Telit Wireless Solutions GE863-PY Microphone Paths Characteristic and Requirements, + 20dB, +10dB

GE863-QUAD

GE863-PY

1vv0300715 Rev. 1 - 19/09/06

7.1 Microphone Paths Characteristic and Requirements

TIP: being the microphone circuitry the more noise sensitive , its design and layout must be done with particular care. 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

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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.

“Mic_MT” 1st differential microphone path

•	line coupling	AC
•	line type	balanced
•	coupling capacitor	≥ 100nF
•	differential input resistance	50kΩ
•	differential input voltage	≤ 1,03Vpp (365mVrms)
•	microphone nominal sensitivity	-45 dBVrms/Pa
•	analog gain suggested	+ 20dB
•	echo canceller type	handset
“Mic_HF” 2nd differential microphone path
•	line coupling	AC
•	line type	balanced
•	coupling capacitor	≥ 100nF
•	differential input resistance	50kΩ
•	differential input voltage	≤ 65mVpp (23mVrms)
•	microphone nominal sensitivity	-45 dBVrms/Pa
•	analog gain suggested	+10dB
•	echo canceller type	car kit hands-free

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