MT9300AL datasheet(7/29 Pages) MITEL

7 / 29 page

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

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

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

Figure 5 - Device conﬁguration

Rin

Rout

Sout

Sin

echo

path A

Optional -12dB pad

echo

path B

channel A

channel B

E.C.A

E.C.B

a) Normal Conﬁguration (64ms)

Adaptive

Filter (64ms)

Adaptive

Filter (64ms)

Optional -12dB pad

PORT1

PORT2

channel A

E.C.A

Sin

Sout

Rout

Rin

b) Extended Delay Conﬁguration (128ms)

echo

path A

Adaptive Filter

(128 ms)

Optional -12dB pad

PORT1

PORT2

E.C.A

Sin

Sout

Rout

Rin

c) Back-to-Back Conﬁguration (64ms)

E.C.B

echo

path

Adaptive

Filter (64ms)

Optional -12dB pad

Adaptive

Filter (64ms)

Optional -12dB pad

PORT1

PORT2

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