GL865-DUAL V3 Hardware User Guide
1vv0301018 Rev.5 – 2013-08-05
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 48 of 76
Mod. 0805 2011-07 Rev.2
10.4.
Electrical Characteristics
10.4.1.
Input Lines
Microphone/Line-in path
Line Type
Differential
Coupling capacitor
≥
100nF
Differential input resistance
5
0kΩ
Levels
To have 0 dBfs @1KHz
(*)
Differential input voltage
MIC Gain = 0dB
290mVrms
MIC Gain = +6dB
145mVrms
MIC Gain = +12dB
72mVrms
MIC Gain = +18dB
36mVrms
MIC Gain = +24dB
18mVrms
MIC Gain = +30dB
9mVrms
MIC Gain = +36dB
4.5mVrms
MIC Gain = +42dB
2.25mVrms
(*)
0 dBfs in the network are +3.14 dBm0
TIP:
The Electret microphone is internally amplified by a J-Fet transistor, thus the sound
is carried out as saturation drain current; this means that the Norton equivalence has to be
considered. The signal is converted to voltage on the 2.2KOhm resistance, from there on
circuitry has to be routed in order to not pick up common mode noise; beware of the return
path (ground).