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SARA-G3 series - System Integration Manual

UBX-13000995 - R06

Objective Specification

Design-in

Page 101 of 218



Coupling between

VCC

and audio lines (especially microphone inputs) must be avoided, because the

typical GSM burst has a periodic nature of approx. 217 Hz, which lies in the audible audio range.



The tank bypass capacitor with low ESR for current spikes smoothing described in

Figure 30Figure 30

and

Table 16Table 16

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 the

VCC

track

length. Otherwise consider using separate capacitors for DC-DC converter and SARA-G3 module tank
capacitor.



The bypass capacitors in the pF range described in

Figure 30Figure 30

and

Table 16Table 16

should

be placed as close as possible to the

VCC

pins. This is highly recommended if the application device

integrates an internal antenna.



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 series modules in the worst case.



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 SARA-G3
module, preferably closer to the DC source (otherwise protection functionality may be compromised).

2.1.1.9

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.



If the application board is a multilayer PCB, then it is required to connect together each GND area
with complete via stack down to main board ground layer.



It is recommended to implement one layer of the application board as ground plane as wide as
possible.



Good grounding of

GND

pads 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.

2.1.2

RTC supply (V_BCKP)

2.1.2.1

Guidelines for V_BCKP circuit design

If RTC timing is required to run for a time interval of T [s] at 25 °C when