PCB review nrf52832

RE: PCB review nrf52832

jake11212 — Fri, 09 Jul 2021 23:07:40 GMT

Thanks so much for all the assistance, this has been monumentally helpful. I've made all the changes to the antenna and I think it would be easiest to just submit another PCB review with that board.

RE: PCB review nrf52832

Kaja — Fri, 09 Jul 2021 06:38:16 GMT

You can start be leaving Z1 and Z3 N.C, and then Z2 = 1.5 nH, as this is the suggestion from the antenna vendor.. you can simulate, but this will probably not give you a better result then the suggestion from the antenna vendor.
The best ting to do is to du conducted measurements, and adjust the components values, and match the antenna to 50 Ohm. See our white paper on antenna tuning

You can send us boards for tuning yes, we would need two boards and one housing/enclosure. We would adjust the components values of Z1, Z2 and Z3 to tune the antenna.
We would also alter the components values on C3 and L1 for tuning the radio, output power and harmonics.
This is good to do as preparation before certification and performance testing.
- This is a free service we provide to our costumers, you just have to pay the shipping.
Due to summer vacation we will not have the opportunity to do this in week 28, 29 and 30.
I will be out of office for the next three weeks, but I will add the shipping info, so you can ship them to me while I'm away, and then we can have a look at your device at the lab after summer.

Please mark the package with the case ID (272650) and here is the shipping information:

For DHL or Fedex:
Nordic Semiconductor
Att: Kaja G. Sørbotten
Otto Nielsens vei 12
7052 Trondheim
Norway

Other shipping companies:
Nordic Semiconductor
Att: Kaja G. Sørbotten
Postboks 2336 Torgarden,
7004 Trondheim

In case it is needed by the shipping company:
Tel: +47 72 89 89 41
email: kaja.soerbotten@nordicsemi.no

Also, update the case with the tracking number when the package is sent.

Best regards,
Kaja

RE: PCB review nrf52832

jake11212 — Thu, 08 Jul 2021 16:13:16 GMT

[quote userid="77059" url="~/f/nordic-q-a/77219/pcb-review-nrf52832/319080#319080"]In addition you need a matching network for impedance matching for the antenna, for the antenna you sent, the antenna vendors tuning option 1, only includes one series component, but I would recommend that you add a full pi-network.[/quote]

Okay, so how do I decide on values for Z1 Z2 and Z3?

I've found calculators (such as: https://www.eeweb.com/tools/pi-match/) which requires a frequency, source resistance, source reactance, load resistance, load reactance, and Q factor. How can I find these values without taking any measurements? Can they be estimated?

Thanks for the power profiler for BLE, that's very helpful.

[quote userid="77059" url="~/f/nordic-q-a/77219/pcb-review-nrf52832/319080#319080"]We are happy to do tuning of the radio and antenna for you!
[/quote]

So after we fabricate boards we could send them to you and you would adjust them? Would we need to leave room for variants so that they could be modified, or are there other design requirements to allow for tuning?

RE: PCB review nrf52832

Kaja — Thu, 08 Jul 2021 07:50:59 GMT

[quote user="jake11212"]

The feed line coming off of L1 in my schematic is configured to have an impedance of 50 ohm, correct?

As long as I keep the trace to the antenna short and don't put many components near it, it should be okay to simply use the L1/C3 matching network and attach the chip antenna at the end of L1 to be approximately correct right? I was thinking of just doing this, then tuning the network in later iterations.

[/quote]

No, this is not correct. C3 and L1 is there to transform the output impedance of the radio to ~50 Ohm, and to give you desired output power and work as a filter to give low enough harmonics.

In addition you need a matching network for impedance matching for the antenna, for the antenna you sent, the antenna vendors tuning option 1, only includes one series component, but I would recommend that you add a full pi-network.

[quote user="jake11212"]Also, I know it's hard to estimate power consumption because of how much it varies by component/use but are there estimates for order of magnitude differences between the different options? Such as chip antennas being half as efficient as meander antennas or just general guidelines for estimating this before we do a board fabrication and power profile?[/quote]

Power consumption or antenna efficiency?
For power consumption the antenna will not influence, you can use the Online Power Profiler for BLE to get an estimate.
Antenna efficiency, difficult to stat for sure, also depends how well the antenna is placed, and tuned on the board.

We are happy to do tuning of the radio and antenna for you!

Best regards,
Kaja

RE: PCB review nrf52832

jake11212 — Thu, 08 Jul 2021 05:22:40 GMT

Thanks for all the info on different antennas, this is really helpful. Small footprint is much more important than the antenna functionality for now, so I think chip antennas make the most sense for this iteration.

