GE865 Hardware User Guide
1vv0300799 Rev.9 – 27-07-2009
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 45 of 70
10.1 Electrical Characteristics
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 must be balanced designed to reduce the common mode noise
typically generated on the ground plane. However the customer can use the
unbalanced circuitry for particular application.
10.1.1 Input Lines
“MIC 1” differential microphone path
Line Coupling
AC*
Line Type
Balanced
Coupling capacitor
≥
100nF
Differential input resistance
50k
Ω
Differential input voltage
≤
1,03V
pp
@
MicG=0dB
(*) WARNING :
AC means that the signals from the microphone have to be connected
to input lines of the module through capacitors which value has to be
≥
100nF.
Not respecting this constraint, the input stages will be damaged.
WARNING: when particular OEM application needs a
Single Ended Input
configuration,
it is forbidden connecting the unused input directly to Ground, but only through a
capacitor
which value has to be
≥
100nF.
.
Don’t forget that in Single Ended configuration the useful input signal will be halved.
