User's Manual

GE865 Hardware User Guide
1vv0300799 Rev.6 - 04/06/09
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 37 of 58
9 Audio Section Overview
The Base Band Chip of the GE865 Telit Module provides one audio Line usable in transmit (Uplink)
and in receive (Downlink) direction:
9.1 Microphone Paths Characteristic and Requirements
TIP: being the microphone circuitry the more noise sensitive, its design and layout must be
done with particular care. The microphone path is balanced and the OEM circuitry should be
balanced designed to reduce the common mode noise typically generated on the ground
plane. However also an unbalanced circuitry can be used for particular OEM application needs.
“Mic” differential microphone path
• line coupling AC
• line type balanced
• coupling capacitor ≥ 100nF
• differential input resistance 50kΩ
• differential input voltage ≤ 1,03V
pp
(365mV
rms
)
• microphone nominal sensitivity -45 dBV
rms
/Pa
• analog gain suggested + 20dB
• echo canceller type handset