LUCL9312AP-D AGERE [Agere Systems], LUCL9312AP-D Datasheet - Page 32

• Manufacturer Part Number: LUCL9312AP-D
• Description: Line Interface and Line Access Circuit Forward Battery SLIC and Ringing Relay for TR-57 Applications
• Manufacturer: AGERE [Agere Systems]

Forward Battery SLIC and Ringing Relay for TR-57 Applications
ac Applications
ac Parameters
There are four key ac design parameters. Termination
impedance is the impedance looking into the 2-wire
port of the line card. It is set to match the impedance of
the telephone loop in order to minimize echo return to
the telephone set. Transmit gain is measured from the
2-wire port to the PCM highway, while receive gain is
done from the PCM highway to the transmit port.
Transmit and receive gains may be specified in terms
of an actual gain, or in terms of a transmission level
point (TLP), that is, the actual ac transmission level in
dBm. Finally, the hybrid balance network cancels the
unwanted amount of the receive signal that appears at
the transmit port.
Codec Types
At this point in the design, the codec needs to be
selected. The interface network between the SLIC and
codec can then be designed. Below is a brief codec
feature summary.
First-Generation Codecs. These perform the basic
filtering, A/D (transmit), D/A (receive), and -law/A-law
companding. They all have an op amp in front of the
A/D converter for transmit gain setting and hybrid bal-
ance (cancellation at the summing node). Depending
on the type, some have differential analog input stages,
differential analog output stages, +5 V only or 5 V
operation, and -law/A-law selectability. These are
available in single and quad designs. This type of
codec requires continuous time analog filtering via
external resistor/capacitor networks to set the ac
design parameters. An example of this type of codec is
the Agere T7504 quad 5 V only codec.
This type of codec tends to be the most economical in
terms of piece part price, but tends to require more
external components than a third-generation codec.
Further ac parameters are fixed by the external R/C
network so software control of ac parameters is diffi-
cult.
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Third-Generation Codecs. This class of devices
includes all ac parameters set digitally under micropro-
cessor control. Depending on the device, it may or may
not have data control latches. Additional functionality
sometimes offered includes tone plant generation and
reception, PPM generation, test algorithms, and echo
cancellation. Again, this type of codec may be +5 V
only or 5 V operation, single quad or 16-channel, and
ples of this type of codec are the Agere T8536/7 (5 V
only, quad, standard features), T8533/4 (5 V only, quad
with echo cancellation), and the T8531/36 (5 V only,
16-channel with self-test).
ac Interface Network
The ac interface network between the L9312 and the
codec will vary depending on the codec selected. With
a first-generation codec, the interface between the
L9312 and codec actually sets the ac parameters. With
a third-generation codec, all ac parameters are set dig-
itally, internal to the codec; thus, the interface between
the L9312 and this type of codec is designed to avoid
overload at the codec input in the transmit direction,
and to optimize signal to noise ratio (S/N) in the receive
direction.
Because the design requirements are very different
with a first- or third-generation codec, the L9312 is
offered with two different receive gains. Each receive
gain was chosen to optimize, in terms of external com-
ponents required, the ac interface between the L9312
and codec.
-law/A-law or 16-bit linear coding selectable. Exam-
Agere Systems Inc.
July 2001