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3.2.4 Analog audio with hands free
The audio In/Out from the D15 for analog Hands free is the same as for non-Hands free. All the
consideration from Paragraph 3.2.2 is applicable for this mode too.
The additional consideration in this case is to switch the D15 DSP to Echo cancelling mode.
In order to switch to hands free mode use the RS232 port by sending a switch command at the
start up.
ATS96=1 Echo canceller is activate. (Hands free)
ATS96=0
But during an active call the echo canceller can be activate but not disabled.
The block diagram for the required drivers are shown below, But detailed example of drivers
design you can see the Evaluation board design, Annex C
SPKR
MIC
Headset
VCC
The requirements from the drivers and audio devices are the follow:
Microphone impedance:
S/N ratio
Gain from headset to D15 (A2)
Frequency response
(including microphone)
D15 input impedance
TX Distortion
Speakerphone Load
S/N
Gain from D15 to Headset (A1)
Frequency response
(including SPKR)
D15 output impedance
Distortion
d15 Modem Integration and Application Developers Guide version draft 0.53
Echo canceller is disabled. (Headset - Default)
12V
A1
Hands Free
Selection
A2
VCC
Hands Free
Selection
REF
Vref
(for Audio amp)
Figure 15 – EV audio block diagram
Typical 700Ω
Minimum 35dB
45 – 49 dB
-11 to +1 dB 300 to 3400Hz.
10KΩ
Maximum 5%.
25 to 39 ohm
Minimum 35dB
-13 to –9 dB
-10 to +1 dB 300 to 3400Hz.
<1KΩ
Maximum 5%.
D15
Audio out
Audio In
Analog GND
Hands Free
Selection via
ATS96 command.
Page 33 of 181
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