Nortel-networks Circuit Card 311 Instrukcja Użytkownika Pobierz pdf (Strona 27)

Line cards 27

Figure 4

Typical analog line interface unit block diagram

Coder/Decoder circuit

The Coder/Decoder (CODEC) performs Analog to Digital (A/D) and Digital

to Analog (D/A) conversion of the line analog voiceband signal to and from

a digital PCM signal. This signal can be coded and decoded using either

the A-Law or the µ-Law companding algorithm.

On some analog line cards, the decoding algorithm depends of the type of

CODEC installed when the board is built. On others, it is an option selected

using a software overlay.

Variable gain ﬁlters

Audio signals received from the analog phone line are passed through a

low-pass A/D monolithic ﬁlter that limits the frequency spread of the input

signal to a nominal 200 to 3400 Hz bandwidth. The audio signal is then

applied to the input of the CODEC. Audio signals coming from the CODEC

are passed through a low-pass A/D monolithic ﬁlter that integrates the

amplitude modulated pulses coming from the CODEC, and then ﬁlters and

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311 01.04 Standard

Release 5.0 23 May 2008

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Nortel-networks Circuit Card 311 Instrukcja Użytkownika Strona 27