OP97 Datasheet, PDF (7/12 Pages) Analog Devices – Low-Power, High-Precision Operational Amplifier

APPLICATIONS INFORMATION
The OP97 is a low power alternative to the industry standard
precision op amp, the OP07. The OP97 may be substituted
directly into OP07, OP77, 725, 112/312, and 1012 sockets with
improved performance and/or less power dissipation, and may
be inserted into sockets conforming to the 741 pinout if nulling
circuitry is not used. Generally, nulling circuitry used with earlier
generation amplifiers is rendered superfluous by the OP97’s
extremely low offset voltage, and may be removed without com-
promising circuit performance.
Extremely low bias current over the full military temperature
range makes the OP97 attractive for use in sample-and-hold
amplifiers, peak detectors, and log amplifiers that must operate
over a wide temperature range. Balancing input resistances is
not necessary with the OP97. Offset voltage and TCV_OS are
degraded only minimally by high source resistance, even when
unbalanced.
The input pins of the OP97 are protected against large differen-
tial voltage by back-to-back diodes. Current-limiting resistors
are not used so that low noise performance is maintained. If
differential voltages above ± 1 V are expected at the inputs,
series resistors must be used to limit the current flow to a
maximum of 10 mA. Common-mode voltages at the inputs are
not restricted, and may vary over the full range of the supply
voltages used.
The OP97 requires very little operating headroom about the
supply rails, and is specified for operation with supplies as low
+V
R_POT = 5k⍀ TO 100k⍀
OP97
as ± 2 V. Typically, the common-mode range extends to within
one volt of either rail. The output typically swings to within one
volt of the rails when using a 10 kΩ load.
Offset nulling is achieved utilizing the same circuitry as an
OP07. A potentiometer between 5 kΩ and 100 kΩ is connected
between pins 1 and 8 with the wiper connected to the positive
supply. The trim range is between 300 µV and 850 µV, depend-
ing upon the internal trimming of the device.
AC PERFORMANCE
The OP97’s ac characteristics are highly stable over its full
operating temperature range. Unity-gain small-signal response
is shown in Figure 2. Extremely tolerant of capacitive loading
on the output, the OP97 displays excellent response even with
1000 pF loads (Figure 3). In large-signal applications, the
input protection diodes effectively short the input to the output
during the transients if the amplifier is connected in the usual
unity-gain configuration. The output enters short-circuit current
limit, with the flow going through the protection diodes. Improved
large-signal transient response is obtained by using a feedback
resistor between the output and the inverting input. Figure 4
shows the large-signal response of the OP97 in unity gain with a
10 kΩ feedback resistor. The unity gain follower circuit is shown
in Figure 5.
The overcompensation pin may be used to increase the phase
margin of the OP97, or to decrease gain-bandwidth product at
gains greater than 10.
OP97
C_OC
–V
Figure 1. Optional Input Offset Voltage Nulling
and Overcompensation Circuits
Figure 3. Small-Signal Transient Response
(C_LOAD = 1000 pF, A_VCL = 1)
Figure 2. Small-Signal Transient Response
(C_LOAD = 100 pF, A_VCL = 1)
Figure 4. Large-Signal Transient Response (A_VCL = 1)
REV. D
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