To balun or not to balun...

[Greg Balmer]

We're starting out on BLE project with the nRF51822 and trying to get a prototype design together having completed a POC with the developer kit and PCA10004, and are considering using a trace antenna initially.

Looking at the 2 reference designs for the QFN package as hopefully a good place to start, I'm wondering what the advantage of using the one with the ST balun is or if it is even relevant when using a trace antenna?

Sooner or later I guess we will migrate to a chip antenna as we would like to achieve decent range performance in a domestic scenario, but I fear our current skill-set and resources are not up to designing the necessary additional circuitry atm... (the antenna tuning guide looks a bit like black magic to me)

Any advice much appreciated,

Thanks,

Greg.

P.s Are the reference designs available in Diptrace format? or in some other portable encoding? as Altium is pretty pricey for an early days startup...

[FormerMember]

Hello,

1) The adventage of using the balun is that it is smaller than the discrete matching network, so that is makes the design slightly more compact. The performance of the balun and the discrete matching network is the same.

2) The performance of a chip antenna and a PCB antenna is the same. The main differences between them are the size and the price. Both a chip and PCB antenna have to be tuned; the chip antenna with a pi-network and the PCB antenna with a shunt component, like described chapter 4 in the "Antenna tuning" white paper. For design of a PCB antenna I recommend you to read the "Quarterwave printed monopole antenna for 2.4GHz" white paper. It may also be useful to take a look at this post.

Regards, Kristin

[FormerMember]

Yes, the difference between PCA 10004 and the reference layout is that C17 is added. The reason that C17 is not in the reference layout, is that C17 is more related to the antenna than the chip. In addition, what kind of matching network that should be used depends on the antenna. I agree that it can be a cunfusing. The value of C17 should be found during tuning, so while the antenna is not tuned, it is not necessary to mount any component on C17. Normally, there will be some range when the antenna is not tuned. However, by tuning it, the range will often be increased significantly.