AD9631-EB Analog Devices, AD9631-EB Datasheet - Page 14

• Manufacturer Part Number: AD9631-EB
• Description: Ultralow Distortion/ Wide Bandwidth Voltage Feedback Op Amps
• Manufacturer: Analog Devices

REV. A
For general voltage gain applications, the amplifier bandwidth
can be closely estimated as:
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 C
where NG is the Noise Gain (1 + R
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/ s) 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,
V
O
5.5 V p-p).
f
(R
3 dB
F
R
G
2
) C
F
1
will not be required if:
I
F
O
/R
R
R
4
NG
G
G
F
) of the circuit. For
O
–14–
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 F) will be required to provide the best
settling time and lowest distortion. A parallel combination of at
least 4.7 F, and between 0.1 F and 0.01 F, is recommended.
Some brands of electrolytic capacitors will require a small series
damping resistor 4.7
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 R
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 R
Figure 61. Recommended R
R
IN
40
30
20
10
0
Figure 60. Driving Capacitive Loads
R
IN
5
AD9631/32
for optimum results.
SERIES
R
F
10
C
and C
L
– pF
AD9631/AD9632
SERIES
15
L
.
R
vs. Capacitive Load
SERIES
1k
R
L
20
SERIES
25
C
vs.
L