LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 97 of 116
C1-Public
2.17.2
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
and the
ANT_GNSS
ports (antenna RF interfaces).
Ensure no coupling occurs between the RF interface and noisy or sensitive signals (primarily the
VCC
line, analog audio input/output 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 the module as illustrated in section
Route
VCC
supply line away from RF lines / parts 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 a multilayer application board,
providing a dense line of vias at the edges of each ground area, in particular along the 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.
Ensure appropriate RF precautions for the RF coexistence of GNSS and Cellular technologies.
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.
2.17.3
Antenna checklist
Antenna termination should provide a 50
characteristic impedance with VSWR 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).
Ensure compliance with any regulatory agency RF radiation requirement, as for example reported
in sections
and/or
for FCC US and/or ISED Canada.
Ensure high isolation between the cellular antennas and any other antenna or transmitter.
Ensure high isolation between the cellular and the GNSS antennas.
