GL865 Hardware User Guide
1vv0300910 Rev.1 – 2011-07-22
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 50 of 79
capacitor (usually a 33pF or a 10pF capacitor placed across the
output terminals inside the case).
LINE-IN connection
If the audio source is not a mike but a different device, the
following connections can be done.
Place a 1Kohm resistor to ground on the negative input, in order
to get balanced the input; than connect the source via 1uF
capacitor, so the DC current is blocked.
Since the input is differential, the common mode voltage noise
between the two (different) ground is rejected, provided that
both AF_IN+ & AF_IN- are connected directly onto the source.
1u
220n
220n
1K
1K
1u
1u
AF_IN+
MIC/AF_IN+
MIC/AF_IN-
AGND
MODULE
-
+
INPUT
ADC
Vmic
AF_IN-
1u
220n
220n
1K
1K
1u
1u
AF_IN+
MIC/AF_IN+
MIC/AF_IN-
AGND
MODULE
-
+
INPUT
ADC
Vmic
Remote_GND