EL4095CS datasheet(11/19 Pages) INTERSIL

11 / 19 page

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 100

Ω 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, 150

Ω 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:

Thus, either -VIN can receive up to 1mA error current for 1V

of input signal and 1k

Ω 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.

FIGURE 1. EL4095 IN INVERTING CONNECTION

Gain

VINA

VINB

I (-VINA)I (-VINB)VOUT

100%

1mA

75%

-250µA

750µA

0.75V

50%

-500µA

500µA

0.5V

25%

-750µA

250µA

0.25V

-1mA

EL4095

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