- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385479 > LM1893 (National Semiconductor Corporation) LM1893/LM2893 Carrier-Current Transceiver PDF資料下載
參數(shù)資料
| 型號： | LM1893 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LM1893/LM2893 Carrier-Current Transceiver |
| 中文描述： | LM1893/LM2893載波電流收發(fā)器 |
| 文件頁數(shù)： | 20/24頁 |
| 文件大?。?/td> | 576K |
| 代理商： | LM1893 |
Basic Data Encoding
(Continued)
TL/H/6750–36
FIGURE 33. Operating waveforms of a line-
synchronized transceiver pair are shown. The diagram
shows how the transmitted data transitions may be
used as received data sampling points
data edges for the line synchronous data transmission
scheme mentioned in the previous paragraph. With the
asynchronous system suggested, the receive controller
must sample the Data Out pin often to determine, with sev-
eral bits of accuracy, where the square-wave data tran-
sitions take place, average their positions assuming a
known data rate, and calculate where the center of the data
bits are and will continue to be as the address and data are
read. A long preamble is helpful. Software that continuously
updates the center-of-bit time estimate, as address and
data are received, works even better. Alternatively, a coding
scheme employing an embedded clock can be used.
LM2893 Application Hints
The LM2893 is intended for advanced applications where
special circuitry is used in the transmit and receive paths.
The LM2893 makes this possible by featuring separate
transmit output and receive input pins.
Examples of enhancements that can be added to the basic
LM1893/2893 circuit include separate transmit and receive
windings on the coupling transformer, high quality ceramic
or LC filters in the receive path, and simple impulse noise
blanking circuits.
In many applications, the additional performance to be
gained outweighs the extra cost of the additional circuitry.
More than likely, high performance industrial applications
such as building energy management will fit into this catego-
ry, since they require the utmost in reliability.
Because of the specialized nature of individual LM2893 ap-
plications, it is not possible to give one circuit that will satisfy
all requirements for performance and cost effectiveness.
Therefore no specific application examples will be given.
Instead the subsequent text describes in general terms the
types of circuits that can be used to increase performance
along with their advantages and disadvantages. It is intend-
ed to be a springboard for ideas.
LM2893 COUPLING NETWORKS
The main disadvantages of the typical LM1893 coupling
network are that it functions as the bandpass filter, has
loose coupling between primary and secondary, and has a
single secondary. The LM1893 coupling network was de-
signed this way mainly because of the restraint that the car-
rier input and output are tied together.
Because the coupling transformer is used as a filter, the
LM1893 circuit is susceptible to pulling of the center fre-
quency under conditions of changing line impedances or
when several LM1893 circuits are close in proximity on the
AC line. Because the tuned transformer has a high value of
‘‘Q’’, ringing also occurs in the presence of impulsive noise.
This ringing occurs at the center frequency and increases
the error rate of transmissions, especially at relatively high
data rates (
l
2000 baud). Because it is the only tuned circuit
in the system, the selectivity characteristics leave a lot to be
desired.
The LM2893, having separate receive input and transmit
output pins, removes the limitations on coupling transformer
design, allowing the design of circuits devoid of the previous
limitations.
The first enhancement that can be made with the LM2893
circuit is the use of a high permeability ferrite toroid for line
coupling along with a separate filter. The transformer would
be of broadband design (untuned) with two secondaries,
one for coupling to the transmit output and one for coupling
to the receive input. This allows impedance matching of
both the transmitter and receiver, with the result of quite a
bit more receive sensitivity.
Because of the increased signal and separate receive signal
path, a 3 or 6 db pad can be used before the selective
stages to eliminate pulling of the center frequency due to
changes in line impedance.
Another advantage of the toroidal transformer is that it can
be designed for use at very low line impedances due to its
inherent tight coupling.
SEPARATE FILTER
Because of the separate receive path of the LM2893, a rela-
tively high quality bandpass filter can be used for selectivity.
Inexpensive ceramic filters are available that have band-
pass and center frequency characteristics compatible with
carrier current operation. Futhermore, the use of these fil-
ters allows multichannel operation, previously made difficult
by the single tuned network of the LM1893. These filters are
easily cascaded for even more off-frequency rejection. If the
pad is added before the filter, there will be negligible pulling
due to changes in line impedance reflected through the cou-
pling transformer.
Alternatively, a Butterworth/Chebyshev bandpass LC filter
or an active filter can be used in place of the ceramic filter.
IMPULSE NOISE BLANKER
Although the LM2893 has adequate impulse noise rejection
for most applications, there is reason to employ impulse
blanking to improve error rates in severe AC line environ-
ments. Typically, errors occur due to pulse jitter in the
LM1893/2893 data output that originates when the internal
time domain filter smooths out an incoming noise pulse.
The solution involves removing the impulse completely and
not simply trying to filter it. Moreover, the pulse should be
removed in the receive signal path before the selective por-
tions of the circuit to eliminate ringing. This also allows the
receiver filter to smooth out the blanks that also occur in the
desired incoming carrier signal.
If a carrier detect circuit is desired in conjunction with the
LM2893 it can be located after the filter and impulse blank-
er. Because impulse noise is removed, the false triggering
that plagues these circuits will be greatly reduced.
20
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM1893N | RES 250K-OHM 1% 0.125W THICK-FILM SMD-0805 5K/REEL-7IN-PA |
| LM2893M | LM1893/LM2893 Carrier-Current Transceiver |
| LM2893N | LM1893/LM2893 Carrier-Current Transceiver |
| LM2895 | AUDIO POWE RAMPLIFIER |
| LM1895 | AUDIO POWE RAMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1893 WAF | 制造商:Texas Instruments 功能描述: |
| LM1893N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1893/LM2893 Carrier-Current Transceiver |
| LM1893N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1893N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Carrier/Multi-Wire Interface |
| LM1894 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dynamic Noise Reduction System DNR |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。