RE: NRF51 design/layout questions

Asbjørn — Thu, 12 Mar 2015 15:26:28 GMT

No, the antennas are generic, but their characteristics may change from design to design. So it's important if you want to optimize radio performance that you tune antenna in your application. The baluns are specific for the chip or for a set of chips, so they might have to be tuned for different chips.

RE: NRF51 design/layout questions

jon — Mon, 09 Mar 2015 09:02:37 GMT

Btw, for question 3, when you say "tune the component values specifically to the chip" - which chip do you mean? Are the baluns normally "matched" to a specific part (ie the NRF51 or a specific chip antenna?)

RE: NRF51 design/layout questions

jon — Mon, 09 Mar 2015 08:55:46 GMT

Thanks, good answers!

RE: NRF51 design/layout questions

Asbjørn — Mon, 09 Mar 2015 08:50:00 GMT

We use regular vias as a part of cost reduction. We have seen some PCB manufacturers charge by the amount of micro-vias and hence we have chosen to use regualr vias as much as possible. There's no problem with using micro vias all over the board. Just make sure you have enough all over the board.
The external 32 kHz crystal is not needed for BLE operations. You can make use of the internal 32 kHz RC oscillator. The internal RC is not as accurate and hence you will have to have slightly longer radio events to ensure you hit the time slot. A lot of our customers use the internal, especially in your situation where they have a small board.
Generally as long as you implement the balun as the manufacturer specifies it we see better overall performance from using baluns than using a discrete solution. In an integrated balun they tune the component values specifically to the chip and hence they can for example make a 8.75 nH inductor in the integrated balung instead of settling with either 8.2 nH or 10 nH. So generally speaking the overall performance is better.
Unless you have a power amplifier there's generally no need to shield the top component side. Just make sure that you are decoupling essential parts of your design and follow Nordics reference layout. Connect all parts of ground together through a lot of vias.
Yes, the footprints are the same, the AC version with 32 kB RAM is slightly bigger, but the footprint under is the same as the AA version. You can replace them later as long as the edge of the large one isn't interfering with anything.