AD9631 datasheet(14/20 Pages) AD

14 / 20 page

AD9631/AD9632

REV. A

–14–

For general voltage gain applications, the amplifier bandwidth

can be closely estimated as:

3 dB ≅

π 1+





















This estimation loses accuracy for gains of +2/–1 or lower due

to the amplifier’s damping factor. For these “low gain” cases,

the bandwidth will actually extend beyond the calculated value

(see Closed-Loop BW plots, Figures 15 and 27).

As a rule of thumb, capacitor CF will not be required if:

F RG ) × CI ≤

where NG is the Noise Gain (1 + RF/RG) of the circuit. For

most voltage gain applications, this should be the case.

Pulse Response

Unlike a traditional voltage feedback amplifier, where the slew

speed is dictated by its front end dc quiescent current and gain

bandwidth product, the AD9631 and AD9632 provide “on de-

mand” current that increases proportionally to the input “step”

signal amplitude. This results in slew rates (1300 V/

µs) compa-

rable to wideband current feedback designs. This, combined

with relatively low input noise current (2.0 pA/

√Hz), gives the

AD9631 and AD9632 the best attributes of both voltage and

current feedback amplifiers.

Large Signal Performance

The outstanding large signal operation of the AD9631 and

AD9632 is due to a unique, proprietary design architecture.

In order to maintain this level of performance, the maximum

550 V-MHz product must be observed, (e.g., @ 100 MHz,

VO ≤ 5.5 V p-p).

Power Supply Bypassing

Adequate power supply bypassing can be critical when optimiz-

ing the performance of a high frequency circuit. Inductance in

the power supply leads can form resonant circuits that produce

peaking in the amplifier’s response. In addition, if large current

transients must be delivered to the load, then bypass capacitors

(typically greater than 1

µF) will be required to provide the best

settling time and lowest distortion. A parallel combination of at

least 4.7

µF, and between 0.1 µF and 0.01 µF, is recommended.

Some brands of electrolytic capacitors will require a small series

damping resistor

≈4.7 Ω for optimum results.

Driving Capacitive Loads

The AD9631 and AD9632 were designed primarily to drive

nonreactive loads. If driving loads with a capacitive component

is desired, the best frequency response is obtained by the addi-

tion of a small series resistance as shown in Figure 60. The ac-

companying graph shows the optimum value for RSERIES vs.

capacitive load. It is worth noting that the frequency response of

the circuit when driving large capacitive loads will be dominated

by the passive roll-off of RSERIES and CL.

SERIES

Ω

AD9631/32

Figure 60. Driving Capacitive Loads

– pF

Figure 61. Recommended RSERIES vs. Capacitive Load

AD9631 Datasheet(PDF) 14 Page - Analog Devices

AD9631 Datasheet(HTML) 14 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL