Reference Layout Changes in custom PCB

[cheezballs]

Hi there,

I am in the process of developing a custom PCB using the nRF52833 SoC. This board is quite simple, and doesn't use many of the pins of the nRF52833 SoC.

I am using reference layout 4 from Nordic. Within the associated documentation, it is strongly recommended not to change the reference layout to ensure optimal performance. Thus I have a few questions:

1. Due to the fact that I am using very few pins on the nRF SoC, I have deleted many of the superfluous traces, effectively leaving the pins NC. Is this fine?
2. I have refrained from putting any USB infrastructure on the board. This means I have no use for VBUS and the associated capacitor (C20), is it fine to delete C20 (and the trace) from the reference layout? I have attached screenshots of my schematic (with C20 highlighted in red) and the original Var 4 reference layout PCB.

Another question which is unrelated: What type of antenna would you advise for good performance in cross-polarisation and co-polarisation scenarios? I am currently using a trace antenna (similar to the antenna on the nRF52833 DK). But I'm wondering if a meander or chip antenna might be more effective. What are your recommendations? I assume RF testing has been performed on the nRF52833 DK antenna with different polarisation settings?

Cheers

[Jared]

Hi,

1. This is fine for the GPIO pins.
2. You can remove the capacitor and ground the pin if you're not going to use the USB interface
3. Monopole antenna is usually the best choice. If you don't have room for that antenna then I would suggest an inverted F as the next best option. If you can't fit an inverted F antenna then I would suggest a Chip antenna. 

regards

Jared

[cheezballs]

Thanks Jared!

This helps a lot. Just out of interest, I notice that through vias and blind vias are used throughout the Development Kit board for ground. What is the purpose/advantage of using a blind via over a a through via in such a design? I have attached a screenshot from the DK board which shows both types being used for ground.

[Jared]

I think that this is merely a decision based on cost. Through vias are less complex and therefore less costly, blind vias are used where it's needed.