SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 78 of 102
2.14.2
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
port
(antenna RF interface).
Ensure no coupling occurs between the RF interface and noisy or sensitive signals (SIM signals,
high-speed digital lines such as USB, and other data lines).
Optimize placement for minimum length of RF line.
Check the footprint and paste mask designed for SARA-R4 series module as illustrated in section 2.11.
VCC
line should be wide and as short as possible.
Route
VCC
supply line away from RF line / part and other sensitive analog lines / parts.
The
VCC
bypass capacitors in the picoFarad range should be placed as close as possible to the
VCC
pins,
in particular if the application device integrates an internal antenna.
Ensure an optimal grounding connecting each
GND
pin with application board solid ground layer.
Use as many vias as possible to connect the ground planes on multilayer application board, providing a
dense line of vias at the edges of each ground area, in particular along RF and high speed lines.
Keep routing short and minimize parasitic capacitance on the SIM lines to preserve signal integrity.
USB_D+
/
USB_D-
traces should meet the characteristic impedance requirement (90
differential and
30
common mode) and should not be routed close to any RF line / part.
2.14.3
Antenna checklist
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.
Follow the recommendations of the antenna producer for correct antenna installation and deployment
(PCB layout and matching circuitry).
Ensure compliance with any regulatory agency RF radiation requirement, as reported in section 4.2.2 for
products marked with the FCC.
Ensure high isolation between the cellular antenna and any other antennas or transmitters present on
the end device.
