hardware design v1.00

Table Of Contents
Smart Machine Smart Decision
4.7 Audio Interfaces
SIM968 provides two analog inputs, MIC1P/1N and MIC2P/2N, which could be used for electret microphone.
The module also provides two analog outputs, SPK1P/1N and SPK2P/2N. The output can directly drive 32
receiver.
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] and document [5].
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. If user needs to use an
amplifier circuit for audio, National Semiconductor Company’s LM4890 is recommended.
4.7.1 Speaker Interface Configuration
SIM968_Hardware Design_V1.00 2013.02.25
31
SPK1P
SPK1N
10pF
10pF
10pF
33pF
33pF
33pF
ESD
ANTI
ESD
ANTI
These components should
be placed to speaker as
close as possible
The lines in bold type should
be accorded to differential
signal layout rules
MODULE
Figure 22: Speaker reference circuit
Figure 23: Speaker with amplifier reference circuit