AD8065 AD8066 Analog Devices, AD8065 AD8066 Datasheet - Page 22

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

AD8065/AD8066
High Speed JFET Input Instrumentation Amplifier
Figure 10 shows an example of a high speed instrumentation
amplifier with high input impedance using the AD8065/AD8066.
The dc transfer function is
For G = +1, it is recommended that the feedback resistors for the
two preamps be set to a low value (for instance 50 W for 50 W
source impedance). The bandwidth for G = +1 will be 50 MHz.
For higher gains, the bandwidth will be set by the preamp, equaling
Common-mode rejection of the inamp will be primarily deter-
mined by the match of the resistor ratios R1:R2 to R3:R4. It can
be estimated
The summing junction impedance for the preamps is equal to
R
F
0.5(R
G
). This is the value to be used for matching purposes.
Inamp
V
OUT
-3dB
V
=
V
CM
(
O
=
V
(
N
=
f
CR
-
(
(
V
1
d
¥
P
+
1
)
R
-
d d
Ê
Á
Ë
1 2
G
1 1000
d
)
) / (
2
+
)
R
G
2
¥
R
ˆ
˜
¯
F
)
–22–
Video Buffer
The output current capability and speed of the AD8065 make it
useful as a video buffer, shown in Figure 11.
The G = +2 configuration compensates for the voltage division of
the signal due to the signal termination. This buffer maintains
0.1 dB flatness for signals up to 7 MHz, from low amplitudes
up to 2 V p-p (TPC 4). Differential gain and phase have been
measured to be 0.02% and 0.028∞ at ± 5 V supplies.
V
I
249
499
AD8065
Figure 11. Video Buffer
V
V
S
S
0.1 F
0.1 F
2.2pF
499
4.7 F
4.7 F
75
75
V
REV. B
O