MSM7603 データシートの表示（PDF） - Oki Electric Industry

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MSM7603

Echo Canceler

Oki Electric Industry 

¡ Semiconductor

MSM7603/7603B

EXPLANATION OF TERMS

Attenuating Function :

Echo Attenuation :

Echo Delay Time :

Acoustic Echo :

Telephone Line Echo :

Gain Control Function :

Center Clipping Function :

Double Talk Detection :

Howling Detection :

Echo Return Loss (ERL) :

PHS :

This function prevents howling and controls the noise level with

the attenuator for the RIN input and SOUT output. Refer to the

explanation of pins (ATT pin).

If there is talking (input only to RIN) in the path of a rising echo

arises, the echo attenuation refers to the difference in the echo

return loss (canceled amount) when the echo canceler is not used

and when it is used.

Echo attenuation = (SOUT level during through mode operation)

– (SOUT level during echo canceler operation) [dB]

This is the time from when the signal is output from ROUT until it

returns to SIN as an echo.

When using a hands-free phone, for example, the signal output

from the speaker echoes and is input again to the microphone. The

return signal is referred to as acoustic echo.

This is a signal which is delayed midway in a telephone line and

returns as an echo, due to reasons such as a hybrid impedance

mismatch.

This function prevents howling and controls the sound level by

with a gain controller for the RIN input. Refer to the explanation

of pins (GC pin).

This function forces the SOUT output to a minimum value when

the signal is below –57 dBm0. Refer to the explanation of pins (NLP

pin).

Double talk refers to a state in which the SIN and RIN signals are

input simultaneously. In a double talk state, a signal other than the

echo signal which is to be canceled can be input to the SIN input,

resulting in malfunction.

The double talk detector prevents such malfunction of the canceler.

This is the oscillating state caused by the acoustic coupling between

the loud speaker and the microphone during hands-free talking.

Howling not only interferes with talking, but can also cause

malfunction of the echo canceler.

The howling detector prevents such malfunction and howling.

When the signal output from ROUT returns to SIN as an echo, ERL

refers to how much loss there is in the signal level during ROUT.

ERL = (ROUT level) – (SIN level of the ROUT signal which returns

as an echo) [dB]

If ERL is positive (ROUT > SIN), acts as an attenuator.

If ERL is negative (ROUT < SIN), acts as an amplifier.

Personal Handyphone System

19/20

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