Smart Machine Smart Decision
SIM800C_Hardware_Design_V1.02
31
2015-4-27
Input level:0dBm0
-
69
-
dB
Table 14: Audio output characteristics
Parameter
Conditions
Min
Typ
Max
Unit
Normal output
R
L
=32
Ω
receiver
-
15
90
mW
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. 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, 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 capacitors and ferrite beads near
audio PA input.
TDD noise has something to do with GND signal. If GND plane 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 15: SIM pin definition
Pin name
Pin number
Function
SIM_VDD
18
Voltage supply for SIM card. Support 1.8V or 3V SIM card
SIM_DATA
15
SIM data input/output
SIM_CLK
16
SIM clock
SIM_RST
17
SIM reset
SIM_DET
14
SIM card detection
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 the following figure.
