WM_PRJ_Q2400_PTS_005 -007
18th January 2006
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2.3.2 Audio interface
Two different microphone inputs and two different speaker outputs are
supported.
An echo cancellation feature, for hands-free application, is also available. In
some cases, ESD protection must be added on the audio interface lines.
2.3.2.1 Microphone inputs
2.3.2.1.1 General
The MIC2 inputs already include the biasing for an electret microphone allowing
an easy connection to a handset.
The MIC1 inputs do not include an internal bias. MIC1/SPK1 is then appropriate
for a hands-free application or a handset with biasing external to the module.
2.3.2.1.2 Recommended characteristics for the microphones
• 2 V – 0.5 mA.
• 2 kΩ.
• Sensitivity -40 to –50 dB.
• SNR > 50 dB.
• Frequency response compatible with the GSM specifications.
For possible references, see § 9.3.
Microphone must be decoupled by a capacitor CM. This one must be as close as
possible to the microphone. Some microphone manufacturers provide this
capacitor directly soldered on the device
CM
Figure 12: Microphone decoupling capacitor
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