Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 74 of 157
 VCC connection must be routed as far as possible from the antenna, in particular if embedded in the
application device: see Figure 28
 Coupling between VCC and digital lines, especially USB, must be avoided.
 The tank bypass capacitor with low ESR for current spikes smoothing described in section 2.2.1.10 should
be placed close to the VCC pins. If the main DC source is a switching DC-DC converter, place the large
capacitor close to the DC-DC output and minimize VCC track length. Otherwise consider using separate
capacitors for DC-DC converter and module tank capacitor
 The bypass capacitors in the pF range described in Figure 27 and Table 19 should be placed as close
as possible to the VCC pins, where the VCC line narrows close to the module input pins, improving the
RF noise rejection in the band centered on the Self-Resonant Frequency of the pF capacitors. This is
highly recommended if the application device integrates an internal antenna
 Since VCC input provide the supply 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-R4/N4 series modules in the worst case
 Shielding of switching DC-DC converter circuit, or at least the use of shielded inductors for the switching
DC-DC converter, may be considered since all switching power supplies may potentially generate
interfering signals as a result of high-frequency high-power switching.
 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 module, preferably
closer to the DC source (otherwise protection function may be compromised)
SARA
VCC
ANT
Antenna
NOT OK
Antenna
SARA
VCC
ANT
OK
Antenna
SARA
VCC
ANT
NOT OK
Figure 28: VCC line routing guideline for designs integrating an embedded antenna
2.2.1.12 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.
 Connect each GND pin with application board solid GND layer. It is strongly recommended that each
GND pad surrounding VCC pins have one or more dedicated via down to the application board solid
ground layer
 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