Rev 1.9.1 Feb.09
Proprietary and Confidential
57
In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.
Audio signal interface
The
differential
microphone
input
offers
superior
noise
rejection
performance
to
the
single
‐
ended
approach.
The
termination
of
the
differential
pair
rejects
common
signals
(such
as
noise).
The
pair
should
be
routed
together
for
optimal
noise
rejection.
Since
MIC_P
and
MIC_N
are
high
impedance
inputs,
it
is
important
to
isolate
these
from
possible
noise
sources
(toggling
digital
lines
with
fast
edges).
The
speaker
interface
can
be
single
‐
ended
or
differential
depending
on
product.
Single
‐
ended
speaker
outputs
rely
on
modem
ground
as
an
audio
reference.
The
audio
passband
for
both
receive
and
transmit
paths
(speaker
and
microphone)
extends
from
300
Hz
to
3.4
kHz.
A
programmable
sidetone
with
a
range
from
mute
to
unity
gain
is
available
for
both
headset
and
main
audio
paths.
Sidetone
should
be
muted
for
speakerphone
use.
Note
that
certain
carriers
now
require
use
of
hearing
‐
aid
compatible
transducers
in
a
handset
design.
The
Primary
audio
path
can
be
interfaced
directly
to
such
devices.
Refer
to
ANSI
C63.19
for
details
regarding
reduced
RF
emissions
(
ʺ
U3
rating
ʺ
)
and
inductive
/
telecoil
coupling
(
ʺ
U3T
ʺ
rating)
devices.
Speakerphone
•
Long echo path (<64 ms travel time from speaker to
microphone)
•
Loud echo
•
For use with speakerphone applications with high
distortion
•
Half-duplex algorithm, very aggressive in near-end
Tx muting to eliminate transmitted echo
Off
Table 4-3: Echo cancellation details
Mode
Details
Table 4-4: Primary audio signal interface
Signal
Pin #
Type
Directions
Description
MIC_P
1
Analog
Input
Non-inverted
microphone input (+)
MIC_N
3
Analog
Input
Inverted microphone
input (-)
