User's Manual

GE910 Hardware User Guide

1vv0300962 Rev.12 2013-10-22

page 57 of 83

Mod. 0805 2011-07 Rev.2

11.2.3. EAR connection

The audio output of the GE910 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 a power budget up to 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.

EAR+

EAR-

TELIT MODULE

OUTPUTDAC