User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 103 of 206
x The bypass capacitors in the pF range and ferrite bead described in Figure 44, Figure 45 and Table 27 should
be placed as close as possible to the VCC pins. This is highly recommended if the application device
integrates an internal antenna.
x Since VCC is directly connected to RF Power Amplifiers, voltage ripple at high frequency may result in
unwanted spurious modulation of transmitter RF signal. This is more likely to happen with switching DC-DC
converters, in which case it is better to select the highest operating frequency for the switcher and add a
large L-C filter before connecting to the SARA-G3 and SARA-U2 series modules in the worst case.
x If VCC is protected by transient voltage suppressor to ensure that the voltage maximum ratings are not
exceeded, place the protecting device along the path from the DC source toward the cellular module,
preferably closer to the DC source (otherwise protection functionality may be compromised).
2.2.1.11 Guidelines for grounding layout design
Good connection of the module GND pins with application board solid ground layer is required for correct RF
performance. It significantly reduces EMC issues and provides a thermal heat sink for the module.
x Connect each GND pin with application board solid GND layer. It is strongly recommended that each GND
pin surrounding VCC pins have one or more dedicated via down to the application board solid ground layer.
x The VCC supply current flows back to main DC source through GND as ground current: provide adequate
return path with suitable uninterrupted ground plane to main DC source.
x It is recommended to implement one layer of the application board as ground plane as wide as possible.
x If the application board is a multilayer PCB, then all the board layers should be filled with GND plane as
much as possible and each GND area should be connected together with complete via stack down to the
main ground layer of the board.
x If the whole application device is composed by more than one PCB, then it is required to provide a good and
solid ground connection between the GND areas of all the different PCBs.
x Good grounding of GND pins also ensures thermal heat sink. This is critical during call connection, when the
real network commands the module to transmit at maximum power: proper grounding helps prevent
module overheating.