Based on the johansontechnology link I think this antenna makes the most sense:

https://www.johansontechnology.com/datasheets/2450AT42E010B/2450AT42E010B.pdf

The feed line coming off of L1 in my schematic is configured to have an impedance of 50 ohm, correct?

Also, I know it's hard to estimate power consumption because of how much it varies by component/use but are there estimates for order of magnitude differences between the different options? Such as chip antennas being half as efficient as meander antennas or just general guidelines for estimating this before we do a board fabrication and power profile?

RE: PCB review nrf52832

Kaja — Wed, 07 Jul 2021 06:16:27 GMT

For a chip antenna, you would need a fill pi-network for impedance matching, so the schematic should look like this:
(meander, inverted F..+++ and chip antennas)

[quote user="jake11212"]Also for the trace antenna, can it just be created in altium by adding a trace as you would between any other components? Or is there a feature specifically for trace antenna drawing?[/quote]

You can copy it directly from the DK, just add some mm to the length, for antenna tuning.. or see how to design your own in our whitepaper

Antenna choice is complex and depends on many factors including technical and commercial considerations. Here are some alternatives, and some considerations:

Monopole, printed PCB antenna: This is easy to make and easy to tune, you also only need one impedance matching component, so it’s cost effective. Here the spacing is the issues, you need to make it about 23 mm long needs a minimum of 5 mm clearance to the ground plane. High bandwidth, making it fairly resistant to detuning. Link to our whitepaper: https://infocenter.nordicsemi.com/pdf/nwp_008.pdf?cp=12_18

Meander antenna, printed PCB antenna, ex. our dongle antenna design: Requires a smaller area than the monopole antenna, but usually requires a pi-network for tuning in addition to length. Lower bandwidth than a quarter wave monopole antenna. Here is a link to our nRF52840 Dongle design files as an example of this: https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52840-Dongle/Download#infotabs

Chip antenna: Higher BOM, but the antenna is small. The downside is that it usually has less gain. It requires a matching network, based on the vendors recommendations. It has a lower bandwidth than a quarter wave monopole antenna so it can be sensitive to detuning.

Considering your target of a very small form factor a chip Antenna makes sense but reducing antenna size most often results in reduced performance. Some of the parameters that suffer are:

Reduced efficiency (or gain)
Shorter range
Smaller bandwidth
Distorted radiation pattern
More critical tuning
Increased sensitivity to component and PCB spread
Increased sensitivity to external factors (“body” effect, ground plane etc.)

It is often better not to reduce antenna size too much, if you can avoid it.

We do not recommend specific chip antennas, and the selection will depend very much on the end application design. The antenna vendors can assist on choosing the right antenna for a specific design, for example Johanson has a useful tool that helps with this selection: https://www.johansontechnology.com/chip-antenna-selection

Best regards,
Kaja

RE: PCB review nrf52832

jake11212 — Tue, 06 Jul 2021 20:40:48 GMT

Thanks so much for the review!

I was planning to just use a ceramic chip antenna (something like this: https://www.digikey.com/en/products/detail/johanson-technology-inc/2450AT42E010BE/6235443) with a 1.2pF capacitor connected to ground after L1, then the chip antenna placed past it. I based this off of the DK as I wasn't sure what else to use for the matching network for the antenna. Here is the updated schematic I'm proposing with the antenna, will this suffice?

devzone.nordicsemi.com/.../nrf52832_5F00_qfaa_5F00_dcdcSecondRevision.SchDoc

My other thought was to use the matching network with a trace antenna that was the same as the one on the development kit (the same 1.2pF capacitor and then copy the width/length of the antenna trace). The chip version seemed easier to implement and kept the size smaller, but do you have a recommendation for which to go with or a better way to implement a matching network? I don't have an oscilloscope or equipment to run tests for the matching network so I just wanted to base it off of something similar.

Also for the trace antenna, can it just be created in altium by adding a trace as you would between any other components? Or is there a feature specifically for trace antenna drawing?

RE: PCB review nrf52832

Kaja — Tue, 06 Jul 2021 13:45:39 GMT

Hi,

so the schematic and layout looks okay. You should add a matching network for an antenna and an antenna:

You might want to use one of the shorter edges for the antenna, so you might want to rotate the chip, and move PCF8523 to the same side as H1.

To program with chip via the SWD interface you can use a nRF52 DK:

You can use the online power profiler for BLE and you can use the PPK to measure on your board, see the user guide.

We use a two pad crystal for X2, 32.768 kHz, and a four pad crystal for X1. There should be plenty of crystals to choose from on the marked.

Size on the crystal is not listed as a specification, you can see what specifications we have LFXO and HFXO

Best regards,
Kaja

RE: PCB review nrf52832

Kaja — Fri, 02 Jul 2021 12:54:12 GMT

Hi,

I will get back to you with a review one of the next couple of business days.

Best regards,
Kaja