el4453c ETC-unknow, el4453c Datasheet - Page 9

• Manufacturer Part Number: el4453c
• Description: Video Fader
• Manufacturer: ETC-unknow

Applications Information
The gain of the feedback dividers are H
H
part is
V
with
merically
A
about 600 The large value of A
((V
Rearranging and substituting
V
Where F
In the above equations F represents the fade
amount with F
but 0% for V
V
ment of the fade gain When F
and the amplifier passes V
gain of 1 H
and the gains vary linearly between fade ex-
tremes
OUT
O
OUT
IN
B
IN
is the open-loop gain of the amplifier and is
A but 100% to V
and 0
a
–(V
b
A
e
e
((V
a
1
F
A
FADE
F
a
e
)– H
e
O c
s
IN
s
(V
c
A
(1
(1
B
V
V
(V
H
A c
b
FADE
V
((V
a
IN
OUT
Similarly for F
OUT
c
b
c
a
F
FADE
IN
s
(V
e
)– H
(1
B F
)) 2
(1
V
IN
c
A
(V
FADE
1 The transfer function of the
b
OUT
a
e
e
1 giving 100% gain on V
b
A
H
IN
a
FADE
B c
a
a
(V
(V
a
)) 2
a
A
V
V
F
B F is 1
e
)– (V
(Sum
Sum
)
FADE
IN
IN
FADE
) – H
a
((V
a
c
V
c
a
OUT
)
A
B
0 giving 0% gain for
(1
a
F
a
IN
H
H
IN
V
(Sum
FADE
e
A c
) – (V
a
a
a
IN
c
a
A
B
A and Sum with a
a
a
B
(V
(Sum
)
e
)– (Sum
Sum
Sum
c
O
)
B
)
a
H
b
e
V
(V
FADE
a
b
a
OUT
(1
drives
B
0
b
)– H
a
F the comple-
(V
FADE
(V
FADE
1
b
)–(Sum
)
a
Sum
FADE
FADE
(V
)
s
) –(Sum
B c
b
b
Contd
FADE
)) 2 and
a
b
a
))
V
)
)) 2
A
b
b
1 nu-
b
OUT
IN
)) 2
)) 2
and
))
b
a
0
A
)
)
)
9
The EL4453C is stable for a direct connection be-
tween V
gain of
higher output gain although with the traditional
loss of bandwidth It is important to keep the
feedback dividers’ impedances low so that stray
capacitance does not diminish the feedback loop’s
phase margin The pole caused by the parallel im-
pedance of the feedback resistors and stray ca-
pacitance should be at least 150 MHz typical
strays of 3 pF thus require a feedback impedance
of 360
across R
quency-compensated divider The value of the ca-
pacitor should scale with the parasitic capaci-
tance at the FB input It is also practical to place
small capacitors across both the feedback resis-
tors (whose values maintain the desired gain) to
swamp out parasitics For instance two 10 pF
capacitors across equal divider resistors for a gain
of two will dominate parasitic effects and allow a
higher divider resistance Either input channel
can be set up for inverting gain using traditional
feedback resistor connections
At 100% gain an input stage operates just like
an op-amp’s input and the gain error is very low
around
vastly improved since the gain core sees only
small error signals not full inputs Unfortunate-
ly distortions increase at lower fade gains for a
given input channel
The Sum pins can be used to inject an additional
input signal but it is not as linear as the V
paths The gain error is also not as good as the
main inputs being about 1% Both sum pins
should be grounded if they are not to be used
a
b
OUT
F
or less Alternatively a small capacitor
1 The feedback divider may be used for
0 2% Furthermore nonlinearities are
can be used to create more of a fre-
and V
IN
A
b
EL4453C
or V
Video Fader
IN
B
b
yielding a
IN