Technical data

4.9.3 Microphone Signals (MICIP, MICIN)
MICIP and MICIN 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 CPU® as shown below.
Figure 18: Microphone input connections to the Wireless CPU®
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 15dB, which provides
optimal performance for many standard types of electret-microphones. An additional
gain adjustment can be made through an AT-command to the PGA which can be set
to high and low gain. The Wireless CPU® 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 340 3400 Hz
AC input impedance 300–3400 Hz 10 kohm
Output dc bias level 2.16 2.4 2.64 V
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GR64 Integrators’ Manual
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