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參數(shù)資料
| 型號(hào)： | EL4093C |
| 元件分類： | 視頻放大器 |
| 英文描述： | 300 MHz DC-Restored Video Amplifier(300MHz 直流恢復(fù)放大器) |
| 中文描述： | 300兆赫的DC -恢復(fù)視頻放大器（300MHz的直流恢復(fù)放大器） |
| 文件頁(yè)數(shù)： | 6/16頁(yè) |
| 文件大?。?/td> | 342K |
| 代理商： | EL4093C |
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EL4093C
300 MHz DC-Restored Video Amplifier
Applications Information
Contd
A remedy for this situation is to attenuate the
colorburst before applying it to the SH input
Figure 6 below shows a 358 MHz chroma trap
which would notch out the colorburst while pre-
serving the video DC level
4093 – 42
Figure 6 Colorburst Trap for NTSC Applications
One may be tempted to use a RC lowpass filter to
suppress the colorburst as shown in Figure 7 be-
low This technique however poses several prob-
lems First to obtain enough attenuation we
need to set the pole frequency 10 to 20 times low-
er than 358 MHz This pole being close to the
auto zero loop pole would destabilize the system
and cause the loop to oscillate
4093 – 43
Figure 7 Caution Lowpass Filter Does Not
Work in NTSC Applications
Although we can cancel this pole by introducing
a zero the RC network introduces a time delay
between the CFA output and the SH input This
has undesirable effects in some NTSC applica-
tions as Figure 8 below illustrates There is only
06
ms from the rising edge of sync to the color-
burst If we are autozeroing over the back porch
the autozero period would begin somewhere in
this 06
ms interval Since the edge of sync is now
delayed by the RC network autozero begins be-
fore the video back porch reaches its final value
Consequently the autozero loop performs a cor-
rection on every line and never settles
4093 – 44
Figure 8 Lowpass Filter Delays Input to Sample and Hold
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