u-blox SARA-G3 Series, Руководство по системной интеграции

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SARA-G3 series - System Integration Manual
UBX-13000995 - R06 Objective Specification Design-in
Page 129 of 218
2.4.1.2 Guidelines for SIM layout design
The layout of the SIM card interface lines ( VSIM , SIM_CLK , SIM_IO , SIM_RST ) may be critical if the
SIM card is placed far away from the SARA-G3 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: keep the traces short and avoid coupling with 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 GSM receiver channels whose carrier frequency is coincidental with harmonic frequencies:
placing the RF bypass capacitors suggested in
Figure 45Figure 45 near the SIM connector will mitigate
the problem.
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 in
Figure 45Figure 45 to protect module SIM pins
near the SIM connector.
Limit 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