User Guide

GE9
GE9GE9
GE910 Hardware User Guide
10 Hardware User Guide10 Hardware User Guide
10 Hardware User Guide
1vv0300962 Rev.4 2012-06-25
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 46 of 73
Mod. 0805 2011-07 Rev.2
10. Audio Section Overview
The Base Band Chip of the GE910 provides one differential input for audio to be transmitted
(Uplink) and a balanced BTL output for audio to be received (downlink).
The bias for the microphone has to be as clean as possible; the first connection (single ended) is
prefearable since the Vmic noise and ground noise are fed into the input as common mode and
then rejected. This sounds strange; usually the connection to use in order to reject the common
mode is the balanced one. In this situation we have to recall that the microphone is a sound to
current transducer, so the resistor is the current to tension transducer, so finally the resistor feeds
the input in balanced way even if the configuration, from a microphone point of view, seems to
be un-balanced.
For more information refer to Telit document: "80000NT10007a Audio Settings Application
Note".