Dual Picoampere Input
Current Bipolar Op Amp
AD706
FEATURES
High DC Precision
100 V Max Offset Voltage
1.5 V/ C Max Offset Drift
200 pA Max Input Bias Current
0.5 V p-p Voltage Noise, 0.1 Hz to 10 Hz
750 A Supply Current
Available in 8-Lead Plastic Mini-DlP
and Surface-Mount (SOIC) Packages
Available in Tape and Reel in Accordance with
EIA-481A Standard
Quad Version: AD704
APPLICATIONS
Low Frequency Active Filters
Precision Instrumentation
Precision Integrators
CONNECTION DIAGRAM
Plastic Mini-DIP (N) and
Plastic SOIC (R) Packages
AMPLIFIER 1
OUTPUT
1
–IN
2
IN
3
V–
4
AMPLIFIER 2
AD706
8
7
6
5
V
OUTPUT
–IN
IN
TOP VIEW
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD706 is a dual, low power, bipolar op amp that has the
low input bias current of a JFET amplifier, but which offers a
significantly lower I
B
drift over temperature. It utilizes superbeta
bipolar input transistors to achieve picoampere input bias current
levels (similar to FET input amplifiers at room temperature),
while its I
B
typically only increases by 5 at 125°C (unlike a
JFET amp, for which I
B
doubles every 10°C for a 1000
increase at 125°C). The AD706 also achieves the microvolt
offset voltage and low noise characteristics of a precision bipolar
input amplifier.
Since it has < 200 pA of bias current, the AD706 does not
require the commonly used “balancing” resistor. Furthermore,
the current noise is only 50 fA/√Hz, which makes this amplifier
usable with very high source impedances. At 600 A max supply
current (per amplifier), the AD706 is well suited for today’s
high density boards.
The AD706 is an excellent choice for use in low frequency
active filters in 12-bit and 14-bit data acquisition systems, in
precision instrumentation, and as a high quality integrator. The
AD706 is internally compensated for unity gain and is available
in five performance grades. The AD706J is rated over the
commercial temperature range of 0°C to +70°C. The AD706A is
rated for the extended industrial temperature range of –40°C
to +85°C.
The AD706 is offered in two varieties of an 8-lead package:
plastic mini-DIP and surface-mount (SOIC).
1. The AD706 is a dual low drift op amp that offers JFET
level input bias currents, yet has the low I
B
drift of a bipolar
amplifier. It may be used in circuits using dual op amps
such as the LT1024.
2. The AD706 provides both low drift and high dc precision.
3. The AD706 can be used in applications where a chopper
amplifier would normally be required but without the
chopper’s inherent noise.
100
10
TYPICAL I
B
– nA
TYPICAL JFET AMP
1
0.1
AD706
0.01
–55
+25
+110
TEMPERATURE – C
+125
Figure 1. Input Bias Current vs. Temperature
REV. E
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© 2003 Analog Devices, Inc. All rights reserved.
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