January 2001/ version 1.4
WMOi3 Integrated Modem
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4.1.10 Audio Interface
Two different microphone inputs and two different speaker outputs are supported.
The connection can be either differential or single-ended but using a differential
connection in order to reject common mode noise and TDMA noise is
recommended.
4.1.10.14.1.10.1 MicrophoneMicrophone 2 Inputs 2 Inputs
The MIC2 inputs are differential ones. They already include the convenient
biasing for an electret microphone (0,5 mA and 2 Volts). This electret
microphone can be directly connected on these inputs. The impedance of the
microphone 2 has to be around 2kΩ. These inputs are the standard ones for a
handset design while MIC1 inputs can be connected to an external headset or a
handsfree kit.
The gain of MIC2 inputs is internally adjusted. The gain can be tuned from 30dB
to 51dB. The connection to the microphone is direct. The gain can be tuned
using the AT+VGR command.
See chapter Connector suppliers and peripheral devices.
C1 = 22pF to 100pF
33 pF recommanded
figure 10 : microphone 2 input
C1 has to be the nearest as possible to the microphone. Microphone
manufacturers provide this capacitor directly soldered on the microphone.
Table 18 : microphone 2 input pin description
Signal Pin # I/O I/O type* Description
MIC2P 16 I Analog Microphone 2 positive input
MIC2N 18 I Analog Microphone 2 negative input
*See Table 3 “operating conditions” in subdivision 4.1.1The 50-pin
connector description
C1
MIC2P
MIC2N
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