User's Manual

Smart Machine Smart Decision
SIM868_Hardware_Design_V1.00 33 2016-06-20
SIM868 internal has class-AB audio amplifier, the following table is class-AB performance:
Table 14: Performance of audio amplifier
Test Conditions Class-AB AMP
4.2V 8Ω THD+N=1% 0.87W
3.3V 8Ω THD+N=1% 0.53W
4.2V 8Ω THD+N=10% 1.08W
3.3V 8Ω THD+N=10% 0.65W
SPK2P/2N output can directly drive 8Ω speaker.
AT command “AT+CMIC” is used to adjust the input gain level of microphone. AT command “AT+SIDET”
is used to set the side-tone level. In addition, AT command “AT+CLVL” is used to adjust the output gain level.
For more details, please refer to document [1].
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
SPK1P/2P
Close to speaker
ESD
ESD
10pF
33pF
33pF
33pF
Module
SPK1N/2N
10pF
10pF
10pF
33pF
33pF
33pF
10pF
10pF
Figure 28: Speaker reference circuit