AD9631-EB Analog Devices, AD9631-EB Datasheet - Page 15

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

REV. A
APPLICATIONS
The AD9631 and AD9632 are voltage feedback amplifiers well
suited for such applications as photodetectors, active filters, and
log amplifiers. The devices’ wide bandwidth (320 MHz), phase
margin (65 ), low noise current (2.0 pA/ Hz), and slew rate
(1300 V/ s) give higher performance capabilities to these appli-
cations 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 su-
perb linearity at relatively high signal frequencies, the AD9631
and AD9632 are ideal drivers for ADCs up to 12 bits.
Operation as a Video Line Driver
The AD9631 and AD9632 have been designed to offer out-
standing 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.
Active Filters
The wide bandwidth and low distortion of the AD9631 and
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 and AD9632
in a voltage feedback configuration. Many active filter configu-
rations are not realizable with current feedback amplifiers.
V
IN
CABLE
75
274
75
Figure 62. Video Line Driver
2
3
AD9631/
AD9632
+V
–V
274
7
4
S
S
0.1 F
0.1 F
10 F
10 F
6
75
CABLE
75
75
V
OUT
–15–
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
ten times the bandwidth of the filter if problems due to phase
shift of the amplifier are to be avoided.
Figure 63 is an example of a 20 MHz low pass multiple feed-
back active filter using an AD9632.
Choose:
F
H = Absolute Value of Circuit Gain =
Then:
O
= Damping Ratio = 1/Q = 2
= Cutoff Frequency = 20 MHz
V
IN
154
R1
Figure 63. Active Filter Circuit
154
R4
C2
100pF
78.7
k 2
C2
R1
R3
R4
R3
100
2 HK
4 C1(H 1)
2 K (H 1)
H(R1)
C1
50pF
F
2
3
O
AD9632
AD9631/AD9632
C1
–5V
2
1
4
+5V
0.1 F
10 F
7
5
–R4
R1 = 1
0.1 F
10 F
6
V
OUT