參數(shù)資料
型號: LUCL8560AU-DT
英文描述: Low-Power SLIC with Ringing
中文描述: 低功耗振鈴用戶接口
文件頁數(shù): 37/46頁
文件大小: 842K
代理商: LUCL8560AU-DT
Data Sheet
April 2000
Lucent Technologies Inc.
37
L8560 Low-Power SLIC with Ringing
Applications
(continued)
Design Considerations
(continued)
Table 13 shows the design parameters of the application circuit shown in Figure 35. Components that are adjusted
to program these values are also shown.
Table 13. 600
Design Parameters
Design Parameter
Parameter Value
10 mA
25 mA
55
3.14 dBm
600
600
0 dB
0 dB
Components Adjusted
R
LCTH
R
PROG
R
T3
, R
GP
, R
RCV
R
HB1
R
T6
, R
X
R
RCV
, R
GP
, R
T3
Loop Closure Threshold
dc Loop Current Limit
dc Feed Resistance
2-wire Signal Overload Level
ac Termination Impedance
Hybrid Balance Line Impedance
Transmit Gain
Receive Gain
ac Design
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.
Finally, the
hybrid balance
network cancels the
unwanted amount of the receive signal that appears at
the transmit port.
At this point in the design, the codec needs to be
selected. The discrete network between the SLIC and
the codec can then be designed. Below is a brief codec
feature and selection 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 balance (cancellation at the summing
node). Depending on the type, some have differential
analog input stages, differential analog output stages,
and
μ
-law/A-law selectability. This generation of codec
has the lowest cost. It is most suitable for applications
with fixed gains, termination impedance, and hybrid bal-
ance.
Second-Generation Codecs
This class of devices includes a microprocessor inter-
face for software control of the gains and hybrid bal-
ance. The hybrid balance is included in the device. ac
programmability adds application flexibility and saves
several passive components. It also adds several I/O
latches that are needed in the application. It does not
have the transmit op amp, since the transmit gain and
hybrid balance are set internally.
Third-Generation Codecs
This class of devices includes the gains, termination im-
pedance, and hybrid balance—all under microproces-
sor control. Depending on the device, it may or may not
include latches.
In the codec selection, increasing software control and
flexibility are traded for device cost. To help decide, it
may be useful to consider the following: Will the appli-
cation require only one value for each gain and imped-
ance Will the board be used in different countries with
different requirements Will several versions of the
board be built If so, will one version of the board be
most of the production volume Does the application
need only real termination impedance Does the hybrid
balance need to be adjusted in the field
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