REV. A
AD8047/AD8048
–13–
R
F
R
L
1k
C
L
AD8047
R
SERIES
Figure 6. Driving Capacitive Loads
5ns
500mV
Figure 7. AD8047 Large Signal Transient Response;
V
O
= 2 V p-p, G = +1, R
F
= 0
Ω
, R
SERIES
= 0
Ω
, C
L
= 27 pF
R
F
R
IN
R
L
1k
C
L
AD8048
R
SERIES
Figure 8. Driving Capacitive Loads
5ns
500mV
Figure 9. AD8048 Large Signal Transient Response;
V
O
= 2 V p-p, G = +2, R
F
= R
IN
= 200
Ω
, R
SERIES
= 0
Ω
,
C
L
= 27 pF
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
(1000 V/µs) 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
superb 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.
+V
S
–V
S
V
IN
V
OU
10F
10F
0.1F
0.1F
AD8047/
AD8048
3
2
7
6
4
75
75
75
75
CABLE
75
CABLE
200200
Figure 10. Video Line Driver
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
10 times the bandwidth of the filter if problems due to phase
shift of the amplifier are to be avoided.
Figure 11 is an example of a 20 MHz low-pass multiple feed-
back active filter using an AD8048.
+5V
–5V
V
OUT
C1
50pF
C2
100pF
R3
78.7
R4
154
R1
154
10F
10F
0.1F
0.1F
AD8048
3
2
7
6
5
1
4
100
V
IN
Figure 11. Active Filter Circuit
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
SERIES
and C
L
.
