Low Noise Amplifier (LNA) Design for GNSS Device

Thread Starter

JCL24

Joined Dec 12, 2019
5
Hello Everyone

I am busy designing a board that will include the U-Blox ZED-FP9 GNSS module.

For my prototyping phase I made use of the Sparkfun GPS-15136 (A breakout board for the ZED-FP9, link below)
https://www.sparkfun.com/products/15136

I am basing the design for the circuitry surrounding the ZED-FP9 off the schematics of the Sparkfun GPS-15136 (link below).
https://cdn.sparkfun.com/assets/9/a/0/0/a/Qwiic_GPS-RTK2_-_ublox_ZED-F9P.pdf

My question is regarding the RF aspects of the part of the circuit highlighted below:

1653040613909.png

Firstly, it is my understanding that the trace between the UFL connector and the RF_IN pin needs to be impedance matched to 50 ohms. To this end I need to calculate the correct trace width according to my boards parameters to get 50 ohm impedance at 1575 MHz. Is this correct?

Secondly, i am wondering about the the circuitry going to the V_RF pin. I believe this is an external Low Noise Amplifier (LNA), but i'm not completely sure. I wanted to just copy the design that is show here, but I do not know the characteristics of the ferrite bead FB1.

Since I have very limited RF knowledge, I was hoping someone could give me some insight regarding how I can select a suitable ferrite bead for FB1 and also perhaps explain how this LNA works and how I can duplicate and verify its design.

Thanks in advance :)
 
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