AD8005 데이터 시트보기 (PDF) - Analog Devices

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AD8005

270 MHz, 400 μA Current Feedback Amplifier

Analog Devices 

Increasing Feedback Resistors

Unlike conventional voltage feedback op amps, the choice of feed-

back resistor has a direct impact on the closed-loop bandwidth

and stability of a current feedback op amp circuit. Reducing the

resistance below the recommended value makes the amplifier

more unstable. Increasing the size of the feedback resistor

reduces the closed-loop bandwidth.

360␮A (rms)

562⍀

4.99k⍀

+5V

AD8005

In power-critical applications where some bandwidth can be

sacrificed, increasing the size of the feedback resistor will yield

significant power savings. A good example of this is the gain of

+10 case. Operating from a bipolar supply (± 5 V), the quiescent

current is 475 µA (excluding the feedback network). The recom-

mended feedback and gain resistors are 499 Ω and 56.2 Ω

respectively. In order to drive an rms output voltage of 2 V, the

output must deliver a current of 3.6 mA to the feedback net-

work. Increasing the size of the resistor network by a factor of

10 as shown in Figure 33 will reduce this current to 360 µA.

The closed loop bandwidth will however decrease to 20 MHz.

VIN

0.2V (rms)

AD8005

VOUT

2V (rms)

QUIESCENT CURRENT

475␮A (MAX)

–5V

Figure 33. Saving Power by Increasing Feedback Resistor

Network

REV. A

–11–

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