Rainbow Electronics GE863-PY - Manual (Page 48)

GE863 Hardware User Guide
1vv0300783 Rev.0 - 10/06/08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 48 of 80
7.1 INPUT LINES (Microphone)
7.1.1 Short description
The Telit GE863 provides two audio paths in transmit section. Only one of the two paths can be active
at a time, selectable by AXE hardware line or by AT command.
You must keep in mind the different audio characteristics of the transmit blocks when designing:
The “MIC_MT” audio path should be used for handset function, while the “MIC_HF” audio path is
suited for hands-free function (car kit).
TIP: being the microphone circuitry the more noise sensitive, its design and layout must be
done with particular care. Both microphone paths are 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.
TIP: due to the difference in the echo canceller type, the “Mic_MT” audio path is suited for
Handset applications, while the “Mic_HF”audio path is suited for hands-free function (car kit).
The Earphone applications should be made using the “Mic_HF” audio path but DISABLING the
echo canceller by software AT command. If the echo canceller is left active with the Earphone,
then some echo might be introduced by the echo cancel algorithm.