GSM/GPRS Modules
GSM Module Audio Design Guide
GSM Module Audo Design Guide Confidential/Release 20 / 35
2.3. Hands-free Application at Channel AIN1/AOUT1
Channel AIN1/AOUT1 could be used as hands-free function, because input audio signal is differential
circuit and it is a good way to suppress common-mode noise.
SPK circuit is recommended as following:
IN-
IN+
SHUT_DOWN
BYPASS
VO+
VO-
GND
VDD
C312
10pF
C311
10pF
10pF
C313 C4
33pF
C2
33pF
C3
33pF
VBAT
FB301
FB302
Close to speaker
C19
10uF
C20
33uF
5
8
SPK1N
SPK1P
C308
C309
100nF
100nF
R308
R309
20K
20K
R310
100K
C310
220nF
R313 100K
R314 100K
GPIO_SHUTDOWN
4
3
1
2
6
7
Figure 17：Hands-free Reference Circuit at Channel AIN1/AOUT1
GPIO_SHUTDOWN is controlled by I/O of external chip.
AT+QAUDCH=0, ringtone will output via AOUT1)
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