In order to improve audio performance, the following reference circuits are recommended. The audio signals
have to be layout according to differential signal layout rules as shown in following figures.
4.7.1.
Speaker Interfaces Configuration
S P K P
S P K N
M odul e
4.7.2.
Microphone Interfaces Configuration
M I C P
M I C N
M odul e
4.7.3.
Audio Electronic Characteristic
Table 13: Microphone input characteristics
Parameter
Microphone biasing voltage
Working current
Input impedance(differential)
Idle channel noise
SINAD
Input level:-40dBm0
SIM800C_Hardware_Design_V1.02
33pF
10pF
33pF
10pF
33pF
10pF
Figure 28: Speaker reference circuit
The lines in bold type should
be accorded to differential
signal layout rules
Figure 29: Microphone reference circuit
Min
-
-
13
-
29
30
Smart Machine Smart Decision
C l ose t o speaker
33pF
10pF
33pF
10pF
33pF
10pF
These components should
be placed to microphone
as close as possible
E S D
10pF
33pF
33pF
10pF
E S D
33pF
10pF
Typ
Max
1.9
2.2
-
2.0
20
27
-
-67
-
-
E S D
E S D
Electret
Microphone
Unit
V
mA
KΩ
dBm0
dB
2015-4-27