TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 85 of 143
2.5.2
Guidelines for SIM layout design
The layout of the SIM card interfaces lines (
VSIM
,
SIM_CLK
,
SIM_IO
,
SIM_RST
for the SIM0 interface, and
VSIM1
,
SIM1_IO
,
SIM1_CLK
,
SIM1_RST
for the SIM1 interface) may be critical if the SIM card is placed far
away from the TOBY-L4 series modules or in close proximity to the RF antenna: these two cases should be
avoided or at least mitigated as described below.
In the first case, the long connection can cause the radiation of some harmonics of the digital data frequency as
any other digital interface. It is recommended to keep the traces short and avoid coupling with the RF line or
sensitive analog inputs.
In the second case, the same harmonics can be picked up and create self-interference that can reduce the
sensitivity of LTE/3G/2G receiver channels whose carrier frequency is coincidental with the harmonic frequencies.
It is strongly recommended to place the RF bypass capacitors suggested in Figure 37 near the SIM connector.
In addition, since the SIM card is typically accessed by the end user, it can be subjected to ESD discharges. Add
adequate ESD protection as suggested to protect the module SIM pins near the SIM connector.
Limit the capacitance and series resistance on each SIM signal to match the SIM specifications. The connections
should always be kept as short as possible.
Avoid coupling with any sensitive analog circuit, since the SIM signals can cause the radiation of some harmonics
of the digital data frequency.
