User's Manual

GL865-DUAL/QUAD V3 Hardware User Guide
1vv0301018 Rev.7 – 2013-10-30
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 47 of 78
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 50kΩ
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).