User's Manual

UMTS/HSDPA Module Series
UC15 Hardware Design
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The severity degree of the RF interference in the voice channel during GSM transmitting period largely
depends on the application design. In some cases, GSM850/EGSM900 TDD noise is more severe; while
in other cases, DCS1800/PCS1900 TDD noise is more obvious. Therefore, customer can have a choice
based on test results. Sometimes, even no RF filtering capacitor is required.
The capacitor which is used for filtering out RF noise should be close to audio interface. 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 should be placed according to the differential signal layout rules.
3.11.2. Microphone Interfaces Application
AIN1/AIN2 channels come with internal bias supply for external electret microphone. A reference circuit is
shown in the following figure.
Figure 21: Microphone Reference Design for AIN1&AIN2