EL4095 데이터 시트보기 (PDF) - Intersil
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EL4095 Datasheet PDF : 19 Pages
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EL4095
FIGURE 1. EL4095 IN INVERTING CONNECTION
Stray capacitance at each -VIN terminal should absolutely be
minimized, especially in a positive-gain mode, or peaking will
occur. Similarly, the load capacitance should be minimized. If
more than 25pF of load capacitance must be driven, a load
resistor from 100Ω to 400Ω can be added in parallel with the
output to reduce peaking, but some bandwidth degradation
may occur. A “snubber” load can alternatively be used. This
is a resistor in series with a capacitor to ground, 150Ω and
100pF being typical values. The advantage 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 +VIN terminals is within 3.5V
of either supply rail.
One must also consider the range of error currents that will
be handled by the -VIN terminals. Since the -VIN of a CFA is
the output of a buffer which replicates the voltage at +VIN,
error currents will flow into the -VIN terminal. When an input
channel has 100% gain assigned to it, only a small error
current flows into its negative input; when low gain is
assigned to the channel the output does not respond to the
channel’s signal and large error currents flow.
Here are a few idealized examples, based on a gain of +1 for
channels A and B and RF = 1kΩ for different gain settings:
Gain
100%
75%
50%
25%
0%
VINA
1V
1V
1V
1V
1V
VINB
0
0
0
0
0
I (-VINA) I (-VINB)
0
1mA
-250µA 750µA
-500µA 500µA
-750µA 250µA
-1mA
0
VOUT
1V
0.75V
0.5V
0.25V
0V
Thus, either -VIN can receive up to 1mA error current for 1V
of input signal and 1kΩ feedback resistors. The maximum
error current is 3mA for the EL4095, but 2mA is more
realistic. The major 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.
If maximum bandwidth is not required, distortion can be
reduced greatly (and signal voltage range enlarged) by
increasing the value of RF and any associated gain-setting
resistor.
11
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