EL2071 Ver la hoja de datos (PDF) - Intersil

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EL2071

150MHz Current Feedback Amplifier

Intersil 

Equivalent Circuit

EL2071, EL2171

Burn-In Circuit

ALL PACKAGES USE THE SAME SCHEMATIC.

Applications Information

Theory of Operation

The EL2071/EL2171 have a unity gain buffer from the non-

inverting input to the inverting input. The error signal of the

EL2071/EL2171 is a current flowing into (or out of) the

inverting input. A very small change in current flowing

through the inverting input will cause a large change in the

output voltage. This current amplification is called the

transimpedance (ROL) of the EL2071/EL2171

[VOUT = (ROL) * (-IIN)]. Since ROL is very large, the current

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flowing into the inverting input in the steady-state (non-

slewing) condition is very small.

Therefore we can still use op-amp assumptions as a first-

order approximation for circuit analysis, namely that:

1.The voltage across the inputs is approximately 0V.

2.The current into the inputs is approximately 0mA.

Resistor Value Selection and Optimization

The value of the feedback resistor (and an internal capacitor)

sets the AC dynamics of the EL2071/EL2171. The nominal

value for the feedback resistor is 1.5kΩ, which is the value

used for production testing. This value guarantees stability.

For a given closed-loop gain the bandwidth may be

increased by decreasing the feedback resistor and,

conversely, the bandwidth may be decreased by increasing

the feedback resistor.

Reducing the feedback resistor too much will result in

overshoot and ringing, and eventually oscillations. Increasing

the feedback resistor results in a lower -3dB frequency.

Attenuation at high frequency is limited by a zero in the

closed-loop transfer function which results from stray

capacitance between the inverting input and ground.

Consequently, it is very important to keep stray capacitance

to a minimum at the inverting input.

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