Nortel Networks Circuit Card 311 - Manual (Page 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
Copyright © 2003-2008, Nortel Networks
.