Users Manual

GSM/GPRS Module Series
M66 Hardware Design
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Sometimes, even no RF filtering capacitor is required.
The capacitor which is used for filtering out RF noise should be close to audio interface or other audio
interfaces. Audio alignment should be as short as possible.
In order to decrease radio or other signal interference, the position of RF antenna should be kept away
from audio interface and audio alignment. Power alignment and audio alignment should not be parallel,
and power alignment should be far away from audio alignment.
The differential audio traces have to be placed according to the differential signal layout rule.
3.8.2. Microphone Interfaces Design
AIN channel come with internal bias supply for external electret microphone. A reference circuit is shown
in the following figure.
Figure 22: Reference Design for AIN