Coder/decoder circuit, Variable gain filters – Nortel Networks 1000 User Manual

Page 27

Line cards

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

02.06

Standard

27 August 2008