Preliminary Information
Functional Description
The MT9123 architecture contains two individually
controlled echo cancellers (Echo Canceller A and B).
They can be set in three distinct configurations:
Normal, Back-to-Back and Extended Delay (see
Figure 3). Under Normal configuration, the two echo
cancellers are positioned in parallel providing 64
millisecond echo cancellation in two channels
simultaneously. In Back-to-Back configuration, the
two echo cancellers are positioned to cancel echo
coming from both directions in a single channel. In
Extended-Delay configuration, the two echo
cancellers are internally cascaded into one 128
millisecond echo canceller.
Each echo canceller contains the following main
elements (see Figure 1).
•
•
•
•
•
Adaptive Filter for estimating the echo channel
Subtracter for cancelling the echo
Double-Talk detector for disabling the filter
adaptation during periods of double-talk
Non-Linear Processor for suppression of
residual echo
Narrow-Band Detector for preventing Adaptive
Filter divergence caused by narrow-band
signals
•
•
•
•
MT9123
Offset Null filters for removing the DC
component in PCM channels
12dB attenuator for signal attenuation
Serial controller interface compatible with
Motorola, National and Intel microcontrollers
PCM encoder/decoder compatible with
µ/A-
Law ITU-T G.711,
µ/A-Law
Sign-Mag or linear
2’s complement coding
The MT9123 has two modes of operation:
Controllerless
and
Controller.
Controllerless mode is
intended for applications where customization is not
required. Controller mode allows access to all
registers for customizing the MT9123 operation.
Refer to Table 7 for a complete list. Controller mode
is selected when CONFIG1 and CONFIG2 pins are
both connected to Vss.
Each echo canceller in the MT9123 has four
functional states:
Mute, Bypass, Disable Adaptation
and
Enable Adaptation.
These are explained in the
section entitled Echo Canceller Functional States.
PORT 2
PORT 2
Sin
echo
path A
channel A
Rout
E.C.A
channel B
+
-
echo
path B
channel B
Rout
E.C.B
Optional -12dB pad
Optional -12dB pad
PORT 1
channel A
+
-
Sout
PORT 1
channel A
+
-
Adaptive
Filter (64ms)
Rin
Sout
Sin
echo
path A
Adaptive Filter
(128 ms)
channel A
Rin
E.C.A
Optional -12dB pad
Rout
b) Extended Delay Configuration (128ms)
PORT 2
Sin
-
echo
path
+
Optional -12dB pad
PORT 1
Sout
Adaptive
Filter (64ms)
-
+
E.C.A
Optional -12dB pad
Adaptive
Filter (64ms)
Adaptive
Filter (64ms)
echo
path
Rin
E.C.B
a) Normal Configuration (64ms)
c) Back-to-Back Configuration (64ms)
Figure 3 - Device Configuration
8-49
MITEL [ MITEL NETWORKS CORPORATION ]
