el4095c ETC-unknow, el4095c Datasheet - Page 12

• Manufacturer Part Number: el4095c
• Description: Video Gain Control/fader/multiplexer
• Manufacturer: ETC-unknow

Applications Information
Stray capacitance at each
absolutely be minimized especially in a positive-
gain mode or peaking will occur Similarly the
load capacitance should be minimized If more
than 25 pF of load capacitance must be driven a
load resistor from 100
parallel with the output to reduce peaking but
some bandwidth degradation may occur
‘‘snubber’’ load can alternatively be used This is
a resistor in series with a capacitor to ground
150
vantage of a snubber is that it does not draw DC
load current A small series resistor low tens of
ohms can also be used to isolate reactive loads
Distortion
The signal voltage range of the
is within 3 5V of either supply rail
One must also consider the range of error cur-
rents that will be handled by the
nals Since the
buffer which replicates the voltage at
ror currents will flow into the
When an input channel has 100% gain assigned
to it only a small error current flows into its neg-
ative input when low gain is assigned to the
channel the output does not respond to the chan-
nel’s signal and large error currents flow
Here are a few idealized examples based on a
gain of
for different gain settings
Thus either
current for 1V of input signal and 1 k
resistors The maximum error current is 3 mA for
the EL4095 but 2 mA is more realistic The ma-
jor contributor of distortion is the magnitude of
error currents even more important than loading
effects The performance curves show distortion
versus input amplitude for different gains
Gain
100%
EL4095C
Video Gain Control Fader Multiplexer
75%
50%
25%
0%
and 100 pF being typical values The ad-
V
a
1V
1V
1V
1V
1V
INA
1 for channels A and B and R
b
V
b
V
INB
0
0
0
0
0
IN
V
IN
can receive up to 1 mA error
I (
of a CFA is the output of a
b
b
b
b
b
250 A
500 A
750 A
1 mA
to 400
V
0
INA
b
V
)
IN
I (
a
b
terminal should
can be added in
750 A
500 A
250 A
b
1 mA
V
V
V
b
0
IN
IN
INB
V
a
F
IN
terminals
terminal
)
Contd
feedback
V
e
IN
termi-
V
0 75V
0 25V
0 5V
1 k
OUT
1V
0V
er-
A
12
If maximum bandwidth is not required distor-
tion can be reduced greatly (and signal voltage
range enlarged) by increasing the value of R
and any associated gain-setting resistor
100% Accuracies
When a channel gain is set to 100% static and
gain errors are similar to those of a simple CFA
The DC output error is expressed by
The input offset voltage scales with fed-back
gain but the bias current into the negative input
I
ally I
E
The gain error is about 0 3% for a gain of one
and increases only slowly for increasing gain
R
buffer and R
plifier 80 k
Gain Control Inputs
The gain control inputs are differential and may
be biased at any voltage as long as V
than 2 5V below V
ferential input impedance is 5 5 k
mon-mode impedance is more than 500 k
zero differential voltage on the gain inputs both
signal inputs have a 50% gain factor Nominal
calibration sets the 100% gain of V
of gain control V
that of V
at V
gain The gain control does not have a complete-
ly abrupt transition at the 0% and 100% points
There is about 10 mV of ‘‘soft’’ transfer at the
gain endpoints To obtain the most accurate
100% gain factor or best attenuation of 0% gain
it is necessary to overdrive the gain control input
by about 30 mV This would set the gain control
voltage range as
30 mV beyond the maximum guaranteed 0% to
100% range
a
B
GAIN
IN
V
The fractional gain error is given by
0 5V of gain control voltage and 0% at
b
OUT
b
INB
adds an error not dependent on gain Gener-
B
is the input impedance of the input stage
b
e
and
INA
Offset
dominates up to gains of about seven
(R
a
F
b
OL
A
and 350 k
a
a
V
0 5V gain control sets 100% V
0 5V of gain control sets 0% gain
e
is the transimpedance of the am-
R
INB
A
a
IN
b
V
V
OS
) R
0 565 mV to
’s gain is complementary to
and 3V above V
R
IN
OL
A
respectively
b
V
) R
a
F
(I
B
b
INA
a
GAIN
b
and a com-
) R
0 565V or
input at
The dif-
F
b
is less
With
0 5V
INB
F