ADA4310-1ACPZ-R2 datasheet(10/16 Pages) AD

10 / 16 page

ADA4310-1

Rev. 0 | Page 10 of 16

THEORY OF OPERATION

The ADA4310-1 is a current feedback amplifier with high

output current capability. With a current feedback amplifier, the

current into the inverting input is the feedback signal, and the

open-loop behavior is that of a transimpedance, dVO/dIIN or TZ.

The open-loop transimpedance is analogous to the open-loop

voltage gain of a voltage feedback amplifier. Figure 20 shows a

simplified model of a current feedback amplifier. Because RIN is

proportional to 1/gm, the equivalent voltage gain is just TZ × gm,

where gm is the transconductance of the input stage. Basic

analysis of the follower with gain circuit yields

()

where:

= 1

1 ≈

Because G × RIN << RF for low gains, a current feedback

amplifier has relatively constant bandwidth vs. gain, the 3 dB

point being set when |TZ| = RF.

Of course, for a real amplifier there are additional poles that

contribute excess phase, and there is a value for RF below which

the amplifier is unstable. Tolerance for peaking and desired

flatness determines the optimum RF in each application.

VOUT

VIN

RIN

IIN

Figure 20. Simplified Block Diagram

ADA4310-1ACPZ-R2 Datasheet(PDF) 10 Page - Analog Devices