Telit EVK2 User Guide
1vv0300704 Rev.13- 2012/06/25
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page
29 of 149
7.2.
Actual
The
HS
and
HF
definitions have been kept in the Software and on the schematics of the Telit
modules, but with EVK2 we will refer to
Audio1
and
Audio2
section instead of
Handset
and
Handsfree
respectively, remembering that:
they can have fully equivalent electrical performances (
like the two microphone amplifiers
)
they can activate the same functionalities (
like the Echo Canceller module
)
they can offer slightly different performances (
like the two speaker buffering stages)
7.2.1.
The choice
The activation of the audio path is made Hardware by
AXE
line or Software by
AT#CAP
command.
If you don’t have any load driving constraint (
like a speaker with an impedance coil lower
than 16 ohm
), the choice between one or other “
block
” could be done without consideration
related to the electrical performances; for example in order to overcome the PCB design
difficulties.
7.3.
Differential and Single Ended
7.3.1.
Concepts
Any voltage can be characterized by a potential difference between two terminals.
The configuration of the two terminals and how the signal is delivered from output to input
allows the signal to be more generally described in one of three ways:
Single-ended signal
. This is a signal delivered between a signal trace and a ground.
One terminal for a single-ended connection is always at fixed potential (
usually
Ground
).
Differential Signals
. These are signals that travel through a pair of traces. On the
signal pair, neither of the terminals is Ground.
Common mode Signals. They represent a special case of differential signals, also
travelling between a pair of traces, where the voltage potential on both signals is
the same.
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