nrf51822: Inductor selection

[JohnC]

I'm interested in working off the reference design for the nrf51822 to create my own board. I have a few questions about the 3 inductors specified on the schematic/BOM:

1. 0402 SMD size parts are specified. Are larger SMD parts OK? (Say, 0603 or 1005)

2. What exactly is meant by "high frequency chip inductor"? Does this relate to the resonant frequency of the inductor and, if so, what resonant frequencies would I want to consider?

3. Are there any recommended (or min/max) current rating or current saturation values?

4. I assume that a multilayer ceramic inductor is what I want. If not, what should I use?

5. I assume that the same selection criteria would also govern the selection of inductors for the antenna. If not, what are the differences?

[mnhs]

Hi,

Just to let you know - there are also specialized chips which include all the balun into one component. I use those and I am extremely satisfied with them. For example Johanson technology makes baluns specifically for nRF51 family. I will post a photo here in an hour or so to show my latest prototype design with these.

1. Yes, but larger parts also induce more parasitic inductance and other not wanted effects. The space occupied by matching circuitry is also larger 0603 are OK in my opinion.

2. The self-resonant frequency should be at least 2 times the carrier frequency - 2.45 Ghz, so anything above 5 Ghz is fine.

3. Personally I think this is not an issue when transmitting at 0 dBm (1 mW) power. But I am not sure so wait for answer of anyone else. I always used something around 300 mA minimum.

4. If I am right there are reference components listed. If possible, use the same components to assure optimum performance.

5. The parameters of components used to make matching circuitry near the antenna can be the same as the balun circuitry.

After you make your final design and you are planning to make it commercial, you should make a proper measurement using spectrum analyser to ensure that everything is working fine. This can also save a lot of money during cerfitication process.

[mnhs]

Here is the photo - sorry for bad soldering, it is a first working prototype soldered by hand including all the 0201 components which was literally a hell to do only with tweezers and hot air :-).

www.mnhs.cz/nrf_balun.jpg