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5.9.3 Microphone Signals (MICIP, MICIN)
MICP and MICN are balanced differential microphone input pins. These inputs are
compatible with an electret microphone. The microphone contains a FET buffer with
an open drain output, which is supplied with at 2.4V ±10% relative to ground by the
wireless modem as shown below.
Figure 5.9-1 Microphone connections to the wireless modem
The input low-noise amplifier stage is constructed out of standard low-noise op
amps. External resistors set the gain of this stage.
The input gain is scaled by the input resistors to be around 18, which provides
optimal performance for many standard types of electret microphones. The module
provides a microphone bias at 2.4V, and can supply at least 1mA of current.
Parameter Conditions Min Typ Max Unit
max input gain 14 16 18 mVrms
Input voltage full scale
min input gain 45 50 56 mVrms
Frequency response -3dB cut-off 300 3400 Hz
Output dc bias level 2.16 2.4 2.64 V