Hands-Free Application At Channel Ain1/Aout1 - Quectel GSM Series Audio Design Manual

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:
C308
SPK1N
C309
SPK1P
GPIO_SHUTDOWN
Figure 17：Hands-free Reference Circuit at Channel AIN1/AOUT1
Note
GPIO_SHUTDOWN is controlled by I/O of external chip.
GSM Module Audo Design Guide
AT+QAUDCH=0, ringtone will output via AOUT1)
R313
R314
4
R308 20K
100nF
IN-
3
R309 20K
100nF
IN+
1
SHUT_DOWN
2
BYPASS
R310
C310
220nF
100K
GSM Module Audio Design Guide
100K
100K
5
FB301
VO+
8
FB302
VO-
6
VDD
7
C19
GND
10uF
Confidential/Release
GSM/GPRS Modules
C313 C4
33pF
10pF
C311 C2
10pF 33pF
C312
C3
10pF 33pF
C20
33uF
Close to speaker
VBAT
20 / 35