Application Section

Application Introduction

Offered in an 8-pin package for reduced space and cost, the

wideband LMH6715 dual current-feedback op amp provides

closely matched DC and AC electrical performance charac-

teristics making the part an ideal choice for wideband signal

processing. Applications such as broadcast quality video

systems, IQ amplifiers, filter blocks, high speed peak detec-

tors, integrators and transimedance amplifiers will all find

superior performance in the LMH6715 dual op amp.

FEEDBACK RESISTOR SELECTION

One of the key benefits of a current feedback operational

amplifier is the ability to maintain optimum frequency re-

sponse independent of gain by using appropriate values for

the feedback resistor (R

Typical Performance plots specify an R

Ω, a gain of

Generally, lowering R

peak the frequency response and extend the bandwidth

while increasing the value of R

response to roll off faster. Reducing the value of R

below it’s recommended value will cause overshoot, ringing

and, eventually, oscillation.

Frequency Response vs. R

F

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The plot labeled “Frequency Response vs. R

LMH6715’s frequency response as R

Ω,

A

Ω results in

peaking and marginal stability. An R

Ω gives near

maximal bandwidth and gain flatness with good stability, but

with very light loads (R

Ω) the device may show some

peaking. An R

Ω gives excellent stability with good

bandwidth and is the recommended value for most applica-

tions. Since all applications are slightly different it is worth

some experimentation to find the optimal R

circuit. For more information see Application Note OA-13

which describes the relationship between R

loop frequency response for current feedback operational

amplifiers.

When configuring the LMH6715 for gains other than +2V/V,

it is usually necessary to adjust the value of the feedback

resistor. The two plots labeled “R

and “R

resistor values for a number of gain selections.

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FIGURE 1. Non-Inverting Configuration with Power

Supply Bypassing

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FIGURE 2. Inverting Configuration with Power Supply

Bypassing

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