LM6104M datasheet(4/6 Pages) NSC

4 / 6 page

Applications Information

CURRENT FEEDBACK TOPOLOGY

The small-signal bandwidth of conventional voltage feed-

back amplifiers is inversely proportional to the closed-loop

gain based on the gain-bandwidth concept In contrast the

current feedback amplifier topology such as the LM6104

enables a signal bandwidth that is relatively independent of

the amplifier’s gain (see typical curve Frequency Response

vs Closed Loop Gain)

FEEDBACK RESISTOR SELECTION RF

Current feedback amplifier bandwidth and slew rate are

controlled by RF RF and the amplifier’s internal compensa-

tion capacitor set the dominant pole in the frequency re-

sponse The amplifier therefore always requires a feed-

back resistor even in unity gain

Bandwidth and slew rate are inversely proportional to the

value of RF (see typical curve Frequency Response vs RF)

This makes the amplifier especially easy to compensate for

a desired pulse response (see typical curve Large Signal

Pulse Response) Increased capacitive load driving capabili-

ty is also achieved by increasing the value of RF

The LM6104 has guaranteed performance with a feedback

resistor of 2 kX

CAPACITIVE FEEDBACK

It is common to place a small lead capacitor in parallel with

feedback resistance to compensate voltage feedback am-

plifiers Do not place a capacitor across RF to limit the band-

width of current feedback amplifiers The dynamic imped-

ance of capacitors in the feedback path of the LM6104 as

with any current feedback amplifier will cause instability

LM6104M Datasheet(PDF) 4 Page - National Semiconductor (TI)