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M20 Hardware Design
3.10 Audio interfaces
The module provides two audio input channels and two audio output channels and one serial
digital audio interface (DAI) on the B2B connector.
AIN1 and AIN2, which may be used for both microphone and line inputs.An electret
microphone is usually used. AIN1 and AIN2 are both differential input channels.
AOUT1 and AOUT2, which may be used for both receiver and speaker outputs. AOUT1
channel is typically used with a receiver built into a handset, while AOUT2 channel is
typically used with headset or hands-free speaker. AOUT1 channel is a differential channel
and AOUT2 is a single-ended channel. SPK2P and AGND can establish a pseudo differential
mode.
These two audio channels can be swapped by "AT+QAUDCH" command. For more details,
please refer to document [1].
For each channel, customer can use AT+QMIC to adjust the input gain level of microphone.
Customer can also use "AT+CLVL" to adjust the output gain level of receiver and speaker.
"AT+QECHO" is to set the parameters for echo cancellation control. "AT+QSIDET" is to set
the side-tone gain level. For more details, please refer to document [1].
Note:
Use AT command "AT+QAUDCH" to select audio channel:
0--AIN1/AOUT1 (normal audio channel), the default value is 0.
1--AIN2/AOUT2 (aux_audio channel) .
Table 16: Pin definition of audio interface
Interface
Name
MIC1P
MIC1N
(AIN1/AOUT1)
SPK1P
SPK1N
MIC2P
(AIN2/AOUT2)
MIC2N
SPK2P
AGND
One of the following matching circuits can be chosen in order to improve audio performance. The
differential audio traces have to be placed according to the differential signal layout rule. As
shown in the following figures (Note: the package of the 10p and 33p capacitors is 0603.) Texas
Instruments's TPA6205A1is recommended for a suitable differential audio amplifier. There are
plenty of excellent audio amplifiers in the market.
M20_HD_V1.01
Pin
Function
44
Microphone1 input +
43
Microphone1 input -
48
Audio1 output+
47
Audio1 output-
45
Microphone2 input +
46
Microphone2 input -
49
Audio2 output+
50
Suggest to be used as the analog ground in
external audio circuit. Don't connect it to
digital GND.
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