Note 13: The THD measurement at low frequency is limited by the test instrument.

Simplified Schematic Diagram

Application Notes

LM7171 Performance Discussion

The LM7171 is a very high speed, voltage feedback ampli-

fier. It consumes only 6.5 mA supply current while providing

a unity-gain bandwidth of 200 MHz and a slew rate of 4100V/

µs. It also has other great features such as low differential

gain and phase and high output current.

The LM7171 is a true voltage feedback amplifier. Unlike cur-

rent feedback amplifiers (CFAs) with a low inverting input im-

pedance and a high non-inverting input impedance, both in-

puts of voltage feedback amplifiers (VFAs) have high

impedance nodes. The low impedance inverting input in

CFAs and a feedback capacitor create an additional pole

that will lead to instability. As a result, CFAs cannot be used

in traditional op amp circuits such as photodiode amplifiers,

I-to-V converters and integrators where a feedback capacitor

is required.

LM7171 Circuit Operation

The class AB input stage in LM7171 is fully symmetrical and

has a similar slewing characteristic to the current feedback

amplifiers. In the LM7171 Simplified Schematic, Q1 through

Q4 form the equivalent of the current feedback input buffer,

R

Harmonic Distortion

vs Frequency

DS012385-74

Harmonic Distortion

vs Frequency

DS012385-75

Maximum Power Dissipation

vs Ambient Temperature

DS012385-20

DS012385-9

Note: M1 and M2 are current mirrors.

www.national.com

12