SIM802 Hardware Design
3.10 Audio interfaces
Table 14: Audio interface signal
Name
Pin
Function
MIC1P
21
Microphone1 input +
MIC1N
20
Microphone1 input -
SPK1P
23
Audio1
(AIN1/AOUT1)
SPK1N
24
Audio1 output-
MIC2P
18
Microphone2 input +
MIC2N
19
Microphone2 input -
SPK2P
26
Audio2
(AIN2/AOUT2)
SPK2N
25
Audio2 output-
The module provides two analogy input channels, AIN1 and AIN2, which may be used for both
microphone and line inputs. The AIN1 and AIN2 channels are identical. One of the two channels
is typically used with a microphone built into a handset. The other channel is typically used with
an external microphone or external line input. The module analogy input configuration is
determined by control register settings and established using analogy multiplexers.
For each channels, you can use AT+CMIC to adjust the input gain level of microphone, use
AT+SIDET to set the side-tone level. In addition, you can also use AT+CLVL to adjust the output
gain level of both receiver and speaker at the same time, use AT+CHFA to activate one of the two
audio channels and deactivate the other one. For more details, please refer to
document [1]
.
Note: Use AT command AT+CHFA to select audio channel:
0—
AIN1/AOUT1 (normal audio channel), the default value is 0.
1—
AIN2/AOUT2(aux_audio channel) .
It is suggested that you adopt one of the following two matching circuits in order to improve
audio performance. The difference audio signals have to be layout according to difference signal
layout rules. As show in following figures
(Note: all components package are 0603.)
If you want
to adopt an amplifier circuit for audio, we recommend National Company’s LM4890. Of course
you can select it according to your requirement.
SIM802_HD_V2.01
12.01.2010
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