HW User Guide
1vv0301018 Rev. 15
Page
44
of
72
2019-01-07
EAR connection
The audio output of the GL865 V3/V3.1 is balanced, this is helpful to double the level and
to reject common mode (click and pop are common mode and therefore rejected);
furthermore the output stage is class-D, so it can manage directly a loudspeaker with
electrical impedance of at least 8
Ω.
This stage is powered by switching from Vbatt to gnd
at a frequency ranging from 0.6 to 2MHz, so it has a good efficiency and thus a big power
budget; being a class-D architecture, please use some caution (see the NOTE below).
NOTE:
When the loudspeaker is connected with a long cable, an L-C filter is
recommended.
When the EAR+/- are feeding some electronic circuitry, an R-C filter is
recommended.
TIP:
in order to get the maximum audio level at a given output voltage level
(dBspl/Vrms), the following breaking through procedure can be used. Have
the loudspeaker as close as you can to the listener (this simplify also the
echo cancelling); choose the loudspeaker with the higher sensitivity (dBspl
per W); choose loudspeakers with the impedance close to the limit (ex: 16
or 8Ω), in order to feed more power inside the transducer (it increases the
W/Vrms ratio). If this were not enough, an external amplifier should be used.
WARNING:
The audio output hardware of the GL865 V3/V3.1 is based on a Class-D
amplifier so any singled-end output configuration MUST NOT BE USED,
otherwise the presence of GSM buzzing and low level audio performance
will result.
EAR+
EAR-
TELIT MODULE
-
+
OUTPUT
DAC
