nRF52840 RF ground CKAA vs QIAA

[lukesnow]

Hello,

There is a comment in the v1.1 manual (shown below) which states that the first capacitor in the matching network (C3 in the reference designs) shouldn't be connected directly to ground, but that it should be grounded through the VSS_PA pin.  However, consulting the reference layouts for the CKAA and the QIAA package, it looks like only the QIAA package reference design employs this advice.

My question is, would it be beneficial (and decrease spurious harmonics) to include this same practice in the CKAA layout?  We have a design using the CKAA package, and I'd like to include this in the design if it'll help with lowering the 2nd and 3rd harmonics, as the 8dBm setting is not meeting regulatory requirements.

Thanks in advance,

Luke

QIAA ref design 1

CKAA ref design 1

[ketiljo]

The layout and the components values of the matching networks for the various devices and packet variants are all optimized for that specific part. So always use the  layout and component values that can be found in the reference layouts. 

For the CIAA packet, there's no benefit to change the grounding of the capacitor. You risk making it worse. If you fail the regulatory testing, you must ask for a review if your design, all reference designs are tested and will comply if done correcly.