User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 168 of 206
2.16.2 Layout checklist
The following are the most important points for a simple layout check:
5 Check 50 : nominal characteristic impedance of the RF transmission line connected to the ANT pad
(antenna RF input/output interface).
5 Follow the recommendations of the antenna producer for correct antenna installation and deployment
(PCB layout and matching circuitry).
5 Ensure no coupling occurs between the RF interface and noisy or sensitive signals (primarily analog audio
input/output signals, SIM signals, high-speed digital lines).
5 VCC line should be wide and short.
5 Provide the suggested series ferrite bead and bypass capacitors close to the VCC pins implementing the
recommended layout and placement, especially if the application device integrates an internal antenna.
5 Route VCC supply line away from sensitive analog signals.
5 Ensure proper grounding.
5 Optimize placement for minimum length of RF line and closer path from DC source for VCC.
5 Design USB_D+ / USB_D- connection as 90 : differential pair, with 30 : common mode impedance.
5 Route analog audio signals away from noisy sources (primarily RF interface, VCC, switching supplies).
5 The audio outputs lines on the application board must be wide enough to minimize series resistance.
5 Keep routing short and minimize parasitic capacitance on the SIM lines to preserve signal integrity.
5 Ensure optimal thermal dissipation from the module to the ambient, in particular for SARA-U2 modules.
2.16.3 Antenna checklist
5
Antenna termination should provide 50 : characteristic impedance with V.S.W.R at least less than 3:1
(recommended 2:1) on operating bands in deployment geographical area.
5 Follow the recommendations of the antenna producer for correct antenna installation and deployment
(PCB layout and matching circuitry).
5 Follow the additional guidelines for products marked with the FCC logo (United States only) reported in
section 4.2.2
5 Follow the guidelines in section 2.4.2 to get proper antenna detection functionality, if required.