MT9122AP 데이터 시트보기 (PDF) - Mitel Networks

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MT9122AP

Dual Voice Echo Canceller with Tone Detection

Mitel Networks 

Preliminary Information

MT9122

where 0 < NLPTHR(dec) < 1

The comfort noise injection can be disabled by

setting the INJDis bit to 1 in Control Register 1.

It should be noted that the NLPTHR is valid and the

comfort noise injection is active only when the NLP is

enabled.

Disable Tone Detector

G.165 recommendation defines the disable tone as

having the following characteristics: 2100 Hz

(± 21Hz) sinewave, a power level between -6 to

-31dBm0, and a phase reversal of 180 degrees (± 25

degrees) every 450ms (± 24ms). If the disable tone is

present for a minimum of one second with at least

one phase reversal, the Tone Detector will trigger.

G.164 recommendation defines the disable tone as a

2100 Hz (±21Hz) sinewave with a power level

between -6 to -31dBm0. If the disable tone is present

for a minimum of one second, with or without phase

reversal, the Tone Detector will trigger.

The MT9122 has four Tone Detectors in order to

monitor the occurrence of a valid disable tone on

channels A and B on both Rin and Sin. Upon

detection of a disable tone, output pins TD1 or TD2

will go low as illustrated in Figure 4.

Rin

Tone Detector

TD1

Sin

Tone Detector

Echo Canceller A

Rin

Tone Detector

TD2

Sin

Tone Detector

Echo Canceller B

Figure 4 - Disable Tone Detection

Once a Tone Detector has been triggered, the

MT9122 no longer needs a valid disable tone (G.164

or G.165) to maintain Tone Detector status (e.g.

TD1, TD2 pins low). The Tone Detector status will

only release (e.g. TD1, TD2 pins high) if the signals

Rin and Sin fall below -30dBm0, in the frequency

range of 390Hz to 700Hz, and below -34dBm0, in the

frequency range of 700Hz to 3400Hz, for at least

400ms.

Controllerless Mode

The selection between G.165 and G.164 tone

disable is controlled by the REV pin. When the REV

pin is connected to Vss, G.164 is selected. This

applies to all four Tone Detectors.

In response to a valid disable tone, the MT9122 must

be switched from the Enable Adaptation state to the

Bypass state. In an application, the Tone Detect

outputs, TD1 and TD2, may be used to switch the

echo cancellers between these two states. This is

achieved by connecting S1 and S3 pins to Vdd and

by connecting the TD1 and TD2 outputs to the S2

and S4 input pins respectively.

Controller Mode

The selection between G.165 and G.164 tone

disable is controlled by the PHDis bit in Control

Register 2. When the PHDis bit is set to 1, G.164

tone disable requirements are selected. This applies

to all four Tone Detectors.

In response to a valid disable tone, the MT9122 must

be switched from the Enable Adaptation state to the

Bypass state. This can be done in two ways,

automatically or externally. In automatic mode, the

Tone Detectors internally control the switching

between Enable Adaptation and Bypass states. The

automatic mode can be activated by setting the

AutoTD bit in Control Register 2 to high. In external

mode, an external controller is needed to poll the TD

bit in Status Register A or B. Following the detection

of a disable tone (TD bit high), the external controller

should switch the echo canceller from Enable

Adaptation to Bypass state.

The TD1 and TD2 output pins remain active, as in

Controllerless mode, and they can be used as an

interrupt to an external controller.

Narrow Band Signal Detector (NBSD)

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

present in the reference 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.

8-23

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