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參數(shù)資料
| 型號(hào)： | LM1865M |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 接收器 |
| 英文描述： | Advanced FM IF System |
| 中文描述： | FM, AUDIO DEMODULATOR, PDSO20 |
| 封裝： | 0.300 INCH, PLASTIC, SOP-20 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大?。?/td> | 309K |
| 代理商： | LM1865M |
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Application Notes
(Continued)
First examine what happens with a single in-band signal as
we vary the strength of this signal.Figures 6 and 7 illustrate
what happens at the tuner and AGC outputs.
FIGURE 6
TL/H/7509–10
FIGURE 7
In Figure 7 there is no AGC output until the tuner output
equals the wide band threshold. At this point both SW2 and
SW1 are closed and the AGC holds the tuner output in Fig-
ure 6 relatively constant.
Another simple case to examine is that of the single out-of-
band signal. Here there is no AGC output even if the signal
exceeds V
WB
. There is no output because the ceramic fil-
ters prevent the out-of-band signal from getting to the input
of the IF. With no signal at the IF input there is no meter
output and SW1 is open, which means No AGC.
Figures 8 and 9 illustrate what happens at the tuner and
AGC outputs when the strength of an in-band signal is var-
ied in the presence of a strong out-of-band signal (i.e.,
greater than V
WB
) which is held constant at the tuner input.
For this example, the in-band signal at the tuner output will
be referred to as V
D
(desired signal), and the out-of-band
signal as V
UD
(undesired signal).
In Figure 9, we see that there is no AGC output until the
tuner output exceeds the narrow band threshold, V
NB
. At
this point V
m
l
1V and SW1 closes. Further increase of the
desired signal at the tuner input results in an AGC current
that tries to hold the desired signal at the tuner output con-
stant. This gain reduction of the tuner forces the undesired
signal at the tuner output to fall. At the point that V
UD
reach-
es the wide band threshold, no further gain reduction can
occur as V
o
would fall below V
WB
(refer toFigure 5). At this
point, control of the AGC shifts from the meter output
(narrow band loop) to the out-of-band signal (wide band
loop). Here V
UD
is held constant along with the AGC
FIGURE 8
TL/H/7509–11
Prime indicates referenced to tuner input
FIGURE 9
10
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| LM1865N | Advanced FM IF System |
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| LM1868N | Radio System |
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| LM1871 | RC Encoder/Transmitter |
相關(guān)代理商/技術(shù)參數(shù) |
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| LM1865N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:FM Receiver Circuit |
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