AD8047-EB Analog Devices, AD8047-EB Datasheet - Page 13

• Manufacturer Part Number: AD8047-EB
• Description: 250 MHz/ General Purpose Voltage Feedback Op Amps
• Manufacturer: Analog Devices

REV. 0
circuit when driving large capacitive loads will be dominated by
the passive roll-off of R
APPLICATIONS
The AD8047 and AD8048 are voltage feedback amplifiers well
suited for such applications as photodetectors, active filters, and
log amplifiers. The devices’ wide bandwidth (260 MHz), phase
margin (65 ), low noise current (1.0 pA/ Hz), and slew rate
V
Figure 55. AD8047 Large Signal Transient Response;
V
C
Figure 57. AD8048 Large Signal Transient Response;
O
O
L
= 2 V p-p, G = +1, R
= 27 pF
= 2 V p-p, G = +2, R
R
IN
Figure 54. Driving Capacitive Loads
Figure 56. Driving Capacitive Loads
AD8047
500mV
500mV
R
SERIES
F
AD8048
R
F
F
F
= 0 , R
and C
= R
IN
R
SERIES
L
= 200 , R
.
1k
SERIES
R
R
L
SERIES
5ns
5ns
1k
= 0 , C
R
L
SERIES
C
L
L
= 0
= 27 pF
C
L
,
–13–
(1000 V/ s) give higher performance capabilities to these appli-
cations over previous voltage feedback designs.
With a settling time of 30 ns to 0.01% and 13 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 AD8047
and AD8048 are ideal drivers for ADCs up to 12 bits.
Operation as a Video Line Driver
The AD8047 and AD8048 have been designed to offer out-
standing performance as video line drivers. The important
specifications of differential gain (0.01%) 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 AD8047 and
AD8048 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 AD8047 and AD8048
in a voltage feedback configuration. Many active filter configu-
rations 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
ten times the bandwidth of the filter if problems due to phase
shift of the amplifier are to be avoided.
Figure 59 is an example of a 20 MHz low pass multiple feed-
back active filter using an AD8048.
Choose:
F
O
= Damping Ratio = 1/Q = 2
V
IN
= Cutoff Frequency = 20 MHz
V
IN
CABLE
75
200
154
75
R1
Figure 59. Active Filter Circuit
Figure 58. Video Line Driver
154
R4
C2
100pF
2
3
AD8047/
AD8048
78.7
+V
–V
R3
200
7
4
S
S
100
0.1 F
0.1 F
10 F
10 F
C1
50pF
6
2
3
AD8047/AD8048
AD8048
–5V
4
1
+5V
5
7
75
10 F
0.1 F
0.1 F
10 F
6
CABLE
75
V
75
OUT
V
OUT