MT9300 データシートの表示（PDF） - Mitel Networks

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MT9300

Multi-Channel Voice Echo Canceller

Mitel Networks 

Advance Information

MT9300

in the Status Registers. Following the detection of a

disable tone (TD bit high) on a given channel, the

external controller must switch the echo canceller

from Enable Adaptation to Bypass state.

Narrow Band Signal Detector (NBSD)

Single or dual frequency tones (i.e. DTMF tones)

present in the receive input (Rin) of the echo

canceller for a prolonged period of time may cause

the Adaptive Filter to diverge. The Narrow Band

Signal Detector (NBSD) is designed to prevent this

divergence by detecting single or dual tones of

arbitrary frequency, phase, and amplitude. When

narrow band signals are detected, the adaptation

process is halted but the echo canceller continues to

cancel echo.

The NBSD can be disabled by setting the NBDis bit

to “1” in Control Register 2.

Offset Null Filter

Adaptive filters in general do not operate properly

when a DC offset is present at any inputs. To remove

the DC component, the MT9300 incorporates Offset

Null filters in both Rin and Sin inputs.

The offset null filters can be disabled by setting the

HPFDis bit to “1” in Control Register 2.

Device Configuration

The MT9300 architecture contains 32 echo

cancellers divided into 16 groups. Each group has

two echo cancellers which can be individually

controlled (Echo Canceller A and B). They can be set

in three distinct configurations: Normal, Back-to-

Back, and Extended Delay. See Figure 5.

Normal Configuration

In Normal configuration, the two echo cancellers

(Echo Canceller A and B) are positioned in parallel,

as shown in Figure 5a, providing 64 milliseconds of

echo cancellation in two channels simultaneously.

Back-to-Back Configuration

In Back-to-Back configuration, the two echo

cancellers from the same group are positioned to

cancel echo coming from both directions in a single

channel providing full-duplex 64ms echo

cancellation. See Figure 5c. This configuration uses

only one timeslot on PORT1 and PORT2 and the

second timeslot normally associated with ECB

contains undefined data. Back-to-Back configuration

allows a no-glue interface for applications where

bidirectional echo cancellation is required.

Back-to-Back configuration is selected by writing “1”

into the BBM bit of both Control Register A1 and

Control Register B1 of a given group of echo

cancellers. Table 2 shows the 16 groups of 2

Sin

echo

path A

Rout

PORT2

echo

path B

channel A

+

-

Adaptive

Filter (64ms)

channel A

E.C.A

Optional -12dB pad

channel B

+

-

Adaptive

Filter (64ms)

channel B

E.C.B

Optional -12dB pad

a) Normal Configuration (64ms)

Sout

Rin

PORT1

Sin

echo

path A

channel A

+

-

Adaptive Filter

(128 ms)

Sout

Rout

PORT2

channel A

E.C.A

Optional -12dB pad

Rin

PORT1

b) Extended Delay Configuration (128ms)

Sin

echo

path

Rout

+

-

Optional -12dB pad

Adaptive

Filter (64ms)

Adaptive

Filter (64ms)

-

+

Sout

echo

path

Rin

PORT2

E.C.A

Optional -12dB pad

E.C.B

PORT1

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

Figure 5 - Device configuration

7

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