recommended chip antenna, debugger for nRF52 based design

RE: recommended chip antenna, debugger for nRF52 based design

vredzhepov — Mon, 29 May 2017 10:47:09 GMT

The link provided above seems to not be working

RE: recommended chip antenna, debugger for nRF52 based design

Håkon Alseth — Wed, 15 Jul 2015 20:43:35 GMT

It's set from our side, and we always strongly recommend to use the values and layout recommendations that we provide to ensure that the performance of your design is ideal.

If you do not follow our ref. design, you will have to use spectrum analyzer and tune the output impedance to 50 ohm, as well as suppress noise, and you will have to repeat measurement of output power and harmonics until you find a sufficient combination. A sufficient margin (what FCC/ETSI requires) in terms of the harmonics level, these shall be less than -30 dBm, ideally with a 5-10 dB margin to account for chip- and component variation. If you have not done this before, or and/do not have a spectrum analyzer, this will be a time-consuming task. Soldering skills must be above average, and you will also need to have access to various values of inductors and C0G/NP0 grade caps in 0402 size.

Cheers, Håkon

RE: recommended chip antenna, debugger for nRF52 based design

EL34PP — Wed, 15 Jul 2015 18:10:14 GMT

If i'm not completely following Nordic reference PCB layout, how to design that T-network value?

RE: recommended chip antenna, debugger for nRF52 based design

Øyvind Karlsen — Wed, 15 Jul 2015 10:55:16 GMT

For making the Pi-network please see the whitepaper on Antenna Tuning

RE: recommended chip antenna, debugger for nRF52 based design

Øyvind Karlsen — Wed, 15 Jul 2015 10:48:41 GMT

Please see the update to my original answer.

RE: recommended chip antenna, debugger for nRF52 based design

Lakerno — Wed, 15 Jul 2015 10:47:10 GMT

Sorry I think I am a bit confused. I see that NRF52 has an internal balun and is matched to 50ohm, For matching the external chip antenna to 50 ohm, do I need to another matching Pi Network? If yes the L1 and C3 in the reference design are part of this Pi network and I need to add only a 3rd component? Or L1 and C3 and just filtering ckt and not part of the Pi network, and I need a seperate Pi network?

In both cases, how exactly do I design the Pi network to match the Antenna to 50ohm? Can I find the values of this Pi network only after I have the PCB fabricated? Or is there any way to calculate it before hand? If it can be calculated only after having the PCB back, then can just leave the footprint for components open and then solder the Pi network components back to the PCB board? How exactly to find the values of this network?

Any help will be greatly appreciated?

RE: recommended chip antenna, debugger for nRF52 based design

Øyvind Karlsen — Wed, 15 Jul 2015 10:16:46 GMT

Yes, in a way. Their role is to choke out unwanted RF characteristics.

RE: recommended chip antenna, debugger for nRF52 based design

Lakerno — Wed, 15 Jul 2015 09:25:24 GMT

Is L1 and C3 part of the matching network?

RE: recommended chip antenna, debugger for nRF52 based design

Øyvind Karlsen — Wed, 15 Jul 2015 07:25:43 GMT

L1 and C3 are part of a RF-choke network that removes unwanted noise.

RE: recommended chip antenna, debugger for nRF52 based design

oliverhu — Wed, 15 Jul 2015 07:12:51 GMT

hi, as the reference circuit states, what is the L1 and C3 used for? is it used as standard matching network ?

RE: recommended chip antenna, debugger for nRF52 based design

Øyvind Karlsen — Mon, 13 Jul 2015 11:54:31 GMT

Hi,

Any 2.4GHz chip antenna will work, select the one that fits your size, price and gain criteria. Be sure to place the chip antenna as specified in its datasheet.

You do not need an external balun, however you will need a matching network between the antenna output and the antenna. See the general PCB design guidelines for 51, this is still highly relevant. Follow the reference circuitry.

For a custom board you can add a J-Link port and debug using the debug out port of the development kit, see this blogpost for a setup overview.

Role of the T-network:

Internal balun: Matches the output of the chip to 50ohm

T-Network: Removes unwanted RF characteristics, this can be noise on the harmonics(2nd, 3rd, 4th etc) unclean signal and other effects. The T-Network is often called an RF choke since it chokes out unwanted parts of your RF signal. If you remove this you may have problems with the regulatory tests.

If you look at T-networks online you will see that they often consist of three components, our circuit may look like it breaks that rule. The trick is that for high frequency signals a short cable or PCB trace will acquire capacitive and inductive effects, so our third component is in the wiring. Have a look at the wikipedia article on transmission lines for more information.

Pi-Network: Matches the antenna to 50ohm

Best regards,

Øyvind