AD8067 Analog Devices, AD8067 Datasheet - Page 20

• Manufacturer Part Number: AD8067
• Manufacturer: Analog Devices

Specifications of AD8067

• Vcc-vee: 5V to 24V
• Isy Per Amplifier: 7mA
• Packages: SOT
• -3db Bandwidth: 54MHz
• Slew Rate: 640V/µs
• Vos: 200µV
• Ib: 0.6pA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 6.6nV/rtHz

AD8067
SINGLE-SUPPLY OPERATION
The AD8067 is well suited for low voltage single-supply
applications, given its N-channel JFET input stage and rail-to-
rail output stage. It is fully specified for 5 V supplies. Successful
single-supply applications require attention to keep signal
voltages within the input and output headroom limits of the
amplifier. The input stage headroom extends to 1.7 V
(minimum) on a 5 V supply. The center of the input range is
0.85 V. The output saturation limit defines the hard limit of the
output headroom. This limit depends on the amount of current
the amplifier is sourcing or sinking, as shown in Figure 29.
Traditionally, an offset voltage is introduced in the input
network replacing ground as a reference. This allows the output
to swing about a dc reference point, typically midsupply.
Attention to the required headroom of the amplifier is
important, in this case, the required headroom from the
positive supply is 3 V; therefore, 1.5 V was selected as a
reference, which allows for a 100 mV signal at the input. Figure 56
shows the AD8067 configured for 5 V supply operation with a
reference voltage of 1.5 V. Capacitors C1 and C5 ac couple the
signal into and out of the amplifier and partially determine the
bandwidth of the input and output structures.
Resistors R2 and R3 set a 1.5 V output bias point for the output
signal to swing about. It is critical to have adequate bypassing to
provide a good ac ground for the reference voltage. Generally,
the bandwidth of the reference network (R2, R3, and C2) is
selected to be one tenth that of the input bandwidth. This
ensures that any frequencies below the input bandwidth do not
pass through the reference network into the amplifier.
V
V
INPUT
OUTPUT
CH1
–
–
3
200mV
dB
3
dB
Figure 55. Gain of 2 Pulse Response
Bandwidth
Bandwidth
T
CH2
200mV
=
=
2
π
2
R1C1
π
1
V
V
R
1
OUT
IN
L
C5
M 50ns CH1 288mV
Rev. A | Page 20 of 24
Reference network:
Resistors R4 and R1 set the gain, in this case, an inverting gain
of 10 was selected. In this application, the input and output
bandwidths were set for approximately 10 Hz. The reference
network was set for a tenth of the input and output bandwidth,
at approximately 1 Hz.
HIGH GAIN, HIGH BANDWIDTH COMPOSITE
AMPLIFIER
The composite amplifier takes advantage of combining key
parameters that can otherwise be mutually exclusive of a
conventional single amplifier. For example, most precision
amplifiers have good dc characteristics but lack high speed ac
characteristics. Composite amplifiers combine the best of both
amplifiers to achieve superior performance over their single op
amp counterparts. The AD8067 and the
for a composite amplifier circuit, combining dc precision with
high gain and bandwidth. The circuit runs off a ±5 V power
supply at approximately 20 mA of bias current. With a gain of
approximately 40 dB, the composite amplifier offers <1 pA
input current, a gain bandwidth product of 6.1 GHz, and a slew
rate of 630 V/μs.
V
IN
+5V
V
47μF
Figure 56. Single-Supply Operation Schematic
+
C1
REF
6.8μF
70kΩ
R2
C2
−
300Ω
3
R1
dB
30kΩ
R3
Bandwidth
4
3
AD8067
+5V
5
2
2.7kΩ
=
R4
2
0.1μF
10μF
1
π
C4
C3
AD8009
(
R2
||
1
R3
)
are well suited
C2
15μF
C5
1kΩ
R
V
L
OUT