Quectel UC20 Hardware Design page 43

Module
In order to enhance the reliability and availability of the USIM card in your application, please follow the
following criterion in the USIM circuit design:

Keep layout of USIM card as close as possible to the module. Assure the length of the trace is less
than 200mm.

Keep USIM card signal away from RF and VBAT alignment.

Assure the ground between module and USIM connector short and wide. Keep the width of ground
and USIM_VDD no less than 0.5mm to maintain the same electric potential. The decouple capacitor
of USIM_VDD should be less than 1uF and must be near to USIM connector.

To avoid cross-talk between USIM_DATA and USIM_CLK, keep them away with each other and
shield them with surrounded ground.
 In order to offer good ESD protection, it is recommended to add TVS. The 22Ω resistors should be
added in series between the module and the USIM card so as to suppress the EMI spurious
transmission and enhance the ESD protection. The 33pF capacitors are used for filtering interference
of EGSM900. Please note that the USIM peripheral circuit should be close to the USIM connector.

The pull-up resistor on USIM_DATA line can improve anti-jamming capability when long layout trace
and sensitive occasion is applied, and should be placed close to the USIM connector.
UC20_Hardware_Design
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USIM_VDD
15K
USIM_GND
USIM_VDD
22R
USIM_RST
USIM_CLK
22R
22R
USIM_DATA
33pF 33pF 33pF
Figure 23: Reference Circuit of the 6 Pin USIM Card
Confidential / Released
100nF
GND GND
UMTS/HSPA Module Series
UC20 Hardware Design
USIM Connector
VCC GND
RST VPP
CLK IO
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