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參數資料
| 型號： | L9310 |
| 英文描述： | Line Interface and Line Access Circuit Full-Feature SLIC,Ringing Relay,and Test Access Device |
| 中文描述： | 線路接口和線路接入電路全功能用戶接口，振鈴繼電器，測試接入設備 |
| 文件頁數： | 44/60頁 |
| 文件大小： | 1053K |
| 代理商： | L9310 |
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Data Sheet
July 2001
Full-Feature SLIC, Ringing Relay, and Test Access Device
L9310 Line Interface and Line Access Circuit
44
Agere Systems Inc.
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
μ
-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
μ
-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.
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
μ
-law/A-law or 16-bit linear coding selectable. Exam-
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 T8531/36 (5 V only, 16-
channel with self-test).
ac Interface Network
The ac interface network between the L9310 and the
codec will vary depending on the codec selected. With
a first-generation codec, the interface between the
L9310 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 L9310 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 L9310 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 L9310
and codec.
With a first-generation codec, the termination imped-
ance is set by providing gain shaping through a feed-
back network from the SLIC VITR output to the SLIC
RCVN/RCVP inputs. The L9310 provides a transcon-
ductance from T/R to VITR in the transmit direction and
a single-ended to differential gain in the receive direc-
tion from either RCVN or RCVP to T/R. Assuming a
short from VITR to RCVN or RCVP, the maximum
impedance that is seen looking into the SLIC is the
product of the SLIC transconductance times the SLIC
receive gain, plus the protection resistors. The various
specified termination impedance can range over the
voiceband as low as 300
up to over 1000
. Thus, if
the SLIC gains are too low, it will be impossible to syn-
thesize the higher termination impedances. Further, the
termination that is achieved will be far less than what is
calculated by assuming a short for SLIC output to SLIC
input. In the receive direction, in order to control echo,
the gain is typically a loss, which requires a loss net-
work at the SLIC RCVN/RCVP inputs, which will
reduce the amount of gain that is available for termina-
tion impedance. For this reason, a high-gain SLIC is
required with a first-generation codec.
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