Tdd; Sim Card Interface; Sim Card Application - SIM Tech SIMCom SIM800C Hardware Design

Table 15: Audio output characteristics
Parameter Conditions
=32 Ω receiver
R
L
Normal output
=8 Ω speaker
R
L
4.7.4.

TDD

Audio signal could be interferenced by RF signal. Coupling noise could be filtered by adding 33pF and 10pF
capacitor to audio lines. 33pF capacitor could eliminate noise from GSM850/EGSM900MHz, while 10pF
capacitor could eliminate noise from DCS1800/PCS1900Mhz frequency. Coupling noise should have something
to do with PCB layout. Under some scenarios, TDD noise from GSM850/EGSM900MHz frequency affects
heavily, but some different story is from DCS1800/PCS1900Mhz frequency, so customer should develop this
filter solution according to field test result.
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 and antenna and VBAT pin. The bypass capacitor for filtering
should be placed near module and another group needs to be placed near to connector.
Conducting noise is mainly caused by the VBAT drop. If audio PA was powered by VBAT directly, then there
will be some cheep noise from speaker output easily. So it is better to put big capacitor and ferrite bead near
audio PA input.
TDD noise has something to do with GND signal. If GND signal is not good, lots of high-frequency noises will
interference microphone and speaker over bypass capacitor. So a good GND during PCB layout could avoid
TDD noise.

4.8. 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.
4.8.1.

SIM Card Application

Table 16: SIM pin definition
Pin name Pin number
SIM_VDD 18
SIM_DATA 15
SIM_CLK 16
SIM_RST 17
SIM_DET 14
It is recommended to use an ESD protection component such as ST
SEMI (www.onsemi.com
card holder. The reference circuit of the 8-pin SIM card holder is illustrated in the following figure.
SIM800C_Hardware_Design_V1.00
Min
-
-
Function
Voltage supply for SIM card. Support 1.8V or 3V SIM card
SIM data input/output
SIM clock
SIM reset
SIM card detection
) SMF05C. The SIM card peripheral components should be placed close to the SIM
Typ Max
90 -
- 1080
(www.st.com
33
Smart Machine Smart Decision
Unit
mW
mW
) ESDA6V1-5W6 or ON
2014-10-30