LMH6723MASLASHNOPB datasheet(14/28 Pages) TI1

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0.1

100

1000

FREQUENCY (MHz)

-8

-7

-6

-5

-4

-3

-2

-1

RF = 800:

RF = 1200:

RF = 2000:

VS = ±2.5V

VOUT = 1VPP

LMH6723, LMH6724

SNOSA83I – AUGUST 2003 – REVISED AUGUST 2014

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7.4 Feedback Resistor Selection

One of the key benefits of a current feedback operational amplifier is the ability to maintain optimum frequency

response independent of gain by using appropriate values for the feedback resistor (RF). The Electrical

Characteristics and Typical Performance plots were generated with an RF of 1200Ω, a gain of +2V/V and ±5V or

±2.5V power supplies (unless otherwise specified). Generally, lowering RF from its recommended value will peak

the frequency response and extend the bandwidth; however, increasing the value of RF will cause the frequency

response to roll off faster. Reducing the value of RF too far below it's recommended value will cause overshoot,

ringing, and eventually, oscillation.

Figure 31. Frequency Response vs. RF

Figure 31 shows the LMH6723/LMH6724's frequency response as RF is varied (RL = 100Ω, AV = +2). This plot

shows that an RF of 800Ω results in peaking. An RF of 1200Ω gives near maximal bandwidth and gain flatness

with good stability. Since each application is slightly different, it is worth experimenting to find the optimal RF for a

given circuit. In general, a value of RF that produces ~0.1 dB of peaking is the best compromise between stability

and maximal bandwidth. Note that it is not possible to use a current feedback amplifier with the output shorted

directly to the inverting input. The buffer configuration of the LMH6723/LMH6724 requires a 2000-

Ω feedback

resistor for stable operation. For other gains see the charts Figure 32 and Figure 33. These charts provide a

good place to start when selecting the best feedback resistor value for a variety of gain settings.

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