AD9631_15 Datasheet, PDF (17/20 Pages) Analog Devices – Ultralow Distortion, Wide Bandwidth Voltage Feedback Op Amps

Data Sheet
APPLICATIONS INFORMATION
The AD9631/AD9632 are voltage feedback amplifiers well
suited for applications such as photodetectors, active filters,
and log amplifiers. The wide bandwidth (320 MHz), phase
margin (65°), low current noise (2.0 pA/√Hz), and slew rate
(1300 V/µs) of the devices give higher performance capabilities
to these applications over previous voltage feedback designs.
With a settling time of 16 ns to 0.01% and 11 ns to 0.1%, the
devices are an excellent choice for DAC I/V conversion. The
same characteristics along with low harmonic distortion make
them a good choice for ADC buffering/amplification. With
superb linearity at relatively high signal frequencies, the
AD9631/AD9632 are ideal drivers for ADCs up to 12 bits.
OPERATION AS A VIDEO LINE DRIVER
The AD9631/AD9632 have been designed to offer outstanding
performance as video line drivers. The important specifications
of differential gain (0.02%) and differential phase (0.02°) meet
the most exacting HDTV demands for driving video loads.
274Ω
274Ω
+V_S ^10µF
0.1µF
75Ω
CABLE
V_IN
AD9631/
AD9632
0.1µF
75Ω
10µF
75Ω
75Ω ^CABLE
V_OUT
75Ω
–V_S
Figure 64. Video Line Driver
ACTIVE FILTERS
The wide bandwidth and low distortion of the AD9631/
AD9632 are ideal for the realization of higher bandwidth active
filters. These characteristics, while being more common in
many current feedback op amps, are offered in the AD9631/
AD9632 in a voltage feedback configuration. Many active
filter configurations are not realizable with current feedback
amplifiers.
A multiple feedback active filter requires a voltage feedback
amplifier and is more demanding of op amp performance than
other active filter configurations, such as the Sallen-Key. In
general, the amplifier should have a bandwidth that is at least
10 times the bandwidth of the filter if problems due to phase
shift of the amplifier are to be avoided.
AD9631/AD9632
Figure 65 is an example of a 20 MHz low-pass multiple feedback
active filter using an AD9632.
R4
154Ω
C1
50pF
+5V _10µF
R1
154Ω
V_IN
R3
78.7Ω
0.1µF
C2
100pF
AD9632
100Ω
0.1µF
V_OUT
10µF
–5V
Figure 65. Active Filter Circuit
Choose
FO = cutoff frequency = 20 MHz
α = damping ratio = 1/Q = 2
H = absolute value of circuit gain = ^−R4 = 1
R1
Then
k = 2πF_OC1
C2
=
4C1(H
α²
+ 1)
R1 = ^α
2HK
R3 = ^α
2K(H + 1)
R4 = H(R1)
Rev. D | Page 17 of 20