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 46 of 76
Mod. 0805 2011-07 Rev.2
10.3.
EAR connection
The audio output of the GL865-DUAL V3 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 8Ohm. 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 0.7W;
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 8 Ohm), 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-DUAL V3 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
