u-blox LEXI-R422, Руководство по системной интеграции

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LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 69 of 108
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2.5.2 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 LEXI-R422 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 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 receiver channels whose carrier frequency is coincidental with harmonic
frequencies. It is strongly recommended to place the RF bypass capacitors suggested in
Figure 43 ,
Figure 44 , and Figure 45 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 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.