User's Manual

CL865-DUAL Hardware User Guide
1vv0301104 Rev.1 – 2014-03-07
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Reserved. Page 44 of 70
Mod. 0805 2011-07 Rev.2
10. Audio Section Overview
The CL865 provides an analog audio interface and digital audio interface.
10.1. Analog Audio Interface (AVI)
The CL865 provides an analog audio interface; one differential input for audio to be
transmitted(Uplink) and a balanced 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 preferable 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.