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SIM868_Series_Hardware_Design_V1.06 37 2017-07-13
GSM antenna is the key coupling interfering source of TDD noise. Thereat, pay attention to the layout of audio
lines which should be far away from RF cable, antenna and GSM_VBAT pin. The bypass capacitor for filtering
should be placed near module.
Conducting noise is mainly caused by the GSM_VBAT drop. If audio PA is powered by GSM_VBAT directly,
then there will be some cheep noise from speaker output easily. So it is better to put big capacitors and ferrite
beads near audio PA input.
TDD noise is related to GND signal. If GND plane is not good, lots of high-frequency noises will interfere
microphone and speaker over bypass capacitor.
5.8. SIM Card Interface
The SIM interface complies with the GSM Phase 1 specification and the new GSM Phase 2+ specification for
FAST 64kbps SIM card. Both 1.8V and 3.0V SIM card are supported. The SIM interface is powered from an
internal regulator in the module.
5.8.1. SIM Card Application
Table 17: SIM pin definition
Pin name
Pin number Function
SIM1_VDD 18 Voltage supply for SIM card. Support 1.8V or 3V SIM card
SIM1_DATA 15 SIM data input/output
SIM1_DET 14 SIM card detection
SIM2_VDD 56 Voltage supply for SIM card. Support 1.8V or 3V SIM card
SIM2_DATA 53 SIM data input/output
SIM2_CLK 54 SIM clock
SIM2_RST 55 SIM reset
It is recommended to use an ESD protection component such as ST (
www.st.com ) ESDA6V1-5W6 or ON
SEMI (
www.onsemi.com ) SMF05C. The SIM card peripheral components should be placed close to the SIM
card holder. The reference circuit of the 8-pin SIM card holder is illustrated in Figure 30.
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