u-blox TOBY-L4 Series System Integration Manual

Contents

TOBY-L4 series - System Integration ManualUBX-16024839 - R04 Design-inPage 85 of 1432.5.2 Guidelines for SIM layout designThe layout of the SIM card interfaces lines (VSIM, SIM_CLK, SIM_IO, SIM_RST for the SIM0 interface, andVSIM1, SIM1_IO, SIM1_CLK, SIM1_RST for the SIM1 interface) may be critical if the SIM card is placed faraway from the TOBY-L4 series modules or in close proximity to the RF antenna: these two cases should beavoided 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 asany other digital interface. It is recommended to keep the traces short and avoid coupling with the RF line orsensitive analog inputs.In the second case, the same harmonics can be picked up and create self-interference that can reduce thesensitivity 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. Addadequate 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 connectionsshould always be kept as short as possible.Avoid coupling with any sensitive analog circuit, since the SIM signals can cause the radiation of some harmonicsof the digital data frequency.