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MT9123

Dual Voice Echo Canceller

Mitel Networks 

Preliminary Information

MT9123

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

• 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 1

Sin

echo

path A

Rout

channel A

+

-

Adaptive

Filter (64ms)

channel A

Sout

Rin

E.C.A

Optional -12dB pad

PORT 2

channel A

Sin

+

echo

path A

-

Adaptive Filter

(128 ms)

Rout

channel A

PORT 1

Sout

Rin

E.C.A

Optional -12dB pad

b) Extended Delay Configuration (128ms)

echo

path B

channel B

+

-

Adaptive

Filter (64ms)

channel B

E.C.B

Optional -12dB pad

a) Normal Configuration (64ms)

PORT 2

PORT 1

Sin

echo

path

Rout

+

-

Optional -12dB pad

Adaptive

Filter (64ms)

Adaptive

Filter (64ms)

-

+

Sout

echo

path

Rin

E.C.A

Optional -12dB pad

E.C.B

c) Back-to-Back Configuration (64ms)

Figure 3 - Device Configuration

8-49

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