nRF9160 external LNA requirements?

RE: nRF9160 external LNA requirements?

Andreas — Thu, 03 Oct 2019 09:04:50 GMT

Update Oct 3 2019: Please see the White paper on nRF9160 Antenna and RF Interface Guidelines for latest recommendations and specifications for GPS front-end. Summarized requirements:

GPS LNA recommended minimum gain is 15 dB (maximum gain not limited, but anything beyond 15 dB won’t improve the system performance noticeably).
GPS LNA recommended maximum NF is 1 dB (with filter 1.5 dB).
GPS LNA input and output nominal impedance 50 Ohm.
Interference at any frequency coupling into SIP GPS input should be < -7 dBm when GPS is OFF.
Interference at any frequency coupling into SIP GPS input should be < -30 dBm when GPS is ON.
Interference at any frequency coupling into GPS LNA input should be verified from selected GPS LNA datasheet, but same figures can be used as rule of thumb as for SIP GPS input case (4 and 5).
- Recommended minimum attenuation for own LTE TX signal coupling into GPS LNA input is 30 dB. Attenuation can be implemented by combination of LTE and GPS antenna isolation and using filter in GPS LNA input.

RE: nRF9160 external LNA requirements?

AndreasF — Wed, 28 Aug 2019 09:38:01 GMT

Hi.

1. If you look at the datasheet for QM14501 LNA, you can read that Input 1dB Compression Point is -2 dBm, so that is the level you will get distortion in the signal.

2. The purpose of U34 and C73 is to reduce the impact of interference from the LTE antenna when transmitting.

Best regards,

Andreas

RE: nRF9160 external LNA requirements?

ABM — Tue, 27 Aug 2019 15:18:30 GMT

[quote userid="73423" url="~/f/nordic-q-a/43096/nrf9160-external-lna-requirements/168483"]The most important thing is that the LNA is turned of or deactivates the signal-chain once GPS_enable is low. Usually you would turn the LNA off when you transmit, and therefore its important that the signal which is transmitted do not re-enter the radio. [/quote]

Thanks for spelling that out. A couple of questions (though if they're already covered in the documentation and I've missed it please do point me at it):

How low do we need to reduce the level of the cellular signal present at the GPS input to avoid improper operation?
Can you explain what the purpose of U34 and C73 is in nRF9160 DK schematics v0.8.5 is? What it does is shunt the antenna with 33pF when GPS_EN is low. Why is that done as I assume the LNA will be disabled at that time anyway?

RE: nRF9160 external LNA requirements?

AndreasF — Fri, 23 Aug 2019 11:43:15 GMT

Hi.

I can't comment on future plans, you have to contact your RSM and ask that.

Best regards,

Andreas

RE: nRF9160 external LNA requirements?

Lauri Jämsä — Fri, 23 Aug 2019 07:51:31 GMT

Thingy:91 hardware design files just got released and seems that it has QM14501. No Skyworks.

Are you going to migrate Thingy:91 to SKY65943-11 too?

https://www.nordicsemi.com/Software-and-Tools/Prototyping-platforms/Nordic-Thingy-91/Download

RE: nRF9160 external LNA requirements?

AndreasF — Wed, 21 Aug 2019 11:59:00 GMT

Hi.

Any later tags are not public and I cannot share them here.

Please contact your RSM and talk with him/her about that.

Best regards,

Andreas

RE: nRF9160 external LNA requirements?

ABM — Wed, 21 Aug 2019 09:47:39 GMT

Hi AndreasF. The schematics you linked to still show the qm14501 being used for the LNA. I've not opened the Altium files yet (I've just had a PC upgrade and not yet installed Altium). I assume they're not the latest?

RE: nRF9160 external LNA requirements?

AndreasF — Wed, 21 Aug 2019 07:31:26 GMT

Hi.

The schematics and altium files for the nRF91 v0.8.5 DK is available for download on nordicsemi.com:

Altium files for nRF9160

Schematics and layout for nRF9160DK

Best regards,

Andreas

RE: nRF9160 external LNA requirements?

Lauri Jämsä — Tue, 20 Aug 2019 14:52:53 GMT

No info about this new nRF91 DK available online. Where are the schematics?

RE: nRF9160 external LNA requirements?

AndreasF — Thu, 11 Jul 2019 07:27:40 GMT

Hi.

The last recommendations I read was that the LNA should have min. gain = 12dB, recommended gain = 25 dB, NF (without filter) < 1dB, NF (with filter) < 1.5 dB

The latest version of the nRF91 DK uses SKY65943-11.

I'm unsure if we have any later recommendations after this one.

Best regards,

Andreas

RE: nRF9160 external LNA requirements?

Lauri Jämsä — Wed, 10 Jul 2019 18:24:21 GMT

Could you share the recommended LNA part numbers? No Qorvus parts please because those are not easily available.

RE: nRF9160 external LNA requirements?

AndreasF — Tue, 29 Jan 2019 13:53:28 GMT

Hi.

The most important thing is that the LNA is turned of or deactivates the signal-chain once GPS_enable is low. Usually you would turn the LNA off when you transmit, and therefore its important that the signal which is transmitted do not re-enter the radio. The compression characteristics is more important in situations which have a lot of noise. The sensitivity given in the datasheet is probably excluding the LNA.

Best regards,

Andreas