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參數(shù)資料
| 型號： | GB4550ACSA |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Monolithic Video Buffer/Clamp |
| 中文描述： | 單片視頻緩沖器/鉗 |
| 文件頁數(shù)： | 3/5頁 |
| 文件大?。?/td> | 152K |
| 代理商： | GB4550ACSA |
3
520 - 34 - 4
DETAILED DESCRIPTION
The GB4550(A) is intended for video applications requiring
coarse DC restoration coupled with flat frequency response.
As shown in Figure 1, the signal path features a wide band
operational amplifier designed to be unity gain stable. While
this amplifer is not intended to drive 75
transmission lines,
it is ideal for applications where high capactive loads, up to
several hundred picofarads, must be driven, such as input
buffering and DC restoration of video signals.
Optimal frequency response for the GB4550(A) occurs with
load capacitances in the range of 80 pF to 100 pF as shown in
Figure 4. For smaller loads, an external capacitor can be
added to extend the bandwidth and improve the flatness of the
device response.
The clamping function is achieved through the use of a simple
comparator. The inverting input of the comparator is connected
to the GB4550(A) output, while the non-inverting input is
connected to the clamp voltage reference. For output signal
voltages more positive than the clamp reference the comparator
output is essentially open-circuit, while signal voltages more
negative than the clamp reference result in the charging of C
X
.
The action of the comparator is to provide a positive current
which is fed back to the op-amp non-inverting input under
conditions where the op-amp output is more negative than the
clamp reference voltage. This negative feedback raises the
DC level of the input signal to the point where all signal
fluctuations occur at voltages above the clamp reference
level. This is the desired clamp action.
The input to the op-amp must be AC coupled using an
appropriate size of capacitor, which then acts as a DC "reservoir"
for the corrective level shift.
Under equilibrium conditions the average current supplied by
the comparator output is just sufficient to balance the current
discharging the input capacitor. This discharge current is
simply the input bias current of the op-amp, typically less than
20
μ
A . However, an external resistor can be added to increase
the pull down current. Under dynamic conditions, where the
system is adjusting for a change in the signal level, the
charging current may be in the milliamp range. Because the
corrective current is small under equilibrium conditions, the
error voltage at the comparator input is small also, so clamping
accuracy to within
±
7 mV is achievable.
The clamp circuit makes use of a "peak hold" capacitor, C
X
, at
the output of the comparator . This gives rise to a more
constant voltage at the comparator output which is translated
to a more constant corrective current by an internal 100 k
resistor connected between the comparator output and the
signal input.
To avoid excessive phase shift and consequent instability of
the clamp feedback loop, the peak hold capacitor needs to be
considerably smaller (e.g. 1000 times) than the input coupling
capacitor. If a faster clamp is desirable (e.g. for 60 Hz hum
elimination) the peak hold capacitor can be removed and a
smaller input coupling capacitor employed. In this application
some distortion of the signal "tip" is unavoidable.
+IN
10pF
C
X
V
CL
COMP
OUT
30k
100k
7mA
Nominal
+
-
-IN
V
CC
V
EE
30k
(+2 V OUTPUT CLAMP)
+
-
(NC on
GB4550A)
All resistors in ohms, all capacitors in microfarads unless otherwise stated.
Fig. 1 Simplfied Circuit Diagram
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| GB4570 | Monolithic Video Buffer/Clamp |
| GB4570-CDA | Monolithic Video Buffer/Clamp |
| GB4570-CKA | Monolithic Video Buffer/Clamp |
| GB4570-CTA | Monolithic Video Buffer/Clamp |
| GB4571-CTA | Video Buffer with Precision Strobed DC Restore |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| GB4550-CSA | 制造商:GENNUM 制造商全稱:GENNUM 功能描述:Monolithic Video Buffer/Clamp |
| GB4551 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Video Op Amp with Strobed DC Restore |
| GB4551-CSA | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog Buffer/Voltage Follower |
| 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 |
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