MT9123AP 데이터 시트보기 (PDF) - Mitel Networks

부품명

상세내역

일치하는 목록

MT9123AP

Dual Voice Echo Canceller

Mitel Networks 

Preliminary Information

MT9123

NLPTHR(hex) = hex(NLPTHR(dec) * 32768)

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.

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.

Controllerless Mode

The NBSD is always active and automatically

disables the filter adaptation process when narrow

band signals are detected.

Controller Mode

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 on either the reference

signal (Rin) or the echo composite signal (Sin). To

remove the DC component, the MT9123

incorporates Offset Null filters in both Rin and Sin

inputs.

Controllerless Mode

The Offset Null filters are always active.

Controller Mode

The offset null filters can be disabled by setting the

HPFDis bit to 1 in Control Register 2.

Echo Canceller Functional States

Each echo canceller has four functional states: Mute,

Bypass, Disable Adaptation and Enable Adaptation.

Mute:

The Mute state forces the echo canceller to

transmit quiet code and halts the filter adaptation

process.

In Normal configuration, the PCM output data on

Rout is replaced with the quiet code according to

the following table.

LINEAR

SIGN/

16 bits MAGNITUDE

2’s

µ-Law

complement A-Law

+Zero

0000h

80h

(quiet code)

CCITT (G.711)

µ-Law

A-Law

FFh

D5h

Table 1 - Quiet PCM Code Assignment

In Back-to-Back configuration, both echo cancellers

are combined to implement a full duplex echo

canceller. Therefore muting Echo Canceller A

causes quiet code to be transmitted on Rout, while

muting Echo Canceller B causes quiet code to be

transmitted on Sout.

In Extended Delay configuration, both echo

cancellers are cascaded to make one 128ms echo

canceller. In this configuration, muting Echo

Canceller A causes quiet code to be transmitted on

Rout.

Bypass:

The Bypass state directly transfers PCM codes from

Rin to Rout and from Sin to Sout. When Bypass state

is selected, the adaptive filter coefficients are reset

to zero.

Disable Adaptation:

When the Disable Adaptation state is selected, the

adaptive filter coefficients are frozen at their current

value. In this state, the adaptation process is halted

however the MT9123 continues to cancel echo.

Enable Adaptation:

In Enable Adaptation state, the adaptive filter

coefficients are continually updated. This allows

the echo canceller to model the echo return path

characteristics in order to cancel echo. This is the

normal operating state.

Controllerless Mode

The four functional states can be selected via S1,

S2, S3, and S4 pins as shown in the following table.

8-51

Share Link: