SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
Design-in
Page 175 of 217
2.16.2
Layout checklist
The following are the most important points for a simple layout check:
Check 50
nominal characteristic impedance of the RF transmission line connected to the
ANT
pad
(antenna RF input/output interface).
Follow the recommendations of the antenna producer for correct antenna installation and deployment
(PCB layout and matching circuitry).
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).
VCC
line should be wide and short.
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.
Route
VCC
supply line away from sensitive analog signals.
Ensure proper grounding.
Optimize placement for minimum length of RF line and closer path from DC source for
VCC
.
Design
USB_D+ / USB_D-
connection as 90
differential pair, with 30
common mode impedance.
Route analog audio signals away from noisy sources (primarily RF interface,
VCC
, switching supplies).
The audio outputs lines on the application board must be wide enough to minimize series resistance.
Keep routing short and minimize parasitic capacitance on the SIM lines to preserve signal integrity.
Ensure optimal thermal dissipation from the module to the ambient, in particular for SARA-U2 modules.
2.16.3
Antenna checklist
Antenna termination should provide a 50
characteristic impedance with V.S.W.R at least less than 3:1
(recommended 2:1) on operating bands in the deployment geographical area.
Follow the recommendations of the antenna producer for correct antenna installation and deployment
(PCB layout and matching circuitry).
Follow the additional guidelines for products marked with the FCC logo (United States only) reported in
section 4.2.2
Follow the guidelines in section 2.4.2 to get proper antenna detection functionality, if required.
