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参数资料
| 型号： | LM1881MX-X/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 信号分离 |
| 英文描述： | SYNC SEPARATOR IC, PDSO8 |
| 封装： | PLASTIC, SO-8 |
| 文件页数： | 9/11页 |
| 文件大小： | 275K |
| 代理商： | LM1881MX-X/NOPB |
Application Notes (Continued)
APPLICATIONS
Apart from extracting a composite sync signal free of video
information, the LM1881 outputs allow a number of interest-
ing applications to be developed. As mentioned above, the
burst gate/backporch clamp pulse allows DC restoration of
the original video waveform for display or remodulation on
an R.F. carrier, and retrieval of the color burst for color
synchronization and decoding into R.G.B. components. For
frame memory storage applications, the odd/even field lever
allows identification of the appropriate field ensuring the
correct read or write sequence. The vertical pulse output is
particularly useful since it begins at a precise time — the
rising edge of the first vertical serration in the sync wave-
form. This means that individual lines within the vertical
blanking period (or anywhere in the active scan line period)
can easily be extracted by counting the required number of
transitions in the composite sync waveform following the
start of the vertical output pulse.
The vertical blanking interval is proving popular as a means
to transmit data which will not appear on a normal T.V.
receiver screen. Data can be inserted beginning with line 10
(the first horizontal scan line on which the color burst ap-
pears) through to line 21. Usually lines 10 through 13 are not
used which leaves lines 14 through 21 for inserting signals,
which may be different from field to field. In the U.S., line 19
is normally reserved for a vertical interval reference signal
(VIRS) and line 21 is reserved for closed caption data for the
hearing impaired. The remaining lines are used in a number
of ways. Lines 17 and 18 are frequently used during studio
processing to add and delete vertical interval test signals
(VITS) while lines 14 through 18 and line 20 can be used for
Videotex/Teletext data. Several institutions are proposing to
transmit financial data on line 17 and cable systems use the
available lines in the vertical interval to send decoding data
for descrambler terminals.
Since the vertical output pulse from the LM1881 coincides
with the leading edge of the first vertical serration, sixteen
positive or negative transitions later will be the start of line 14
in either field. At this point simple counters can be used to
select the desired line(s) for insertion or deletion of data.
VIDEO LINE SELECTOR
The circuit in
Figure 3 puts out a singe video line according
to the binary coded information applied to line select bits
b0–b7. A line is selected by adding two to the desired line
number, converting to a binary equivalent and applying the
result to the line select inputs. The falling edge of the
LM1881’s vertical pulse is used to load the appropriate
number into the counters (MM74C193N) and to set a start
count latch using two NAND gates. Composite sync transi-
tions are counted using the borrow out of the desired number
of counters. The final borrow out pulse is used to turn on the
analog switch (CD4066BC) during the desired line. The fall-
ing edge of this signal also resets the start count latch,
thereby terminating the counting.
The circuit, as shown, will provide a single line output for
each field in an interlaced video system (television) or a
single line output in each frame for a non-interlaced video
system (computer monitor). When a particular line in only
one field of an interlaced video signal is desired, the
odd/even field index output must be used instead of the
vertical output pulse (invert the field index output to select
the odd field). A single counter is needed for selecting lines 3
to 14; two counters are needed for selecting lines 15 to 253;
and three counters will work for up to 2046 lines. An output
buffer is required to drive low impedance loads.
MULTIPLE CONTIGUOUS VIDEO LINE
SELECTOR WITH BLACK LEVEL RESTORATION
The circuit in
Figure 4 will select a number of adjoining lines
starting with the line selected as in the previous example.
Additional counters can be added as described previously
for either higher starting line numbers or an increased num-
ber of contiguous output lines. The back porch pulse output
of the LM1881 is used to gate the video input’s black level
through a low pass filter (10 k
, 10 F) providing black level
restoration at the video output when the output selected
line(s) is not being gated through.
LM1881
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM1881N | 功能描述:视频 IC RoHS:否 制造商:Fairchild Semiconductor 工作电源电压:5 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:TSSOP-28 封装:Reel |
| LM1881N | 制造商:Texas Instruments 功能描述:VIDEO SYNC SEPARATOR 1881 DIP8 |
| LM1881N/NOPB | 功能描述:视频 IC RoHS:否 制造商:Fairchild Semiconductor 工作电源电压:5 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:TSSOP-28 封装:Reel |
| LM1881N/NOPB | 制造商:Texas Instruments 功能描述:Special Function IC |
| LM1881N-8/NOPB | 制造商:Texas Instruments 功能描述: |
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