since we runed with some problems during our EMC testing.

In that regard, what is the impedance (both input and output) of the antenna pin (pin 30), when used for Bluetooth?

I know that for the nRF51 series it was 15 + j85 (Between ANT1 and ANT2), but I don't think that holds for the nRF52 series.

Thanks in advance

Hi Rodrigo,

the load impedance of the antenna pin should be 53 + j66 Ohms.

Best regards

Bjørn

This is somewhat confusing for me.

Assuming that these components result in 50Ohm I calculated the impedance of the pin and got 78 + j48 Ohms. The reason why this bothers me is that I'd like to match the nRF and the antenna with one single PI-filter and not with the proposed LC and an additional PI-filter due to size limitation constraints.

Hello,

I have the same question as noe in the follow up. Is the optimum load impedance of the antenna pin dependent on package for the nRF52832?

Thanks,

Steve

There are a few questions here so:

1. Yes antenna port impedance is package dependent. You will notice on the spec the recommended load is a little different for the WLCSP vs. QFN versions.

2. No you can't calculate it like that. For starters your calculation doesn't include the effects of the vias, component to component spacing, it should use real not idealized component physics and also it assumes a 50 ohm strip going into the WLCSP. The designs always have a parasitic inductance going into the chip due to the pin pitch.

Also, you can't assume the recommended antenna load results in a 50 ohm match. Power amplifiers rarely perform optimally in a conjugate match condition. Mis-match is often included to optimize the IP3 and harmonic performance.

On your custom board, your only course of action is to come up with a match that optimally conveys power to your antenna, while maximizing IP3 performance and minimizing harmonic output.