LUCL9216AGF-D AGERE [Agere Systems], LUCL9216AGF-D Datasheet - Page 32

• Manufacturer Part Number: LUCL9216AGF-D
• Description: Short-Loop Ringing SLIC with Ground Start
• Manufacturer: AGERE [Agere Systems]

Short-Loop Ringing SLIC with Ground Start
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 balance (cancellation at the
summing node). Depending on the type, some have
differential analog input stages, differential analog out-
put 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.
32
Third-Generation Codecs
This class of devices includes all ac parameters set
digitally under microprocessor 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 3.3 V, 5 V only, or 5 V operation, sin-
gle quad or multichannel, and -law/A-law or 16-bit lin-
ear coding selectable. Examples of this type of codec
are the Agere T8535/6 (5 V only, quad, standard fea-
tures), T8537/8 (3.3 V only, quad, standard features),
T8533/4 (5 V only, quad with echo cancellation), and
the T8531/32 (5 V only multichannel).
ac Interface Network
The ac interface network between the L9216 and the
codec will vary depending on the codec selected. With
a first-generation codec, the interface between the
L9216 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 L9216 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 L9216 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 L9216
and codec.
September 2001
Agere Systems Inc.