nRF9160 DK (PCA10090) Schematics

[David]

Hi!,

Im curious of what the below module (U34) does within the GPS circuit?

Also, what does the MAGPIO0 "55" do?, can I use one of the GPIOS for enabling the GPS?

- David

[Andreas]

Hi,

 

U34 was added to disconnect the GPS antenna when GPS is not used, in order to improve the isolation when the LTE modem is transmitting. It was found that the LTE signal would couple into the GPS front-end, where it would intermodulate, and radiate from the GPS antenna, violating regulatory requirements. This version is a quick fix, the upcoming production version will use an LNA with filter on the input, which eliminates this problem.

Not necessarily all boards need this, it all depends on the isolation between the antennas, and how the specific LNA reacts to the incoming signal. However as you will not know if it is needed or not until you get your boards back and actually measure it, it might be worth taking preventive actions, either a switch alternative or an LNA alternative.

 

MAGPIO0 is used to toggle the GPS LNA and antenna switch, when the modem enters GPS mode. It can be controlled though the AT%XMAGPIO AT command. After this version was released, COEX0 is now the recommended pin to simply toggle the GPS LNA, you then do not have to route the MAGPIO pins past the LTE antenna path.

 

Best regards,

Andreas

[David]

Hi Andreas,

Ok, I understand.

See image below, marked in red. Is this the "filter on the input" location  you are talking about, for the upcoming production version?

Also, when are Nordic planning this upcoming production version ?

Regarding the GPS,

could I add an external GPS antenna with 50 Ohm, without any matching impedanse circuitry?

---

Ok, I will then use  COEX0 to toggle "EN", but can it be controlled through the AT command aswell ?

- David

[Andreas]

Hi,

 

No, a different LNA (U3) is used, which has a built-in filter on the IN pin. I do not have a date for when this will be available, you will have to contact the Nordic Regional Sales Manager who is responsible for your region for roadmap related queries. Let me know if you do not know who this is or if you need contact information.

 

Correct, the GPS pin is 50 ohm, so you do not need any impedance matching components if the antenna is 50 ohm. GPS LNA control using COEX0 is enabled by setting the AT%XCOEX0 AT command.

 

Best regards,

Andreas