Am79D2251

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GENERAL DESCRIPTION

The Intelligent Access

 voice chipsets integrate all functions of the subscriber line for two subscriber

lines. One or more of two chip types are used to implement the linecard; an ISLIC device and a dual

ISLAC device. These provide the following basic functions:

1. The ISLIC device: A high voltage, bipolar IC that drives the subscriber line, maintains

longitudinal balance and senses line conditions.

2. The dual ISLAC device: A low voltage CMOS IC that provides conversion and DSP functions

for 2 channels.

Complete schematics of linecards using the Intelligent Access voice chipsets for internal and external

ringing are shown in Figure 4 and Figure 5.

The ISLIC device uses reliable, bipolar technology to provide the power necessary to drive a wide

variety of subscriber lines. It can be programmed by the ISLAC device to operate in eight different

modes that control power consumption and signaling modes. This enables it to have full control over

the subscriber loop. The ISLIC device is customized to be used exclusively with the ISLAC device

as part of a multiple-line chipset. The ISLIC device requires only +5 V power and the battery supplies

for its operation.

The ISLIC device implements a linear loop-current feeding method with the enhancement of

intelligent thermal management in a controlled manner. This limits the amount of power dissipated

on the ISLIC chip by dissipating excess power in external resistors.

Each ISLAC device contains high-performance codec circuits that provide A/D and D/A conversion

for voice (codec), DC-feed and supervision signals for two subscriber channels. The ISLAC device

contains a DSP core that handles signaling, DC-feed, supervision and line diagnostics for both

channels.

The DSP core selectively interfaces with three types of backplanes:

s Standard PCM/MPI

s Standard GCI

s Modified GCI with a single analog line per GCI channel

The Intelligent Access voice chipset provides a complete software configurable solution to the

BORSCHT functions as well as complete programmable control over subscriber line DC-feed

characteristics, such as current limit and feed resistance. In addition, these chipsets provide system

level solutions for the loop supervisory functions and metering. In total, they provide a programmable

solution that can satisfy worldwide linecard requirements by software configuration.

Software programmed filter coefficients, DC-feed data and supervision data are easily calculated

with the WinSLAC

 software. This PC software is provided free of charge. It allows the designer to

enter a description of system requirements. WinSLAC then computes the necessary coefficients

and plots the predicted system results.

The ISLIC interface unit inside the ISLAC device processes information regarding the line voltages,

loop currents and battery voltage levels. These inputs allow the ISLAC device to place several key

ISLIC performance parameters under software control.