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參數(shù)資料
| 型號： | L8551 |
| 廠商： | Lineage Power |
| 英文描述： | Low-Power SLIC(低功耗用戶線接口（SLIC）) |
| 中文描述： | 低功耗用戶接口（低功耗用戶線接口電路（SLIC）） |
| 文件頁數(shù)： | 24/32頁 |
| 文件大?。?/td> | 526K |
| 代理商： | L8551 |
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24
Lucent Technologies Inc.
Data Sheet
March 1997
L8551 Low-Power SLIC
Applications
(continued)
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. Here 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 out-
put stages, and
μ
-law/A-law selectability. This genera-
tion of codecs have the lowest cost. They are most
suitable for applications with fixed gains, termination
impedance, and hybrid balance.
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. The
ac programmability adds application flexibility, saves
several passive components, and also adds several I/O
latches that are needed in the application. However,
there is no transmit op amp, since the transmit gain and
hybrid balance are set internally.
Third-Generation Codecs
This class of devices includes the gains, termination
impedance, and hybrid balance—all under micropro-
cessor control. Depending on the device, they may or
may not include latches.
Selection Criteria
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
In the following examples, use of a first-generation
codec is shown. The equations for second- and third-
generation codecs are simply subsets of these. There
are two examples: The first shows the simplest circuit,
which uses a minimum number of discrete components
to synthesize a real termination impedance. The sec-
ond example shows the use of the uncommitted op
amp to synthesize a complex termination.
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| L8561 | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:The UTC L8561 is a Power Factor Corrector, which can work in wide input voltage range applications (from 85V ~ 265V) with an excellent THD. |
| L8561_11 | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:POWER FACTOR CORRECTOR |
| L8561G-D08-T | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:POWER FACTOR CORRECTOR |
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