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參數(shù)資料
| 型號(hào)： | GB4551-CSA |
| 英文描述： | Analog Buffer/Voltage Follower |
| 中文描述： | 模擬緩沖器/電壓跟隨 |
| 文件頁數(shù)： | 3/5頁 |
| 文件大?。?/td> | 140K |
| 代理商： | GB4551-CSA |
3
520 - 52 - 2
680k
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10V
10
NON-POLAR
470p
+10V
4 2 6
1 8
5 3 7
COMPOSITE
VIDEO INPUT
COLOR BURST
FILTER
0.1
6
4
8
5
2
CLAMPED
VIDEO OUTPUT
BACK
PORCH
PULSE
10V
0V
+10V
0.1
0.1
0.1
0.1
GS4881
SYNC. SEP.
Fig.1 Clamping Operation
DETAILED DESCRIPTION
The GB4551 is intended for video applications requiring
precision DC restoration coupled with very flat frequency
response. The signal path features a wide band operational
amplifier designed to be unity gain stable. While this amplifier
is not intended to drive 75
transmission lines, it is ideal for
applications where high capacitive loads, up to several
hundred picofarads, must be driven. These applications
include input and internal system buffering and DC restoration
of video signals.
Optimal frequency response for the GB4551 occurs with load
capacitances in the range of 80 pF. For smaller loads, an
external capacitor can be added to extend the bandwidth of
the device. As shown in Figure 7, a small resistor, R
OUT
,
should be included in series with the GB4551 output to obtain
optimal response flatness. The value of this resistor should be
chosen to match the value of the load capacitance, as shown
in Figure 5.
The DC restoration function is achieved through the use of a
strobed operational transconductance amplifier (OTA), as
shown in the Simplified Block Diagram. When enabled by
taking STROBE low, the OTA sources or sinks a current
depending on whether the output of the GB4551 is below or
above ground, respectively. The output current from the OTA
is integrated by the hold capacitor connected to pin 5, CX.
The resulting voltage is buffered and fed to the non-inverting
input of the op-amp through a 30 k
resistor. The non-inverting
input also receives the input video signal through a large
capacitor which acts as the DC reservoir for the corrective
level shift.
A 500
resistor in series with the input provides some phase
advance to improve the stability of the DC restoration feedback
loop, and provides fast recovery for offset steps as large as
±
100 mV (
±
14 IRE). The values of the input and hold capacitors
can be reduced to speed up the offset recovery time. The ratio
of the capacitors should be maintained at approximately
20,000:1 to ensure closed loop stability.
The OTA receives its inputs from a differential low pass filter.
This filter has a corner frequency of 600 kHz which attenuates
the color burst and any high frequency noise that may be
present in the signal. One input to the low pass filter senses the
output of the GB4551 while the other input is connected to the
ground reference.
In the application shown in figure 1, the input to pin 3 of the
GB4551, STROBE, is provided by the back porch output of the
GS4881 sync separator. The GS4881 generates back porch
pulses which remain at horizontal rate throughout the vertical
interval. Constant rate sample pulses eliminate the possibility
of introducing additional DC offset due to a change in duty
cycle.
The method of adjusting the DC level of the video signal used
in the GB4551 integrates over the entire back porch period.
This reduces sensitivity to noise and improves the accuracy of
the DC restoration compared with systems using sample and
hold techniques. Typical clamping accuracy of
±
1 mV is
achieved by the GB4551.
TEST CIRCUITS
All resistors in ohms, all capacitors
in microfarads unless otherwise stated.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| GB4600 | Wideband Unity Gain Voltage Follower |
| GB4600-CDA | Analog Buffer/Voltage Follower |
| GB4600-CKA | Analog Buffer/Voltage Follower |
| GB570 | GB570 - DynamEQ? II WDRC IC |
| GC570 | GC570 - DynamEQ? II WDRC IC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| GB4570 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Monolithic Video Buffer/Clamp |
| GB4570-CDA | 制造商:GENNUM 制造商全稱:GENNUM 功能描述:Monolithic Video Buffer/Clamp |
| GB4570-CKA | 制造商:GENNUM 制造商全稱:GENNUM 功能描述:Monolithic Video Buffer/Clamp |
| GB4570-CTA | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Monolithic Video Buffer/Clamp |
| GB4571 | 制造商:GENNUM 制造商全稱:GENNUM 功能描述:Video Buffer with Precision Strobed DC Restore |
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