TOBY-R2 series - System integration manual
UBX-16010572 - R10
Design-in
Page 78 of 151
2.2.1.11
Guidelines for VCC supply layout design
Good connection of the module VCC pins with DC supply source is required for correct RF
performance. Guidelines are summarized in the following list:
All the available VCC pins must be connected to the DC source
VCC connection must be as wide as possible and as short as possible
Any series component with Equivalent Series Resistance (ESR) greater than few milliohms must
be avoided
VCC connection must be routed through a PCB area separated from RF lines / parts, sensitive
analog signals and sensitive functional units: it is good practice to interpose at least one layer of
PCB ground between the VCC track and other signal routing
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
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
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 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 functionality may be affected)
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
It is recommended to design one layer of the application PCB as ground plane as wide as possible
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 PCB. Use as many vias as possible to connect the GND planes
Provide a dense line of vias at the edges of each ground area, in particular along RF and high speed
lines
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
Good grounding of GND pads also ensures thermal heat sink. This is critical during connection,
when the real network commands the module to transmit at maximum power: proper grounding
helps prevent module overheating.
