AD8065 AD8066 Analog Devices, AD8065 AD8066 Datasheet - Page 16

• Manufacturer Part Number: AD8065 AD8066
• Description: High Performance, 145 MHz Fast FET Op Amps
• Manufacturer: Analog Devices

AD8065/AD8066
THEORY OF OPERATION
The AD8065/AD8066 are voltage feedback operational amplifiers
that combine a laser-trimmed JFET input stage with Analog
Devices’ eXtra Fast Complementary Bipolar process, resulting
in an outstanding combination of precision and speed. Supply
voltage range is from 5 V to 24 V. The amplifiers feature a
patented rail-to-rail output stage capable of driving within 0.5 V
of either power supply while sourcing or sinking up to 30 mA.
Also featured is a single-supply input stage that handles common-
mode signals from below the negative supply to within 3 V of the
positive rail. Operation beyond the JFET input range is possible
because of an auxiliary bipolar input stage that functions with
input voltages up to the positive supply. The amplifiers operate
as if they have a rail-to-rail input and exhibit no phase reversal
behavior for common-mode voltages within the power supply.
With voltage noise of 7 nV/÷Hz and –88 dBc distortion for 1 MHz
2 V p-p signals, the AD8065/AD8066 are a great choice for high
resolution data acquisition systems. Its low noise, sub-pA input
current, precision offset, and high speed make it a superb preamp
for fast photodiode applications. The speed and output drive
capability of the AD8065/AD8066 also make them useful in
video applications.
Closed-Loop Frequency Response
The AD8065/AD8066 are classic voltage feedback amplifiers
with an open-loop frequency response that can be approximated
as the integrator response shown in Figure 3. Basic closed-loop
frequency response for inverting and noninverting configurations
can be derived from the shown schematics.
80
60
40
20
R
V
0
Figure 3. Open-Loop Gain vs. Frequency and Basic Connections
G
I
V
0.01
E
R
F
A
0.1
V
FREQUENCY – MHz
O
A = (2p
1
f crossover )/s
–16–
Noninverting Closed-Loop Frequency Response
Solving for the transfer function
where f
gain equals 0 db.
At dc
Closed-loop –3 dB frequency
Inverting Closed-Loop Frequency Response
At dc
Closed-loop –3 dB frequency
10
crossover
V
I
V
V
is the frequency where the amplifier’s open-loop
V
V
100
O
O
I
I
=
=
f crossover = 65MHz
R
f
f
s R
(
G
-
-
(
R
3
3
dB
dB
F
F
V
2
+
E
V
=
=
V
+
p
-
R
R s
O
I
V
R
V
2
F
f
f
¥
G
crossover
crossover
O
p
G
I
A
=
)
f
)
crossover
¥
= -
R
+
+
F
f
2
2
crossover
R
¥
¥
p
+
p
R
R
G
(
F
G
¥
R
¥
R
R
R
V
G
F
F
G
f
f
O
crossover
R
crossover
R
¥
+
+
+
G
G
R
R
R
R
F
G
G
F
)
¥
¥
R
R
G
G
REV. B