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參數(shù)資料
| 型號： | LT1228IS8#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1 CHANNEL, VIDEO AMPLIFIER, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SOP-8 |
| 文件頁數(shù)： | 7/20頁 |
| 文件大小： | 401K |
| 代理商： | LT1228IS8#TR |
15
LT1228
1228fc
Video Fader
Video DC Restore (Clamp) Circuit
LT1228 TA12
–
+
–
+
1k
100
gm
LT1223
CFA
VOUT
3
2
5
1
VIN1
1k
–
+
gm
3
1k
VIN2
10k
5.1k
10k
5.1k
10k
100
2
1k
5
1
–5V
VS = ±5V
LT1228 TA13
–
+
–
+
gm
CFA
VOUT
8
3
2
5
V–
3k
RF
RG
4
10k
3k
5V
LOGIC
INPUT
RESTORE
0.01
F
VIDEO
INPUT
2N3906
1
6
V+
7
200
1000pF
NOT NECESSARY IF THE SOURCE RESISTANCE IS LESS THAN 50
The video fader uses the transconductance amplifiers
from two LT1228s in the feedback loop of another current
feedback amplifier, the LT1223. The amount of signal
from each input at the output is set by the ratio of the
set currents of the two LT1228s, not by their absolute
value. The bandwidth of the current feedback amplifier
is inversely proportional to the set current in this
configuration. Therefore, the set currents remain high
over most of the pot’s range, keeping the bandwidth over
15MHz even when the signal is attenuated 20dB. The pot
is set up to completely turn off one LT1228 at each end of
the rotation.
The video restore (clamp) circuit restores the black level of
the composite video to zero volts at the beginning of every
line. This is necessary because AC coupled video changes
DC level as a function of the average brightness of the
picture. DC restoration also rejects low frequency noise
such as hum.
The circuit has two inputs: composite video and a logic
signal. The logic signal is high except during the back porch
time right after the horizontal sync pulse. While the logic is
high, the PNP is off and ISET is zero. With ISET equal to zero
the feedback to Pin 2 has no affect. The video input drives
the noninverting input of the current feedback amplifier
whose gain is set by RF and RG. When the logic signal is
low, the PNP turns on and ISET goes to about 1mA. Then the
transconductance amplifier charges the capacitor to force
the output to match the voltage at Pin 3, in this case zero
volts.
This circuit can be modified so that the video is DC coupled
by operating the amplifier in an inverting configuration.
Just ground the video input shown and connect RG to the
video input instead of to ground.
TYPICAL APPLICATIO S
U
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| LT1304CS8-3.3#PBF | 1.2 A SWITCHING REGULATOR, 300 kHz SWITCHING FREQ-MAX, PDSO8 |
| LT1304CS8-3.3#TRPBF | 1.2 A SWITCHING REGULATOR, 300 kHz SWITCHING FREQ-MAX, PDSO8 |
相關代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT1228M | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100MHz Current Feedback Amplifier with DC Gain Control |
| LT1228MJ8 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100MHz Current Feedback Amplifier with DC Gain Control |
| LT1229 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Dual and Quad 100MHz Current Feedback Amplifiers |
| LT1229C | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Dual and Quad 100MHz Current Feedback Amplifiers |
| LT1229CJ8 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Dual and Quad 100MHz Current Feedback Amplifiers |
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